Backreaction

The Planck length as a minimal length

2012-01-25T06:33:00.003-05:00

The best scientific arguments are those that are surprising at first sight, yet at second sight they make perfect sense. The following argument, which goes back to Mead's 1964 paper "Possible Connection Between Gravitation and Fundamental Length," is of this type. Look at the abstract and note that it took more than 5 years from submission to publication of the paper. Clearely, Mead's argument seemed controversial at this time, even though all he did was to study the resolution of a microscope taking into account gravity.

For all practical purposes, the gravitational interaction is far too weak to be of relevance for microscopy. Normally, we can neglect gravity, in which case we can use Heisenberg's argument that I first want to remind you of before adding gravity. In the following, the speed of light c and Planck's constant ℏ are equal to one, unless they are not. If you don't know how natural units work, you should watch this video, or scroll down past the equations and just read the conclusion.

Consider a photon with frequency ω, moving in direction x, which scatters on a particle whose position on the x-axis we want to measure (see image below). The scattered photons that reach the lens (red) of the microscope have to lie within an angle ε to produces an image from which we want to infer the position of the particle.

According to classical optics, the wavelength of the photon sets a limit to the possible resolution Δx But the photon used to measure the position of the particle has a recoil when it scatters and transfers a momentum to the particle. Since one does not know the direction of the photon to better than ε, this results in an uncertainty for the momentum of the particle in direction xTaken together one obtains Heisenberg's uncertainty principle
We know today that Heisenberg's uncertainty principle is more than a limit on the resolution of microscopes; up to a factor of order one, the above inequality is a fundamental principle of quantum mechanics.

Now we repeat this little exercise by taking into account gravity.

Since we know that Heisenberg's uncertainty principle is a fundamental property of nature, it does not make sense, strictly speaking, to speak of the position and momentum of the particle at the same time. Consequently, instead of speaking about the photon scattering off the particle as if that would happen in one particular point, we should speak of the photon having a strong interaction with the particle in some region of size R (shown in the above image).

With gravity, the relevant question now will be what happens with the measured particle due to the gravitational attraction of the test particle.

For any interaction to take place and subsequent measurement to be possible, the time elapsed between the interaction and measurement has to be at least of the order of the time, τ, the photon needs to travel the distance R, so that τ is larger than R. (The blogger editor has an issue with the "larger than" and "smaller than" signs, which is why I avoid using them.) The photon carries an energy that, though in general tiny, exerts a gravitational pull on the particle whose position we wish to measure. The gravitational acceleration acting on the particle is at least of the orderwhere G is Newton's constant which is, in natural units, the square of the Planck length l_Pl. Assuming that the particle is non-relativistic and much slower than the photon, the acceleration lasts about the duration the photon is in the region of strong interaction. From this, the particle acquires a velocity of v ≈ aRThus, in the time R, the aquired velocity allows the particle to travels a distance of L ≈ Gω.

Since the direction of the photon was unknown to within ε, the direction of the acceleration and the motion of the is also unknown. Projection on the x-axis then yields the additional uncertainty ofCombining this with the usual uncertainty (multiply both, then take the square root), one obtainsThus, we find that the distortion of the measured particle by the gravitational field of the particle used for measurement prevents the resolution of arbitrarily small structures. Resolution is bounded by the Planck length, which is about 10^-33cm. The Planck length thus plays the role of a minimal length.

(You might criticize this argument because it makes use of Newtonian gravity rather than general relativity, so let me add that, in his paper, Mead goes on to show that the estimate remains valid also in general relativity.)

As anticipated, this minimal length is far too small to be of relevance for actual microscopes; its relevance is conceptual. Given that Heisenberg's uncertainty turned out to be a fundamental property of quantum mechanics, encoded in the commutation relations, we have to ask then if not this modified uncertainty too should be promoted to fundamental relevance. In fact, in the last 5 decades this simple argument has inspired a great many works that attempted exactly this. But that is a different story and shall be told another time.

To finish this story, let me instead quote from a letter that Mead, the author of the above argument, wrote to Physics Today in 2001. In it, he recalls how little attention his argument originally received:

"[In the 1960s], I read many referee reports on my papers and discussed the matter with every theoretical physicist who was willing to listen; nobody that I contacted recognized the connection with the Planck proposal, and few took seriously the idea of [the Planck length] as a possible fundamental length. The view was nearly unanimous, not just that I had failed to prove my result, but that the Planck length could never play a fundamental role in physics. A minority held that there could be no fundamental length at all, but most were then convinced that a [different] fundamental length..., of the order of the proton Compton wavelength, was the wave of the future. Moreover, the people I contacted seemed to treat this much longer fundamental length as established fact, not speculation, despite the lack of actual evidence for it."

A real thought experiment that shows virtually nothing

2012-01-22T07:24:00.005-05:00

Two weeks ago, we discussed Hannah and Eppley's thought experiment. Hannah and Eppley argued that a fundamental theory that is only partly quantized leads to contradictions either with quantum mechanics or special relativity; in particular we cannot leave gravity unquantized.

However, we also discussed that this thought experiment might be impossible to perform in our universe, since it requires a basically noiseless system and detectors more massive than we have mass available. Unless you believe in a multiverse that offers such an environment - somewhere -, this leaves us in a philosophical conundrum, since we conclude that any contradiction in Hannah and Eppley's thought experiment is unobservable, at least for us. And if you do believe in a multiverse, maybe gravity is only quantized in parts of it.

So you might not be convinced and insist that gravity may remain classical. Here I want to examine this option in more detail and explain why it is not a fruitful approach. If you know a thing or two about semi-classical gravity, you can skip the preliminaries.

Preliminaries

If gravity remained classical, we would have a theory that couples a quantum field to classical general relativity (GR). GR describes the curvature of space-time (denoted R with indices) that is caused by distributions of matter and energy, encoded in the so-called "stress-energy-tensor" (denoted T with indices). The coupling constant is Newton's constant G.

In a quantum field theory, the stress-energy-tensor becomes an operator that acts on elements of the Hilbert-space. But in the equations of GR, one can't just replace the classical stress-energy-tensor with a quantum operator, since the latter has non-vanishing commutators that the former doesn't have. Since both would have to be equal to a tensor-valued function of the classical background, this will not work. Instead, we have to take the classical part of the operator that is it's expectation value, in some quantum state, denoted as usual by the bra-kets

This is called semi-classical gravity; quantum fields coupled to a classical background. Why, you might ask, don't we just settle for this?

To begin with, semi-classical gravity doesn't actually solve the problems that we were expecting quantum gravity would solve. In particular, semi-classical gravity is the origin rather than the solution of the black-hole information loss problem. It also doesn't prevent singularities (though in some cases it might help). But, you might argue, maybe we were just expecting too much. Maybe the answers to these problems lie entirely elsewhere. That semi-classical gravity doesn't help us here doesn't mean the theory isn't viable, it just means it doesn't do what we wanted it to do. This explains a certain lack of motivation for studying this option, but isn't a good scientific reason to exclude it.

Okay, you have a point here. But semi-classical gravity doesn't only not solve any problems, it brings with it a bunch of new problems. To begin with, the expectation value of the stress-energy-tensor is divergent and has to be regularized, a problem that becomes considerably more difficult in curved space. This is a technical problem which has been studied for some decades now, and that actually with great success. While some problems remain, you might take the point of view that they will be addressed sooner or later.

But a much more severe problem with the semi-classical equations is the measurement process. If you recall, the expectation value of a field that is in a superposition of states that are with probability 1/2 here, and with probability 1/2 there, has to be updated upon measurement. Suddenly then, the particle and its expectation value are with probability 1 here or there. This process violates local conservation of the expectation value of the stress-energy-tensor. But this local conservation is built into GR: It is necessarily always identically fulfilled. This means that semi-classical gravity can't be valid during the measurement. But still, you might insist, we haven't understood the measurement in quantum mechanics anyway, and maybe the theory has to be modified suitably during measurement, so that in fact the conservation law can be temporarily violated.

You are really stubborn, aren't you?

So you insist, but I hope the latter problem illuminated just how absurd semi-classical gravity is if you think about a quantum state in a superposition of different positions, eg a photon that went through a beam splitter. Quantum mechanically, it had 50% chance to go this or that way. But according to semi-classical gravity, its gravitational field went half both ways! If the photon went left, its gravitational field went half with the photon, and half to the right. Surely, you'd think there must be some way to experimentally exclude this absurdity?

Page and Geilker's experiment

Page and Geilker set out in 1981 to show exactly that, the absurdity of semi-classical gravity with a suitably designed experiment. The most amazing thing about their study is that it got published in PRL, for the experiment is absurd in itself.

Their reasoning was as follows. Consider you have a Cavendish-like setup, consisting of two pairs of massive balls connected by rods, see image below (you are looking at the setup from above)

The one rod (grey) hangs on a wire that has a mirror attached to it, so you can measure its motion by tracking the position of a laser light shining onto the mirror. The other rod (not shown) connecting the two other balls (blue) will be turned to bring the balls into one of two positions A or B. The gravitational attraction between the balls will cause the wire to twist into one of two directions, as indicated by the arrows.

Or so you think if you know classical gravity. But if the blue balls are in a quantum superposition of A and B, then the gravitational attraction of the expectation value of their mass distribution on the grey balls cancels, the wire doesn't twist, and the laser light doesn't move.

To bring the grey balls into a superposition, Page and Geilker used a radioactive sample that decayed with some probability within 30 seconds, and about with equal probability within a longer time-span after this. Depending on the outcome of the decay, the blue balls remain in position A or assume B. The mirror moved, they concluded the gravitational field of the balls can't have been the expectation value of the superpositions A and B, thus semi-classical gravity is wrong.

Well, I hope you saw Schrödinger's cat laughing. While the decay of a radioactive sample is a purely quantum mechanical process, the wavefunction is long decohered by the time the rod has been adjusted. The blue balls have no more been in a quantum superposition than Schrödinger's cat ever was in a superposition of dead and alive.

This begs the question then if not Page and Geilker's experiment can be realized de facto. The problem is, as always with quantum gravity, that the gravitational interaction is very weak. The heaviest masses that can be brought into a superposition of different locations, presently molecules with some thousand GeV, still have gravitational fields far too weak to be measurable. More can be said about this, but that deserves another post another time.

Bottomline

Semi-classical gravity is not considered a fundamentally meaningful description of Nature for theoretical reasons. These are good and convincing reasons, yet semi-classical gravity has stubbornly refused experimental falsification. This tells you just how frustrating the search for quantum gravity phenomenology can be.

The Academic Dollar

2012-01-18T12:09:00.001-05:00

I didn't know whether to laugh or to cry when I read this article:

An Auction Market for Journal Articles

The authors are two economists and the above article proposes an improvement to the current publication system in academia. They propose to introduce a virtual currency, the "Academic Dollar" (A$), that would be traded among editors, authors, and reviewers and create incentives for each involved party to improve the quality of articles.

The idea to measure scientific quality by one single parameter, currency in a market economy, is not new. It has been proposed before, in various forms, to rate scientific papers or ideas by monetary value. The problem with this is twofold. First, the scientific community is global and incomes differ greatly from one institution to the next. If money would influence the rating of scientific quality, the largest influence would rest in the wealthy nations' most wealthy institutions. Second, market economies deal very poorly with intangible, long-term, public benefits, which is exactly why most of basic research is tax-funded. It is thus questionable that a neo-liberal reformation of academic culture would be beneficial.

The introduction of an Academic Dollar that could be exchanged according to its own rules circumvents these problems, so it is an interesting idea. Prufer and Zetland motivate their study as follows

"The [auction market for journal articles] quantifies academic output through A$ income, and academics need an accurate measure now more than ever. Long ago, decisions on professional advancement depended on subjective factors. These were replaced over time by "objective" factors such a publication or citation counts. As publication has grown more important, the number of submitted papers has increased... [T]he multiplication of titles has made measurement (and professional decisions) more difficult. Neither tenure candidates nor committees are happy with current evaluation methods; they need a simple indicator."

In more detail, what the authors suggest is the following: The scientist writes a paper and submits it to a journal auction market where editors bid for the papers. The winning bid gets the permission to send the paper to peer review. If it passes peer review satisfactorily, and the editor decides to publish it, the bid in A$ goes to the authors, editors, and referees of the articles that are cited in the auctioned paper.

Let me repeat this so you don't miss the relevant part: the A$ does not go to the author, it goes to the authors, editors and referees of the cited articles. Authors and referees are obliged to reassign their A$ to any editor they chose within one year to close the circle.

The vision is that

"It is a simple step to sum an individual's A$ income... to get an accurate signal of academic productivity. This signal could facilitate decisions on tenure, promotion, grants, and so on."

Five questions that sprang to my mind immediately:

First, I know plenty of researchers who have strong dislikes of certain journals and refuse to work with them. This point the authors address, if I understood correctly, with a "handicap" that the scientist can put on certain journals that would disable or make it more difficult for an editor of these journals to make a bid.

Second, what about self-citations? They write they just wouldn't count them.

Third, where does the A$ come from and who decides who gets what? This is addressed in the article with one bracketed sentence "The initial allocation of A$ may be in proportion to subscribers, citations, impact factor, or some other variable." I am not sure that will be sufficient. There will be a loss of A$ from people who don't care to 'reassign them' for example because they are leaving academia, and a further decrease of the available A$ per person just because the number of scientists is increasing.

Fourth, if the A$ is worth real money because it is relevant for tenure decisions and grants, somebody who has no need for the virtual money will go and trade it for real money. In other words, there'll be a black market for A$, not to mention the problem of smart people hacking the software. The authors write that "The fixed supply of A$, reallocation norm and trading costs are likely to limit the importance of cash in an A$ black market." I think they'd be surprised.

Five, what about editors who are also authors? Are they supposed to have two different accounts of A$ and not mingle them? I couldn't find anything in the paper about this, but suppose this can be addressed somehow.

Prufer and Zetland have added to their paper a calculation of Pareto efficiency, to show that their proposal is beneficial for everybody involved. For this, they have assumed that the quality of a scientific article is a single-valued universal parameter whose optimization is equally well-defined as the optimization of the most cost efficient way to run a factory.

But my biggest problem with the authors proposal is one that we have discussed previously at this blog (for example here). Any measure that is universal streamlines the way research is pursued. Since your measure is in the best case a rough estimate for long-term success, this amplifies behavior that optimizes currently fashionable measures rather than contributes to scientific knowledge in the first line. It might be saving hiring committees time in the short run, but it will cost the community much more time in the long run.

I have preached it many times, and here it is once again: There is no substitute for scientists' judgement. There is no shortcut and there is no universal measure that could improve or replace this individual and, yes, fallible judgement. The individual assessment of quality and potential impact, possibly centuries into the future, if you'd really want to parameterize it, would lie in a very high dimensional space whose dimensions represent very many continuous parameters. If one attempts to project these opinions onto a one-dimensional axis, the universal measure, one inevitably loses information, and optimization becomes dependent on the choice of measure and thus, ultimately ambigious and questionable in its use. At the very least, we should make sure there are several projections and several criteria for what constitutes an "optimal" scientist.

The trend towards use of simple measures is nothing but a way to delegate responsibility for decisions, till they are diluted enough so that one can just go an blame an anonymous "system."

It is far from my intention to make fun of serious and well worked-out proposals to improve the shortcomings of the current academic system, and I find this is a good try. This proposal however has serious shortcomings itself, and it would make a good example for Verschlimmbesserung ;op

Molecei

2012-01-16T05:59:00.000-05:00

During the last 50 years, physicists made remarkable progress in creating materials that would not exist on Earth without scientists. Custom designed materials that react to temperature, vibrations, humidity or electric currents, absorb or reflect light in desired ways, absorb or repel liquids where needed, stick or don’t stick, hopefully where you want them, are but a few examples.

The maybe most important development in our ability to create new materials have been a large variety of semi-conductors that are instrumental to many now common gadgets, and high temperature superconductivity though, at typically 70 K, the temperatures at which these materials become superconducting is “high” only compared to outer space (or to a physicist who spent too many of his days with liquid Helium).

The most amazing new developements are graphene nano-structures, light yet strong, thin yet impermeable, with high thermal conductivity (possibly directed), high conductivity, and large capacity for hydrogen storage. Nanotechnology has also many potential medical applications that are currently being explored, but enough for now with the praise of modern science.

With that in mind, let us fast forward in time, into the unknown. Imagine our understanding and technical expertise would allow us to do what we do today with atoms to the constituents of atomic nuclei (the protons and neutrons, collectively called “nucleons”). Imagine we could build structures of nucleons that do not occur in nature, structures that are to nuclei what molecules are to atoms. Let us call them “molecei.”

Humans have already brought into existence formations of nucleons that do not occur in nature. By colliding very heavy nuclei, particle physicists have created ever heavier elements. Most recently, the super-heavy elements darmstadtium (Ds), roentgenium (Rg) and copernicium (Cn) with atomic number 110, 111 and 112 have been added to the periodic table. For practical purposes however, these nuclei are not particularly useful because they are very short-lived. It has long been conjectured however, that at even higher atomic numbers, the lifetimes might increase again.

With today’s knowledge of the forces acting in atomic nuclei, and with presently existing technology, it is not possible to create molecei, and maybe they are fundamentally not possible. But if you had asked alchemists 400 years ago what they thought about wires with memory, aerogel, liquid crystals, and ferrofluids, they’d have declared it either magic or impossible. As history has demonstrated over and over again, even experts often fail to properly distinguish the possible from the impossible. So let us be daring, and leave behind the academic carefulness for a moment to speculate what we could do with molecei.

If a positively charged nucleus has a difficult shape, as it would be with molecei, strange and uncommon electron orbits would be the consequence. Electrons might be very loosely bound or highly degenerate, allowing for astonishing optical and electric properties, possibly including superconductivity at room temperature.

The more complicated the shape of a molecei, the more excitations it would have, which would dramatically affect the ability of phonons to propagate. This could cause a medium doted with molecei to have acoustic, and thermal properties the world has never seen, from perfect soundproofing to liquids with enormous heat capacity.

The maybe most exciting possibility is that suitably designed molecei might enable interactions between atomic nuclei that normally require extreme temperatures or densities. Molecei could act as catalysts for nuclear reactions much like molecules can act as catalysts for chemical reactions; it is the old dream of cold nuclear fusion that could solve all our energy problems – provided it does not take more energy to produce the molecei to begin with.

Finally, molecei would be the next step in our ability to design miniature tools and to unravel nature’s secrets on even smaller distances.

Away Note

2012-01-12T03:22:00.002-05:00

I'll be in Stockholm during the next days for the Nordita Winterschool 2012. I have some issues with the Internet connection in the Stockholm apartment because the provider cuts me off if it hasn't been used for a while. So chances are I'll be offline. In other words, don't worry if you don't hear from me for a while. Back next week.

Eppley and Hannah's thought experiment

2012-01-09T12:37:00.000-05:00

We have many reasons to believe that our present knowledge of the fundamental laws of nature is incomplete. Not only because it is unaesthetic that classical general relativity and the quantum field theories of the standard model stand conceptually apart. More pressing is that general relativity, under very general circumstances, brings with it the formation of singularities, and without quantizing gravity black hole evaporation seems incompatible with quantum mechanics. More trivial and, in my opinion, also more pressing is that we don't know what is the gravitational field of a superposition of quantum states, think double slit: Quantum mechanics tells us we know that the particle is neither here nor there, and yet both at once, completely described by its wave-function. In general relativity however its gravitational field is classical and has to have distinct properties. It has to be either here or there, and cannot be both at once.

Eric Hannah and Kenneth Eppley in 1977 presented a thought experiment that illuminated nicely why coupling a quantized to an unquantized field inevitably spells trouble, published in their article "The necessity of quantizing the gravitational field." The experiment is deceptively simple. You prepare a quantum particle in a state with a well-known momentum (in some direction). It doesn't necessarily have to be a momentum eigenstate, but something with a small momentum uncertainty. From Heisenberg's uncertainty principle, we know then that its position uncertainty will be large. Now you measure the position of the particle with a classical gravitational wave.

If gravity wasn't quantized, gravitational waves wouldn't have to fulfill the relation p = ℏk, which was famously shown to hold for photons by Einstein, using the photoelectric effect. It would then be possible to prepare a gravitational wave with a small wavelength (high frequency) but small momentum. If you use this gravitational wave to measure the position of the quantum particle, there are, so argue Hannah and Eppley, three different possible outcomes:

You collapse the wavefunction of the quantum particle and measure its position to a precision determined by the short wavelength of the gravitational wave yet without transferring a large momentum. It is then possible to violate Heisenberg's uncertainty principle, thus the quantum part of the theory doesn't survive.
You collapse the wavefunction of the quantum particle without violating Heisenberg's uncertainty principle, then you will violate energy conservation because your wave can't provide the necessary spread in momentum.
You don't collapse the wavefunction, in which case you can use your measurement for superluminal communication. You then had two types of measurements, one that does and one that doesn't collapse the wavefunction. By spatially separating an entangled state and monitoring one part of it without collapsing it, you can find out, instantaneously, when a collapse was induced in the other part.

Since gravity is an extremely weak interaction, this experiment is far beyond experimental possibility; the detector's mass for example would have to exceed that of our galaxy. Hannah and Eppley claimed that their experiment would at least in principle be possible to construct with the matter content of our universe. It was however later shown by James Mattingly, in his paper Why Eppley and Hannah's Experiment Isn't (the title evidently did not make it through peer review), that Hannah and Eppley underestimated the experimental challenges. Mattingly crunched the numbers and showed that the cosmic background radiation spoils the sensitivity of the detectors and, worse, that the detector would have to be so massive it would sit inside a black hole.

Thus, Hannah and Eppley's experiment isn't even in principle possible. While their reasoning is physically plausible, this puts one into a philosophically difficult spot. There clearly is a theoretical problem with coupling a classical to a quantum field, but if we can show there are no practical consequences in our universe, is it a problem we should worry about?

I like Hannah and Eppley's thought experiment. It is not the best motivation one can have for quantizing gravity, but it is a lean way to illuminate the problem.

What is science?

2012-01-04T03:30:00.005-05:00

As long as there has been science people have asked themselves how to identify it. Centuries of philosophers have made attempts and I don't intend to offer an answer in the confines of a blogpost. Instead, always the pragmatist, I want to summarize some points of view that I have encountered, more or less explicitly so, and encourage you to share your own in the comments. With this post, I want to pick up a conversation that started in this earlier post.

There is the question of content and that of procedure. The question of content is mainly a matter of definition and custom. When a native English speaker says "science" they almost always mean "natural science." On occasion they include the social sciences too. Even rarer so mathematics. The German word for science is "Wissenschaft" and in its usage is much closer to the Latin root "scientia."

According to the Online Ethymology Dictionary

Science

scientia

sciens

scientis

scire

The German "Wissenschaften" include besides the natural sciences not only the social sciences and mathematics, but also "Kunstwissenschaft," "Musikwissenschaft," "Literaturwissenschaft," etc, literally the science of art, the science of music, the science of literature. It speaks for itself that if you Google "Kunstwissenschaft" the first two suggestions are the completions "in English" and "translation." In the following I want to leave the content of "science" as open as the German and Latin expressions leave it, and let it be constrained by procedure, which for me is the more interesting aspect.

As for the procedure, I have come across these three points of view:

A: Science is what proceeds by the scientific method

When pushed, the usually well-educated defender of this opinion will without hesitation produce a definition for scientific method along the lines hypothesis, experimental test, falsification or gradual acceptance as established fact.

The problem, as Feyerabend pointed out, is that a lot of progress in science did simply not come about this way. Worse, requiring a universal method may in the long run stifle progress for the reason that the scientific method itself can't adapt to changing circumstances. (I'm not sure if Feyerabend said that, but I just did.) Requiring people in a field in which creativity is of vital importance to obey certain rules, however sane they seem, begs for somebody to break the rules - and succeed nevertheless.

There are many examples of studies that have been pursued for the sake of scientia without the possibility or even intention of experimental test, and they have later become tremendously useful. A lot of mathematics falls into this category and, until not so far ago, a big part of cosmology. Do you know what will be possible in 100 years? Prediction is very difficult, especially about the future, as Niels Bohr said.

The demand of falsifiability inevitably brings with it the question for patience. How long should we wait for an hypothesis to be tested before we have to discard it as unscientific? And who says so? If you open Pandora's box, out falls string theory and the technological singularity.

Finally, let me mention that if you sign up to this definition of science, then classifications, that make up big parts of biology and zoology, are not science. Science however are literature studies, for you can well formulate a hypothesis about, say, Goethe's use of the pluralis majestatis and then go and falsify it.

B: Science is what scientists do

This definition begs the question who is a scientist. The answer is that science is a collective enterprise of a community that defines its own membership. Scientists form, if you want to use a fashionable word, a self-organizing system. They define their own rules, and the viability of these rules depends on the rules' success. The rules cannot only change over time, allowing for improvement, there can also exist different ones next to each other that compete in the course of history.

I personally prefer this explanation of science. I like the way it fits into the evolution of the natural world, and I like how it fits with history. I also like that it's output oriented instead of process oriented: it doesn't matter how you do it as long as it works.

In this reading, the scientific method, as summarized in A, is so powerful for the same reason that animals have the most amazing camouflage: Selection and adaption. It does not necessitate infallibility. Maybe the criteria of membership we use today are too strict. Maybe in the future they will be different. Maybe there will be several ones.

The shortcoming of this definition is that there is no clear-cast criterion by which you can tell what of today's efforts are scientific, in much the same way that you can't tell whether some species is well adapted to a changing environment till they go extinct, possibly because they fall prey to a "fitter" species. That means that this definition of science will inevitably be unpopular in circumstances that require short and simple answers, circumstances in which the audience isn't expected to think for themselves.

Given the time to think, note that the lack of simple criteria doesn't mean one can't say anything. You can clearly say the scientific method, as defined in A, has proven to be enormously successful and, unless you are very certain you have a better idea, discarding it is the intellectual equivalent of an insect dropping its camouflage and hoping birds don't notice. Your act of rebellion might be very short.

That having been said, in practice there is little difference between A and B. The difference is that B leaves the future open for improvement.

C: Science is the creation, collection, and organization of knowledge

"All science is either physics or stamp collecting," said Ernest Rutherford. This begs the question whether stamp collection is a science. The definition C is the extreme opposite to A; it does not demand any particular method or procedure, just that it results in knowledge. What that knowledge is about or good for, if anything, is left up to the scientist operating under this definition.

The appeal of this explanation is that scientists are left to do, and collect what they like, with the hope that future generations find something useful in it; it's the "You never know" of the man who never throws anything away, and has carefully sorted and stored his stamps (and empty boxes, and old calendars, and broken pens, and...).

The problem with this definition is that it just doesn't overlap with most people's understanding of science, not even with the German "Wissenschaft." There is arguably a lot of knowledge that doesn't have any particular use for most people. I know for example that the VW parked in front of the house is our upstairs neighbor's, but who cares. Where exactly does knowledge stop being scientific? Is knowledge scientific if it's not about the real world? These are the question you'll have to answer to make sense of C.

(img sources: click on image)

Book review: "Quips, Quotes and Quanta" by Anton Z. Capri

2012-01-01T00:10:00.001-05:00

Quips, Quotes, and Quanta: An Anecdotal History of Physics
By Anton Z. Capri
World Scientific Publishing (2007)

I came across Capri's book "Quips, Quotes and Quanta" while searching fodder for our 2011 advent calendar with anecdotes about physicists. It took a while for the book to arrive, but I finally received it a few days before Christmas.

Capri's book is a collection of stories and quotations from the history of physics of the late 19th and early 20th century. The author uses these stories to embed the physics of that time and covers some parts of thermodynamics, quantum mechanics and atomic physics around the lives of Dirac, Schrödinger, Pauli, Bohr, Boltzmann, Ehrenfest, Hilbert, Heisenberg, Planck, to only mention the usual suspects. I will admit on not reading the physics elaborations too carefully, but for all I can tell the scientific content was flawless, if with the superficiality that brevity brings.

While it sounds like a nice idea to get across science with anecdotes, the realization of that idea is poor. The writing is uninspired, sloppy and without style. It is so bad that in parts it reads like copy and pasted from Wikipedia; a list of paragraphs with things soandso allegedly said or did, vaguely collected by name or topic. At least one paragraph appears twice in the book (search inside for "Sommerfeld had this to say about Pauli").

The book does not list a single reference. None of the stories or quotations comes with a source, not even the biographical details. I happened to know some of the sources, and the respective paragraphs appear to me just as scrambled enough so they cannot be identified as exact copies. Bohr's theory of the Wild West for example probably originated in Gamow's recollection. Other anecdotes I know to be wrong, for example that of Bohr and the horseshoe and that Donald Glaser allegedly invented the bubble chamber after watching bubbles raise in beer (which even Wikipedia knows to be made up).

