ESQG 2012 - Conference Summary

Conference Photo: Experimental Search for Quantum Gravity 2012.

The third installment of our conference "Experimental Search for Quantum Gravity" just completed. It was good to see both familiar faces and new ones, sharing a common interest and excitement about this research direction. This time around the event was much more relaxing for me because most of the organizational work was done, masterfully, by Astrid Eichhorn, and the administrative support at Perimeter Institute worked flawlessly. In contrast to 2007 and 2010, this time I also gave a talk myself, albeit a short one, about the paper we discussed here.

All the talks were recorded and can be found on PIRSA. (The conference-collection tag isn't working properly yet, I hope this will be fixed soon. You'll have to go to "advanced search" and search for the dates Oct 22-26 to find the talks.) So if you have a week of time to spare don't hesitate to blow your monthly download limit ;o) In the unlikely event that you don't have that time, let me just tell you what I found most interesting.

For me, the most interesting aspect of this meeting was the recurring question about the universality of effective field theory. Deformed special relativity, you see, has returned in the reincarnation "relative locality" as to boldly abandon locality altogether after the problem could no longer be ignored. It still doesn't have, however, a limit to an effective field theory. A cynic might say "how convenient," considering that 5th order operators in Lorentz-invariance violating extensions of the standard model are so tightly constrained you might as well call them ruled out.

If you're not quite as cynic however, you might take into account the possibility that the effective field theory limit indeed just does not work. That, it was pointed out repeatedly -- among others by David Mattingly, Stefano Liberati and Giovanni Amelino-Camelia -- would actually be more interesting than evidence for some higher order corrections. If we find data that cannot be accommodated within the effective field theory framework, such as for example evidence for delayed photons without evidence for 5th order Lorentz-invariance violating operators, that would give us quite something to think about.

I agree: Clearly one shouldn't stop looking just because one believes to know nothing can be found. I have to add however that the mere absence of an effective field theory limit doesn't convince me there is none. I want to know why such a limit can't be made before I believe in this explanation. For all I know it might be absent just because nobody has made an effort to derive it. After all there isn't much of an incentive to do so. As the German saying goes: Don't saw on the branch you sit on. That having been said, I understand that it would be exciting, but I'm too skeptic myself to share the excitement.

A related development is the tightening of constraints on an energy-dependence of the speed of light. Robert Nemiroff gave a talk about his and his collaborator's recent analysis of the photon propagation time from distant gamma ray bursts (GRB). We discussed this paper here. (After some back and forth it finally got published in PRL.) The bound isn't the strongest in terms of significance, but makes it to 3σ. The relevance of this paper is the proposal of a new method to analyse the GRB data, one that, given enough statistics, will allow for tighter constraints. And, most importantly, it delivers constraints on scenarios in which the speed of highly energetic photons might be slower as well as on the case in which it might be faster than the photons with lower energy. And for an example on how that is supposed to happen, see Laurent Freidel's talk.

A particularly neat talk was delivered by Tobias Fritz who summarized a simple proof that a periodic lattice cannot reproduce isotropy for large velocities, and that without making use of an embedding space. Though his argument works so far for classical particles only, I find it interesting because with some additional work it might become useful to quantify just how well a discretized approach reproduces isotropy or, ideally, Lorentz-invariance, in the long-distance limit.

Another recurring theme at the conference was dimensional reduction at short distances which has recently become quite popular. While there are meanwhile several indications (most notably from Causal Dynamical Triangulation and Asymptotically Safe Gravity) that at short distances space-time might have less than three spatial dimensions, the ties to phenomenology are so far weak. It will be interesting to see though how this develops in the coming years, as clearly the desire to make contact to experiment is present. Dejan Stojkovic spoke on the model of "Evolving Dimensions" that he and his collaborators have worked on and that we previously discussed here. There has however, for all I can tell, not been progress on the fundamental description of space-time necessary to realize these evolving dimensions.

Noteworthy is also that Stephon Alexander, Joao Magueijo and Lee Smolin have for a while now been poking around on the possibility that gravity might be chiral, ie that there is an asymmetry between left- and right-handed gravitons, which might make itself noticeable in the polarization of the cosmic microwave background. I find it difficult to tell how plausible this possibility is, though Stephon, Lee and Joao all delivered their arguments very well. The relevant papers I think are this and this.