The author, Anton Capri is a retired professor for Engineering Physics. He is not a historian, but as a scientist he should have learned to check and list sources. If you have a scale on which you'd want me to rate this book, mark the lowest possible score. Unless you don't care if an allegedly historical anecdote is entirely fabricated, I recommend you do not spend money on this book.

Happy New Year!

2011-12-31T05:59:00.002-05:00

We wish all our readers a good start into the year 2012! We hope that you find the insight you have been looking for, get the job you want or the grant you need. May it be a delightful year for you.

I'll use the opportunity to dump a few interesting links I've come across lately:

I enjoyed very much the NYT technology future timeline, where readers have proposed upcoming innovations and guessed when they would become reality.

In 2014 for example, "Scott Aaronson predicts, scientific publishing will move away from the current journal-and-conference model to a model that takes better advantage of online tools." I have now tried three times with different groups of colleages to make use of an online wiki or at least Google docs to avoid sending emails with updates and files or links around. I have failed three times, afaics for no reason other than that it was apparently too much of a new thing to try. Taking into account that physics is allegedly quick with adapting new tools, I think Scott is off by at least a decade. Scientific publishing will move when more than half of all tenured faculty will have been born past 1980.

In 2015 "Voting by phone" is on the timeline. Given that in Sweden you can make your tax reimbursement by phone (yes, I did!), and text messages are about to replace stamps, I wouldn't be surprised if the Swedes will be the first to make this reality.

Should mankind still exist in 2100, NYT readers believe that "physical sciences produce abundance so great that wealth becomes meaningless as a difference between people" and we'll be living in a post-scarcity world. This estimate seems to be ignoring reality. My personal estimate would be some thousand years later, maybe even longer, and that only under the condition that progress continues sufficiently long for us to find a sustainable way to meet our energy requirements.
Something entirely different, a while ago I went to a workshop under the COST initiative "Black Holes in a violent Universe." This initiative has now produced a video with a brief introduction about what different types of black holes there are. I could have lived without a reminder of the earth-swallowing tiny black holes, but besides that it's a nice summary. (Thanks to Xavier for the link!)
Mount Everest has now a webcam.
A few months ago, I wrote a post about citation-loops that can be created by citing Wikipedia without noting the date of retrieval. xkcd dubbed this process citogenesis.
And finally some good news: The budget of the German ministry for education and research (BMBF) will raise in 2012 by 11% to a total of 12.9 billion Euro.

Happy Birthday, Lara and Gloria

2011-12-29T04:00:00.004-05:00

Today, Lara and Gloria are one year old!

In this year, they have more than tripled their birth weight and they have grown more than 50%. In terms of growth, Lara is still ahead of her sister, meanwhile 2cm taller and 2 pounds heavier. In an amazing demonstration of neural network growth, the girls have learned to smile, to laugh, to hold their head, to turn around, to grab and to pick up crumbles. They have learned to eat from a spoon, to crawl, to sit up, and to stand. They have been through all vowels and are currently working their way through the consonants. They like to take and give toys, and as of lately have learned to throw them. They have both made the first stumbling step, but still deem crawling safer.

Lara has meanwhile two teeth and has found out that grinding them makes her daddy draw funny faces. Gloria has one tooth and now discovers all the possible ways to make noise with it, like running it up and down the bed posts or biting on cups.

It is interesting that while the girls are very different in character, they have made all developmental steps almost simultaneously. If one of them learned something new, the other would soon follow. The one exception is that before Lara could crawl, she had a phase of moving by rolling sideward that Gloria entirely skipped.

Every month, somebody told us the worst is yet to come. The worst are the first three months because they don't sleep through the night. The worst are months four to six because they sleep less during the day but can't yet use any toys, so want to be entertained around the clock. But wait, the worst are months six to nine because they get mobile and you can no longer just put them somewhere and go about your own business. Months nine to twelve are the worst because they get teeth and there goes your night rest. Now that the first year comes to an end, we've been told 12 to 18 months are the worst, because they start to walk and you can't leave them alone for a second. And just wait till they start talking!

As for me, the worst were month -3 to 0, everything after delivery was a vast improvement; I clearly wasn't constructed to carry around 17kg excess weight.

Still, this year has been very exhausting to say the least. We changed an estimated 5000 diapers, picked up pacifiers 20000 times, and our commuting from Heidelberg to Stockholm and my occasional conference attendance has been organizationally challenging. Scientifically, it went better than expected, in that I did manage to write two proposals (one of which was meanwhile declined however), gave a few talks, am organizing a workshop, and did indeed publish a paper. For me, the main problem working from home is the difficulty staying in touch with colleagues, which is also why there are some papers in the pipe that are not making much progress.

Stefan and I, we have been fighting now for more than a year with various institutions in Germany and Sweden for our parental benefits. Just in time for Christmas, we received good news: three quarters of what Stefan applied for has been approved. The problem with the remaining quarter is a fundamental incompatibility between counting in German and Swedish. The Germans count the months of parental benefits starting with the day the child is born (i.e. the 29th in our case); the Swedes count from the 21st on. In addition, the Germans count a month of leave as "taken" even if only one day has been taken. Based on this, they have calculated that for us the year 2011 has 13 months, and we've applied for one month in excess since we mistakenly assumed the year has 12 months.

We still haven't seen a single cent child allowance.

We have also encountered an ambitious local photographer, who has plastered the town with advertisements for "baby-shooting," and whom you have to thank for the creative arrangement in the below photo.

PS: You find some little videos here.

PPS: For birthday greetings more material than words, on Lara and Gloria's Amazon wishlist you can find what the girls will need in the coming months.

The fifth candle: Advent calendar encore

2011-12-26T05:00:00.001-05:00

While I was looking for fodder for the advent calendar, I came across this story in "A Passion for Discovery," by Peter Freund. Freund, a professor emeritus for theoretical physics, recalls anecdotes that he has witnessed or has been told throughout his career, such as this one:

Cranks approach scientists more often than you would guess. The main strategy for dealing with them is never to get into an argument, for they will not spare any of your time to convince you that they are right. The other useful trick is to convince the crank that you do not have the required expertise to be initiated in their sacred truth.

Another strategy: Academician N.N. Bogoliubov at Moscow State University was once approached by a crank. "I unfortunately am not qualified to discuss your work" Bogoliubov told the man, "but Academician Lev Landau is working on related problems. He is the man you are looking for." [...]

On another occasion... two men from the Shah of Iran's Vienna Embassy showed up [at the Institute for Theoretical physics in Vienna where the author was located at that time]. One of the two Iranians excitedly told us about their discovery, while his companion nodded along. They had apparently discovered that time does not exist. Their proof was eminently simple. "By the time I say now, now is already over. Quot Erat Demonstrandum." Did we not agree that this was a major discovery, and what should they do with it? Armed with our two principles, we agreed that the discovery was major and suggested they work out all its implications, especially practical applications, for they would likely make a great deal of money. This did the trick; the two left happy men.

Merry Christmas

2011-12-25T10:00:00.003-05:00

We wish all our readers a merry Christmas! And if you're not into heathen traditions turned Christian turned capitalist, we wish you a peaceful and happy day anyway :o) As promised, we conclude our advent calendar with a quiz:

Erwin Schrödinger had a daughter with the wife of which physicist colleague? (First and last name, 11 letters.)

The catholic church of which town has windows that were designed by an artist with education in physics who used pictures of three-jet events, spectroheligrams and Feynman diagrams? (6 letters)

Which physicist introduced constants of length, mass and time with the motivation that they would be meaningful also for extraterrestrials? (Last of his middle names, 6 letters).

According to a study published in the Journal "Sex Roles" in 1979, at which age in months are human female infants the cutest? (Write down English word for the number.)

Which chemical element forms together with chloride a solid that at room temperature is blue in its pure form but turns purple when it binds (pure) water? (6 letters)

Approximately at which volume, in liters, does an (average) human stomach burst, according to a study performed on organs of deceased, published in Revue médicale de la Suisse romande, in 1885? (One digit).

If you write down the answers in the order of the questions you should get a string with 34 symbols. The following entries give you the solution to this year's quiz: 33-11-1-24-15-34-17-27-31-20-22-26-23.

This year's prize is a BackRe(Action) mug and it will go to the first who submits the right answer in the comments. (For the shipment, we'll need your snail-mail address. If you are not willing to provide your address, please do not spoil the fun.)

Hint: The answers to question 1,3,4 and 6 can be found on this blog. The answers to question 2 and 5 can be found on Wikipedia. If I notice you're stuck, I will provide more hints in the comments.

Advent calendar #24: Bohr's theory of the Wild West

2011-12-24T04:00:00.002-05:00

Today's anecdote about Niels Bohr comes from George Gamow's book "Thirty years that shook physics - The story of quantum theory." This is the same Gamow we have met earlier in correspondence with Wolfgang Pauli. Gamow is the person who famously predicted the cosmic background radiation long before it was discovered. In the late 1920s, he was a student in Copenhagen under Niels Bohr, and tells the following:

The only movies [Bohr] liked were Wild Westerns (Hollywood style), and he always needed a couple of his students to go with him and explain the complicated plots... But his theoretical mind showed even in this movie expeditions. He developed a theory to explain why although the villain always draws first, the hero is faster and manages to kill him. This Bohr theory was based on psychology. Since the hero never shots first, the villain has to decide when to draw, which impedes his action. The hero on the other hand acts according to conditioned reflexes and grabs the gun automatically as soon as he sees the villain's hand move. We disagreed with this theory, and the next day I went to a toy store and bought two guns in Western holders. We shot it out with Bohr, he being the hero, and he "killed" all his students.

Advent calendar #23: Moonshine in Rutherford's brain

2011-12-23T04:00:00.006-05:00

Ernest Rutherford is known for his achievements in atomic and nuclear physics, most essentially the insight that the mass of the atom is concentrated in a small nucleus. This is known today as the Rutherford model of the atom, and was experimentally shown by scattering alpha particles on gold. Rutherford won the Nobel prize for Chemistry in 1908 for his investigations into the disintegration of the elements, and the chemistry of radioactive substances.

In 1933, he gave a talk at a meeting of the British Association for the Advancement of Science, from which he was quoted in The London Times of September 12, 1933 about the possibility of energy-efficient nuclear fission as follows:

We might in these processes obtain very much more energy than the proton supplied, but on the average we could not expect to obtain energy in this way. It was a very poor and inefficient way of producing energy, and anyone who looked for a source of power in the transformation of the atoms was talking moonshine. But the subject was scientifically interesting because it gave insight into the atoms.

The 16 September 1933 issue of Nature tells its readers about the talk:

One timely word of warning was issued to those who look for sources of power in atomic transmutations ‒ such expecations are the merest moonshine.

It is easy to invoke this statement as a further example for a severe scientific misjudgement by a senior scientist. But in context, it was perfectly reasonable: Rutherford was discussing nuclear reactions tiggered by the proton beam from the then brand-new accelerator of Cockroft and Walton. Trying to gain nuclear energy that way is about as efficient as producing antimatter at CERN to fuel a matter-antimatter-annihilation engine.

Moreover, in his paper Atomic Energy is "Moonshine": What did Rutherford Really Mean?, historian of science John G. Jenkin argues that Rutherford was well aware that there might be ways to harness nuclear energy, especially using neutrons as tools to induce reactions. He suggests that Rutherford "in all of his later negative pronouncements regarding the possibility of atomic energy, was adopting a quite deliberate policy to disguise and postpone, for as long as possible, the awful prospect that he saw looming over the horizon: a new and dreadful war, a new and devastating weapon, and unprecedented destruction."

On a lighter side, Rutherford also allegedly warned (quoted for example in "The Strangest Man: The hidden life of Paul Dirac" by Graham Farmelo):

"Don't let me catch anyone talking about the universe in my department!"

and said about special relativity (quoted for example in "The Nobel Prize: A History of Genius, Controversy, and Prestige" by Burton Feldman):

"Oh, that stuff. We never bother with that in our work."

Though I am not sure about the origin of this latter quotation.

Rutherford was reportedly skeptic about special relativity in its early days, and for most of atomic physics it can be safely neglected and one does indeed not have to bother. But when in 1930 he prepared a new and updated edition of his book "Radiation from Radioactive Substances", he did add a discussion of the mass defect based on E = mc².

Advent calendar #22: Space, Time and Birds

2011-12-22T04:00:00.000-05:00

Today's anecdote about Werner Heisenberg has been preserved by Felix Bloch in his article "Heisenberg and the early days of quantum mechanics" Physics Today, December 1976:

We [Werner Heisenberg and Felix Bloch] were on a walk and somehow began to talk about space. I had just read Weyl's book Space, Time and Matter, and under its influence was proud to declare that space was simply the field of linear operations.

"Nonsense," said Heisenberg, "space is blue and birds fly through it."

This may sound naive, but I knew him well enough by that time to fully understand the rebuke. What he meant was that it was dangerous for a physicist to describe Nature in terms of idealized abstractions too far removed from the evidence of actual observation. In fact, it was just by avoiding this danger in the previous description of atomic phenomena that he was able to arrive at his great creation of quantum mechanics. In celebrating the fiftieth anniversary of this achievement, we are vastly indebted to the men who brought it about: not only for having provided us with a most powerful tool but also, and even more significant, for a deeper insight into our conception of reality.

Advent calendar #21: Bohr and the horseshoe

2011-12-21T04:00:00.002-05:00

The web is full with anecdotes and quotations about physicists and mathematicians. It would not be difficult to fill a whole year with stories Google put at my fingertips, but then I could as well make them up myself. The time-intensive part of this advent calendar has not been to find the stories but to find out if they have a reliable source. Inevitably, some widely spread stories, if they had any source at all, turned out to have been altered several times, much like a digital game of Chinese whispers.

One such story is for example that of Niels Bohr and the horseshoe. The version on this website goes like this:

"An American scientist once visited the offices of the great Nobel prize winning physicist, Niels Bohr, in Copenhagen. He was amazed to find that over Bohr's desk was a horseshoe, securely nailed to the wall, with the open end up in the approved manner (so it would catch the good luck and not let it spill out). The American said with a nervous laugh,

"Surely you don't believe the horseshoe will bring you good luck, do you, Professor Bohr? After all, as a scientist --" Bohr chuckled.

"I believe no such thing, my good friend. Not at all. I am scarcely likely to believe in such foolish nonsense. However, I am told that a horseshoe will bring you good luck whether you believe in it or not."

In some other versions that you can find online it's a student who asks the question, in yet some other versions the horseshoe is not above the desk but above the door to Bohr's cottage. The above version is particularly interesting for the amount of irrelevant details that somebody or maybe several people have added. Wikipedia lists the quote as disputed.

To find the origin of that story it is useful if you speak German, since it goes back to Werner Heisenberg's book "Der Teil und das Ganze" (The part and the whole). Most of the book is a recollection of conversations Heisenberg had with Niels Bohr and Wolfgang Pauli, among others. Heisenberg wrote down these conversations long after they had taken place, so one should not expect the exchange to have been word by word exactly as he reported. Heisenberg finishes Chapter 8 on "Atomphysik und pragmatische Denkweise" (atomic physics and pragmatism) with an anecdote that Niels Bohr told:

Niels schloß das Gespräch ab mit einer jener Geschichten, die er bei solchen Gelegenheiten gern erzählte: "In der Nähe unseres Ferienhauses in Tisvilde wohnt ein Mann, der hat über der Eingangstür seines Hauses ein Hufeisen angebracht, das nach einem alten Volksglauben Glück bringen soll. Als ein Bekannter ihn fragte: "Aber bist du denn so abergläubisch? Glaubst du wirklich, dass das Hufeisen dir Glück bringt?", antwortete er: "Natürlich nicht; aber man sagt doch, daß es auch dann hilft, wenn man nicht daran glaubt.""

Niels finished with one of these stories he liked to tell on such occasions: "Near by our vacation house in Tisvilde lives a man who has a horseshoe above his door, after the old superstition that it brings luck. When a friend asked him "Are you superstitious? Do you really believe the horseshoe brings luck?" He replied "Of course not; but they say it also helps if you don't believe it."

~Werner Heisenberg, Der Teil und das Ganze, 1973, p. 112/13

So if you plan on winning a Nobel prize, be careful with the anecdotes you tell. Later generations might unashamedly turn the narrator into a subject and the details may be buried in translation.

Advent Calendar #20: Fermi's driver

2011-12-20T04:00:00.003-05:00

Enrico Fermi had quite a dry sense of humor. George Gamow, in his book Thirty Years that Shook Physics: The Story of Quantum Theory, relates the following story from the time when Fermi was a professor in Rome in the 1930s:

Once Fermi had to attend a meeting of the Academy of Sciences at the Palazzo di Venezia, which was strongly guarded because Mussolini himself was to address it. All other members arrived in large foreign-made limousines driven by uniformed chauffers, while Fermi drew up in his little Fiat. At the gate of the Palazzo he was stopped by two carabinieri who crossed their weapons in front of his little car and asked his business there. According to the story he told to the author of this book, he hesitated to say to the guards: "I am His Excellency Enrico Fermi," for fear that they would not believe him. Thus, to avoid embarrassment, he said: "I am the driver of His Excellency, Signore Enrico Fermi." "Ebbene," said the guards, "drive in, park, and wait for your master."

Upcoming Christmas Quiz

2011-12-20T03:00:00.000-05:00

In good tradition, we'll finish our seasonal program with a quiz, which is prescheduled for December 25th, 4pm Central European Time, that's 10am on the East Coast. This year's prize is a BackRe(action) mug (see photo), though of course it's more about the fun than about the prize.

Every year I put together the questions and use Stefan as a guinea pig. If he manages to solve the quiz in less than 10 minutes it's too easy. If he hasn't worked it out in 2 hours, taking into account that he knows fairly well the likely sources I have used, it's too difficult. On the Stefan-scale, this year's quiz is more difficult than the ones before, so don't miss it!

The quizzes from the previous years are here: 2007, 2008, 2009, 2010.

Advent Calendar #19: Confident Einstein

2011-12-19T04:00:00.001-05:00

In September 1919, Ilse Schneider was working on her Ph.D. thesis in philosophy at the university of Berlin on the "space-time problem in Kant and Einstein". She did profit from the fact that the creator of the theory of relativity was a professor in the physics department: She attended Einstein's lectures, and met regulary with him to discuss the meaning and implications of his theory.

At that time, Einstein was eagerly waiting for news about the results of the British eclipse expedition by Eddington, who had tried to measure the deflection of light by the sun as predicted by the general theory of relativity. Einstein's theory of general relativity is a remarkable achievement of a brilliant mind that knew how to make use of mathematics. Einstein had to try around somewhat before he found the correct equations, but once he had arrived there, he had little doubt they did describe nature correctly.

In her memoir "Reality and Scientific Truth: Discussions with Einstein, von Laue, and Planck", Ilse Rosenthal-Schneider remembers on of her meetings with Einstein from that time:

Suddenly Einstein interrupted the reading and handed me a cable that he took from the window-sill with the words, "This may interest you." It was Eddington's cable with the results of the famous eclipse expedition. Full of enthusiasm, I exclaimed, "How wonderful! This is almost the value you calculated!" Quite unperturbed, he remarked, "I knew that the theory is correct. Did you doubt it?" I answered, "No, of course not. But what would you have said if there had been no confirmation like this?" He replied, "Da könnt' mir halt der liebe Gott leid tun. Die Theorie stimmt doch." ("I would have had to pity our dear God. The theory is correct anyway.")

We thank Toby Bryant for reminding us of that story! According to the Einstein biography by Albrecht Fölsing, Einstein did receive a telegram from Lorentz in Leiden on September 22, 1919, reporting preliminary results on the light deflection as compatible with the prediction of general relativity.

Advent calendar #18: Heisenberg and the microscope

2011-12-18T04:00:00.003-05:00

Werner Heisenberg is well known for his analysis of the inevitable uncertainty in observations with a microscope that eventually lead him to formulate the uncertainty principle. Less known is the origin of his obsession with microscopes. In 1923, Heisenberg was heading towards the final oral examination for his doctorate. He passed mathematics, theoretical physics and astronomy just fine, but he run into troubles with experimental physics where he was to be examined by Wilhelm Wien.

Wien had required that Heisenberg did a "Praktikum" (basically a practice in physics experiments), but there was some equipment lacking and Heisenberg wasn't interested enough to find out where to get it. He thus turned towards other things without looking much into the experiments he was supposed to do, for example measuring the splitting of spectral lines by help of an interferometer. Then came the day of the oral exam:

"Wien was annoyed when he learned in the examination that Heisenberg had done so little in the experimental exercise given to him. He than began to ask him questions to gauge his familiarity with the experimental setup; for instance, he wanted to know what the resolving power of the Fabry-Perot interferometer was... Wien had expained all this in one of his lectures on optics; besides, Heisenberg was supposed to study it anyway... But he had not done so and now tried to figure it out unsuccessfully in the short time available during the examination. Wien... asked about the resolving power of a microscope; Heisenberg did not know that either. Wien questioned him about the resolving power of telecopes, which [Heisenberg] also did not know."

(From Jagdish Mehra, Helmut Rechenberg: "The Historical Development of Quantum Theory Vol. 2 - The Discovery of Quantum Mechanics 1925" p. 67)

Wien wanted to fail Heisenberg, but Sommerfeld, in whose exam on theoretical physics Heisenberg had excelled, put in a strong word for Heisenberg. Heisenberg passed the doctoral examination with the lowest possible grade. Many years later Heisenberg would recall

"So one might even assume, that in the work on the gamma-ray microscope and the uncertainty relation I used the knowledge which I had acquired by this poor examination."

Advent Calendar #17: Fermi's paper snippets

2011-12-17T04:00:00.004-05:00

Enrico Fermi is famous for his ingenious ways to arrive at quantitive estimates for the solution of complicated physical problems. One of the most legendary examples is his estimate of the energy released by the first atomic bomb. As Fermi himself recalls in My Observations During the Explosion at Trinity on July 16, 194,

About 40 seconds after the explosion the air blast reached me. I tried to estimate its strength by dropping from about six feet small pieces of paper before, during, and after the passage of the blast wave. Since, at the time, there was no wind I could observe very distinctly and actually measure the displacement of the pieces of paper that were in the process of falling while the blast was passing. The shift was about 2 1/2 meters, which, at the time, I estimated to correspond to the blast that would be produced by ten thousand tons of T.N.T.

Emilio Segrè, who witnessed the event together with Fermi, gives a few more details. In his biography Enrico Fermi, Physicist, he writes that Fermi had done the necessary calculations in advance, "having prepared himself a table of numbers, so that he could tell immediately the energy liberated from this crude but simple measurement."

At Los Alamos, Enrico Fermi had the role of an "oracle": Because of his enormous knowledge and competence in all areas of physics, he was consulted for all kinds of physical problems. However, his mastery of physics could be intimidating to other physicists.

As a bonus, here is a story remembered by Subrahmanyan Chandrasekhar, who was a colleague of Fermi at the University of Chicago in the early 1950s (Bull. Amer. Math. Soc. Vol. 84, No. 3 (1978), p. 431):

Some twenty-five years ago, I met a colleague of mine emerging from the office of Enrico Fermi. He told me that he had been discussing physics with Fermi; and after a moment's pause asked, "Why am I doing physics? I should probably be a grocer".

Advent calendar #16: Stern's cigar

2011-12-16T04:00:00.008-05:00

This is a story one cannot escape if one studies physics in Frankfurt am Main.

In 1922 Otto Stern and Walther Gerlach demonstrated the directional quantization of angular momentum by sending silver atoms through an inhomogeneous magnetic field. Silver has only one electron in the valence shell, so the orbital angular momentum vanishes and only the electron spin contributes to the total angular momentum of the atom. Depending on the orientation of the spin relative to the magnetic field, the atom takes one out of two trajectories, leading to a discrete splitting of the beam after it passed the magnetic field. Classically, one would expect a smooth distribution. This experiment, conducted in Frankfurt am Main, is known today as the Stern-Gerlach experiment, and was one of the milestones on the way to quantum mechanics.

But it was not just the ingenuity of the experimenters that lead to success since originally Stern and Gerlach couldn't see anything on the screen that should be showing two discrete lines. Dudley Herschbach, who won the Nobel prize for Chemistry in 1986, retold Stern's description of the discovery as follows:

"After venting to release the vacuum, Gerlach removed the detector flange. But he could see no trace of the silver atom beam and handed the flange to me [Stern]. With Gerlach looking over my shoulder as I peered closely at the plate, we were surprised to see gradually emerge the trace of the beam... Finally we realized what [had happened]. I was then the equivalent of an assistant professor. My salary was too low to afford good cigars, so I smoked bad cigars. These had a lot of sulfur in them, so my breath on the plate turned the silver into silver sulfide, which is jet black, so easily visible. It was like developing a photographic film."

The complete story of Stern and Gerlach's experiment can be found in Physics Today 56 (December 2003) Stern and Gerlach: How a Bad Cigar Helped Reorient Atomic Physics (pdf), by Bretislav Friedrich and Dudley Herschbach. They also went on to test the plausibility of this story and repeated the original experiment at its 80st anniversary. The found that bad breath alone wouldn't do the trick, but that more likely Stern was actually puffing on a cigar when Gerlach handed him the invisible result.

Advent calendar #15: The end is nigh

2011-12-15T04:00:00.002-05:00

In 1903, briefly before the dawn of Special Relativity and Quantum Mechanics, Albert Abraham Michelson offered his view on physics:

“The more important fundamental laws and facts of physical science have all been discovered, and these are so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote.”

~A.A. Michelson, Light waves and their uses, University of Chicago Press (1903)

Advent calendar #14: From Hilbert with Sympathy

2011-12-14T04:00:00.001-05:00

Hilbert had a student who one day presented him with a paper purporting to prove the Riemann hypothesis. Hilbert studied the paper carefully and was really impressed by the depth of the argument; but unfortunately he found an error in it which even he could not eliminate. The following year the student died. Hilbert asked the grieving parents if he might be permitted to make a funeral oration. While the student's relatives and friends were weeping beside the grave in the rain, Hilbert came forward. He began by saying what a tragedy it was that such a gifted young man had died before he had an opportunity to show the world what he could accomplish. But, he continued, in spite of the fact that this young man's proof of the Riemann hypothesis contained an error, it was still possible that some day a proof of the famous problem would be obtained along the lines which the deceased had indicated. "In fact," he continued with enthusiasm, standing there in the rain by the dead student's grave, "let us consider a function of one complex variable..."

Quoted from "Hilbert" by Constance Reid, where it is noted that this story is "perhaps apocryphal."

Advent Calendar #13: A Postdoc's Nightmare

2011-12-13T04:00:00.002-05:00

Pascual Jordan was, along with Werner Heisenberg, Paul Dirac, and Wolfgang Pauli, one of the Wunderkinder contributing to the development of quantum mechanics. He had obtained his Ph.D. in 1924, at the age of 22. In the following year, together with his Ph.D. advisor Max Born and with Heisenberg, he created the matrix formulation of quantum mechanics, formulating the canonical commutation relations between position and momentum. Jordan kicked off quantum field theory, and found the anti-commutation relation for creation and annihilation operators of particles with spin 1/2. These particles, now known as fermions, actually could be linked directly to Jordan, were it not for a case of extremely bad luck. As Max Born remembers:

In December of 1925 I went to America to give lectures at MIT. I was editor of the Zeitschrift für Physik, and Jordan gave me a paper to be published in the journal. I didn't find time to read it and put it in my suitcase. I forgot about it, and when I returned half a year later and unpacked, I found the paper at the bottom of the suitcase. It contained the Fermi-Dirac statistics. Meanwhile both Fermi and Dirac had discovered it. But Jordan was the first.

The Max Born quote, and more about Jordan, can be found in Engelbert Schuckings reminescences "Jordan, Pauli, Politics, Brecht... and a Variable Gravitational Constant" (in On Einstein's path: Essays in Honor of Engelbert Schucking).

Advent calendar #12: All of astronomy

2011-12-12T04:00:00.002-05:00

In 1904, Max Born, a German born physicist who would win the Nobel prize in 1954, went to Göttingen to study mathematics and physics. He soon made friends with Professor Karl Schwarzschild, who taught astronomy, and at that time was not much older than his students. Schwarzschild's name might be familiar to you from the Schwarzschild-metric - the first known exact solution to Einstein's field equations that he would derive about a decade later.

In their book "Der Luxus des Gewissens" (The Luxury of Conscience) by Max Born and his wife Hedwig, Born recalls that he used to play tennis with Schwarzschild. Max Born (who was called "Maxel" by his friends) liked Schwarzschild's astronomy class, but did not feel very inspired by the lectures on geometry, held by the great mathematician Felix Klein, namegiver of the Klein bottle:

"Die geometrischen Vorlesungen... waren aber nicht nach meinem Geschmack, und ich besuchte sie nicht sehr regelmäßig... Mein Reinfall im müdlichen Examen, das in nur sechs Monaten bevorstand, schien unvermeidlich."

"The lectures in geometry... were not to my taste and I did not attend them on a regular basis. That I would flop at the oral exam, to which there were only six months to go, seemed unavoidable."

Maxel asked his friend Schwarzschild for advice. Schwarzschild suggested to instead take the exam in astronomy:

"[E]r sagte, ein halbes Jahr sei reichlich Zeit, die ganze Astronomie zu lernen."

"He said, half a year is more than enough time to learn all of astronomy."

Max passed the oral exam in astronomy, even though he answered the question "What do you do when you see a falling star?" with "I make a wish!" and only after Schwarzschild's further inquiry remembered to add "I note down the time and location, the direction and the length of the visible trace."

Advent calendar #11: Prescient Einstein

2011-12-11T04:00:00.003-05:00

From Bertram Kostant (Professor Emeritus of Mathematics at MIT) via Garrett Lisi @ Physics Forums comes the following anecdote:

"I was a visiting member of Princeton's Institute for Advanced Study in 1955. It was a Good Friday in April and Einstein was looking for the Institute bus to take him back home to 112 Mercer Street. Being Good Friday, the driver was on holiday amd I offered to drive him home. We had a wonderful conversation and at one point he asked me what I was working on. I told him Lie groups. He then remarked, wagging his finger, that that will be very important. Actually, I was quite surprised that he knew who Lie was. About a week later Einstein was dead."

Advent calendar #10: It sounds Greek to me!

2011-12-10T04:00:00.000-05:00

Of course we cannot allow Richard Feynman to be missing when we tell physics anecdotes. He told his anecdotes well himself, and they have been captured by Ralph Leighton in the book "Surely You're Joking, Mr. Feynman!" One of my favorites is this story:

I don't know why, but I'm always very careless, when I go on a trip, about the address or telephone number or anything of the people who invited me. I figure I'll be met, or somebody else will know where we're going; it'll get straightened out somehow.

One time, in 1957, I went to a gravity conference at the University of North Carolina. I was supposed to be an expert in a different field who looks at gravity. I landed at the airport a day late for the conference (I couldn't make it the first day), and I went out to where the taxis were. I said to the dispatcher, "I'd like to go to the University of North Carolina."

"Which do you mean," he said, "the State University of North Carolina at Raleigh, or the University of North Carolina at Chapel Hill?"

Needless to say, I hadn't the slightest idea. "Where are they?" I asked, figuring that one must be near the other.

"One's north of here, and the other is south of here, about the same distance."

I had nothing with me that showed which one it was, and there was nobody else going to the conference a day late like I was.

That gave me an idea. "Listen," I said to the dispatcher. "The main meeting began yesterday, so there were a whole lot of guys going to the meeting who must have come through here yesterday. Let me describe them to you: They would have their heads kind of in the air, and they would be talking to each other, not paying attention to where they were going, saying things to each other, like 'Gmunu.Gmunu.'"

His face lit up. "Ah, yes," he said. "You mean Chapel Hill!" He called the next taxi waiting in line. "Take this man to the university at Chapel Hill."

"Thank you," I said, and I went to the conference.

Advent calender #9: Prof. Jolly's advice

2011-12-09T05:00:00.000-05:00

When Max Planck had finished high school in 1874, he was unsure which career path to chose. He had many different talents and interests, and pondered becoming a concert pianist, or study classical philology, or maybe mathematics and physics. Planck's father, a professor of law, mediated an appointment with his colleague, physicist Philipp von Jolly, for Max to get some advice. Prof. Jolly was a bit gloomy about the prospects of physics, and didn't want to raise false hopes in the young man. As Max Planck remembered,

Als ich meine physikalischen Studien begann und bei meinem ehrwürdigen Lehrer Philipp von Jolly wegen der Bedingungen und Aussichten meines Studiums mir Rat erholte, schilderte mir dieser die Physik als eine hochentwickelte, nahezu voll ausgereifte Wissenschaft, die nunmehr, nachdem ihr durch die Entdeckung des Prinzips der Erhaltung der Energie gewissermassen die Krone aufgesetzt sei, wohl bald ihre endgültige stabile Form angenommen haben würde. Wohl gäbe es vielleicht in einem oder dem anderen Winkel noch ein Stäubchen oder ein Bläschen zu prüfen und einzuordnen, aber das System als Ganzes stehe ziemlich gesichert da, und die theoretische Physik nähere sich merklich demjenigen Grade der Vollendung, wie ihn etwa die Geometrie schon seit Jahrhunderten besitze. (Max Planck, Wege zur physikalischen Erkenntnis, S. Hirzel, 1933, p. 128)

Philipp von Jolly described physics as a highly developed, almost fully matured science, which was about to reach a final form, now that the principle of conservation of energy had been discovered. He thought that there may be a speck or a vesicle left to be studied and classified in one or the other angle of the field, but that as a whole, the system had a fairly safe standing, and that theoretical physics was approaching the same degree of perfection reached by geometry already centuries ago.

Max Planck did not let himself be dissuaded from studying physics by this assessment, and the rest is history.

Advent calendar #8: Einstein's old envelopes

2011-12-08T04:00:00.000-05:00

When Herr Professor Doktor Einstein and his wife visited Mr and Mrs Hubble at Mt Wilson, at one stage the two ladies were left alone to swap confidences. Mrs Hubble pointed at the great telescope and explained that her husband used it “to study the nature of the universe” whereupon Frau Einstein retorted that “my husband does that on the back of an old envelope!”

Submitted by Cormac O' Raifeartaigh. This anecdote is mentioned for example in “The Day We Found the Universe” by Marcia Bartusiak.

Advent calendar #7: Bullshit with equations

2011-12-07T04:00:00.000-05:00

“In [high energy] quantum physics, to observe something, you have to create it. Now this sounds scarily close to bullshit. But if it is bullshit, then at least it's bullshit with equations.”

~Frank Wilczek, public lecture at Perimeter Institute

(Recycled from November 2008)

Advent calendar #6: The dissolved Nobel Prizes

2011-12-06T04:00:00.003-05:00

This is the most wondrous story in our advent calendar.

The two German physicists Max von Laue and James Franck won the Nobel Prize in 1914 and 1925 respectively. When the Nazis grew strong in Germany von Laue and Franck sent their medals, made of 23-karat gold, to Niels Bohr in Copenhagen. During these troublesome times many people were hiding or burying their family jewelry or anything of timeless value that they wanted to keep out of the Gestapo's hands, though it was illegal to send valuables out of country.

Unfortunately, by 1940 the Nazis made it to Copenhagen. Bohr was now in possession of two large gold pieces that carried von Laue's and Franck's names and clearly left Germany unapproved. Bohr had to get rid of the Nobel medals, and quickly so. It was Georgy de Hevesy, a colleague and friend from the department of chemistry, who came up with a ingeneous solution, quite literally: he would dissolve the medals.

Now gold is a precious metal and what makes it so precious is that it is slow to react with anything. It takes a mixture of acids known as aqua regia and time to dissolve gold, but at the end of a seemingly endless afternoon the medals were gone and left was a glass with a bright orange solution that didn't catch the interest of the Nazis.

But that wasn't the end of the story. After the war, de Hevesy returned to his lab and found the orange solution undisturbed in his shelf. He precipitated out the gold and sent it back to the Nobel Foundation in Stockholm. They recast the medals and gave them back to von Laue and Franck.

De Hevesy won the Nobel price for chemistry in 1943.

This story can be found in many books. It was recently told in some more details at NPR blogs: Dissolve my Nobel Prize! Fast!.

Advent calendar #5: Share the love

2011-12-05T04:00:00.003-05:00

In 1933, Erwin Schrödinger moved to Oxford. The physicist Arthur March, best known for his (failed) attempt to give physical meaning to a Lorentz-invariant minimal length scale, was not only Schrödinger's colleague but also a close friend. Due to Schrödinger's initiative, March too got a position in Oxford. Summer 1933, on a vacation in Tyrol, Schrödinger went on a bike excursion with Arthur March's wife Hilde. Nine months later Hilde gave birth to Schrödinger's daughter. Arthur March did not seem to mind much, but Schrödinger's wife went on to have an affair with the mathematician Hermann Weyl, while Weyl's wife in return found comfort with the physicist Paul Scherrer.

This and other details of Schrödinger's illustrious life can be found in Walter Moore's biography Schrödinger: Life and Thought.

Advent calendar #4: Einstein's haircut

2011-12-04T04:00:00.003-05:00

In Stefan's bookshelf I found a little book "Einstein privat" by Friedrich Herneck who, on the book cover, is described as "one of today's leading Einstein researchers." Herneck interviewed Einstein's former household aid, Herta W., about everything from Einstein's smoking habits, over nicknames used in the family to how often Einstein fed the goldfish. Herta W. had the following to say about Einstein's haircut which, next to going sockless, has become trademark of the ingenious theoretical physicist:

"Wenn seine Haare zu lang waren, wenn es gar zu schlimm geworden war, dann hat [seine Frau Elsa] ihm das Haar mit der Schere abgeschnitten. Das hat er sich dann auch machen lassen. Da Frau Professor aber sehr kurzsichtig war und beim Haarschneiden ihre Lorgnette, ihre Stielbrille, nicht ständig benutzen konnte... Aber Herr Professor war eben nicht zu bewegen, zu einem Berufsfrisör zu gehen."

"When his hair grew too long, when it got really intolerable, then [his wife Elsa] cut his hair off with a scissor. He let her do that. But since Frau Professor was very shortsighted and, during cutting, could not always use her Lorgnette... But Herr Professor could not be bothered to see a professional barber."

"Frau Professor" is (here) the form of address for the professor's wife and a lorgnette are old-fahioned glasses that have to be held on a handle in front of one's eyes. Later in the interview there's more talk about Frau Professor's shortsightedness and it seems it was indeed serious. She was however too vain to permanently wear thick glasses.

Interna

2011-12-03T11:00:00.002-05:00

Lara and Gloria are now 11 months old. They can both stand, on wobbly knees, though most of the time they insist on holding onto the furniture. Lara has half of a first tooth and a second in the making, and Gloria's first tooth is just about visible. I of course have dutifully brushed Lara's halftooth with pink toothpaste, which she seems to find very amusing. The babies have both suffered through their first cold, luckily a mild version, and have learned to nibble on bread and cookies.

It is interesting to see how different the girls are, even though they share not only the same parents, but also a room, clothes and toys. Lara is now a few centimeters taller and also an estimated two pounds heavier than Gloria. (We'll know more precisely at their next doctor's visit, which is in 2 weeks.) When Gloria falls, she inevitably starts crying dramatically until you pick her up. When Lara falls, she might make some surprised sound, though not always, and just move on. She does however occasionally start crying just because her sister cries. Gloria sucks her thumb (the left one), day and night; Lara never does. Lara does however gnaw on the bedposts with her half tooth.

Trying to change Lara's cloths has become a fight because she kicks, throws towels and cloths around, and tries to grab everything close enough. If you pull her away or turn her back around, she laughs and tries even harder. Gloria is one charmingly smiling baby on the changing table, as long as she has her rubber ducky to suck on. But try to take the ducky away...

I meanwhile am fighting once again with the paperwork. Not only are my Swedish parental benefits running out on Tuesday, but the Germans are refusing to pay Stefan's parental benefits. After a lot of calls and letters, it turned out that they seem to have misread one of the Swedish documents I sent them and thought the amount I got for 5 months was for one month, then concluded we're too rich to apply for benefits in Germany. Now they want more paperwork, that I have to rout to Sweden and back. For that and some other reasons I am somewhat stressed out in these darkest weeks of the year, so excuse the lack of originality on this blog. Finally, Lara sends her greetings:

Advent calendar #3: Details are missing

2011-12-03T05:00:00.001-05:00

In 1958, Pauli and Heisenberg were working an a unified theory which is today still the holy grail of particle physicists. Heisenberg gave a talk about their recent results, appearing confident that they had found a unified theory, only technical details were missing. An eager journalist who sat in the audience spread the news about the "world-equation," very much to Pauli's dismay. In a 1958 letter to George Gamov, Pauli commented on Heisenberg's radio announcement: "This is to show the world that I can paint like Titian. Only technical details are missing," illustrated by an empty rectangle.

This alleged all-explaining world equation came about before Yang and Mill's contribution to physics became appreciated. Looking at the Lagrangian in question today, it doesn't seem to be gauge invariant and with a four-fermion coupling won't fare well in terms of renormalizability.

Pauli's letter can be found in the CERN archive.

Advent calendar #2: Pauli and the anomalous Zeeman effect

2011-12-02T04:00:00.000-05:00

The Zeeman effect is the splitting of spectral lines in an external magnetic field, first observed by Pieter Zeeman in the late 19th century. The magnetic field removes a degeneracy between electron shells with different magnetic quantum number. By 1920 that was fairly well understood, unfortunately most of the observed atoms showed much more complicated spectra than expected. This became known as the "anomalous Zeeman effect" and caused the theoretical physicists of the time quite some headache. We know today that the additional splitting is due to the electron spin, but it was still a decade till Dirac would write down the equation for spin 1/2 particles that is now named after him. Recalling the time in 1946, Wolfgang Pauli wrote:

“A colleague who met me strolling rather aimlessly in the beautiful streets of Copenhagen said to me in a friendly manner, “You look very unhappy,” whereupon I answered fiercely, “How can one look happy when he is thinking about the anomalous Zeeman effect?””

Call to readers: Send us your favorite physics anecdote!

2011-12-01T03:13:00.000-05:00

Reminded by a recent comment, Stefan and I noticed that time has come to open the first door on the advent calendar. This year, we will have a daily anecdote from the lives and works of well-known physicists. These are all quotations or stories that many of you will be familiar with from your physics lectures, but I hope for the rest of our readers it will be a little daily entertainment one the way to the holidays. We also have a few anecdotes that while widely known I learned are actually fabricated.

Unfortunately, Stefan's and my brainstorming only brought up 19 items! So we need you to help us out: Send us your favorite physics anecdote or quotation (if possible with source), or we'll run out of stories a week before Christmas. To save an element of surprise for our readers, please do not post it in the comments here, but send an email to hossi[@]nordita.org (remove brackets), subject: physics anecdote. Don't be shy, I won't tell anybody you're reading blogs ;o)

We start today with the 1st anecdote. It's one of my favorites and, I guess, probably also among the best known ones. A journalist who goes under the name Roundy, interviews Paul Dirac. The interview appeared in the Wisconsin State Journal in April 1929 and its complete version can be found on this website.

"Professor," says I, "I notice you have quite a few letters in front of your last name. Do they stand for anything in particular?"

"No," says he.

"You mean I can write my own ticket?"

"Yes," says he.

"Will it be all right if I say that P.A.M. stands for Poincaré Aloysius Mussolini?"

"Yes," says he.

"Fine," says I, "We are getting along great! Now doctor will you give me in a few words the low-down on all your investigations?"

"No," says he.

"Good," says I. "Will it be all right if I put it this way --- `Professor Dirac solves all the problems of mathematical physics, but is unable to find a better way of figuring out Babe Ruth's batting average'?"

"Yes," says he.

"What do you like best in America?", says I.

"Potatoes," says he.

"Same here," says I. "What is your favorite sport?"

"Chinese chess," says he.

That knocked me cold! It was sure a new one on me! Then I went on: "Do you go to the movies?"

"Yes," says he.

"When?", says I.

"In 1920 --- perhaps also in 1930," says he.

"Do you like to read the Sunday comics?"

"Yes," says he, warming up a bit more than usual.

"This is the most important thing yet, doctor," says I. "It shows that me and you are more alike than I thought. And now I want to ask you something more: They tell me that you and Einstein are the only two real sure-enough high-brows and the only ones who can really understand each other. I wont ask you if this is straight stuff for I know you are too modest to admit it. But I want to know this --- Do you ever run across a fellow that even you can't understand?"

"Yes," says he.

"This well make a great reading for the boys down at the office," says I. "Do you mind releasing to me who he is?"

"Weyl," says he.

What is all the thinking good for?

2011-11-29T09:53:00.001-05:00

The other day I had to write a text explaining the importance of theoretical high energy physics and quantum gravity for the future of mankind. In layman's terms and less than two paragraphs.

I volunteered to do this because my frontal lobe starts shriveling whenever I have to endure somebody working in this area trying to justify their existence by confidently explaining that spin foams will one day dramatically improve the iPhone or so.

Okay, I'm exaggerating. But as I wrote previously it saddens me considerably that knowledge for the sake of knowledge doesn't seem to count as progress anymore. It's not that I don't value technological progress, I just don't think that's all that can “benefit the future of mankind.” As much as I criticized Slouka's article “Dehumanized”, I agree with him that we should stand our ground rather than adapting to external pressure that asks for material short-term outcomes. I finally wrote the following.

“What are we made of?,” “Where do we come from?,” and “What are the laws of Nature that we conform to?” are fundamental questions about our existence that scientists have studied for thousands of years. The quest to answer these questions and to understand the place of mankind in the vastness of the cosmos has lead to a great many of technological improvements. Material prosperity is a, welcome and desired, result that better knowledge of the fundamental laws of Nature brings. But knowledge by itself has also an immaterial value that feeds our desire to understand the world which brought about planet Earth and conscious life on it.

In the last century we have made dramatic progress with our understanding of space, time and matter, but open problems in today's best theories tell us that our knowledge is incomplete. New observations that can guide our learning have moved to very high energies and large distances. It is subject of our research in the areas of high energy physics, quantum gravity, and cosmology to combine the requirements of mathematical consistency and compatibility with observation to learn about the earliest moments of the universe, the elementary constituents of matter, and the structure of space and time itself. Among the most exciting and unforeseen recent insights is the connection between this research and condensed matter physics that is one of the focus areas at Nordita.

Nordita's website btw has undergone a general overhaul and is now remarkably improved.

You can go and shatter my world view by telling me the actual reason you're working on quantum gravity is that you want to become a billionaire with a new and improved GPS that locates your car keys with a precision of a Planck length.

New Template

2011-11-27T06:04:00.001-05:00

As you can see, we have finally switched to the new blogger template. Feedback is welcome!

Book review: "Impossibility" by John D. Barrow

2011-11-23T06:00:00.000-05:00

Impossibility: The Limits of Science and the Science of Limits
John D. Barrow
Oxford University Press (1999)

In his book "Impossibility: The Limits of Science and the Science of Limits" John Barrow has carried together everything that sheds light on the tricky question what is possible, practically as well as conceptually. It is an extensive answer to the question of FQXi's 2009 essay contest "What is ultimately possible in physics?" but takes into account more than just physics. Barrow also covers economical, biological and, most importantly, mathematical aspects of the question what we can and can't do, what we can and can't know.

The book discusses paradoxa, timetravel, computabily, complexity and the multiverse, though Barrow never uses the word multiverse. The book was written somewhat more than a decade ago, but the summary of eternal inflation and bubble universes, varying constants and the question if it is still science to speculate about something that's unobservable is timely, and Lee Smolin's cosmological natural selection also makes an appearance. Barrow does mention some of his own work (on varying constants and universes with non-trivial topologies) but only in a paragraph or two.

Barrow briefly introduces most of the concepts he needs, but I suspect if you don't already have a rough idea what cosmology and quantum mechanics is about, some sections will not make a lot of sense. He mentions for example the many worlds interpretation in the passing without ever explaining what it is, and has the possibly shortest explanation of inflation and the expanding universe I've ever seen. But if you've read one or the other book that covers these topics you might (as I) be relieved Barrow keeps it short.

The presentation is very non-judgmental. Barrow essentially goes through all aspects of the issue and reports who has contributed what to the discussion, without imposing an opinion on the reader. He also gives an interesting historical perspective on how our view on these questions has changed esp. with Gödel's contributions. However, the writing reads more like a review than a book in that it lacks a narrative, and Barrow also doesn't offer own conclusions, he just summarizes others' arguments. I don't mind so very much about the lack of narrative since I have grown a little tired by the current pop sci fashion to make up a story around the facts so it sells better, but I'd have expected some original thoughts here or there. It is also unfortunate that the book is very superficial on some topics, for example time travel and free will, and if you know a little about that already you won't hear anything new. On the other hand, if you just want a flavor and some references for further reading, Barrow does a good job. I ceartainly learned about some aspects of the possible and impossible that I hadn't thought about before.

Barrow's book is well structured with a summary at the end of each chapter and a final summary in the last chapter. This is very convenient if you put the book down and only pick it up again a few months later and need a reminder what you've already read.

I've been reading for a while on this book. Since 2008 in fact, if I believe the receipt. The reason it took me so long has very little to do with the actual content of the book which, now that I managed to finish it I like very much, and more mundanely with the representation of that content. The book is printed in tiny and in addition the print is crappy, so I get tired just by opening it and looking at a page. It has a few illustrations that are very helpful and to the point, but not particularly inspired. There are also a few photos. As you can guess however, Hubble Deep Field in a crappy black and white print on some square inch isn't too compelling, and it's difficult to see the Château in Magritte's Château de Pyrénées.

Taken together, you may enjoy this book if you are interested in a summary of aspects of the possible and impossible, but you would be disappointed if you're looking for an in-depth treatment of any particular aspect. The book is well written, though not very inspired, and the scientific explanations are well referenced and, for all I can tell, flawless. I'd give four out of five stars if I had stars to give.

Google Scholar Citations

2011-11-19T12:15:00.000-05:00

Google Scholar has a new feature, Google Scholar Citations, that allows you to generate a profile page with your papers. It also lists citations and calculates the infamous h-index. Have a look at my profile here to see if it's an interesting feature for you.

Is it?

To set up a profile page, you first need a Google account. If you already have one, it takes like 2 minutes or so. If you set up your page and enter your name, you'll be offered a list of papers that might be yours, that you can then edit. Mine was pretty good, probably because my name is not very common. A few papers seem to be missing, some listed items weren't papers but deceased websites that I wrote a looong time ago, and my research statement also appeared, but by and large it worked well.

The citation count is not exactly the same as on inSPIRE. In some cases Google Scholar counts more, in other cases less. It's not clear to me what causes the difference.

And my dear husband is evidently author of a paper with 3990 citations. Yes, I am very proud of him :o)

Spreng's triangle

2011-11-18T11:59:00.002-05:00

There, I've done it again. I came across some figure in the passing and ended up digging out the original reference in an attempt to make sense of it. In this case the figure is the energy-time-information triangle, proposed by Daniel Spreng in 1978, also known as Spreng's triangle. It supposedly conveys the message that new information technology (whatever that was in 1978) allows to save either time or energy, or a combination thereof. Clearly, I thought, the paper was written before the dawn of Wikipedia...

Spreng has a background that is noteworthy. Trained as a physicist, he later worked as engineer and developed an interest in economics. His triangle is an attempt to connect these areas, and as such very interesting. The example he starts with is purely thermodynamical. A reversible process, without loss of energy, would take an infinite amount of time. Any faster, and the process becomes irreversible. The faster it is, the more energy is needed (at least in the examples Spreng discusses). So there is a trade-off between time and energy that carries over to manufacturing. Information then comes in as an improved technology that makes the process more efficient, and so, more information saves time or energy. That is the basic idea.

Spreng's original paper is here, but I couldn't get access to it, so I settled for the 1993 remake and the following is my summary. You can find the original version of Spreng's triangle on page 13 of this file. I've redrawn it for your convenience, click to enlarge.

Spreng's triangle is a plane with 3 axes at 120° to each other. The 3 axes are energy (E), time (T) and information (I) respectively. I have drawn lines with constant time in blue, constant information in red, and constant information in green. In the lower right E=0 corner, that Spreng refers to as the "starving philosopher," one needs no energy, but has an infinite amount of time and all the information in the world. In the lower left, I=0, corner, that Spreng refers to as the "primitive man," one has no information and needs an infinite time to get anything done with maximal energy. In the upper corner, the "industrial man," one has plenty of information and energy to get things done in zero time. The corners are however unrealistic limits that shouldn't be taken too seriously, they're just to show the trends if you move around in the diagram.

Now to define a point in a plane you only need two axes, so the relevant statement here would be that all possible points of combinations E,T,I lie in a plane. I say "would be" because I will argue in the following that though superficially plausible and appealing, I don't think it is actually the case.

In his paper, Spreng discusses in which way energy, time, and information partly substitute for each other from several different aspects.

At some point, he claims for example that in industrial countries on a national level working hours substitute for energy use, citing himself in mentioned earlier paper that I had no access to. So I plotted the working time per year per worker from this table, against the annual energy consumption per capita from this table (in kilogrammes of oil equivalent per year).

I don't know about you, but I can't see any correlation or anti-correlation in that. Well, the data I used is from 2003, so, possibly 40 years ago that looked different, but I can't say I am very convinced. However, this turns out not to be of much importance later, he just uses this because he wants to send a message that civilization should slow down the hamster wheel (invest time) to instead save energy:

"Whether the time saved is simply used to produce and consume more, or whether some saved time is set aside as time for cultural development is of prime importance."

One easily sees from Spreng's discussion, that the "information" he is referring to is ill-defined. To be fair however, it does become clear that he is talking about manufacturing processes and their improvement. So Wikipedia isn't really a counterexample. At some point he specifies information to mean 'relevant' information, yet one doesn't know relevant for what. Maybe it's the information needed to decrease energy or time, but then the argument becomes circular. I think the name "information" is very misleading. What he seems to mean is something like the complexity of a technological process. Not that this is better defined.

However, just when I was about to throw the paper in the garbage, Spreng goes and admits that the "relevant information" is totally ill-defined and pulls the following trick that helped me to make more sense out of his triangle. He says, let's just consider information as an unknown parameter and assume it is measured by the market: "[T]he market measures the information content of goods and services." So, let Y be the market value of a good or service, then he defines information (I) by the following equation

where L is input to production of the good in working hours, p_L the price per hour, E is the energy input in some units, and p_E the price for that energy unit.

That would indeed define a surface if this equation would be fulfilled, so the question is, does it work? First, we note that this equation almost certainly isn't fulfilled for goods with cultural value like, say, Marilyn Monroe's dress. I don't see what difference it should make for the right side of the equation whether Marilyn or I wear a dress before auction, yet I have some doubts anybody would pay me some million bucks for that, so it does make a difference for the left side of the equation which is no good.

So then let's look at goods without cultural value, if such exist, maybe a banana will do. Still, something seems to be really funny with this equation. The alleged market value of the good doesn't at all depend on supply and demand for that good. I mean, I don't know a lot about economics, but if you're growing bananas in your backyard with input E,I,L and suddenly all bananas in Brazil fall victim to epidemic monkey obesity, your backyard bananas would be in high demand and up goes Y without any change to the right side of the equation.

This is not to say that it is not possible to make sense out of Spreng's triangle, but at least from what's in his 1993 paper it seems to me it would take more work to integrate this idea with economics. Spreng concludes his paper with the words

The importance of new information technology, NIT, in respect of future energy use can hardly be overstated. However, NIT can do two things. It can be used to substitute time by information or to substitute energy by information. NIT can, in other words, both be used to speed up the pace of life (work and leisure), thus promoting a society of harried mass consumers, or it can be used to conserve precious natural resources (energy and non-energy) by doing things more intelligently and improving the quality of life without adding stress to the environment. It is up to the society as a whole, politics of course included, to decide which of the
two roads are taken.”

You could then summarize my criticism as these are not the only two roads. Your NIT can also cost you more energy and more time. Like this damned Windows that never seems to finish updating and keeps popping up a message that I have to restart.

Bottomline: Plausible ideas are the most dangerous ones.

The Oscillating Universe

2011-11-14T12:31:00.004-05:00

I came across this short story “The Oscillating Universe” by Dennis E. Piper, published in The Observatory, Vol. 97, p. 10P-10P (1977), (PDF available here), and thought you might enjoy it:

One day the Professor called me in to his Laboratory. “At last I have solved the equation,” he said. “Time is a field. I have made this machine which reverses the field. Look! I press this switch and time will run backwards run will time and switch this press I. Field a is time.” Said he, “Equation the solved have I last at”. Laboratory his to in me called Professor the day one. “For heaven's sake, SWITCH IT BACK,” I shouted. Click! Shouted I, “BACK IT SWITCH, sake heaven's for.” One day the Professor called me in to his Laboratory...

Nerdy Riddle

2011-11-13T10:23:00.001-05:00

What am I?