I very much enjoyed James Overduin's talk on tests of the equivalence principle, as I agree that this is one of the cases in which pushing the frontiers of parameter space might harbor surprises. He has a very readable paper on the arxiv about this here. And Xavier Calmet is among the brave who haven't given up hope on seeing black holes at the LHC, arguing that the quantum properties of these objects might not be captured by thermal decay at all. I agree with him of course (I pointed this out already in this post 6 years ago), yet I can't say that this lets me expect the LHC will see anything of that sort. More details about Xavier's quantum black holes are in his talk or in this paper.

As I had mentioned previously, the format of the conference this year differed from the previous ones in that we had more discussion sessions. In practice, these discussion sessions turned into marathon sessions with many very brief talks. Part of the reason for this is that we would have preferred the meeting to last 5 days rather than 4 days, but that wasn't doable with the budget we had available. So, in the end, we had the talks of 5 days squeezed into 4 days. There's a merit to short and intense meetings, but I'll admit that I prefer less busy schedules.

The Craziness Factor

Hello from Canada and sorry for the silence, I'm here for the 2012 conference on Experimental Search for Quantum Gravity, and the schedule is packed. As with the previous two installations of the conference, we have experimentalists and theorists mixed together, which has the valuable benefit that you actually get to speak to people who know what the data means.

I learned yesterday from Markus Risse for example that the Auger Collaboration has a paper in the making to fit the penetration depth data which has earlier been claimed could not be explained neither with protons nor heavier ions or compositions thereof. Turns out the data can be fitted with a composition of protons and ions after all, though we'll have to wait for the paper to learn how well this works.

Today I just want to pick up an amusing remark by Holger Müller from Berkeley, who gave the first talk on Monday, about his experiments in atom interferometry. He jokingly introduced the "Craziness Factor" of a model, arguing that the a preferred frame, and the thereby induced violations of Lorentz-invariance, have a small craziness factor.

Naturally, this lead me to wonder what terms contribute to the craziness factor. Here's what came to my mind:

+ additional assumptions not present in the Standard Model and General Relativity. Bonus: if these assumptions are unnecessary
+ principles and assumptions of the Standard Model and General Relativity dropped. Bonus: without noticing
+ problems ignored. Bonus: problems given a name
+ approach has previously been tried. Bonus: and abandoned, multiple times
+ additional parameters. Bonus: parameters with unnatural values, much larger or smaller than one, without any motivation
+ model does not describe the real world (Euclidean, 2 dimensions, without fermions, etc). Bonus: Failure to mention this.
+ each time the model is being referred to as "speculative," "radical" or "provocative". Bonus: By the person who proposed it.
+ model has been amended to agree with new data. Bonus: multiple times.

And here is what decreases the craziness factor:

- problems addressed. Bonus: Not only the author worries about these problems.
- relations learned, insights gained. Bonus: If these are new relations or insights, rather than reproductions of findings from other approaches.
- Simplifications over standard approach. Bonus: If it's an operational, not a formal simplification.
- Data matched. Bonus: Additional predictions made.

In practice, perceived craziness has a subjective factor. The more you hear about a crazy idea, the less crazy it seems. Or maybe your audience just gets tired objecting.

Turbulence in a 2-dimensional Box: Pretty

Physicists like systems with fewer than the three spatial dimensions that we are used to. Not so much because that's easier, but because it often brings in qualitatively new features. For example, in two dimensions vortices in a fluid fulfill a conservation law that does not hold in three dimensions.

The vorticity of a fluid is a local quantity that measures, roughly, the spinning around each point of a fluid. In a two dimensional system, the only spinning that can happen is around the axis perpendicular to the two dimensions of the system. That is, if you have fluid in a plane, the vorticity is a vector that is always perpendicular to the plane, so the only thing that matters is the length and direction of this vector. In two dimensions now, the integral of the vorticity is a conserved quantity, called the enstrophy.

Pictorially this means if you create a vortex - a point that is itself at rest but around which the fluid spins - you can only do that in pairs that spin in opposite direction.