In the mirror I see three,
ψ is always part of me,
I am always positive
And like the I with double f.

Open positions at NORDITA

2011-11-10T08:43:00.001-05:00

Yes, it's this time of the year again... the time of writing applications. NORDITA has some open positions, and it's a great place, so make sure to have it on your list:

We have about 5 postdoc positions in the areas of astrophysics and astrobiology, atomic physics, biological physics, condensed matter physics, gravitation and cosmology, high-energy physics, nuclear physics, and statistical physics. These are 2 year positions and successful applicants can do their own research, they will not be assigned to a supervisor. The job description is here, and the application form is here. The Deadline is November 15th, so it's time to upload your files now and hit submit.

We are this year also looking for an assistant professor in theoretical condensed matter physics. The job description is here, and the application form is here. The deadline is November 22nd.

If none of that is for you, NORDITA also has a visiting PhD student program. It says in the announcement that this program is primarily intended for PhD students from the Nordic and Baltic countries, but students from other countries will also be considered, so don't get discouraged if you don't know where the Baltic Sea is. Applications will be accepted between November 15 and December 15, the application form is here.

As you know, I am currently on parental leave, but if you have questions about NORDITA, I'll be happy to answer them. Write me at hossi[at]nordita.org

New constraints on cosmic strings from the South Pole Telescope

2011-11-09T07:30:00.001-05:00

Cosmic strings are stable, one dimensional objects of high energy density that might populate our universe. Cosmic strings can arise in quantum field theories and would form networks that extend throughout the universe. They were discussed three decades ago as a possible origin of cosmological structures, but fell out of favor when that was not compatible with data.

Cosmic strings received renewed interest however since they might appear also in the early universe if superstring theory is taken into account. No longer thought to be necessary to explain present day observational cosmology, the question is now how tightly constrained a possible contribution of cosmic superstrings is and if they may become observable in the soon future, when looked for in the right place with the right means, thus providing a long sought for hint that string theorists are on the right track. For more details, see my earlier post.

A recent paper has now put forward new constraints on the density of such string networks

Cosmic String constraints from WMAP and SPT

arXiv:1109.4947

The brief summary is that the have taken into account new data from the South Pole Telescope and not found anything.

The somewhat longer summary is that cosmic string networks leave an imprint in the anisotropy of the Cosmic Microwave Background (CMB) by actively generating perturbations, even after recombination. Most importantly, they act as lenses for the CMB light, which makes a contribution to the spectrum at large multipole moments or small angular size respectively. See here for an explanation of the CMB anisotropies. The recent measurements from the South Pole Telescope have now much improved the previously available data at large multipole moments. The new data is however perfectly consistent with a string-free universe, which allowed the authors of the above paper to derive improved and tighter constraints on models with cosmic strings.

They are careful to point out however that their constraints directly apply only to the most straigh-forward model of cosmic string networks, and that there are more complicated models (in which cosmic strings are merely meta-stable or there are different types of strings) for which the constraints would look different. In any case, this is yet another negative result for the phenomenology of string theory.

What are natural units?

2011-11-07T06:24:00.002-05:00

I noticed that I confused some readers by referring to temperatures in GeV and distances as the inverse of an energy. 15 years ago, when I first learned about natural units, it seemed really fishy to me. Now Stefan has to remind me on occasion that a second is not a distance, and an entropy is not dimensionless. Since I've experimented lately with some new software, I put together a few slides on the use of natural units and youtubed them.

At 3:20min it should be 5000K, not 500K, sorry about that. At 3:30min, Lara tried to eat the keyboard.

Grassroot funding for science: A good idea?

2011-11-02T06:33:00.006-04:00

Yes, I do give money to homeless people in the street. And, yes, I do on occasion donate to charity. Yet I am divided about the benefits of recent crowdfunding services that promise to help researchers to directly raise public money. Some of these services that collect money are dedicated to specific research areas, others are broadly defined, and most are US-based. Here is a selection:

The Eureka Fund is a U.S. 501(c)3 non-profit organization that collects money for energy and environment research. Proposals are reviewed by a scientific advisory board. If you look at the list of projects and the donations received, the success is not exactly stellar, even though Eureka Fund was featured in the NYT in April this year.

Fund Science is another US based micro-funding organization. According to the brochure, they have applied for 501(c)3 status. They are dedicated to help funding young researchers and pilot projects who have difficulties obtaining funding in other ways. In the first round however, they invite proposals only for "doctoral students pursuing hypotheses related to the pathogenesis or modeling of diseases including Crohns and Familial Mediterranean Fever."

A broadly imagined attempt is Sciflies.org, but the website is mostly filled by placeholders instead of content and nothing seems to be happening there. This is funny since Joanna Scott from Nature Network reported last year that the initiative was on its way. Maybe something went wrong there. The Facebook site and Twitter feed are equally deserted.

Then there is the SciFund Callenge, funded by two biologists in California. This fundraising agency runs through RocketHub, a crowdfunding organization based in New York. Maybe because they didn't attempt to reinvent the wheel of crowdfunding, their project list looks decent.

One last example: OpenGenius, which has been celebrated in the press, has an optimistic vision in which scientists and funding agencies propose projects for public funding and the projects are peer reviewed by a "global and highly motivated community." This project is noteworthy because it seems to be not US-based. The website suffers from a certain lack of actual information, but amounts of money are named in EUR and the partners are all Italian.

Needless to say, I think it is a terrific idea to make use of a simple interface that enables researchers to raise some additional money, may that be to replace the ancient lab fridge or to organize a conference. Much like giving some Euros to the homeless guy in the street, money serves to make life a little easier and the day a little brighter.

But beyond little extras, funding research by appealing to the public is not a good trend. It doesn't solve any systemic problem, much like dropping some Euros into a hat doesn't get homeless people off the street. The primary problem with scientific funding today is a lack of risk-taking and commitment: The ideal research project doesn't take more than 3 years to complete and you know the outcome before you've even started. If one would listen to the general public what projects are worth funding it would just reinforce the problems: Most people want to see immediate and tangible outcomes of their investments. That this doesn't work for basic research is exactly why so much of it is tax funded.

It adds to this that the crowdfunding approach puts at advantage research that can be easily decorated with pictures and produced in a video. If your project is about finding the best milk substitute for orphaned kittens it will score better than, say, the kappa-deformation of the Poincare Hopf algebra on discrete non-metric spaces in arbitrary dimensions. That might seem like an extreme example, but it isn't hard to predict that most of mammalian biology and medicine would produce better videos and more catchy pitches than mathematics or theoretical physics. And alien biology of course... Click to read whole comic.

Via Bad Astronomy. I didn't find it particularly funny. It's more in the category sad but true.

Giving to charity is much more common in North America than it is in Europe. An oversimplified summary is that Europeans pay more taxes and believe in representative democracy while Americans like the idea to distribute the money themselves and mistrust their electees. So it isn't much of a surprise most of the examples above are US based.

There is no generally right or wrong way to invest in non-profit organizations; it depends on the aim. Yes, donors chose. But the big question is how well they chose to invest their money and if not channeling of investment through expert committees puts money to use better. There are some cases where crowds are wise and chose wisely. And while the right circumstances for crowds to make wise decisions are still a subject of research, it seems to be clear that one needs a well-posed and concrete question to begin with. In addition, one person's decision shouldn't be affected by the choices others have made. Otherwise the rich will just get richer. These are conditions not fulfilled when it comes to judging on the promise of a research project.

Without knowing the status of a research field one has no way of telling if an investment is good, and this is not a knowledge one obtains by browsing a video collection. Or look at medicine with its many "orphan diseases" - not diseases of orphans, but all those illnesses you have never heard of because no Hollywood star fell victim to it. Where you invest best should depend on how promising a research proposal is, and that potentially in the course of some centuries. Not on what's currently on TV.

I am not saying the general public is dumb. I am talking about a lack of knowledge here, and a lack of time to obtain that knowledge. Pop sci gets you only so far.

Via Moshe. I did find that one hilarious indeed.

Then there is the problem that slopes may be slippery. I can just see us ending up in a position where scientists are expected to use crowdfunding for their research. And that will not only be an ineffective distribution of money because said crowd is prone to like projects for the wrong reasons, but also because it takes up more of the researchers' precious time for producing a fancy proposal that will appeal to the public. And then somebody still has to do the reviewing.

Summary: Crowdfunding science is a good idea to add additional support to underfunded missions or to enable small projects. It is not a good idea to draw upon the public opinion to fund research projects from scratch. It might appear as if public money is put to good use, but that use is likely to be very inefficient and misdirected and doesn't actually solve any systemic problem. If you must, go occupy Wall Street, vote, and make sure your taxes are put to good use.

Interna

2011-10-30T03:09:00.001-04:00

Lara and Gloria are now 10 months old. They can both stand as long as they have something to hold on to, and they take little steps along the walls. Yesterday Lara dared to take her hands off the table and surprised herself by standing, wobbly, but all on her own.

The babies' first visit at the dentist featured a doctor informing us that they don't yet have teeth and got us two tiny toothbrushes and a booklet that promises to explain everything you ever wanted to know about baby's teeth - as long as you speak Swedish. Since Lara prefers my thumb over her own, I can testify the first tooth is now well on its way, but we're still waiting for it to see the light of the day.

Recently, the little ones have developed an interest in books and chewed to pieces Dan Brown's "Da Vinci Code," and Stefan has taken on the task of teaching the babies some physics. Since a week or so, Gloria takes delight in bringing her toys to us, just to take them back immediately. It becomes increasingly noticeable that the girls now understand quite a few words, especially the essentials yes, no, good, bad, come, play, milk, daddy.

Lara and Gloria have coped well with the flights to and from Stockholm, much better than Superdaddy who has developed a contact allergy to Scandinavian Airlines SAS. The Lufthansa-end of the trip in Frankfurt is flawlessly family friendly. The SAS-end in Arlanda is a complete disaster. Despite the twin stroller being clearly marked for 'Delivery at Gate' it ended up on the oversized baggage belt and Stefan had to carry the baggage, the baby seat and the two girls through the airport, much to the amusement of SAS staff.

Upon inquiry, we learned that in the late 19th century a 73 year old labor union member strained an ankle when lifting a bag tagged as gate claim. Or so. Ever since then, employees at Arlanda airport refuse to bring anything exceeding 7kg to the gate, including strollers. Not that anybody bothered to inform us about that or offered any help. We for certain will have reason to celebrate if Lufthansa takes over SAS as rumors say.

Yes, parenthood changes you. I for example have developed the unfortunate habit of looking into stranger's noses to see if there's something in need of being picked out. Stefan meanwhile has worked on a theory of snot clumping according to which the size of a snot does not depend on the nose. He's now collecting data ;o)

The future of the seminar starts with w

2011-10-27T12:20:00.001-04:00

I've learned a new word: webinar. Stefan has had a few. Maybe it's contagious.

A webinar, so I've learned, is a web-based seminar. It's a hybrid of video conference and desktop sharing. If you know the International Loop Quantum Gravity Seminar (ILQGS) series, this is the pleistocenic predecessor of a webinar. To take part, you download the slides online prior to the seminar, then dial in to hear what the speaker has to say. One thing he'll be telling you is when to go to the next slide.

A webinar now makes use of advanced file-sharing. Somebody plays the role of a moderator who shares a desktop, not necessarily his own, with all participants, for example the powerpoint presentation of the speaker, but it might also be a demonstration of a software or pictures from your latest trip to the pleistocene or whatever. So, you don't have to switch slides on your own and can pleasantly doze off. Just take care not to hit the keyboard for a webinar is interactive and you might accidentally ask the question "Ghyughgggggggggggggggggg?"

In principle one could stream the audio right along with the desktop and also combine it with a video. However, sharing videos of the participants has limits both at bandwidth and feasibility. If you're giving a seminar with an audience of 100 people, you neither want nor need a video of every single one picking their nose. Much more useful is the option to virtually 'raise a hand' and ask a question, either by audio or by a chat interface.

The webinar interface that Stefan has made some experience with is called webex. In these webinars that Stefan has attented, the audio was not streamed along with the desktop sharing over the web. Instead, participants submit a phone number at which the software will call them. That has the disadvantage that you have to be on the phone in addition to sitting at the computer. (You also need to have a phone line to begin with.) It has the advantage however that if the web connection breaks down you can still try to figure out the problem on the phone. Webex is not a free service - I suppose one primarily pays for the bandwidth that allows many participants since desktop sharing and video conferencing with a few people is doable on Skype also. Google brings up some free offers for webinar software, but I don't know any of them. Let me know if you've tried some of these free services, I'd be interested to hear how good or bad they are.

From the speaker's side the situation requires some adaption if one is used to 'real' seminars. One has to stop oneself from mumbling into the laptop. For pointing at some item, one has to use the cursor which is possible but not ideal. One would wish for an easy way to enlarge the icon so it is better visible.

From the side of the audience there's the general temptation of leaving to get a coffee and forgetting to come back because who will notice anyway. One is also left wondering how many of the participants are sitting in bed or have just replaced themselves with a software that will ask the occasional question. It is actually more a comment than a question...

From both sides there is the necessity to get used to the software which is typically the main obstacle for applications to spread.

If one wants to combine a webinar with a real seminar, new technological hurdles are in the way but they aren't too difficult to take. The shared desktop can be projected with a beamer as usual, the audio needs to go on a speaker. The question is how to deal with 'real' audience questions. This requires a good A/V equipment at location.

In any case, the technology is clearly there and one already finds some webinar offers online. The APS for example has some webinars with career advice, and Physics World also has a few listed. Most of the webinars that I have come across so far are however software demonstrations. But after increasingly many institutions routinely record seminars and make them available online, I think webinars are the next step that we might see spreading though academia. I for sure would appreciate the possibility to easily log in to one or the other seminar from home while I am on parental leave.

However, if the nomenclature develops as it did with weblogs, we'll end up sitting in binars, you're either in or you're not.

Have you made experience with a webinar? Would you consider attending, giving, or organizing one?

Interna

2011-10-21T01:36:00.001-04:00

After the previous posts were somewhat heavy in content, for relaxation let me just show you some photos from a recent weekend excursion.

[Click to badastronate]

My month back at work is almost over, and we'll be commuting back to Germany in the coming days so Superdaddy can reappear in his office chair.

Super Extra Loop Quantum Gravity

2011-10-17T03:44:00.002-04:00

In the summer, I noted a recent paper that scored remarkably low on the bullshit index:

But what is the paper actually about? It is an attempt to make contact between Loop Quantum Gravity (LQG) and Superstring Theory (ST). Both are approaches to a quantization of gravity, one of the big open problems in theoretical physics. LQG directly attacks the problem by a careful selection of variables and quantization procedure. String theory does not only aim at quantizing gravity, but at the same time at unifying also the other 3 interactions of the standard model by taking as fundamental the strings that give it its name. If quantizing gravity and unifying the standard model interactions are actually related problems, then string theorists are wise to attack them together. Yet, we don't know if they are related. In any case, it has turned out that gravity is necessarily contained in ST.

Both theories still struggle to reproduce general relativity and/or the standard model, and to make contact to phenomenology, though for very different reasons. This begs the question how the theories compare to each other, whether they give the same results for selected problems. Unfortunately, so far this has not been possible to answer because LQG has been developed for a 3+1 dimensional space-time, while ST famously or infamously, depending on your perspective, necessitates 6 additional dimensions that then have to be compactified. ST is also, as the name says, supersymmetric. It should be noted that these both features, supersymmetry and extra dimensions, are not optional but mandatory for ST to make sense.

I've always wondered why one hasn't extended LQG to higher dimensions since the idea of extra dimensions is appealing and somebody in the field who should have known better once told me it would be straight forward to do. It is however not so because one of the variables (a certain SU(2) Yang-Mills connection) used in the quantization procedure relies on a property (the equivalence of the fundamental and adjoint representations of SU(2)) that is fulfilled only in 3 spatial dimensions. So it took many years and two brilliant young students, Norbert Bodendorfer and Andreas Thurn, to come up with a variable that could be used in an arbitrary number of dimensions and to work through the maths which, as you can imagine, didn't get easier. It required to work around the difficulty that SO(1,D) is not compact and digging out a technique for gauge unfixing, a procedure that I had never heard of before.

Compared to the difficulty of adding dimensions, going supersymmetric can be done by simply generalizing the appropriate matter content which is contained in the supergravity actions, and constructing a supersymmetry constraint operator.

Taken together, this in principle allows one to compare the super extra loop quantized gravity to string theory, to which supergravity is a low energy approximation, though concrete calculations have yet to follow. One of the tasks on the to-do list the entropy of extremal supersymmetric black holes to see if LQG reproduces the ST results. (Or if not, which might be even more interesting.) Since LQG is a manifestly non perturbative approach, this relation to string theory might also help filling in some blanks in the AdS/CFT correspondence in areas where neither side of the duality is weakly coupled.

AdS/CFT confronts data

2011-10-14T08:32:00.002-04:00

One of the most persistent and contagious side-effects of string theory has been the conjectured AdS/CFT correspondence (that we previously discussed here, here and here). The briefest of all brief summaries is that it is a duality that allows to swap the strong coupling limit of a conformal field theory (CFT) with (super)gravity in a higher dimensional Anti-de-Sitter (AdS) space. Since computation at strong coupling is difficult, at the very least this is a useful computational tool. It has been applied to some condensed matter systems and also to heavy ion physics, where one wants to know the properties of the quark gluon plama. Now the theory that one has to deal with in heavy ion collisions is QCD, which is neither supersymmetric nor conformal, but there have been some arguments for why it should be approximately okay.

The great thing about the application of AdS/CFT to heavy ion physics is that it made predictions for the LHC's heavy ion runs that are now being tested. One piece of data that is presently coming in is the distribution of jets in heavy ion collisions, but first some terminology.

A heavy ion is an atom with a high atomic number stripped of all electrons; typically one uses lead or gold. Compared to a proton, a heavy ion is a large clump of bound nucleons (neutrons and protons) that are accelerated and brought to collision. They may collide head-on or only peripherally, quantified in a number called "centrality." When the ions collide, they temporarily form a hot, dense soup of quarks and gluons called the "quark gluon plasma." This plasma rapidly expands and cools and the quarks and gluons form hadrons again (in a process called "hadronization" or also "fragmentation"), that are then detected. The temperature of the plasma depends on the energy of the colliding ions that is provided by the accelerator. At RHIC the temperature is about 350 MeV, in the LHC's heavy ion program it is about 500 MeV. The task of heavy ion physicists is to extract information about matter at nuclear densities and such high temperatures from the detected collision products.

A (di) jet is two back-to-back correlated showers of particles that are a typical signature in perturbative QCD. It is created if a pair of outgoing partons (quarks or gluons) hadronizes and produces a bunch of particles that then hit the detector. Since QCD is confined, the primary, colored, particles never reach the detector. In contrast to proton-proton collisions, in heavy ion collisions the partons have to first go through the quark gluon plasma before they can make a jet. Thus, the distribution of momenta of the observed jets depends on the properties of the plasma, in particular the energy loss that the partons undergo.

Different models predict different energy loss and dependence of that energy loss on the temperature of the medium. Jets are a QCD feature at weak coupling and strictly speaking in the strong coupling limit that AdS/CFT describes there are no jets at all. What one can however do is to use a hybrid model in which one just extracts the energy loss in the plasma from the conformal theory. This energy loss scales with L³ T⁴, where L is the length that the partons travel through the medium and T is the temperature. All other models for the energy loss scale with smaller powers of the temperature.

Heavy ion physicists like to encode observables into how different they are from the corresponding observables for collisions of the ion's constituents. The "nuclear suppression factor," denoted R_AA, plotted in Thorsten Renk's figure below (Slide 17 of this talk), is basically the ratio of the cross-section for jets in lead-lead over the same quantity for proton-proton (normalized to the number of nucleons) and it's depicted as a function of the average transverse momentum (p_T) of the jets. The black dots are the ALICE data, the solid lines are fits from various models. The orange line at the bottom is AdS/CFT.

[Picture credit: Thorsten Renk, Slide 17 of this presentention]
As the saying goes, a picture speaks a thousand words, but since links and image sources have a tendency to deteriorate over time, let me spell it out for you: The AdS/CFT scaling does not agree with the data at all.

A readjustment of parameters might move the total curve up or down, but the slope would still be off. Another problem with the AdS/CFT model is that the model parameters needed to fit the RHIC data are very different from the ones needed for the LHC. The model that does best is Yet another Jet Energy-loss Model (YaJEM) that works with in medium showers (I know nothing about that code). It is described in some detail in this paper. It doesn't only fit well with the observed scaling, it also does not require a large readjustment of parameters from RHIC to LHC.

Of course there's always caveats to a conclusion. One might criticize for example the way that AdS/CFT has been implemented into the code. But the scaling with temperature is such a general property that I don't think nagging at the details will be of much use here. Then one may want to point out that the duality is good actually only in the large N limit and N=3 isn't so large after all. And that is right, so maybe one would have to take correction terms more seriously. But that would then require calculating string contributions and one loses the computational advantage that AdS/CFT seemed to bring.

Some more details on the above figure are in Thorsten Renk's proceedings from the Quark Matter 2011, on the arxiv under 1106.2392 [hep-ph].

Summary: I predict applications of the AdS/CFT duality to heavy ion physics is a rapidly cooling area.

New constraints on energy-dependent speed of light from gamma ray bursts

2011-10-12T04:48:00.004-04:00

Two weeks ago, an arXiv preprint came out with a new analysis of the highest energetic gamma ray bursts (GRBs) observed with the Fermi telescope. This paper put forward a bound on an energy-dependent speed of light that is an improvement of 3 orders of magnitude over existing bounds. This rules out a class of models for Planck-scale effects. If you know the background, just scroll down to "News" to read what's new. If you need a summary of why this is interesting and links to earlier discussions, you'll find that in the "Avant-propos".

Avant-propos

Deviations from Lorentz-invariance are the best studied case of physics at the Planck scale. Such deviations can have two different expressions: Either an explicit breaking of Lorentz-invariance that introduces a preferred restframe, or a so-called deformation that changes Lorentz-transformations at high energies without introducing a preferred restframe.

Such new effects are parameterized by a mass scale that, if it is a quantum gravitational effect, one would expect to be close by the Planck-mass. Extensions of the standard model that explicitly break Lorentz-invariance are very strongly constrained already, to 9 orders of magnitude above the Planck mass. Such constraints are derived by looking for effects on particle physics that are a consequence of higher order operators in the standard model.

Deformations of special relativity (DSR) evade that type of constraints, basically because there is no agreed upon effective limit from which one could actually read off higher order operators and calculate such effects. It is also difficult, if not impossible, to make sense of DSR in position space without ruining locality and these models have so-far unresolved issues with multi-particle states. So, as you can guess, there's some controversy among the theorists about whether DSR is a viable model for quantum gravitational effects. (See also this earlier post.) But that's arguments from theory, so let's have a look at the data.

Some models of DSR feature an energy-dependent speed of light. That means that photons travel with different speeds depending on their energy. This effect is very small. In the best case, it scales with the photon's energy over the Planck mass which, even for photons in the GeV range, is a a factor 10^-19. But the total time difference between photons of different energies can add up if the photons travel over a long distance. Thus the idea is to look at photons with high energies coming to us from far away, such as those emitted from GRBs. It turns out that in this case, with distances of some Gpc and energies at some GeV, an energy-dependent speed of light can become observable.

There's two things one should add here. First, not all cases of DSR do actually have an energy-dependent speed of light. Second, not in all cases does it scale the same way. That is, the above discussed case is the most optimistic one when it comes to phenomenology, the one with the most striking effect. For that reason, it's also the case that has been talked about the most.

There had previously been claims from analysis of GRB data that the scale at which the effect becomes important had been constrained up to about 100 times the Planck mass. This would have been a strong indication that the effect, if it is a quantum gravitational effect, is not there at all, ruling out a large class of DSR models. However, we discussed here why that claim was on shaky ground, and indeed it didn't make it through peer review. The presently best limit from GRBs is just about at the Planck scale.

News

Now, three researchers from Michigan Technological University, have put forward a new analysis that has appeared on the arxiv:

arXiv:1109.5191 [astro-ph.CO]

Previous analysis had studied the difference in arrival times between the low and high energetic photons. In the new study, the authors have exclusively looked at the high energetic photons, noting that the average difference in energies between photons in the GeV range is about the same as that between photons in the GeV and the MeV range, and for the delay it's only the difference that matters. Looking at the GeV range has the added benefit that there is basically no background.

For their analysis, they have selected a subsample of the total of 600 or so GRBs that Fermi has detected so far. From all these events, they have looked only at those who have numerous photons in the GeV range to begin with. In the end they consider only 4 GRBs (080916C, 090510A, 090902B, and 090926A). From the paper, it does not really become clear how these were selected, as this paper reports at least 19 events with statistically significant contributions in the GeV range. One of the authors of the paper, Robert Nemiroff, explained upon my inquiry that they selected the 4 GRBs with the best high energy data, numerous particles that have been identified as photons with high confidence.

The authors then use a new kind of statistical analysis to extract information from the spectrum, even though we know little to nothing about the emission spectrum of the GRBs. For their analysis, they study exclusively the timing of the high energetic photons' arrival. Just by looking at the Figure 2 from their paper you can see that on occasion two or three photons of different energies arrive almost simultaneously (up to some measurement uncertainty). They study two methods of extracting a bunch from the data and then quantify its reliability by testing it against a Monte Carlo simulation. If one assumes a uniform distribution and just sprinkles photons in the time interval of the burst, a bunch is very unlikely to happen by coincidence. Thus, one concludes with some certainty that this 'bunching' of photons must have been present already at the source and was maintained during propagation. An energy-dependent dispersion would tend to wash out such correlations as it would increase the time difference between photons with different energies. Then, from the total time of the bunch of photons and its variability in energy, one can derive constraints on the dispersion that this bunch can have undergone.

Clearly, what one would actually want to do is a Monte Carlo analysis with and without the dispersion and see which one fits the data better. Yet, one cannot do that because one doesn't know the emission spectrum of the burst. Instead, the procedure the authors use just aims at extracting a likely time variability. In that way, they can then identify in particular one very short substructure in GRB 090510A that in addition also has a large spread in energy. From this (large energy difference but small time difference) they then extract a bound on the dispersion and, assuming a first order effect, a bound on the scale of possible quantum gravitational effects that is larger than 3060 times the Planck scale. If this result holds up, this is an improvement by 3 orders of magnitude over earlier bounds!

Comments

The central question is however what is the confidence level for this statement. The bunching they have looked at in each GRB is a 3σ effect, i.e. it would appear coincidentally only in one out of 370 cases that they generated per Monte Carlo trials: "Statistically significant bunchiness was declared when the detected counts... occurred in less than one in 370 equivalent Monte Carlo trials." Yet they are extracting their strong bound from one dataset (GRB) of a (not randomly chosen) subsample of all recorded data. But the probability to expect such a short bunch just by pure coincidence in one out of 20 cases is higher than the probability to find it coincidentally in just one. Don't misunderstand me, it might very well be that the short-timed bunch in GRB 090510A has a probability of less than one in 370 to appear just coincidentally in the data we have so far, I just don't see how that follows from the analysis that is in the paper.

To see my problem, consider that (and I am not saying this has anything to do with reality) the GRB had a completely uniform emission in some time window and then suddenly stops. The only two parameters are the time window and the total number of photons detected. In the low energy range, we detect a lot of photons and the probability that the variation we see happened just by chance even though the emission was uniform is basically zero. In the high energy range we detect sometimes a handful, sometimes 20 or so photons. If you assume a uniform emission, the photons we measure will simply by coincidence sometimes come in a bunch if you measure enough GRBs, dispersion or not. That is, the significance of one bunch in one GRB depends on the total size of the sample, which is not the same significance that the authors have referred to. (You might want to correlate the spectrum at high energies with the better statistic at low energies, but that is not what has been done in this study.)

The significance that is referred to in the paper is how well their method extracts a bunch from the high energy spectrum. The significance I am asking for is a different one, namely what is the confidence by which a detected bunch does actually tell us something about the spectrum of the burst.

Summary

The new paper suggests an interesting new method to extract information about the time variability of the GRB in the GeV range by estimating the probability that the observed bunched arrivals of photons might have occurred just by chance even though there is dispersion. That allows to bound a possible Planck scale effect very tightly. Since I have written some papers arguing from theoretical grounds that there should be no Planck scale effect in the GRB spectra, I would be pleased to see an observational confirmation of my argument. Unfortunately, the statistical relevance of this new claim is not entirely clear to me. The relevance that is referred to in the paper I am not sure how to translate into the relevance of the bound. Robert Nemiroff has shown infinite patience to explain the reasoning to me, but I still don't understand it. Let's see what the published version of the paper says.

Away note

2011-10-05T09:55:00.001-04:00

I'll be away the rest of the week for a brief trip to Jyväskylä, Finland. I'm also quite busy next week, so don't expect to hear much from me.

For your distraction, here's some things that I've come across that you might enjoy:

Correlations between hobbies and impact factors of scientists (via Garrett). It seems I should do more painting again...

If life gives you lemons, well, you know. If life gives you ants, give them food colors.

Money as an incentive doesn't work well for creative labor.

I came across an amusing footnote in a 1994 paper that quotes J.A. Wheeler in private correspondence
[I recall] the well-known statement of Rutherford, "When a student of mine uses the word "universe", I tell him it is time for him to leave." But maybe that's why so many of us live in America!

Those where the days.

Random advice: If you plan on uploading a paper, make sure you've removed all comments...

And a movie wanting to communicate that scientists are human beings, if you had any doubts.

FAZ: Interview with German member of OPERA collaboration

2011-10-02T08:00:00.003-04:00

The German newspaper Frankfurter Allgemeine Zeitung (FAZ) has an interesting interview with Caren Hagner, from the University of Hamburg. Hagner is member of the OPERA collaboration and talked to the journalist Manfred Lindinger. The interview is in German and I thought most of you would probably miss it, so here's some excerpts (translation mine):

Frau Hagner, you are leader of the German group of the OPERA experiment. But one searches in vain for your name on the preprint.

I and a dozen of colleagues did not sign the preprint. I have no reservations about the experiment. I just think it was premature to go public with the results for such an unusual effect like faster than light travel. One should have done more tests. But then the publication would have taken at least 2 months longer. I and other colleagues from the OPERA collaboration wanted these tests to be done.

What tests?

First, a second independent analysis. In particle physics, if one believes to have discovered a new particle or effect, then in general there is not only one group analyzing the data but several. And if all get the same result then one can be convinced it is right. That has not been the case with OPERA.

Why?

Because there hasn't been time. For an effect like faster than light travel the analysis should certainly be controlled. Maybe there is a bug in the program [...] The majority of the collaboration preferred a quick publication.

Hagner also says that the statistical analysis (matching the proton spectrum with that of the neutrinos) should have been redone by different techniques and that this is currently under way. She further points out that the results are only from one of two detection methods that OPERA has, the scintillation-tracker. Another detector, the spectrometer, should yield an independent measurement that could be compared to the first, but that would take about 2 months.

The final question is also worth quoting:

[If true], might satellite navitation in the future be based on neutrino rays rather than light?

Yes, maybe. But then our GPS devices would weigh some thousand tons.

Interna

2011-09-30T07:05:00.002-04:00

Lara and Gloria are now 9 months old, and it's time again for our monthly baby update. The girls are now both crawling well. Lara has learned to sit up on her own and Gloria knows how to pull herself up and stand on her feet. She's been doing that since 2 weeks already, but only now has she learned how to get back down in any other way than just letting go and falling backwards on her head. There's no day the babies don't get new scratches or bruises and they are relentlessly curious. The other day they escaped from the baby-safe part of the room and happily chewed on our passports.

When they are not sleeping or crying, they are babbling most of the time. For a few days in a row they pick a favorite syllable that they then repeat endlessly. Presently, Gloria is commenting everything with na-na-na, and Lara is practicing dadn-dadn. I've speculated she's echoing Stefan's "Was mascht Du dadn?" (What are you doing there? Saarland-style). On Monday we took them to the institute and they were duly impressed by the guy next door drawing Feynman-diagrams on the whiteboard, though more interesting still they found all the cables under my desk together with the occasional woodlouse that we evidently host down there.

I always thought babies typically swallow or choke on everything small enough to fit into their mouth. It turns out though the very little ones put things in their mouth but don't swallow. In fact, at this point ours still refuse to eat anything that's not smoothly mashed. They'll just push it around in their mouth for a little and then spit out. (It's called the "gag reflex" and should vanish by 7-9 months. You better not leave your baby alone with the combustion engine anyway.)

Neither Lara nor Gloria have teeth yet. That has not deterred the Swedish health authorities from assigning us dentists' appointment. It's not like they ask you to come, no, they just send a letter with a time, date, and location you have to appear. We actually missed the first two appointments. I then called them and tried to convey the information that the girls don't even have teeth for the dentist to look at, but to no avail. I'm picturing a long corridor with offices where Swedish doctors sit and cross out names of patients that didn't show up for their appointments, or belatedly notice the body part they wanted to examine is missing. But at least we know where our taxes are going. (The same health authorities that require amputees to prove every other year that the missing part hasn't regrown. Still better than no health insurance...)

Stefan was sent a list of gadgets the modern father needs to have, for example the full color, high-def, video monitoring system, that allows you to check on your babies by Skype, or a cry analyzer. But the gadget that I would really like to have is a diaper with an integrated microchip that sends a note to my BlackBerry when the diaper is full, and a number attached to it. It's somewhat degrading to having to push my nose onto baby-butts in order to examine the matter, and Stefan's nose evidently isn't up to the task. The German comedian Michael Mittermeier aptly referred to the nose-on-butt procedure as "the shit-check." Which reminds me, I should really write the report on that paper now...

On the universal length appearing in the theory of elementary particles - in 1938

2011-09-28T00:29:00.000-04:00

Special relativity and quantum mechanics are characterized by two universal constants, the speed of light, c, and Planck's constant, ℏ. Yet, from these constants one cannot construct a constant of dimension length (or mass respectively as a length can be converted to a mass by use of ℏ and c). In 1899, Max Planck pointed out that adding Newton's constant G to the universal constants c and ℏ allows one to construct units of mass, length and time. Today these are known as Planck-time, Planck-length and Planck-mass respectively. As we have seen in this earlier post, they mark the scale at which quantum gravitational effects are expected to become important. But back in Planck's days their relevance was in their universality, since they are constructed entirely from fundamental constants.

In the early 20th century, with the advent of quantum field theory, it was widely believed that a fundamental length was necessary to cure troublesome divergences. The most commonly used regularization was a cut-off or some other dimensionful quantity to render integrals finite. It seemed natural to think of this pragmantic cut-off as having fundamental significance, though the problems it caused with Lorentz-invariance. In 1938, Heisenberg wrote "Über die in der Theorie der Elemtarteilchen auftretende universelle Länge" (On the universal length appearing in the theory of elementary particles), in which he argued that this fundamental length, which he denoted r₀, should appear somewhere not too far beyond the classical electron radius (of the order some fm).

This idea seems curious today, and has to be put into perspective. Heisenberg was very worried about the non-renormalizability of Fermi's theory of β-decay. He had previously shown that applying Fermi's theory to the high center of mass energies of some hundred GeV lead to an "explosion," by which he referred to events of very high multiplicity. Heisenberg argued this would explain the observed cosmic ray showers, whose large number of secondary particles we know today are created by cascades (a possibility that was discussed at the time of Heisenberg's writing already, but not agreed upon). We also know today that what Heisenberg actually discovered is that Fermi's theory breaks down at such high energies, and the four-fermion coupling has to be replaced by the exchange of a gauge boson in the electroweak interaction. But in the 1930s neither the strong nor the electroweak force was known. Heisenberg then connected the problem of regularization with the breakdown of the perturbation expansion of Fermi's theory, and argued that the presence of the alleged explosions would prohibit the resolution of finer structures:

"Wenn die Explosionen tatsächlich existieren und die für die Konstante r₀ eigentlich charakeristischen Prozesse darstellen, so vermitteln sie vielleicht ein erstes, noch unklares Verständnis der unanschaulichen Züge, die mit der Konstanten r₀ verbunden sind. Diese sollten sich ja wohl zunächst darin äußern, daß die Messung einer den Wert r₀ unterschreitenden Genauigkeit zu Schwierigkeiten führt... [D]ie Explosionen [würden] dafür sorgen..., daß Ortsmessungen mit einer r₀ unterschreitenden Genauigkeit unmöglich sind."

("If the explosions actually exist and represent the processes characteristic for the constant r₀, then they maybe convey a first, still unclear, understanding of the obscure properties connected with the constant r₀. These should, one may expect, express themselves in difficulties of measurements with a precision better than r₀... The explosions would have the effect... that measurements of positions are not possible to a precision better than r₀.")

In hindsight we know that Heisenberg was, correctly, arguing that the theory of elementary particles known in the 1930s was incomplete. The strong interaction was missing and Fermi's theory indeed non-renormalizable, but not fundamental. Today we also know that the standard model of particle physics is perturbatively renormalizable and know techniques to deal with divergent integrals that do not necessitate cut-offs, such as dimensional regularization. But lacking that knowledge, it is understandable that Heisenberg argued gravity had no role to play for the appearance of a fundamental length:

"Der Umstand, daß [die Plancklänge] wesentlich kleiner ist als r₀, gibt uns das Recht, von den durch die Gravitation bedingen unanschaulichen Zügen der Naturbeschreibung zunächst abzusehen, da sie - wenigstens in der Atomphysik - völlig untergehen in den viel gröberen unanschaulichen Zügen, die von der universellen Konstanten r₀ herrühren. Es dürfte aus diesen Gründen wohl kaum möglich sein, die elektrischen und die Gravitationserscheinungen in die übrige Physik einzuordnen, bevor die mit der Länge r₀ zusammenhängenden Probleme gelöst sind."

("The fact that [the Planck length] is much smaller than r₀ gives us the right to leave aside the obscure properties of the description of nature due to gravity, since they - at least in atomic physics - are totally negligible relative to the much coarser obscure properties that go back to the universal constant r₀. For this reason, it seems hardly possible to integrate electric and gravitational phenomena into the rest of physics until the problems connected to the length r₀ are solved.")

Today, one of the big outstanding questions in theoretical physics is how to resolve the apparent disagreements between the quantum field theories of the standard model and general relativity. It is not that we cannot quantize gravity, but that the attempt to do so leads to a non-renormalizable and thus fundamentally nonsensical theory. The reason is that the coupling constant of gravity, Newton's constant, is dimensionful. This leads to the necessity to introduce an infinite number of counter-terms, eventually rendering the theory incapable of prediction.

But the same is true for Fermi's theory that Heisenberg was so worried about that he argued for a finite resolution where the theory breaks down - and mistakenly so since he was merely pushing an effective theory beyond its limits. So we have to ask then if we are we making the same mistake as Heisenberg, in that we falsely interpret the failure of general relativity to extend beyond the Planck scale as the occurence of a fundamentally finite resolution of structures, rather than just the limit beyond which we have to look for a new theory that will allow us to resolve smaller distances still?

If it was only the extension of classical gravity, laid out in many thought experiments (see eg. Garay 1994), that made us believe the Planck length is of fundamental importance, then the above historical lesson should caution us we might be on the wrong track. Yet, the situation today is different from that which Heisenberg faced. Rather than pushing a quantum theory beyond its limits, we are pushing a classical theory and conclude that its short-distance behavior is troublesome, which we hope to resolve with quantizing the theory. And several attempts at a UV-completion of gravity (string theory, loop quantum gravity, asymptotically safe gravity) suggest that the role of the Planck length as a minimal length carries over into the quantum regime as a dimensionful regulator, though in very different ways. This feeds our hopes that we might be working on unraveling another layer of natures secrets and that this time it might actually be the fundamental one.

Aside: This text is part of the introduction to an article I am working on. Is the English translation of the German extracts from Heisenberg's paper understandable? It sounds funny to me, but then Heisenberg's German is also funny for 21st century ears. Feedback would be appreciated!

Theory Carnival: Phenomenological Quantum Gravity

2011-09-24T02:25:00.002-04:00

[Geek Mommyprof from Academic Jungle is hosting a carnival on real people's work in theoretical or computational sciences, and what that work entails. She asked me to contribute some lines about what I do for a living, so here we go.]

I am a theoretical physicist and I work on the phenomenology of quantum gravity. Phenomenology is the part of theory that makes contact with experiment. (For more read my earlier post On the Importance of Phenomenology). Quantum gravity is the attempt to resolve our problems in formulating a common treatment for the quantum field theories of the standard model and Einstein's general relativity. Quantum gravity has for a long time been dominated by theory, and it's only been during the last decade or so that more effort has been invested into phenomenology.

I like working in this area because it offers interesting and still unexplored topics, and if there will ever be an experimentally confirmed theory of quantum gravity there's no way around phenomenology. My work requires keeping track of what the theorists are doing and what the experimentalists are planning and trying to find a way to connect both. Since gravity is a very weak interaction, finding evidence for its quantum effects is difficult to do, and so far there has been no signature. In fact, it can be quite frustrating if one puts in the numbers and finds the effect one considered is 40 orders of magnitude too small to be measurable, which is the normal state of affairs. I've joked on occasion I should write a paper "50 ways you can't measure quantum gravitational effects," just so all my estimates will finally be good for something. But there are areas, early universe and high energy densities, high energies and large distances, where it doesn't look completely hopeless.

Lacking a fully established theory of quantum gravity, phenomenology in this area requires developing a model that tests for some specific features, may that be extra dimensions, violations of Lorentz Invariance, antigravitation or faster-than-light travel. Model building is like having a baby. While you work on it, you have an idea of how it will be and what you can do with it. Yet, once it's come into life, it starts crying and kicking and doesn't care at all what you wanted it to do. Mathematical consistency is a very powerful constraint that is difficult to appreciate if one hasn't made the experience: You can't just go and, for example, introduce antigravitating masses into general relativity. It sounds easy enough to just put in stuff that falls up, but once you look into the details the easy ways are just not compatible with the theory, and it turns out to be so easy not. (I should know, since I spent several years on that question and out came a paper that I doubt anybody read.)

You might ask now, well, what has antigravitation got to do with phenomenological quantum gravity? Nothing actually. It's just that people always ask me what I work on and I used to say: A little bit of particle physics and a little bit of cosmology and my recent paper was about this-and-that and I'm also interested in the foundations of quantum mechanics and organizational design, and then I wrote this paper on the utility function in economics and so on. But I figured that what they actually wanted was a three word answer, so that's why I work on phenomenological quantum gravity. On the institute's website it says I work on "high energy and nuclear physics," which isn't too far off, still, 5 is larger than 3.

But no matter what the headline, what my work looks like is like this: I start with an idea and try to build a model that incorporates it while maintaining mathematical consistency, after all that's what I sat through all these classes for. In addition, the model should be compatible with available data and ideally predict something new. The failure rate is high. But there's the occasional idea that turns out not to be a failure. It gets written up and submitted to a journal and, if all goes well, gets published. I usually publish in Classical and Quantum Gravity, Physics Letters B or Physical Review D.

In the process of working on a paper, I almost always have an ongoing exchange with some people who work on related topics. If the finances allow it, I might visit them or invite them to come here. I might also attend a workshop or conference, or organize one myself. In addition, my work brings the usual overhead like writing or reviewing grant proposals, attending or giving seminars, coming up with a thesis topic, reading applications, reviewing papers, attending faculty meetings and so on. I presently work at a pure research institute, the Nordic Institute for Theoretical Physics in Stockholm, and have no teaching duties, which has advantages and disadvantages. And if you are following this blog you know that I'm only just back from parental leave.

For more on what my work is like, see also What I am is what I am and One day. You can also follow me on Twitter, or Google+.

Interna

2011-09-17T06:24:00.000-04:00

We'll resettle to Stockholm in the coming week and fight some bureaucratic fights, so you might not hear much from us for a while.

Since blogpoll apps have a tendency to vanish, here's a summary of the two recent polls.

Do you die when you go through a transmitter?

Yes, you die. 36.8% (70)
No, you don't die. 33.7% (64)
Some part of the process is physically impossible. 25.3% (48)
Something else (please explain in comments). 4.2% (8)

Do you believe in free will?

I believe human decisions are in principle predictable and there is no free will. 35.4% (45)
I believe human decisions are in principle predictable, but still there can be free will. 28.3% (36)
I believe human decisions are not predictable, neither in practice nor in principle, and we have free will. 27.6% (35)
I believe something else that I'll explain in the comments. 8.7% (11)

And yet it moves

2011-09-14T06:10:00.000-04:00

This September, it's been 16 years since I started studying physics. That's 2^2^2 years which have gone by and bye. Stefan started in 1987. The first physics headline I can recall consciously taking note of was the 1995 discovery of the top quark, and Stefan cites inspiration by the Supernovae 1987a. This got us into a conversation about the most striking insights physics has delivered since we went to university. Here are our winners:

The biggest surprise for everybody except Raffael Sorkin was that the Cosmological constant is not zero. Since 1998, evidence has been adding up and up that our universe undergoes accellerated expansion caused by a small, positive cosmological constant. For more, read my earlier post on the Cosmological Constant and its cousins.

When I was a graduate student, physicists were still debating whether black holes exist or if black holes are just a mathematically possible solution to Einstein's field equations that is however not realized in nature. The first evidence was available already back then, but it took a while for more observations to be made and gradually everybody came to accept that black holes exist for real. (Well, almost everybody.) For more on black holes, see here.

Suspected by many, it still took several decades to unambiguously show that neutrinos have mass. Due to the neutrinos' weak interaction, many years of data had to be collected over different propagation distances at different energies. It wasn't until 2001 that the option of decay rather than oscillation could be ruled out by the SNO results. Yet, the neutrino sector of the standard model still has some mysteries to offer.

In my quantum mechanics class, EPR-type tests of Bell's theorem were Gedankenexperimente. Now they are reality. So are other tests of the foundations of quantum mechanics, down to single photons, double-slit experiments with atoms, while our understanding of entanglement and decoherence has increased and superpositions of larger and larger molecules succeed.

And on the computational side, amazing simulations of large scale structure formation have become possible. If you haven't seen the Millenium Simulation, it's time well spent.

The recent issue of Physik Journal (the membership journal of the German Physical Society) has an article "Physik im Aufwind" that summarizes recent statistical trends in physics. The below shows the number of beginning students in physics by year. I started in the middle dip. It is good to see that physics is drawing in more young people again.

The Third Hand

2011-09-10T02:30:00.000-04:00

Last week at the airport I read the July/August issue of Scientific American Mind, which has an interesting article "Reflections on the Mind" by two Ramachandrans from the Center for Brain and Cognition at UCSD. It is a brief walk through some recent experiments testing how our brain constructs and interprets our own body and how that interpretation can be twisted.

One experiment you have probably heard of is that letting amputees "see" a lost arm or leg with a mirror that doubles the remaining one allows them to scratch or move it. That is, scratching the reflection they see in place of the lost body part does register in the brain, even though there is no direct sensory input. Some months back, we also learned about the "body swap" illusion that makes use of somewhat more sophisticated technology to create the illusion that one is moving a different body, with the aim to test how readily the brain accepts it as one's own. The SciAm Mind article suggests some low tech experiments you can try at home. For example, using a mirror to produce an image of your hand in place of the actual hand and then stroking the image produces a conflict in the brain because the visual input doesn't match the expectation. As a result your hidden arm might feel numb, though there's nothing wrong with it.

This reminded me of a trick we used to play on the mind as children: Lock hands with a friend, with the index fingers straight (see image below). With the free hand, rub up and down your and your friend's index fingers (2nd image). We used to call it "rubber finger." Everybody I know who tried found it to feel weird. I don't know why, but it seems that the brain expects some signal from the friend's finger. It doesn't make a lot of sense to me since you'd need three hands for that. If you have a good interpretation, let me know.

Predetermined Lunch and Moral Responsibility

2011-09-07T12:25:00.002-04:00

The final session of the 2011 FQXi conference concluded with a brief survey. The question “Is a ‘perfect predictor’ of your choices possible?” was answered with “Yes” by 17 out of 40 respondents. The follow-up question “If there were, would it undermine human free will?” was answered with “Yes” by 18 out of 38 respondents.

I’m in the Yes-Yes camp, and I was surprised that doubting one’s own free will was so common among the conference participants. It is striking how unrepresentative this result is for the general population who likes to hold on to the belief that personal choices are undetermined and unpredictable. In a cross-cultural study with participants from the United States, Hong Kong, India and Colombia, Sarkassian et al found that more than two thirds of respondents (82% USA, 85% India, 65% Hong Cong, 77% Colombia) believe that our universe is indeterministic and human decisions are “not completely caused by the past”(exact wording used in the study).

One of the likely reasons many people believe in free will is that if fundamentally there is no such thing as free will, how come that most of us* have the feeling that we do make decisions?

Lacking a good theory of consciousness, it may be that rather than making decisions, the role of our consciousness is to simply provide aggregated information about what our brain and body was doing, is currently doing, and provide a crude extrapolation of this information into the future. As we grow up, we become better at predicting what will be happening next –in our surrounding as well as with our own body and mind – and may mistake our prediction of what we will be doing for an intent to do it, and our imperfection of making precise predictions creates the illusion that we had a choice. (I doubt I'm the first to have this thought. If you know a reference with similar spirit, please let me know.)

This would mean, if you slap your forehead now, rather than consciously deciding to do so and making the choice to perform this action (which we may call the “standard interpretation”) your neuronal network has arrived at the necessary state that immediately precedes this action and your consciousness notes that next thing that will likely happen is you’ll be slapping your forehead, which it interprets as your impulse to do so (we may call it the “self-extrapolation interpretation”). You are not entirely certain about this since you have learned that your subconscious on occasion makes twists that your consciousness fails to properly predict, thus the possibility remains you’ll not be slapping your forehead after all.

It has in fact been argued that the reason why most people reject determinism it is their inability to predict actions, first by Thomas Reid I am told, and later by Spinoza, not that I actually read either. So possibly theoretical physicists are more inclined to believe in determinism because making precise predictions is their day job ;-)

Sean Carroll recently argued that free will can have a peaceful coexistence with modern science on an emergent level, in an effective description of human beings. That only works though if in the process of arriving at that effective level you throw away information that was fundamentally there. I believe Sean is aware of that when he writes “But we don’t know [all the necessary information to predict human decisions], and we never will, and therefore who cares?”

Well, I'd say that if you make room for free will by neglecting in principle available information, then his notion of free will is an empty concept that, as I've learned from the comments to his blogpost, the philosopher Edward Fredkin more aptly named “pseudo free will.”

I'm only picking around on Sean's post because it's short enough for you to go and read it unlike hundreds of pages that some philosophers have spent to say essentially the same thing. In any case, it is interesting how some scientists desperately try to hold on to some notion of free will in the face of an uncaring universe. I believe one of the reasons is that rejecting free will sheds a light of doubt on ones' moral responsibility, and since I feel personally offended, some words on that.

Morals and Responsibility

Whether the universe evolves deterministically, or whether its time evolution has a random element, an individual, fundamentally, has no choice over his or her actions in either case. It is then difficult to hold somebody responsible for actions if they had no way to make a different choice. This and similar thoughts have spurred a number of studies that claim to have shown that priming people’s belief in a deterministic universe reduces their moral responsibility.

For example, a study by psychologists Kathleen Vohs and Jonathan Schooler (summary here) had half of the participants read a text passage arguing against the existence of free will. All participants then filled out a survey on their belief in free will and completed an arithmetic test in which they had an option to cheat, but were asked not to. It turned out that disbelief in free will was correlated with the amount of cheating. Also, in the previously mentioned study by Sarkassian et al, most participants held the opinion that in a deterministic universe people are not responsible for their actions.

However, the issue of moral responsibility is a red herring, for morals are human constructs whether or not we have free will . From the viewpoint of natural selection, the reason why most of us don’t go around cheating, stealing, or generally making others suffer is not that it’s illegal or immoral or both, but that our self-extrapolation correctly predicts we will be suffering in return. Not primarily because we may be thrown into jail but because our brains would keep returning to that moment of offense, imagining how other people suffered because of our wrongdoing, telling us that way that we did act against the interests of our species, and more generally reducing our overall fitness.

In fact, that our species still exists and seems to be doing reasonably well means that most of us do not take pleasure in letting others suffer. The reason we don’t perform “immoral” acts is that we can’t: We’re the product of a billion years of natural selection that has done well to sort out those who pose a risk to our future, and we've called the result “moral.” (I am far from saying one can derive morals.)

The less consequences an act has for ones’ own future and that of others the larger the variety in people’s behavior. (There are more people jaywalking than strangling talk show hosts in front of running cameras.) That we have laws enforcing rules is because there remain people among us whose brains are some sigma away from the average and our laws are one more channel of natural selection, keeping these people off the streets, trying to readjust their brain’s functionality, or at least generally making their lives difficult. David Eagleman recently made a very enlightened argument for a rethinking of our justice system in light of neurobiological evidence for our reduced capability to change our brain’s working.

In a world without free will, we should not ask if a person is worth blaming, but simply look for the dominant cause of the problem and take steps to solve it.

Similarly, instead of asking if who is morally responsible we should ask what incentives do people have. The problem with the above mentioned test for moral responsibility in a deterministic universe it that the consequences of the alleged “immoral” act of cheating are entirely negligible. Putting forward the plausible thesis that the illusion of free will is beneficial to our brain’s performance (or otherwise, why is it so universal?), the test subject’s cheating might have been simply a reassurance of their illusion. If one would replace the temptation to cheat on a test with a questionnaire for the participant’s likings in food and then offer snacks, chances are those who were suggested a deterministic universe would feel the urge to select a food they do not usually prefer. Better still, one may have told the test subjects that the better their brains in the deterministic universe are adapted to living a modern life in modern times, the less likely they will be to perform “immoral acts” that violate the (written or unwritten) rules and values of that society (whether that is true or not doesn't matter).

Predetermined Lunch: Not Free Either

That our decisions are determined does not mean that we do not have to make them, which is a common misunderstanding, nicely summarized by Sean Carroll’s anecdote

“John Searle has joked that people who deny free will, when ordering at a restaurant, should say ‘just bring me whatever the laws of nature have determined I will get.’”

The decision what you will eat may be predetermined, but your brain still has to crunch the numbers and spit out a result. One could equally well joke that your computer, rather than running the code you’ve written, returns it back to you with the remark that the result is predetermined and follows from your input. Which is arguably true, but still somebody or something has to actually perform the calculation. Though in a deterministic universe it is in principle possible, it is highly questionable that the cook will be able to make the prediction about your order in your place, even after asking Laplace’s demon for input.

In other words, even if you don't have a free will, to make a decision you still have to collect all the information you deem necessary and scan your memory and experience to build an opinion, or perform whatever other process you have come to think is a good way to make decisions, may that be rolling a dice or calling your mom. Whether or not you believe you have a freedom in making a decision doesn’t save you the energy needed to do it.

Let me finish this post with a poll:

* The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, describes Depersonalization Disorder as follows: “The essential features of Depersonalization Disorder are persistent or recurrent episodes of depersonalization characterized by a feeling of detachment or estrangement from one's self. The individual may feel like an automaton or as if he or she is living in a dream or a movie. There may be a sensation of being an outside observer of one's mental processes, one's body, or parts of one's body.”

Thus, interestingly enough, not all of us share the feeling of being in charge of one's actions. That the failure to relate to oneself is filed under "disorder" seems to me to show that believing in free will is beneficial to the individual's functionality and well-being.

From my notepad

2011-09-04T07:28:00.001-04:00

The 2011 FQXi conference was an interesting mix of people. The contributions from the life sciences admittedly caught my attention much more than those of the physicists. Thing is, I’ve heard Julian Barbour’s and Fotini Markopoulou’s talk before, I’ve seen Anthony Aguirre’s piano reassemble from dust before, and while I hadn’t heard Max Tegmark’s and George Ellis’ talk before I’ve read the respective papers. The discussions on physics conferences also seem to have a fairly short recursion time and it’s always the same arguments bouncing back and forth. One thing I learned from David Eagleman’s talk is that neuronal response decreases upon repetitive stimuli – so now I have a good excuse for my limited attention span in recursive discussions ;-)

All the talks on the conference were recorded and they should be on YouTube sooner or later. Stefan also just told me that the talks from the 2009 FQXi conference are on YouTube now. (My talk is here. Beware, despite the title, I didn’t actually speak on Pheno QG. Also, I can’t for the hell of it recall what that thing is I’m wearing.) Anyways, here is what I found on my notepad upon return, so you can decide what recording you might want to watch:

Mike Russell gave a very interesting talk on the origin of life or at least its molecular ancestors. He explained the conditions on our home planet 2 billion years ago and the chemical reactions he believes must have taken place back then. He claims that under these circumstances, it was almost certain that life would originate. With that he means a molecule very similar to ADP, the most important cellular energy source, is very easy to form under certain conditions that he claims were present in the environment. From there on, he says, it’s only a small step to protein synthesis, RNA and DNA and they are trying to “re-create” life in the lab.

Chemical reactions flew by a little too fast on Russell’s slides, and it’s totally not my field, so I have no clue if what Russell says is plausible. Especially I don’t know how sure we really can be the environment was as he envisions. In any case, I took away the message that the molecular origins of life might not be difficult to create in the right environment. Somewhat disturbingly, in the question session he said he has trouble getting his work funded.

Kathleen McDermott, a psychologist from Washington University, reports the results of several studies in which they were trying to find out which brain regions are involved in recalling memory and imagining the future. Interestingly enough, in all brain regions they looked at, they found no difference in activity in between people recalling an event in the past and envisioning one in the future.

David Eagleman gave a very engaging talk about how our brains slice time and process information without confusing causality. The difficulty is that the time which different sensory inputs needs to reach your brain differs by the type and location of input, and also the time needed for processing that might differ from one part of the brain to the next. I learned for example that the processing of auditory information is faster than that of visual information. So what your brain does to sort out the mess is that it waits till all information has arrived, then presents you with the result and calls it “right now,” just that at this point it might be something like 100ms in the past actually.

Even more interesting is that your brain, well trained by evolution, goes to lengths to correct for mismatches. Eagleman told us for example that in the early days of TV broadcast, producers were worried that they wouldn’t be able to send audio and video sufficiently synchronized. Yet it turned out, that up to 20ms or so your brain erases a mismatch between audio and video. If it gets larger, all of a sudden you’ll notice it.

Eagleman told us about several experiments they’ve made, but this one I found the most interesting: They let people push a button that would turn on a light. Then they delayed the light signal by some small amount of time 50ms or so past pushing the button (I might recall the numbers wrong, but the order of magnitude should be okay). People don’t notice any delay because, so the explanation, the brain levels it out. Now they insert one signal that comes without delay. What happens? People think the light went on before they even pushed the button and, since the causality doesn’t make sense, claim it wasn’t them! (Can you write an app for that?) Eagleman says that the brains ability to maintain temporal order, or failure to do so, might be a possible root of schizophrenia (roughly: you talk to yourself but get the time order wrong, so you believe somebody else is talking) and they’re doing some studies on that.

From Simon Saunders talk I took away the following quotation from a poem by Henry Austin Dobson on “The Paradox of Time:”

Malcom MacIver, who blogs at Discover, studies electric fish. If that makes you yawn, you should listen to his talk, because it is quite amazing how the electric fish have optimized their energy needs. MacIver also puts forward the thesis that the development of consciousness is tied to life getting out of water simply because in air one can see farther and thus arises the need for ahead planning. In a courageous extrapolation of that, he claims that our problem as a species on this planet is that we can’t “see” the problems in other parts of the world (e.g. starving children) and thus fail to properly react to them. I think that’s an oversimplification and I’m not even sure that is the main part of the problem, but it’s certainly an interesting thesis to think about. He has a 3 part series on posts about this here: Part I, Part II, Part III.

Henry Roediger from the Memory Lab at Washington University explained us, disturbingly enough, that there is in general no correlation between the accuracy of a memory and the confidence in it. For example, shown a list of 16 words with a similar theme (bed, tired, alarm clock, etc) 60% of people (or so, again: I might mess up the numbers) will “recall” the word “sleep” with high confidence though it was not on the list. A true scientist, he is trying to figure out under which circumstances there is a good correlation and what this means for the legal process.

Alex Holcombe told us about his project evidencechart.com, a tool to collect and rate pro and con arguments on a hypothesis. I think this can be very useful, though more so in fields where there actually is some evidence to rate on.

Scott Aaronson's talk on free will deserves a special mentioning, but I found it impossible to summarize. I recommend you just watch the video when it comes out.

Interna

2011-09-03T05:55:00.002-04:00

I am back in Germany and happily reunited with the family. Time might not exist and its passage be an illusion, but the babies are growing irrespective, and our arrow of time points towards baby gates. Lara and Gloria are now 8 months old. They spent the previous week, that I was away for the FQXi conference, with Stefan at their grandma's place. It is difficult to say if they missed me during my absence or if they recognize me upon coming back. They do however clearly recognize our apartment and their own beds. Lara for example had found a way to lie in the corner of her bed in exactly the right angle that she could just look out through the door and onto the corridor - a position she immediately resumed.

The girls are now both moving around by doing the army crawl and Gloria has made first attempts to crawl on her knees. At present, she seems to be aiming at a career as breakdancer, standing on hands and the toes of one foot, turning around chasing the other foot, sometimes slipping and bumping on her head. Interestingly enough, Gloria has completely skipped the phase of moving around by rolling sidewards that Lara has had. Gloria meanwhile has learned how to clap her hands, which she does with enthusiasm. They can now both grab a pacifier and put them into their own mouth and if Lara is in a good mood, she'll try to put it into your mouth.

The babies are both fascinated by all things shiny and tiny and stringy and I've had the somewhat belated insight that the purpose of baby toys is not to entertain the baby but to distract the baby from mommy's toys till it's old enough to realize that pulling on a cable isn't always a good idea.

Our rapid throughput of clothes has been slowing down and we've childproofed the apartment as far as possible. However, in 2 weeks we're packing bags and going back to Stockholm where I will be working while Stefan is on parental leave. So, we'll have to childproof a second apartment and that with the difficulty that we can't remove items or drill into walls because the items aren't ours and the walls are solid concrete.

But, hey, we'll manage somehow. Baby reading this month is an article on "Baby Power" in SciAm Mind according to which mommy brains sprout new neurons, and body chemistry changes towards higher risk taking and better memory performance, at least when it comes to tracking down food. If you are a rat that is. The same article also informs us "that (human) mothers are more likely to rate their infant's odors as pleasant, compared with nonmothers" (Look, an English compound noun! And it's not my making!). Maybe I'm an aberration but, prolactin or not, shit still smells like shit to me. Spiegel Online informs us that we're supposed to train baby's concentration skills by the age of one (at the latest), but then Parents don't matter that much at least when it comes to the child's education and income, and the Globe and Mail reports that striving to be supermom is correlated with depression. So maybe we'll wait with teaching the babies differential geometry on complex spaces for some more while.

Will AI cause the extinction of humans?

2011-08-31T01:07:00.004-04:00

Yesterday, at the 2011 FQXi conference in Copenhagen, Jaan Tallinn told us he is concerned. And he is not a man of petty worries. Some of us may be concerned they’ll be late for lunch or make a fool of themselves with that blogpost. Tallinn is concerned that once we have created an artificial intelligence (AI) superior to humans, the AIs will wipe us out. He said he has no doubt we will create an AI in the near future and he wishes that more people would think about the risk of dealing with a vastly more intelligent species.

Tallinn looks like a nice guy and he dresses very well and I wish I had something intelligent to tell him. But actually it’s not a topic I know very much about. Then I thought, what better place to talk about a topic I know nothing about than my blog!

Let me first say I think the road to AI will be much longer than Tallinn believes. It’s not the artificial creation of something brain-like with as many synapses and neurons that’s the difficult part. The difficult part is creating something that runs as stable as the human body for a sufficiently long time to learn how the world works. In the end I believe we’ll go the way of enhancing human intelligence rather than creating new ones from scratch.

In any case, if you would indeed create an AI, you might think of making humans indispensible for their existence, maybe like bacteria are for humans. If they’re intelligent enough, they’ll sooner or later find a way to get rid of us, but at least it’ll buy you time. You might achieve that for example by never building any AI with their own sensory and motor equipment, but make them dependent on the human body for that. You could do that by implanting your AI into the, still functional, body of braindead people. That would get you in a situation though where the AIs would regard humans, though indispensable, as something to grow and harvest for their own needs. Ie, once you’re adult and have reproduced, they’ll take out your brain and move in. Well, it kind of does solve the problem in the sense that it avoids the extinction of the human species, but I’m not sure that’s a rosy future for humanity either.

I don’t think that an intelligent species will be inherently evil and just remove us from the planet. Look, even we try to avoid the extinction of species on the planet. Yes, we do grow and eat other animals but that I think is a temporary phase. It is arguably not a very efficient use of resources and I think meat will be replaced sooner or later with something factory-made. You don’t need to be very intelligent to understand that life is precious. You don’t destroy it without a reason because it takes time and resources to create. The way you destroy it is with negligence or call it stupidity. So if you want to survive your AI you better make them really intelligent.

Ok, I’m not taking this very seriously. Thing is, I don’t really understand why I should be bothered about the extinction of humans if there’s some more intelligent species taking over. Clearly, I don’t want anybody to suffer in the transition and I do hope the AI will preserve elements of human culture. But that I believe is what an intelligent species would do anyway. If you don’t like the steepness of the transition and want more continuous predecessors of humans, then you might want to go the way I’ve mentioned above, the way of enhancing the human body rather than starting from scratch. Sooner or later genetic modifications of humans will take place anyway, legal or not.

In the end, it comes down to the question what you mean by “artificial.” You could argue that since humans are part of nature, nothing human made is more “artificial” than, say, a honeycomb. So I would suggest then instead of creating an artificial intelligence, let’s go for natural intelligence.

FQXi Conference 2011

2011-08-29T00:26:00.001-04:00

We just arrived in Copenhagen after a 2-day trip on the National Geographic Explorer, a medium sized cruise ship, along Norway’s coast. On board were about 130 scientists and a couple of spouses in different sizes, plus an incredibly efficient, friendly, and competent crew that didn’t mind having nosy physicists hanging around on the bridge.

The 2011 FQXi conference turns out to be very different from the previous one (2009 on the Azores), and that not only thanks to the unique bonding experience of shared sea-sickness. As Sean Carroll mentioned the other day, during the organization of this conference on the nature of time, the FQXi folks were confronted with an application for a similar event with a similar topic and so they decided to join forces. As a result, this conference is larger and much more interdisciplinary than the previous one. Besides the physicists and philosophers, there are neurobiologists, biologists and psychologists, and a selection of guys interested in artificial intelligence from one or the other perspective, as well as a crew with cameras that are here for PBS I am told.

Among the physicists, the usual suspects are Max Tegmark and Anthony Aguirre, Paul Davies, George Ellis, David Albert, Garrett Lisi, Fotini Markopoulou, Julian Barbour, and Scott Aaronson. But there’s also Geoffrey West from the Santa Fe Institute, Jaan Tallinn, one of the developers of Skype, and David Eagleman the possibilian, just to mention a few. Also around are George Musser from Scientific American and Zeeya Merali who is blogging for FQXi here. There’s a list of alleged attendees here, though some of them I haven’t seen so far.

It is an interesting mix of people. I do enjoy interdisciplinary events a lot because there is always some cool research to learn about that I didn’t know of before. I have however grown skeptic about the benefits of interdisciplinarity when it comes to pushing forward on a particular problem. Take a topic such as free will or the origin of our impression of “now” that might or might not be an illusion. Yes, neurobiologists and psychologists have something to say about that. But they don’t in fact mean the same as physicists and I am not sure that, for example, the question how we achieve to remember the past and imagine the future, or fail to distinguish between true and false memory has any relevance for physicists trying to figure out the relevance of the past hypothesis, the consistency of alternatives to the block universe, or the role of observers in the multiverse. In fact, you already have people talking past each other within one discipline: If you ask three physicists what they mean with “free will” you’ll get four different answers. And after you’ve spent a significant amount of time figuring out what they mean to begin with there isn’t much left they have to say to each other.

That’s the downside of mixing academics – in my experience it does not add depth. Interdisciplinary exchange however adds breadth. Talking to somebody who has addressed a question for a completely different reason and with completely different methods helps one look at it from a different point of view, opening new ways forward. In my opinion though the largest benefit of events like this conference comes from just getting together a group of interesting and intelligent people who make an effort to listen to and complement each other. After some years at PI and NORDITA I’ve pretty much come to take for granted having plenty of folks at my disposal to talk to should I feel like it, but after the baby break I appreciate the opportunity for such exchange much more.

The idea with putting us on a ship was clearly to get us off the Internet for some while. I personally don’t have the impression people on the conferences I usually go make obsessive use of the internet, but evidently some need to have an evil third party as an excuse for not being available at least for a few days. I don’t find it such a great idea to punish all of us because a few guys can’t live without their newsfeed. I wasn’t the only one with family at home who would have appreciated at least a phone. (For an appropriate price that is. If you really, really had to you could have paid for an internet connection at $10 per kB or something like that.)

These are some first impressions. If I've had some time to process what I've heard and learned I might summarize some of the main questions that were discussed. But now (whatever that might be) I have to locate my baggage which I've last seen this morning vanishing into a bus somewhere.

Away note

2011-08-25T01:57:00.002-04:00

I'll be away for a week on the FQXi conference "Setting Time Aright." A significant amount of the participants are reportedly nuts, so I will be in good company. I'm supposed to moderate a session on "Choice" for reasons that are somewhat mysterious to me, but since I don't believe in free will I guess they had no choice, haha.

This is my first conference attendance since the babies and, believe me, it's required a significant amount of organization. It didn't help they're doing half of it on a ship and the idea of having to get around on a ship with a twin stroller didn't really appeal to Stefan and me. So I go, and Superdaddy stays with the babies while I'll cry over the no-signal sign on my BlackBerry. Side effects may include blogging congestion.

Physics and Philosophie

2011-08-21T06:17:00.000-04:00

I'm looking for topics where theoretical physics has a relevance for philosophy, for no particular reason other than my curiosity and maybe yours as well. Here's the usual suspects that came to my mind:

Are there limits to what we can possibly know? The human brain has a finite capacity and computing power. What limits does this set? Is it possible to extend? What is consciousness?

Why is the past different from the future? What is "The Now" and why do we have an "arrow of time"? (Or several?)

Is there a fundamental theory that explains everything we observe and experience? Is this theory unique and does it explain everything only in principle or also in practice?

Do we have free will? And what does that question mean?

Are there cases where reductionism does not work? And what does that imply for 3?

What is the role of chaos and uncertainty in the evolution of culture and civilization? Is it possible to reliably model and predict the dynamics of social systems? If so, what does that mean for 4?

What is reality? What does it mean to "exist" and can an entirely mathematical theory explain this? Does everything mathematical exist in the same way? Why does anything exist at all?

And Stefan submits: What is the ontological status of AdS/CFT?

What makes you you?

2011-08-18T13:00:00.000-04:00

Stefan's life is tough. When he comes home, instead of a cold beer (I support the local wineries) and dinner (ha-ha-ha) he gets one of the crying babies and a washcloth. And then there's his wife who lacks googletime and greets him with bizarre questions. What frequency does a CD player operate on? Something in the near infrared. How many atoms do you need to encode one bit? Maybe somewhat below the million it was in 2008. And why does he actually know all this stuff? Male brains are funny. He does not, for example, know that the Aspirin is in the medicine cabinet, out of all places. But yesterday he gave it a pass, so here's my question to you.

Suppose you have a transmitter, spaceship enterprise style. It reads all the information of all particles in your body (all necessary initial values), disintegrates your body, sends the information elsewhere, and reassembles it. Did you die in that process?

You could object that this process isn't physically possible, either theoretically or practically. Theoretically, there are for example the no-cloning and no-teleportation theorems in quantum information. But you might not actually need all the quantum details to reconstruct a human body. (I'm not sure though the role of quantum physics for consciousness has yet been entirely clarified.) And, if I reassemble you elsewhere you are arguably different in that the relative location of your body to all other objects in the universe has changed. But again, it doesn't seem like that's of any relevance. Or you could say that there won't be enough time to perform this process ever in the history in the universe or something like that. But these answers seem unsatisfactory to me.

Then you might say, well, if it looks like me, walks like me, and quacks like me, it probably is me. That is, nobody, including the person you have assembled could tell any difference. So that would seem like you didn't die.

On the other hand, the operation of your brain has a discontinuity in its timeline in the sense that it didn't do anything during transmission. That is in contrast to, say, anesthesia where your brain is actually quite active. (Interesting SciAm article on that here.) So that would seem like that what constitutes 'you' did cease to operate and 'you' did die.

But then again, who really cares if you stopped thinking for some seconds and then continued that process while in between you changed the set of quarks and electrons you're operating with. However, then consider now I don't send the information to one place, but to ten. And I assemble not one you, but ten. Which one are you?

Oh-uh, headache. I can understand Stefan does prefer to bath the baby. Now where is the Aspirin?

Was there really a man on the moon? Are you sure?

2011-08-14T05:06:00.003-04:00

Some weeks ago, the tree octopus made headlines again. If you had never heard of this creature before, don’t worry, it is an internet hoax used for classes on information literacy. It is easy enough to laugh about the naiveté of students believing in the tree octopus. Or people believing in spaghetti trees for that matter. Scientists in particular are obliged to carefully check all facts they use in their arguments. But in reality, none of us can check all the facts all the time. A lot of what we know is based on trust and an ethereal skill called ‘common sense.’ We’re born trusting adults tell us the truth – about the binky fairy. Most of us grow up adding a healthy dose of skepticism to any new information, but we still rely heavily on trusted sources and the belief that few people are willfully evil. What happened to that in the age of the internet?

When I write a paper, I usually make an effort to check that the references I am citing do actually show what they claim, at least to some level. Sometimes, digging out the roots of a citation tree holds ~~spaghetti~~ surprises. But especially when it comes to experiments, fact checking comes to a quick halt because it would simply take too much time putting under scrutiny each and everything. And then peer review has its shortcomings. In my daily news reading however I am far less careful. After all, I’m not being paid for it and I have better things to do than figuring out if every story I read (Can you really get stuck on an airplane’s vacuum toilet?) is true. Most of the time it doesn’t actually matter because, you see, urban legends are entertaining even if not true. And, well, don’t flush while you s it.

I think of myself as a very average person, so I guess that most of you use similar recipes as I to roughly estimate a trust-value of some online recource. The rule of thumb that I use is based on two simple questions: 1) How much effort would one have to make to fake this piece of information in the present form, and 2) How evil would one have to be.

How much effort would one have to make to put up a website about a non-existing animal? Well, you have to invest the time to write the text, get a domain, and upload it. I.e. not so very much. How evil do you have to be? For the purpose of teaching internet literacy, somebody probably believed he was being good. Trust-value of the tree-octopus: Nil. How much effort do you have to make to fake some governmental website? Some. And it’s probably illegal too, so does require some evil. How much effort would you have to make to fake the moon landing?

Of course such truth-value estimates have large error-bars. Faking somebody else’s writing style for example can be quite difficult (if it wasn’t I’d be writing like Jonathan Franzen), but depends on that writing style to begin with. If you’ve never registered a domain before you might vastly overestimate the effort it takes. And how difficult is it really to convince some billion people the Earth is round? (Well, almost.) Or to convince them some omniscient being is watching over them and taking note every time they think about somebody else’s underwear? There you go. (And Bielefeld, btw, doesn’t exist either.)

The trustworthiness of Wikipedia is a question with more than academic value. For better or worse, Wikipedia has become a daily source of reference for hundreds of millions of people. Its credibility comes from its articles being scrutinized by millions of eyes. Yet, it is very difficult to know how many and which people did indeed check some piece of information, and how much they were influenced by the already existent entry. The English Wikipedia site thus, very reasonably, has a policy that information needs to have a source. Reasonable as that may sound, it has its shortcoming, a point that was made very well in a recent NYT article by Noam Cohen who reports on a criticism by Achal Prabhala, an Indian advisor to the Wikimedia foundation.

There is arguably information about the real world that is not (yet?) to be found in any published sources. Think of something trivial like good places in your neighborhood to find blackberries (the fruit)¹. More interesting, Prabhala offered the example of a children’s game played in some parts of India, and its Wikipedia article in the local language, Malayalam. Though the game is known by about 40 millions of people, there is no peer reviewed publication on it. So what would have constituted a valid reference for the English version of the website? What counts as a trusted source? Do videos count? Do the authors of the Wikipedia article have to random sample and analyze sources with the same care as a scientific publication would require? It seems then, the information age necessitates some rethinking of what constitutes a trusted source other than published works. Prabhala says:

“If we don’t have a more generous and expansive citation policy, the current one will prove to be a massive roadblock that you literally can’t get past. There is a very finite amount of citable material, which means a very finite number of articles, and there will be no more.”

Stefan remarked dryly they could just add a reference to Ind. J. Anth. Cult. [in Malayalam], and nobody would raise an eyebrow. Among physicists this is, tongue-in-cheek, known as “proof by reference to inaccessible literature” (typically to some obscure Russian journal in the early 1950s). The point is, asking for references is useless if nobody checks even the existence of these references. Most journals do now have software that checks reference lists for accuracy and at the same time for existence. The same software will inevitably spit out a warning if you’re trying to reference a living review.

But to come back to Wikipedia: It strikes me as a philosophical conundrum, a reference work that insists on external references. Not only because some of these references may just not exist, but because with a continuously updated work, one can create circular references. Take as an example the paper “Moisture induced electron traps and hysteresis in pentacene-based organic thin-film transistors” by Gong Gu and Michael G. Kane, Appl. Phys. Lett. 92, 053305 (2008). (Sounds seriously scientific, doesn’t it?) Reference [13] cites Wikipedia as a source on fluorescent lamps. There is a paper published in J. Phys. B that cites Wikipedia as a source for the double-slit experiment, and a PRL that cites the Wikipedia entry on the rainbow. Taemin Kim Park found a total of 139 citations to Wikipedia in the fields of Physics and Astronomy in the Scopus database as of January 2011².

That citation of Wikipedia itself would not be a problem. But the vast majority of people who cite websites do not add the date on which they retrieved the site. More disturbingly, the book “World Wide Mind” that I read recently, had a few “references” to essays by mentioning they can easily be found searching for [keywords], totally oblivious to the fact that the results of this search changes by the day, depends on the person searching, and that websites move or vanish. (Proof by Google?)

While the risk for citation loops increases with frequently updated sources, it is not an entirely new phenomenon. A long practiced variant of the “proof by reference” is citing one’s own “forthcoming paper” (quite common if page restrictions don’t allow further elaboration), but in this forthcoming paper - if it comes forth - one references the earlier paper. After ten or so self-referencing papers one claims the problem solved and anybody who searches for the answer will give up in frustration. (See also: Proof by mutual reference.)

Maybe the Wikipedia entry on the octopus hoax is a hoax?

Take away message: References in the age of the internet are moving targets and tracing back citations can be tricky. Restricting oneselves to published works only leaves out a lot of information. Citation loops by referencing frequently updated websites can create alternate realities. But don’t worry, somewhere in the level 5 multiverse it’s as real as, say, the moon landing.

Have you cited or would you cite a Wikipedia article in a scientific publication? If you did, did you add a date?

1 And why isn't there a website where one can enter locations of fruit trees and bushes that nobody seems to harvest? Because where we live a lot of blackberries, cherries, plums, peas, and apples are just rotting away. It’s a shame, really.
2 From Park's paper, it is not clear how many of these articles citing Wikipedia were also about Wikipedia. The examples I mentioned were dug out by Stefan.

Condensed penguins

2011-08-09T12:32:00.000-04:00

[Img: Antarctic Connection]

During my time in Canada, the coldest temperature I recall reading off the digital display on the way back home was -28°C. I couldn't help asking myself why did humans ever settle in such hostile environment (and wtf was I doing there). But if you think Canadians are though (and Germans wimps), hear the story of the Emperor Penguin (Aptenodytes forsteri), that lives in Antarctica.

The Emperor Penguin's adaption to the cold, which can drop down to -50°C during the Antarctic winter, is plainly amazing. Feathers, fat, and their ability to increase the metabolism rate at low temperatures allow the penguins to survive. Equally amazing, but also bizarre, is the Emperor Penguin's breeding behavior.

Penguin colonies up to some thousands have nesting areas inland that are, depending on the annual ice thickness, 50-120 km away from the edge of the pack ice. At the beginning of the Antarctic Winter, some time in March or April, the penguins get out of the water and travel to their nesting areas, mostly walking or sliding on the ice. After mating, the female lays a single egg in late May or early June and passes it on to the male for incubation while she walks back to the shore.

In an environment of ice, snow, and the occasional rock the penguins can't build nests, so they balance the egg on their feet in their brood pouch. And, since there isn't much fish to find on the pack ice, they don't eat. Yes, you read that correctly: They walk a hundred kilometers, the female lays an egg and walks back a hundred kilometers, while the male sits on the egg for another 2 months, during the Antarctic Winter, in the dark, without the female, and all that without eating a thing. By the time the egg hatches, the male has fasted for almost 4 months, lost half of his body weight, and hopes for the female to return because he has nothing to feed the chick. And then he still has to walk back to the shore so he doesn't starve. But hey, my husband assembled the baby cribs!

There's a great documentary, "The March of the Penguins," telling this story:

But the penguins know some physics too!

While a single penguin is able to maintain its core body temperature in the freezing cold, this costs a lot of energy which he can't afford during his Winter fast. So what the Emperor penguins do is they form huddles. The density of the huddles increases with falling air temperature. If the huddle gets very dense, the penguins are in a nearly hexagonal arrangement. In a study from about a decade ago, researchers glued measuring devices to some penguin's lower back. They found that the temperature inside huddles can reach as much as 37.5° (Gilbert et al, arXiv:q-bio/0701051v1 [q-bio.PE]).

The penguins in these huddles do not stand still, but they move in occasional small steps which have recently been subject of another study (Zitterbart et al, PLoS ONE 6(6): e20260). The researchers shot movies of the penguin huddles and tracked the position of the birds. As you will easily notice if you read the paper, David Zitterbart is a condensed matter physicist who compares the huddling penguins to particles with an attractive interaction and the tight huddling to a jamming transition in granular materials. Just that the penguins manage to prevent jamming by coordinated movements. The little steps of the penguins propagate through the huddle like density waves. They measured densities up to 21 birds per square meter.

According to their paper, the penguins' little steps have a three-fold benefit. One is that they help the packing to get denser, much the same way like tapping a bag with ground coffee. The second is that they move the whole huddle, allowing huddles to merge and adjust position and direction. The third one is a turnover of penguins in the huddle, moving those from the outside towards the warmer inside. Though one might argue that what actually is responsible for the turnover is not the little forward steps, but the penguins on the front leaving the huddle and joining it (or another huddle) on the back. But without the forward steps, the turnover would make the huddle move backward.

The below movie from Zitterbart et al's paper (Yes, we live in the age of Harry Potter, where paper has moving pictures!) shows a time lapse of the penguin huddling (actual time about 1h):

I was very confused about the penguin turnover because in all the Emperor Penguin huddles in "The March of the Penguin" and photos I had seen only penguin backs and could not for the hell of it figure out where the penguins are supposed to go if they are all facing towards each other. So I wrote an email to David Zitterbart who kindly explained that there's two different kind of huddles that have been observed. Those that they've described in their paper, which have a forward direction, and circular ones that I had seen images of. He writes that no one really knows how the circular ones work, but they hope to find out with the next experiment.

Rehumanized

2011-08-05T07:51:00.000-04:00

This is the previously mentioned commentary on Mark Slouka’s article “Dehumanized: When math and science rule the school” Since the article is quite lengthy, I’ve added a brief summary.

Summary

In his article “Dehumanized,” Mark Slouka argues that the US education’s focus on math and science and the neglect of the humanities spell the demise of democracy. The American education’s “long running affair with math and science” is “obsessive, exclusionary” and “altogether unhealthy.” And that is because the ways of science are “often dramatically anti-democratic.” “There are many things,” Slouka writes “math and science do well, and some they don’t. And one of the things they don’t do well is democracy.”

Referring to a quote by Dennis Overbye that “Nobody was ever sent to prison for espousing the wrong value for the Hubble constant,” Slouka complains that “To maintain its “sustainable edge,” a democracy require its citizens to actually risk something, to test the limits of the acceptable… If the value you’re espousing is one that could never get anyone, anywhere, sent to prison, then strictly democratically speaking you’re useless.” Democratically useful are only humanists because “upsetting people is arguably the very purpose of the arts and perhaps of the humanities in general.” That is also the reason, Slouka explains, totalitarian societies are skimping the dangerously upsetting humanities: “Why would a repressive regime support a force superbly designed to resist it?”

The last thing his humanist colleagues should do, Slouka says, is to succumb to the capitalist’ demand of accountability and economic utility, and attempt to fit in by justifying their existence on the enemies’ terms. “In a visible world, the invisible does not compute… in a horizontal world of “information” readily convertible to product, the verticality of wisdom has no place.” And Slouka evidently thinks wisdom is in the domain of the humanities. The trend to math and science is “the victory of whatever can be quantified over everything that can’t” and clearly one that one should oppose.

Comments

Slouka sets out to make a case against neglect of the humanities in American education and ends up calling scientists the useless couch potatoes of democratic societies. But in his arguments he makes several leaps. Most importantly, he equates “the sciences” with “the scientists” and he mixes up the role of democracy in science and the role of science for democracy, two very different things.

The process of knowledge discovery in science is not democratic. It has never been, and I hope it never will be for it would be a disaster. It is useful to think of it from a system’s perspective. Scientific progress just doesn’t work by voting. I keep saying that it would be good if we had a better understanding of its working and what feedback mechanisms are beneficial, but we know that much. That scientific knowledge discovery doesn’t operate democratically however doesn’t mean scientists don’t understand democracy or its relevance. Science teaches you to look at the evidence, to search for causal relations, correlations, and to identify and fix problems. Scientists know about the limits of predictability and the inevitability of uncertainty. They know what that statistic means and how to read that figure. They know the value of checking the references and that of reasoned argumentation. (Well, we're all human ;-)) The evidence says women are safer drivers than men. Upsetting? Where would democracy be without scientists?

But yes, scientists aren’t the first to take it to the streets if the world doesn’t run as they think it should. The people you find in the streets, those who start a revolution and throw the stones, are in the majority young unemployed males. Something to do with hormones too I guess, I’m sure somebody somewhere wrote a paper about this. The people who like their jobs, they stay in the lab and crunch the numbers because, actually, the world never runs as they think it should, but isn’t it so damned pretty if you look at it through a microscope, telescope, or binocular HMD? So I guess what Slouka is saying then is that we need the humanities because people who don’t like their job are more likely to join that demonstration tomorrow?

Okay, I’m being unfair because I actually agree with Slouka that the trend towards measuring and quantifying everything including success and knowledge gain is unhealthy. The process of measurement itself disturbs the process it is supposed to help - a problem we have discussed several times on this blog. Though, according to Slouka, a scientist like me should be positive about this trend towards reliance on metrics. Considering how divided the scientific community is over the use of any such measure for scientific success, Slouka doesn’t seem to have bothered talking to his colleagues from the science departments.

Slouka’s main point was about the American education system, and he’d done better not to overgeneralize his argument. Having grown up in Germany, I can’t judge on the quality of the American education system. Clearly, you want to teach children how the society they live in works and that includes politics, history, economics as well as all aspects of human culture. Needless to say, many of these subjects are interrelated. The impression I got during my years in the USA is that many students there have little or no idea what democracy is or how it works, and even less so do they actually know what communism, socialism, and social democracy is – and what the differences. I talked to several people who actually thought consumerism is a form of democracy, and I vividly recall talking to one guy who thought Germany is socialistic. Such confusions explain a lot of nonsense I keep reading online and are certainly not helpful to informed decision making. I am not sure though how representative that impression is. Maybe the people who talk to me are just oddballs.

And isn’t it ironic Slouka is bemoaning the American educations’ failure to produce good citizens, since to some extend I own my school education’s focus on democratic values to the Americans of the last generation? The first time some US officer said to me “I’m just following orders,” I stood in shock, having be taught a million times since Kindergarten to never, ever, justify an action by referral to an order whose purpose I cannot explain and bring in line with my conscience. After several similar incidents, I thought that’s just me till somebody told me about their German friend who in reply to the same remark by an US officer uttered promptly “That’s what the Nazi’s said.” Which, even with German accent however, fell on deaf American ears. (And that hopefully explains why I give a shit about your so-called policies.)

The other day, I came across this article by Bruce Levine listing “8 Reasons Young Americans Don’t Fight Back: How the US Crushed Youth Resistance” which you might like or not like, but point 3 “Schools That Educate for Compliance and Not for Democracy” is interesting in the context of Slouka’s article. Levine lets us know that “Upon accepting the New York City Teacher of the Year Award on January 31, 1990, John Taylor Gatto upset many in attendance by stating: “The truth is that schools don’t really teach anything except how to obey orders.””

Taken together, Slouka makes some bad points and some good points, but he makes both badly. Trying to make a case for the value of good writing, Slouka asks “Could clear writing have some relation to clear thinking?” In reply to which I want to quote Niels Bohr: “Never express yourself more clearly than you are able to think.”

This and That

2011-08-01T06:31:00.000-04:00

Some well-written and interesting paragraphs that I came across recently.

Steve Mirsky in Scientific American reports this amusing anecdote:

I was reminded of preposterously precocious utterances by tiny tykes during a brief talk that string theorist Brian Greene gave at the opening of the 2011 World Science Festival in New York City on June 1. Greene said he sometimes wondered about how much information small children pick up from standard dinner-table conversation in a given home. He revealed that he got some data to mull over when he hugged his three-year-old daughter and told her he loved her more than anything in the universe, to which she replied, “The universe or the multiverse?”

Mark Slouka's article Dehumanized: When math and science rule the school leads a fundamentally flawed argument (which I might make content of a longer post), but is one of the most beautifully written texts I've come across lately. I particularly liked this part:
Consider the ritual of addressing our periodic “crises in education.” Typically, the call to arms comes from the business community. We’re losing our competitive edge, sounds the cry. Singapore is pulling ahead. The president swings into action. He orders up a blue-chip commission of high-ranking business executives (the 2006 Commission on the Future of Higher Education, led by business executive Charles Miller, for example) to study the problem and come up with “real world” solutions.

Thus empowered, the commission crunches the numbers, notes the depths to which we’ve sunk, and emerges into the light to underscore the need for more accountability. To whom? Well, to business, naturally. To whom else would you account? And that’s it, more or less. Cue the curtain.

And David Eagleman's article The Brain on Trial that argues for "a scientific approach to sentencing" gives the reader a lot to think about.
Who you even have the possibility to be starts at conception. If you think genes don’t affect how people behave, consider this fact: if you are a carrier of a particular set of genes, the probability that you will commit a violent crime is four times as high as it would be if you lacked those genes. You’re three times as likely to commit robbery, five times as likely to commit aggravated assault, eight times as likely to be arrested for murder, and 13 times as likely to be arrested for a sexual offense. The overwhelming majority of prisoners carry these genes; 98.1 percent of death-row inmates do. These statistics alone indicate that we cannot presume that everyone is coming to the table equally equipped in terms of drives and behaviors.

And this feeds into a larger lesson of biology: we are not the ones steering the boat of our behavior, at least not nearly as much as we believe. Who we are runs well below the surface of our conscious access, and the details reach back in time to before our birth, when the meeting of a sperm and an egg granted us certain attributes and not others. Who we can be starts with our molecular blueprints—a series of alien codes written in invisibly small strings of acids—well before we have anything to do with it. Each of us is, in part, a product of our inaccessible, microscopic history. By the way, as regards that dangerous set of genes, you’ve probably heard of them. They are summarized as the Y chromosome. If you’re a carrier, we call you a male.

Interna

2011-07-30T07:35:00.001-04:00

Lara and Gloria are now 7 months old. During the last month, they have made remarkable progress. Both can now roll over either which way, and they also move around by pushing and pulling. They have not yet managed to crawl, but since last week they can get on all fours, and I figure it's a matter of days till they put one knee in front of the other and say good-bye to immobility. They still need a little support to sit, but they do better every day.

While the twins haven't paid any attention to each other during the first months, now they don't pay attention to anything else. Gloria doesn't take any note of me if Lara is in the room, and Lara loses all interest in lunch if Gloria laughs next door. The easiest way to stop Gloria from crying is to place her next to her sister. However, if one leaves them unattended they often scratch and hit each other. I too am covered with bruises (but hey, it rattles if I hit mommy's head!), scratches (how do you cut nails on a hand that's always in motion?), and the occasional love bite that Lara produces by furiously sucking on my upper arm (yes, it is very tasty). Gloria is still magically attracted to cables, and Lara has made several attempts to tear down the curtains.

Lara and Gloria are now at German lesson 26: da-da, ch-ch, dei-dei-dei, aga-a-gaga. It is funny that they make all these sounds but haven't yet attempted to use them for communication. They just look at us with big eyes when we speak and remain completely silent. Though they seem to understand a few words like Ja, Nein, Gut, Milch. They also clearly notice if I speak English rather than German.

For the parental reading, this month I've enjoyed Ingrid Wickelgren's article "The Miracle of Birth is that Most of Us Figure Out How to Mother - More or Less." Quoting research that shows some brain is useful for parenting too, she writes:

"To take care of a baby's needs, mom needs to be able to juggle tasks, to prioritize on the fly, rapidly, repeatedly and without a lot of downtime... Mothering tests your attention span, ability to plan, prioritize, organize and reason as much as does a day at the office."

Well, it somewhat depends on what you used to do in that office of course. But yeah, I suppose some organization skills come in handy for raising twins. I won't lie to you though, singing children's rhymes isn't quite as intellectually stimulating as going with your colleague through the new computation. But Gloria always laughs when I read to her the titles of new papers on the arXiv.

On the downside, the Globe and Mail reported the other day on "Divorce, depression: The ugly side of twins," summing up "the infant treadmill":

"Cry. Breastfeed. Bottle-feed. Burp. Breast pump. Diaper. Swaddle. Ninety minutes of baby maintenance, then 90 minutes of trying to stay on top of sleep and domestic chores, then repeat. And so on."

Oh, wait, they forgot cleaning the bottles, doing the laundry, picking up baby because she's been spitting all over herself, washing baby, changing her clothes, changing bed sheets, putting baby back into bed, putting bottles into sterilizer, put laundry into dryer, take the other baby out of bed because she's been spitting... Indeed, that's pretty much how we spent the first months. But it gets better and thanks, we're all doing just fine.

You can also disregard all the above words and just watch the below video. And if you think they're cute, don't forget they'll get cuter for two more months, so check back ;-)

PS: Oh, and please excuse the green thing in the video. New software and I haven't yet really figured out how it works.

Prediction is very difficult

2011-07-28T07:50:00.000-04:00

Niels Bohr was a wise man. He once said: "Prediction is very difficult, especially about the future." That is especially true when it comes to predictions about future innovations, or the impact thereof.

In an article in "Bild der Wissenschaft" (online, but in German, here) about the field of so-called future studies, writer Ralf Butscher looked at some predictions made by the Fraunhofer Institute for Systems and Innovation Research (ISI) in 1998. The result is sobering: In most cases, their expert panel didn't even correctly predict the trends of already developed technologies over a time of merely a decade. They did for example predict the human genome would be sequenced by 2008. In reality, it was sequenced already in 2001. They did also predict that by 2007 a GPS-based toll-system for roads would be widely used (in Germany). For all I know no such system is on the horizon. To be fair, they said a few things that were about right, for example that beginning in 2004, flat screens would replace those with cathode-ray tubes. But by and large it seems little more than guesswork.

Don't get me wrong - it's not that I am dismissing future studies per se. It's just that when it comes to predicting innovations, history shows such predictions are mostly entertaining speculations. And then there are the occasional random hits.

I was reminded of this when I read an article by Peter Rowlett on "The unplanned impact of mathematics" in the recent issue of Nature. He introduces the reader to 7 fields of mathematics that, sometimes with centuries delay, found their use in daily life. It is too bad the article is access restricted, so let me briefly tell you what the 7 examples are. 1) The quaternions who are today used in algorithms for 3-d rotations in robotics and computer vision. 2) Riemannian geometry, today widely used in physics and plenty of applications that deal with curved surfaces. 3) The mathematics of sphere packing, used for data packing and submission. 4) Parrondo's paradox, used for example to model disease spreading. 5) Bernoulli's law of large numbers (or probability theory more broadly) and its use for insurance companies to reduce risk. 6) Topology, long thought to have no applications in the real world and its late blooming in DNA knotting and the detection of holes in mobile phone network coverage. (Note to reader: I don't know how this works. Note to self: Interesting, look this up.) 7) Fourier transform. There would be little electrodynamics and quantum mechanics without it. Applications are everywhere.

Rowlett has a call on his website, asking for more examples.

The same issue of Nature also has a commentary by Daniel Sarewitz on the NSF Criterion 2 and its update, according to which all proposals should provide a description of how they will advance national goals, for example economic competitiveness and national security. Sarewitz makes it brilliantly clear how absurd such a requirement is for many branches of research:

"To convincingly access how a particular research project might contribute to national goals could be more difficult than the proposed project itself."

And, worse, the requirement might actually hinder progress:

"Motivating researchers to reflect on their role in society and their claim to public support is a worthy goal. But to do so in the brutal competition for grant money will yield not serious analysis, but hype, cynicism and hypocrisy."

I fully agree with him. As I have argued in various earlier posts, the smartest thing to do is reducing pressure on researchers (time pressure, financial pressure, peer pressure, public pressure) and let them take what they believe is the way forward. And yes, many of them will not get anywhere. But there is nobody who can do a better job in directing their efforts than they themselves. The question is just what's the best internal evaluation system. It is puzzling to me, and also insulting, that many people seem to believe scientists are not interested in the well-being of the society they are part of, or are somehow odd people whose values have to be corrected by specific requirements. Truth is, they want to be useful as much as everybody else. If research efforts are misdirected, it is not a consequence of researchers' wrongheaded ideals, but of these clashing with strategies of survival in academia.

Blablameter

2011-07-24T06:31:00.000-04:00

"Vigorous writing is concise."

~William Strunk, The Elements of Style (1918)

Fun: Die Zeit writes about Bernd Wurm who studied communication science and got frustrated by the omnipresence of empty words in advertisements and press releases. So he developed a software, the "Blablameter," that checks a text for unnecessary words and awkward grammar that obscures content. The Blablameter ranks text on a scale from 0 to 1: the higher the "Bullshit Index," the more Blabla. You find the Blablameter online at www.blablameter.de; it also works for English input. In the FAQ, Wurm warns that the tool does not check a text for actual content and is not able to judge the validity of arguments, it is merely a rough indicator for writing style. He also explains that scientific text tends to score highly on the Blabla-index.

Needless to say, I couldn't resist piping some abstracts of papers into the website. Here's the results, starting with the no-nonsense writing:

Towards Loop Quantum Supergravity (LQSG)
Norbert Bodendorfer, Thomas Thiemann, Andreas Thurn

Bullshit Index : 0.08
Your text shows no or marginal indications of 'bullshit'-English.

Born in an Infinite Universe: a Cosmological Interpretation of Quantum Mechanics
Anthony Aguirre, Max Tegmark, David Layzer

Bullshit Index :0.24
Your text shows some indications of 'bullshit'-English, but is still within an acceptable range

Unitary Evolution and Cosmological Fine-Tuning
Sean M. Carroll, Heywood Tam

Bullshit Index :0.31
Your text shows indications of 'bullshit'-English. It's still ok for PR or advertising purposes, but more critical audiences may be skeptical.

Relative locality: A deepening of the relativity principle
Giovanni Amelino-Camelia, Laurent Freidel, Jerzy Kowalski-Glikman, Lee Smolin

Bullshit Index :0.38
Your text shows indications of 'bullshit'-English. It's still ok for PR or advertising purposes, but more critical audiences may be skeptical.

Introduction to Quantum-Gravity Phenomenology
Giovanni Amelino-Camelia

Bullshit Index : 0.46
Something's getting a bit fishy. You probably want to sell something, or you're trying to impress somebody. It still may be an acceptable result for a scientific text.

Loop Quantum Gravity and Cosmology: A dynamical introduction
Martin Bojowald

Bullshit Index :0.52
Something's fishy. Obviously you want to sell something, or you're trying to impress somebody. Are you sure that you have a real message, and if so: who would understand it?

Thermodynamical Aspects of Gravity: New insights
T.Padmanabhan

Bullshit Index :0.66
This reeks. I bet you're a PR-Expert, Politician, Consultant or Scientist. If there is a message, it's unlikely it will reach anyone.

And yes, I did pipe in some text from this blog. My performance seems to have large fluctuations, but is mostly acceptable.

Did you come across anything with a Blabla-Index smaller than 0.08 or larger than 0.66?

Do cell phones cause tinnitus?

2011-07-22T04:58:00.001-04:00

Forget about cancer caused by cell phones, what about that ringing in your ear? About 10-15% of the adult population suffer from chronic tinnitus. I've had a case of tinnitus after a back injury. Luckily it vanished after 3 months, but since then I'm very sympathetic to people who go nuts from that endless ringing in their ear. A recent study by a group of researchers from Vienna now looked into the correlation between cell phone use and tinnitus. The results are published in their paper Tinnitus and mobile phone use, Occup Environ Med 2010;67:804-808. It's not open access, but do not despair because I'll tell you what they did.

The researchers recruited a group of 100 sufferers that showed up in some hospital in Vienna. They only picked people for whom no physiological, psychological or medical reason for the onset of their tinnitus was found. They excluded for example patients with diseases of the middle ear, hypertension, and those medicated with certain drugs that are known to influence ear ringing. They also did hearing tests to exclude people with hearing loss, of which one might suspect that their tinnitus was noise induced. Chronic tinnitus was defined as lasting longer than 3 months. About one quarter of the patients had had it already longer than 1 year at the time of recruitment. 38 of the 100 found it distressing "most of the time," and 36 "sometimes." The age of the patients ranged from 16 to 80 years.

The researchers then recruited a control group of also 100 people that were matched to the sufferers in certain demographic factors, among others the age group, years of education and whether they lived in- or outside the city.

At the time the study was conducted (2004), 92% of the recruits used a cell-phone. (I suspect the use was strongly correlated with age, but no details on that in the paper). At the time of onset of their tinnitus, only 84% of the sufferers had used a cellphone, and another 17% had used it for less than a year at that time. The recruits, both sufferers and controls, were asked for their cell phone habits by use of a questionnaire. Statistical analysis showed one correlation at the 95% confidence level: for cellphone use longer than 4 years at the onset of tinnitus. In numbers: In the sufferer's group, the ratio between those who had used a cellphone never or less than one year to those who had used it more than 4 years was 34/33. In the control group it was 41/23.

They then discuss various possible explanations, such as the possibility that cell phone radiation affects the synthesis of nitric oxide in the inner ear, but also more banally that a "prolonged contrained posture" or "oral facial manoeuvres" affect the blood flow unfavorably. (Does chewing gum cause tinnitus?)

The result is just barely significant, i.e. just at the edge of the confidence interval. There's a 5% chance of that result happening just coincidentally by unlucky sampling. So the researchers conclude very carefully that "high intensity and long duration of mobile phone use might be associated with tinnitus." Note that it's "associated with" and not "caused by." Needless to say, if you Google "cell phones tinnitus" you'll find several pages incorrectly proclaiming that "The researchers concluded that long term use of a mobile phone is a likely cause of tinnitus," or that the "study suggests cell phones may cause a chronic ringing in the ears." If such a Google search lead you here, the study concludes nothing of that sort. Instead, the authors finish with saying that there "might" be a link and that the issue should be "explored further."

So, do cell phones cause tinnitus? Maybe. Should you stop sleeping with the phone under your pillow? Probably.

In any case, I was left wondering why they didn't ask for phone habits generally. I mean, if it's the posture or movements connected with calling, what's it matter if it's a cell phone or a landline?

Book review: World Wide Mind by Michael Chorost

2011-07-18T07:25:00.002-04:00

World Wide Mind
The Coming Integration of Humanity, Machines, and the Internet
By Michael Chorost

Is it surprising that self-aware beings become increasingly aware of their self-awareness and start pushing the boundaries? The Internet, Google, iPhones and wifi on every street corner have significantly changed the way we interact, share information and solve problems. Meanwhile, neuroscientists have made dramatic progress in deciphering brain activity. They have developed devices that allow to type using thoughts instead of fingers and monkeys with brain implants have learned how to move a robot arm with their thoughts. These are two examples that Michael Chorost discusses in his book, and that he then extrapolates.

Chorost's extrapolation is a combination of these developments in communication and information technology and neuroscience: Direct brain-to-brain communication by thought transmitted via implants rather than by typed words, combined with wireless access to various soft- and hardware to supplement to our cognitive skills.

I agree with Chorost that this "World Wide Mind" is the direction we are drifting, and that the benefits can be huge. It is interesting though if you read the comments to my two earlier posts that many people seemed to be scared rather than excited by the idea, mumbling Borg-Borg-Borg to themselves. Is is refreshing and also curageous then that Michael Chorost in his book addresses the topic from a quite romantic viewpoint.

Chorost describes himself as a short, deaf, popular science writer. He wears a Cochlear implant that allows him to hear by electric stimulation of the auditory system (content of his previous book, which I however didn't read). Chorost started writing "World Wide Mind" single and finished as a married man. He writes about his search for a partner and what he learned along the way about communication and what today's communication on the internet is lacking. The ills produced by our presently incomplete and insatisfactory online culture he believes will be resolved if we overcome the limitations of this exchange. He does not share the pessimism Jaron Lanier put forward in his book "You are not a gadget". (He does however share Lanier's fondness of octupi and a link to this amazing video with the reader.)

In "World Wide Mind" Chorost wants to offer an outlook of what he believes is doable if today's technology is pushed forward hard enough. He focuses mostly on optogenetics, a recently florishing field of study that has allowed to modify some targeted neurons' genetic code such that their activity can be switched on and off by light signals (most famously, this optogenetically controlled mouse running circles in blue light). He also discusses what scientists have learned about the way our brains store and process input. Chorost then suggests that it seems doable to record each person's pattern of neuronal activity for certain impressions, sights, smells, views, words, emotions and so on (which he calls "cliques") and transmit them to be triggered by somebody else's implant in that person's brain where they would cause a less intense signal of the corresponding clique. That would then allow us, so the idea, to share literally everything.

Chorost offers some examples what consequences this would have that seem to me however quite bizarre. Improving on Google's flu tracker, he suggests that the brain implants could "detect the cluster of physical feelings related to flu -- achiness, tiredness, and so on -- and send them directly to the CDC." I'm imagining in the future we can track the spread of yeast infections via shared itchiness, thank you very much. Chorost also speculates that "The greater share of the World Wide Mind's bandwidht might be devoted to sharing dreams" (more likely it would be devoted to downloadable brain-sex), and that "linking the memory [of what happened at some place to the place] could be done very easily, via GPS." I'm not sure I'd ever sleep in a hotel room again.

He barely touches in one sentence on what to me is maybe the most appealing aspect of increased empathy, a bridging of the gap between the rich and the poor, both locally and globally, and his vision for science gives me the creeps for it would almost certainly stiffle originality and innovation due to a naive sharing protocol.

"World Wide Mind" is a very optimistic book. It is a little too optimistic in that Chorost spends hardly any time discussing potential problems. He has a few pages in which he acknowledges the question of viruses and shizophrenia, but every new technology has problems, he writes, and we'll be able to address them. The Borg, he explains, are scary to us because they lack empathy and erase the individual. A World Wide Mind, in contrast, would enhance individuality because better connectivity fosters specialization that eventually improves performance. Rather than turning us into Borg, "brain-to-brain technologies would be profoundly humanizing."

It is quite disappointing Chorost does not at all discuss the cognitive biases we know we have, and what protocols might prevent them from becoming amplified. Nor does he, more trivially, address the point that everybody has something to hide. Imagine you're ignoring a speed limit sign (not that I would ever do such a thing). How do you avoid this spreading through your network, ending up in a fine? Can you at all? And let's not mention that reportedly a significant fraction of the adult population cheats on their partner. Should we better wait for the end of monogamy before we move on with the brain implants? (It may be close than you think.) And, come to think of it, let's better wait for the end of the Catholic Church as well. Trivial as it sounds, these issues will be real obstacles in convincing people to adapt such a technology, so why didn't Chorost spend a measly paragraph on that?

Chorost's book is an easy read. On the downside, it lacks in detail and explanation. His explanation of MRI for example is one paragraph saying it's a big expensive thing with a strong magnet that "can change the orientation of specific molecules in a person's body, letting viewers see various internal structures clearly." And that's it. He also talks about neurotransmitters without ever explaining what that is, and you're unlikely to learn anything about neurons that you didn't already know. Yes, I can go and look up the details. But that's not what I buy a book for.

"World Wide Mind" sends unfortunately very unclear messages that render Chorost's arguments unconvincing. He starts out stressing that the brain's hardware is its software, and so it's quite sloppy he then later, when discussing whether the Internet is or might become self-aware, confuses the Internet with the World Wide Web. According to different analogies that he draws upon, blogs either "could be seen as a collective amygdala, in that they respond emotionally to events" and Google (he means the search protocol, not the company) "can be seen as forming a nascent forebrain" or some pages later it can be seen as an organ of an organism, or a caste of a superorganism.

Chorost also spends a lot of words on some crazy California workshop that he attended where he learned about the power of human touch (in other words, the workshop consisted of a bunch of people stroking each other), but then never actually integrates his newly found insights about the importance of skin-contact with the World Wide Mind. This left me puzzled because the brain-to-brain messaging he envisions is able to transfer one's own neuronal activity only, which means essentially rather than tapping on your friend's shoulder, you'd have to tap your own shoulder and send it to your friend. And Chorost does not make a very convincing case when he claims that we'd be easily able to distinguish somebody else's memory from our own because it would lack in details. He does that after he discussed in length our brains' tendency to "confabulation," the creation of a narrative for events that didn't happen or didn't make sense to protect our sense of causality and meaning, something he seems to have forgotten some chapters after explaining it.

In Summary: the book is very readable, entertaining and it is smoothly written. If you don't know much about the recent developments in neuroscience and optogenetics, it will be very interesting. The explanations are however quite shallow and Chorost's vision is not well worked out. On the pro-side, this gives you something to think about yourself, and the book requires with only 200 pages not a big time investment.

Undecided? You can read the prologue and 1st Chapter of the book here, and Chapter 4 here. Michael Chorost tweets and is on facebook.

Collective excitement

2011-07-15T06:26:00.002-04:00

I woke up this morning to find my twitter account hacked, distributing spam. I'm currently reading Michael Chorost's new book “World Wide Mind” and if his vision comes true the day might be near when your praise of the frozen pizza leaves me wondering if your brain has been hacked. Book review will follow when I'm done reading. If the babies let me that is. Here, I just want to share an interesting extract.

On the risk of oversimplifying 150 pages, a “clique” is something like an element of the basis of your thoughts. Might be a thing, a motion, an emotion, a color, a number, and so on, like e.g. black, dog, running, scary... It's presumably encoded in some particular pattern of neurons firing in your brain, patterns that however are different from person to person. The idea is that instead of attempting brain-to-brain communication by directly linking neurons, you identify the pattern for these “cliques.” Once you've done that, a software can identify them from your neuronal activity and submit them to somebody else where they get translated into their respective neuronal activity.

In Chapter 10 on “The Future of Individuality,” Chorost speculates on the enhanced cognitive abilities of an interconnected World Wide Mind:

“[I]magine a far-flung group of physicists thinking about how to unify quantum mechanics and general relativity (the most important unsolved problem in physics). One of them has the germ of an "aha" idea, but it's just a teasing sensation rather than a verbally articulated thought. It evokes a sense of excitement that her [brain implant] can pick up. Many cliques in her brain would be activated, many of them subconsciously. The sensation of excitement alerts other physicists that something is up: they suddenly feel that sense of aha-ness themselves. The same cliques in their brains are activated, say these: unification problem, cosmological constant, black holes, Hawking radiation.

An apparent random assortment, but brains are good at finding patterns in randomness. New ideas often come from a fresh conjunction of old ones. In a group intimately familiar with a problem, the members don't need to do a whole lot of talking to understand each other. A few words are all that are needed to trigger an assortment of meaningful associations. Another physicist pushes those associations a little further in his own head, evoking more cliques in the group. Another goes to his keyboard and types out a few sentences that capture it, which go out to the group; perhaps they are shared on a communally visible scratch pad. The original physicist adds a few more sentences. Fairly rapidly, the new idea is sketched out in a symbology of words and equations. If it holds up, the collective excitement draws in more physicists. If it doesn't, the group falls apart and everyone goes back to what they were doing. This is brainstorming, but it's facilitated by the direct exchange of emotions and associations within the group, and it can happen at any time or place.”

Well, I'm prone to like Chorost's book as you can guess if you've read my last year's post It comes soon enough in which I wrote “The obvious step to take seems to me not trying to get a computer to decipher somebody's brain activity, but to take the output and connect it as input to somebody else. If that technique becomes doable and is successful, it will dramatically change our lives.”

Little did I know how far technology has come already, as I now learned from Chorost's book. In any case, the above example sounds like right out of my nightmare. I'm imagining, whenever one of my quantum gravity friends has an aha-moment we're all getting a remote-triggered adrenaline peak and jump all over it. We'd never sleep, brains would start fuming, we'd all go crazy in about no time. Even if you'd manage to dampen this out, the over-sharing of premature ideas is not good for progress (as I've argued many times before). Preemies need intensive care, they need it warm and quiet. A crowd's attention is the last thing they need. Sometimes it's not experience and knowledge of all the problems that helps one move forward, but lack thereof. Arthur C. Clarke put it very well in his First Law:

“When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.”

The distinguished scientist may be wrong, but he certainly will be able to state his opinion very clearly and indeed have a lot of good reasons for it. He still may be wrong in the end, but by then you might have given up thinking through the details. Skepticism and debunking is a central element of research. Unfortunately, one sometimes throws out the baby with the bathwater of bad ideas. “Collective excitement” based on a sharing of emotions doesn't seem like the best approach to science.

Love to wonder

2011-07-10T02:30:00.000-04:00

The July issue of 'Physik Journal' (the membership journal of the German Physical Society) has an interview with Jack Steinberger. Steinberger is an experimental particle physicist who in 1988 won the Nobelprize, with Leon Lederman and Melvin Schwartz, for his 1962 discovery of the muon neutrino. He is German born, but his family emigrated to the USA in 1934. Steinberger just celebrated his 90st birthday. What does a physicist do at the age of 90? Here's an excerpt from the interview (by Stefan Jorda):

You still come to your office at CERN every day?

I came by bike until last year, but then I fell and now I take the bus. I get up at five and arrive at half past six.

Every morning?

Not on Saturdays and Sundays. But I have nothing else to do. I read my email, then I go to the arXiv and look at the new papers in astrophysics. On the average, it's about 50 to 100, many of them are very bad. I read the abstracts, this takes one and a half hour, then I print those 5 to 10 that may be of interest to me. I try to understand them during the rest of the day. Then at 4pm I take the bus back home.

Since when are you interested in astrophysics?

In 1992 COBE detected the inhomogeneities in the cosmic microwave background, that was wonderful. It was a big challenge for me, as a particle physicist, to understand it, because one has to know general relativity and hydrodynamics. Back then I was still a little smarter and really tried to learn these things. Today I am interested for example in active galactic nuclei. The processes there are very complicated. I try to keep track, but there are many things I don't understand, and a lot simply is not understood.

(Any awkward English grammar is entirely the fault of my translation.)

Should I be lucky enough to live to the age of 90, that's how I would like to spend my days, following our ongoing exploration and increasing understanding of nature. Okay, maybe I would get up a little later. And on Saturday I'll bake a cake or two because my grand-grand children come for a visit. All nine of them.

"Men love to wonder, and that is the seed of science."

~Ralph Waldo Emerson

Finetuned

2011-07-06T23:57:00.002-04:00

Melvin the Machine: a Rube Goldberg machine with a twitter account.

Melvin The Magical Mixed Media Machine from HEYHEYHEY on Vimeo.

[via, more info]

Getting cuter by the day...

2011-07-05T04:13:00.001-04:00

If you've been wondering what age babies are the cutest, there's a scientific answer to that. Yes, there is. In the year 1979, Katherine A. Hildebrandt and Hiram E. Fitzgerald from the Department of Psychology at Michigan State University published the results of their study on "Adults' Perceptions of Infant Sex and Cuteness."

A totally representative group of about 200 American college students of child psychology were shown 60 chromatic photographs of infant faces: 5 male and 5 female each for six age levels (3, 5, 7, 9, 11, and 13 months). The babies were photographed by a professional photographer under controlled conditions when their facial expressions were judged to be relatively neutral, and the infants' shoulders were covered with a gray cape to hide clothing.

The study participants were instructed to rate the photos on a 5-point scale of cuteness (1: not very cute, 2: less cute than average, 3: average cuteness, 4: more cute than average, 5: very cute). The average rating was 2.75, ie somewhat less than averagely cute. The authors write that it's probably the selection of photos with neutral facial expressions and the grey cape which accounted for the students' overall perception as slightly less cute than average. And here's the plot of the results:
So, female cuteness peaks at 9 months.

For the above rating the participants were not told the gender of the child, but asked to guess it, which provided a 'perceived gender' assignment to each photo. In a second experiment, the participants were told a gender which however was randomly picked. It turned out that an infant perceived to be male but labeled female was perceived to be less cute than if it was labeled male. Thus the authors conclude that cuter infants are more likely to be perceived as female, and cuteness expectations are higher on females.

Partly related, Gloria just woke up:

Why do we live in 3+1 dimensions? Another attempt.

2011-07-01T06:40:00.000-04:00

It's been a while since we discussed the question why we experience no more and no less than 3 spatial dimensions. The last occasion was a paper by Karch and Randall who tried to shed some light on the issue, if not very convincingly. Now there's a new attempt on the arXiv:

arXiv: 1106.4548 [hep-th]

We argue that the spontaneous creation of de Sitter universes favors three spatial dimensions. The conclusion relies on the causal-patch description of de Sitter space, where fiducial observers experience local thermal equilibrium up to a stretched horizon, on the holographic principle, and on some assumptions about the nature of gravity and the constituents of Hawking/Unruh radiation.

What they've done is to calculate the entropy and energy of the Unruh radiation in a causal patch of any one observer in a de Sitter spacetime with d spatial dimensions. Holding the energy fixed and making certain assumptions about the degrees of freedom of the particles in the radiation, the entropy has a local maxium at d= 2.97 spacelike dimensions, a minimum around 7 and goes to infinity for large d. Since the authors restrict themselves to d less or equal to 10, this seems to say for a given amount of energy the entropy is maximal for 3 spacelike dimensions. Assuming that the universe is created by quantum tunneling, the probability for creation is larger the larger the entropy, thus it would be likely then that we live in a space with 3 dimensions.

To calculate the entropy one needs a cutoff the value of which is fixed by matching it to the entropy associated with the de Sitter horizon, so that's where the holographic principle becomes important.

Not only is it crucial that they add an upper bound on the number of dimensions by some other argument, their counting also depends on the number of particles and the dimensions they can propagate into. They are assuming only massless particles contribute, and these are photons and gravitons. Massive particles even with small masses, the authors write, are "unacceptable" because then the cutoff could be sensitive to the Hubble parameter. By considering only photons and gravitons as massless particles they are assuming the standard model. So even in the best case one could say they have a correlation between the number of dimensions and the particle content. Also, in braneworld models the total number of spatial dimensions isn't necessarily the one determining degrees of freedom at low energy; a possibility the authors explicitly say they're not considering.

Thus, as much as I'd like to see a good answer to the question, I'm not very convinced by this one either.

This and That

2011-06-29T04:41:00.002-04:00

Some random things that caught my attention recently:

If you like PhD comics, they're working on a movie: Trailer here.

The Helmholtz-Zentrum Dresden-Rossendorf set a new world record for magnetic fields with 91.4 teslas.

You have 1 week left to work out some detail of the 100 year spaceship and send in an abstract for the public symposium Sep 30 - Oct 2nd in Orlando "intended to seed creative energy to “kick-start” the long term research goals." It's for sentences like this that you hire PR people.

Partly related, I learned the other day from SciAm that the new buzzword after "synergy" and "horizontal integration" is now "convergence." So let's converge on something then.

Also, the new-name creationists have switched from iIng everything from iKnow to iDontcare and are now replacing spaces with dots, following the ICANN's decision to allow customizable URL suffixes. Ironically though, Google seems to replace the dot with a space if you search for a tag. Anyway, I see huge potential for the arXiv. No more SUSY or MSSM, it's now mond.4u and beyond.higgs. Leave your physics-themed suggestions in the comments!

Something to look at: Camouflage art.

And something else to look at: Dear Photograph

If you like the comic series Asterix and Obelix, you'll love this Study of traumatic brain injuries. To quote from the conclusions "Roman nationality, hypoglossal paresis, lost helmet, and ingestion of the magic potion were significantly correlated with severe initial impairment of consciousness (p ≤ 0.05)."

Interna

2011-06-27T06:12:00.004-04:00

So we're back in Germany. For the next months, I'm on parental leave again and Stefan works 9 to 5. Lara and Gloria are now almost 6 months old. They can now both roll over from back to belly, though not the other way round, and they've discovered their feet which make good toys that don't fall out of reach. They can grab and hold things, give them from one hand to the other, and bang them not only in their own but also in other people's faces. They can meanwhile eat quite well from a spoon, though they try to grab the spoon which makes feeding inevitably a mess.

Lara entertains us with a large variety of funny sounds ranging from moo-moo over uee-wee to fffff. The latter is particularly amusing when executed with a mouth full of mashed carrots. Gloria too finds distraction in her 5 minutes older sister and often turns to look at her or rolls into her direction. If Lara burps, Gloria laughs. Lara's hair finally seems to start growing, and it turns out to be lighter than it was at birth. Her eye color on the other hand is turning more brownish by the day. Gloria is still blue eyed and has a hint of blond hair.

Yes, my life has become very pink.

The girls now sleep reasonably well at night, but are more demanding during the day. Lara in particular manages to move around without actually being able to crawl and then gets stuck in all sorts of impossible positions. Gloria apparently loves to chew on cables, and it's good she doesn't have teeth yet. In the coming weeks, we'll have to childproof the apartment.

I have, to my great delight, meanwhile received parental benefits from the Swedish Försäkringskassan, at least for a couple of months, after I managed to convincingly explain I'm indeed still insured with them. The problem seems to have been caused by some EU agreement that assigns me to a German health insurance during my stay here. On the Swedish side however the health and social insurance are both in the domain of the same institution, so they seem to have concluded I'm back in Germany for good, never mind that I'm paying taxes in Sweden. Now they have some difficultly figuring out how many days I'm eligible for since Stefan doesn't live in Sweden. The Germans on the other hand have so far refused to pay a single cent of Stefan's benefits since they don't know what the Swedes will pay for me. The bottomline is we're still sitting on piles of paperwork and money is short. We've also learned of several people who've had similar difficulties which is both comforting and frustrating.

Our Saab's oil leak caused us some more headache than anticipated. Here in Germany we were told the broken part, some rusty hose, would have to be shipped from Sweden. Since we were on the way to Sweden anyway, we contacted some repair place there after arrival just to be told that Saab has only one warehouse for spare parts left, which is in Nyköping, and the part we need is out of stock. They could put in an order for fourhundredsomething Euro, and it might come in anything between next month or never. The car making more insulted noises by the day, I had the great idea to Google for 'Saab spare parts' in Swedish. Two days later I picked the part up from the post office; it came to about 25 Euro. To my amazement, it was indeed the right part and it's being replaced right now. Lesson learned: If you need a spare part for your car, buy it online yourself and bring it to your dealer.

Weather here in Germany is brilliant, 36 Grad, Es wird immer heisser, Es ist Sommer! and the women's soccer world cup has just begun.

No I wont agree to disagree

2011-06-22T05:55:00.004-04:00

In a recent NYT article, I learned about the "argumentative theory of reasoning," suggested by Dan Sperber, a French social and cognitive scientist, who is director of the International Cognition and Culture Institute. The essence of his theory seems to be that the evolutionary purpose of argumentation is to win an argument. That, apparently, is a groundbreaking hypothesis as his colleagues mostly argue that the purpose of reasoning is to find the truth, leaving them puzzled why the human brain works so inefficiently to that end. Sperber's postdoc Hugo Mercier has a website that lists the predictions of this theory, most of which are actually postdictions.

I think they've forgotten to disentangle argumentation by subject. There's arguably arguments that for the sake of natural selection you're better off finding out the truth. You can convince me all you want that drinking distilled water will cleanse your soul, you're not going to reproduce 6 feet under. But if the argument is about getting your way (what's for dinner?) then you might indeed be better off packing on arguments in your favor and leaving out those that contradict you. The problem is of course that it's difficult to switch from one mode of argumentation to the other. That's why it's beneficial if scientists have some formal training in which they learn, if not actually the names of well-known cognitive biases, so at least procedures that have proven efficient in avoiding pitfalls of human cognition, cognition that has evolved for other purposes than, say, finding evidence for dark matter.

In any case, this reminded me of a little book I once saw on a bargain bin, "50 ways to stall a discussion." ("50 Arten, sich quer zu stellen" by Frans Krips, you can download it here.) If you ever sat in the 5th installment of yet another seemingly endless committee meeting, consider that everybody else read the book and took the advice very seriously. Here's a sample from the 50 ways:

This was not sufficiently discussed
We don't have enough information
We should first find out how the matter has been dealt with elsewhere
This is much too fast
Deficient use of language
Inadequate standard
We first have to discuss some other problem
There are other problems of higher societal relevance
One just can't do it this way
You can't expect that from the people
We've discarded so many plans, who cares if we discard yet another
We tried this already in 1976
We haven't yet assessed the impact of our last decision
Who exactly is responsible?
We should contact an expert
We have to set priorities straight
We need a committee on this aspect

And then there is of course the Web2.0 deadlock: we have to agree to disagree. It too fails to differentiate between seeking for truth and seeking for compromise. We can agree to disagree on all matters of taste: Pizza or Sushi? Pink or blue? NIN or RHCP? but when it comes to science, disagreement means one of us is wrong. Finding the right answer is what science is all about. So it's Pizza tonight, dammit.

[Img Src: Very Demotivational]

Exploring Self-perception: Zakaryah Abdulkarim

2011-06-20T03:58:00.003-04:00

[Last month, I volunteered for a study at the department of neuroscience at Karolinska Institute, if just out of curiosity to see the place. Eventually it didn't work out with my participation, but I got to meet Zakaryah, a student at the Institute, who kindly agreed to tell us a little about his work there. I certainly learned some new vocabulary. Enjoy!]

I read that you are looking for volunteers for a project. Can you tell us what this is all about?

Yes. The project that I am currently involved in is one in the field of cognitive neuroscience. It is part of the research conducted in the lab of Dr. Henrik Ehrsson at the Department of neuroscience, Karolinska Institute. In this project we use an established perceptual illusion called ‘the body swap illusion’ (Petkova & Ehrsson, 2008) in which healthy participants experience the body of a shop mannequin as their own body to understand the behavioral and neural mechanisms underlying the self-attribution of a whole body to oneself. In particular, we are interested in understanding the neural mechanisms underlying the unitary experience of owning an entire body rather than a set of fragmented body parts. My project will contribute important behavioral and physiological data in support of a neuroimaging study conducted by my direct supervisor PhD-candidate Valeria Petkova.

In my experiment the participants wear head-mounted virtual reality displays, through which they see the mannequin’s body. They then receive simultaneous visual and tactile stimulations of various body parts and fill out a questionnaire regarding their experience. Alternatively they might see a knife approaching the mannequin, in which case the sweating of their palms, the so called galvanic skin response, which is a measurement of the sympathetic nervous systems response to dangerous stimuli is measured via electrodes attached to the fingers of the participant. Since the knife is approaching the mannequin and not the body of the participant, the sweating of the palm is used as an objective measurement of the perception of the body ownership illusion.

What is that sort of research good for?

Understanding the perceptual and neural mechanism involved in how we perceive our own body might be useful in the development of neuroprosthetics. Further, understanding the mechanism underlying the healthy perception of body ownership can help develop diagnostic and therapeutic tools in the treatment of pathological disturbances of the bodily self perception in different groups of patients (i.e. stroke, paraplegia, schizophrenia, anorexia etc.). Finally, the results of this type of research are beneficial for some industrial applications, for example in the field of virtual reality, telerobotics or telepresence.

What future studies would you like to do?

I would probably want to investigate more exactly which areas of the brain are involved in producing this feeling of body ownership and various ways to manipulate this. In particular, it would be interesting to see if one could affect this illusion pharmacologically, and how the illusion is correlated to the features of the subjects, because interestingly, not everyone experience this illusion.

What are the presently most pressing open questions in the field?

Here are some examples:

- What are the exact characteristics (i.e. type, receptive field etc) of the neuronal population involved in the neural computation of body ownership?

-What is the exact role of each node in the neural network indentified to be associated with the sense of owning a body. With other words what is the specific role of the ventral premotor cortex, the intraparietal cortex, the putamen, and the cerebellum?

- What is the interplay between body ownership and the sense of agency in the mechanism of self-awareness?

Do you see any relevance for physics or a role for physicists in that kind of research? If so, what?

Of course! Aside from all the technical equipment that is needed to perform these studies, e.g. MRI-scanners, galvanic skin electrodes etc., this research brings up a lot of fundamental questions about how we perceive ourselves and our surroundings, how we make decisions, how effects on different scales interplay, and I believe physics can contribute a lot to those discussions.

For somebody interested in this research, what further reading can you recommend?

One could read some scientific articles about it, however those can be hard to understand if you do not have a background in medicine or neuroscience. I would recommend those who are interested to read bookchapters about this kind of research, which exist in most of the new books in cognitive neuroscience, for example this.

If I'm in Stockholm and interested volunteering for your or similar research, how do I get in contact?

If you are in Stockholm and interested in participating, the best thing to do would probably be to send me an email, my email-adress is: zakaryah.abdulkarim[at]stud.ki.se. The requirements differ depending on the study, but usually there is some experiment in our lab that one can participate in.

Zakaryah is a medical student at Karolinska Institute. In his free time, when he isn’t at Alba Nova taking some evening course that is, he likes exercising, hanging out with friends, and enjoying what the vegetarian cuisine has to offer.

Nonlocal correlations between the Canary Islands

2011-06-15T08:20:00.002-04:00

Bell's inequality is the itch on the back of all believers in hidden variables. Based on only a few assumptions it states that some correlations in quantum mechanics can not be achieved by local realistic hidden variables theories. The correlations in hidden variables theories of that type have to fulfill an inequality, now named after John Bell, violations of which have been observed in experiment, thus hidden variables don't describe reality. But as always, the devil is in the details, and if one doesn't pay attention to the details, loopholes remain. For Bell's inequality, there are actually quite a few of them, and to date no experiment has managed to close them all.

The typical experiment for Bell's theorem makes use of a pair of photons (electrons), entangled in polarization (spin). The two particles are send in different directions and their polarizations are measured along different directions. The correlation among the pairs of repeated measurements is subject to Bell's inequality. (Or the more general CHSH inequality).

The maybe most obvious loophole, called the locality loophole, is that information could be locally communicated from one measurement to the other. Since information can maximally be transmitted by the speed of light this is the case if, for example, the second measurement is made with delay to the first, such that the second measurement is in the forward lightcone of the first. Another loophole is that the detector settings may possibly be correlated with the prepared state without any violations of locality if they are in the forward lightcone of the preparation. Since in this case the experimenter cannot actually set the detector as he wishes, it's called the freedom-of-choice loophole.

A case where both loopholes are present is depicted in the space-time image below. The event marked with "E" is the emission of the photos. The red lines are the worldlines of the entangled electrons or photons (in an optical fiber). "A" and "B" are the two measurements and "a" and "b" are the events at which the detector settings are chosen. Also in the image are the forward lightcones of the event "E" and "A".

So that's how you don't want to make your experiment if you're aiming to disprove locally realistic hidden variables. Instead, what you want to do is an experiment as in the second figure below, where not only the measurement events "A" and "B" are spacelike to each other (ie they are not in each other's lightcone), but also the events "a" and "b" at which the detector settings are chosen are spacelike to each other and to the emission of the photons.

Let us also recall that the lightcone is invariant under Lorentz-transformations and thus the statement whether two events are spacelike, timelike or lightlike to each other does not depend on the reference frame. If you manage to do it in one frame, it's good for all frames.

Looks simple enough in a diagram, less simple to actually do it: Entanglement is a fragile state and the speed of light, which is the maximum speed by which (hidden) information might travel is really, really fast. It helps if you let the entangled particles travel over long distances before you make the measurement, but then you have to be very careful in getting the timing right.

And that's exactly what a group of experimentalists around Anton Zeiliger did and published in November in their paper "Violation of local realism with freedom of choice" (arXiv version here). They closed for the first time both of the two above mentioned loopholes by choosing a setting that disabled communication between the measurement events as well as between the preparation of the photons and the choice of detector settings. The test was performed between two Canary Islands, La Palma and Tenerife.

[Image Source: Lonely Planet]
The polarization-entangled pairs of photons were produced in La Palma. One was guided to a transmitter telescope and sent over a distance of 144 km to Tenerife, where it was received by another telescope. The other photon made 6km of circles in a coiled optical fibre in La Palma. The detector settings in La Palma were chosen by a quantum random number generator 1.2 km away from the source, and in Tenerife by another similar but independent random number generator. The measurements violated Bell's inequality by more than 16 standard deviations.

What a beautiful experiment!

But if you're a believer in local realistic hidden variable theories, let me scratch your itch. You can't close the freedom-of-choice loophole in superdeterministic hidden variables theories with this method because there's no true randomness in that case. It doesn't matter where you locate your "random" generator, its outcome was determined arbitrarily long ago in the backward lightcone of the emission.

New Painting

2011-06-13T07:20:00.000-04:00

Okay, it's not really new. I actually started it last fall, but only finished this week. It's called "Herbstschatten" (Shadow of fall). Click to enlarge.

Extra Dimensions at the LHC: Status Update

2011-06-11T08:43:00.003-04:00

The Planck scale is the scale at which quantum gravitational effects are expected to become important. An extrapolation of the strength of gravity gives a value of 10¹⁶TeV, which is far out of reach for collider experiments. In the late 90s however, it was pointed out by Arkani-Hamed, Dimopoulous and Dvali, that this extrapolation does not hold if our spacetime has additional spacelike dimensions with certain properties. If that was the case, the true Planck scale could actually be at a TeV, an idea that is appealing because it does away with the question why the Planck scale is so large, respectively why gravity is so weak, to begin with. The answer would be, well, it isn't, it is only apparently so: Our naive extrapolation doesn't hold because space-time isn't four-dimensional. (For more details, read my earlier post.)

This (and other) extra dimensional models with a lowered Planck scale have been very popular at the beginning of the last decade and caused an extraordinarily high paper production which reflects not only the number of theoretical particle physicists, but also their desperation to put their skills to work. The most thoroughly analysed consequence of such models are the modification of standard model cross-sections through virtual graviton exchange and the production of black holes at the LHC. The latter possibility in particular received a lot of attention in the media due to some folks who accused physicists of planning the end of the world just to increase their citation count. (For more details, read these earlier posts.)

In any case, the LHC is running now, data is coming in and models are being sorted out, so what's the status?

In arXiv:1101.4919, Franceschini et al have summarized constraints from the LHC's CMS and ATLAS experiments on virtual graviton production. For the calculation of the contributions from virtual gravitons one needs to introduce a cut-off Λ of dimension energy that, next to the lowered Planck scale, becomes another parameter of the result. The constraints are then shown as contour plots in a two parameter space, the one parameter being the 'true' fundamental Planck scale, here denoted M_D, and the other one being mentioned cut-off, or its ratio to M_D respectively. One would expect the cut-off to be in the range of the lowered Planck-scale, though it might be off by a factor 2π or so, so the ratio should be of the order one. The figure below (Fig. 6 from arXiv:1101.4919) shows the bounds for the case of 4 additional spacelike dimensions:

The continuous line is the constraint from CMS data (after 36/pb integrated luminosity. Don't know what that means? Read this), and the dashed line is the constraint from ATLAS. The shaded area shows the excluded area. As you can see, a big part of the parameter space for values in the popular TeV range is meanwhile excluded.

Now what about the black holes? A black hole with a mass a few times the lowered Planck mass would already be well described by Hawking's calculation for particle emission, usually called Hawking-radiation. It would have a temperature (or average energy of primary emitted particles) of some hundred GeV. Just statistically, a big fraction of the emitted particles carry color charges and are not directly detected, but they form color strings that subsequently decay into a shower of hadrons, ie color neutral particles (pions, protons, etc). This process is called hadronization, and the event is called a jet. Depending on how many jets you get, it's a di-jet, tri-jet or multi-jet. The black hole's Hawking radiation would typically make a lot of particles and thus contribute to the multi-jets. One expects some multi-jets already from usual standard-model processes ("the background"), but the production of black holes should significantly increase the number. The figure below (from this paper by the CMS collaboration) shows an actual multi-jet event at the LHC:

In the paper arXiv:1012.3375 [hep-ex], the CMS collaboration summarized constraints on the lower mass of black holes in models with extra dimensions. For this, they analyzed the amount of multi-jet events in their data. The figure below (Fig 2 from arXiv:1012.3375) contrasts the predictions from the Standard Model with those of models with black hole production, for events with multiplicity N larger than 3 (that includes jets, but also photons, electrons and muons that don't hadronize).

On the vertical axis is the number of multi-jet events per bin of 100 GeV, on the horizontal axis the total transverse energy of the event (if you don't know what that means think of it as just the total energy). The solid blue line is the Standard Model prediction, the shaded area depicts the uncertainty. The various dotted and dashed lines are the predictions for the number of such events for different values of the minimal black hole mass, usually assumed to be in the range of the lowered Planck scale. These lines are created by use of event generators, ie numerical simulations. From this and similar data, the CMS collaboration is able to conclude that they haven't seen any black holes for minimum masses up to 4.5 TeV. CMS has an update on these constraints here, where they've pushed the limits up to 5 TeV, if not with amazingly high confidence level.

Some comments are in order though for the latter analysis. It argues with the production of multi-jets by black holes. This is a reliable prediction only for black holes produced with masses at least a few times above the lowered Planck scale. The reason is that a black hole of Planck mass is a quantum gravitational object and it is not correctly described by Hawking's semi-classical calculation. How to correctly describe it, nobody really knows. It is for the sake of numerics typically assumed that a black hole of Planck mass makes a final decay into a few particles. But that's got nothing to do with theory, it is literally just a subroutine in a code that randomly chooses some particles and their momenta such that all conservation laws are fulfilled. (The codes are shareware, look it up if you don't believe it.)

That procedure wouldn't be a problem if that was just some pragmatic measure to deal with the situation that has no impact on the prediction. Unfortunately it is the case that almost all black holes that would be produced at the LHC would be produced in the quantum gravitational regime. The reason is simply that the LHC is a hadron collider, and all the energy from the protons is redistributed on its constituents (called partons). As a result of this, the vast majority of the black holes produced have masses as low as possible, ie close by the new Planck scale.

What that means is that it is actually far from clear what the CMS constraints on excess of multi-jets mean for the production of black holes. A similar argument was recently made by Seong Chan Park in Critical comment on the recent microscopic black hole search at the LHC, arXiv:1104.5129.

Summary: It clearly doesn't look good for models with a lowered Planck scale. While it is in many cases not possible to falsify a model, but just to implausify it, large extra dimensions are becoming less plausible by the day. Nevertheless, one should exert scientific caution and not jump to conclusions. The relevance of CMS constraints on multi-jets depends partly on assumptions about the black holes' final decay that are not theoretically justified.

Question for the experts: Why do the curves in Fig 2 of the CMS paper seem to have a bump around the mininum black hole mass even though N > N^min?

Stronger than the universe

2011-06-05T10:18:00.000-04:00

Two weeks ago, we had hail here in Stockholm. At that time I was homewards bound on the highway, and that's where I would be staying for half an hour while rescue crew scratched a motorbike off the middle lane. On the radio run "Heartbreaker" by Dionne Warwick. It's one of these songs I've heard a million times but never listened to, girl in love, guy who doesn't call, same old story. "Why do you have to be a heartbreaker, When I was bein' what you want me to be?" I probably wouldn't call her either. There's Swedish "nyheter" on the other frequencies, but I already knew the weather was sucking greatly, the highway was clogged, and the rest I wouldn't understand anyway, that being the state of my Swedish. Hail drumming on the car roof, Dionne sang "My love is stronger than the universe," and the physicist in me couldn't avoid asking WTF is that supposed to mean? (It's not a four letter word. No, it isn't.)

Okay, so the universe is supposed to have a strength. It springs to mind the gravitational force exerted by all the mass in the universe. Since you can't place yourself outside the universe (probably where Dionne's guy sits) the question is what's the force acting on you while inside, caused by the expansion of the universe? Well, we know that bound systems up to galactic scales don't take part in the expansion, but let's forget that for a moment and pretend the universe would try to rip lovers apart on planetary surfaces. If Dionne's non-caller was as far away from her as he could possibly get on Earth, ie 10,000 km or so, the force comes to 10^-26N. Not very impressive. The laws of attraction might get you into trouble, but actually gravity is even weaker than the weak force.

No, we have to think about this differently. We should be asking what's the strength of the structure of the universe? So, as everybody knows, the universe is made of strings, and a string has a tension which is something like the square of the Planckmass, take or give some orders of magnitude. Putting all dimensionful units back in, that comes out to be about 10⁴⁴N. We could compare this to the force acting on Dionne on the surface of a neutron star, which is a measly 10¹⁴N. Yes, clearly, there's string theory on the radio. Though I suspect you'd get pretty much the same answer asking what it takes to break a link in a fundamental spin network.

Passing by the accident zone I contemplate the lack of friction and the forces at work. The radio plays Tori Amos, Little Earthquakes. It doesn't take much to rip us into pieces.