This neat paper:

Dynamics of Saturated Energy Condensation in Two-Dimensional Turbulence
Chi-kwan Chan, Dhrubaditya Mitra, Axel Brandenburg
Phys. Rev. E 85, 036315 (2012)
arXiv:1109.6937 [physics.flu-dyn]

studies what happens if you put a 2-dimensional fluid in a box with periodic boundary conditions, and disturb it by a force that is random in direction but at a distinct frequency. Due to dispersion the energy that enters the system at the frequency of the driving force cascades down to longer wavelengths. However, in a box of finite size there's a longest wavelength that will fit in. So the energy "condenses" into this longest possible wavelength. At the same time, the random force creates turbulence that leads to the formation of two oppositely rotating vortices.

Below is a plot of the vorticity of the fluid in the box. The two white/red and white/blue swirls are the vortices.

Fig 1 from arXiv:1109.6937.
Pseudocolor plot of vorticity of fluid in 2-dimensional box,
showing condensation into long wavelength modes.

My mom likes to say "symmetry is the art of the stupid", and she's right in that symmetry all by itself is usually too strict to be interesting. Add a little chaos to symmetry however and you get a good recipe for beauty.

Book Review: "Soft Matter" by Roberto Piazza

Soft Matter: The stuff that dreams are made of
By Roberto Piazza
Springer (April 11, 2011)

Some months ago I had a conversation about nematic films. Or was trying to have. Unfortunately I didn't have the faintest clue what this conversation was about. Neither, to my shame, did I understand much of the papers on the subject. Then I came across a review of Roberto Piazza's book on "Soft Matter" and I thought it sounds like just what I need to learn some new vocabulary.

Roberto Piazza is professor for Condensed Matter Physics at the Politecnico di Milano, and his book isn't your typical popular science book. It is instead a funny mixture of popular science book and what you might find in a textbook introduction, minus the technical details. In some regards this mixture works quite well. For example, Piazza is not afraid to introduce terminology and even uses an equation here and there. In other regards however, this mixture does not work well. The book does introduce far too much terminology in a quite breathless pace. It's a case in which less would have been more.

The book covers a lot of terrain: Colloids, aerosols, polymers, liquid crystals, glasses and gels, and in the last chapter amino acids, proteins, and the basic functions of cells. The concepts are first briefly introduced and then in later chapters there are examples and more details. In principle this is a good structure. Unfortunately, the author has a tendency to pack the pages with too much information, information that isn't always conductive to the flow of the text, and doesn't spend enough time on clarifying the information he wants to get across, or that I believe he might have wanted to get across.

The text is accompanied by several color figures, which are in most cases helpful, but there could have been more, especially to show molecular structures that are often explained in words. The book comes with a glossary that is very useful. It does however not come with references or suggestions for further reading, so if the reader wants to know more about a topic, they are left on their own.

In summary, the book is a useful introduction to soft matter, but it isn't exactly a captivating read. Especially in the last chapter, where Piazza goes on about proteins and their functions - while constantly reminding the reader that he's not a biologist - I had to resist the temptation of skipping some pages. Not because the topic is uninteresting, but because the presentation is unstructured and wasteful on words, and thus wasteful on the reader's time.

That having been said, lack of structure and too many words is just the type of criticism you'd expect from a German about an Italian, so take that with a grain of salt ;o) And, yes, now I know what nematic films are. I'd give this book three out of five stars.

PRL on "Testing Planck-Scale Gravity with Accelerators"

With astonishment I saw the other day that Phys. Rev. Lett. published a paper I had come across on the arxiv earlier this year:

Testing Planck-Scale Gravity with Accelerators
By Vahagn Gharibyan
Phys. Rev. Lett. 109, 141103 (2012)
arxiv:1207.7297

I had ignored this paper for a simple reason. The author proposes a test for effects that are already excluded, by many orders of magnitude, by other measurements. The "Planck-Scale Gravity" that he writes about is nothing but 5th order Lorentz-invariance violating operators. These are known to be extremely tightly constrained by astrophysical measurements. And the existing bounds are much stronger than the constraints that can be reached, in the best case, by the tests proposed in the paper. We already know there's nothing to be found there.

The author himself mentions the current astrophysical constraints, in the PRL version at least, not in the arxiv version - peer review isn't entirely useless. But he omits to draw the obvious conclusion: The test he proposes will not test anything new. He vaguely writes that

"The limits, however, are based on assumptions about the origin, spatial or temporal distribution of the initial photons, and their possible interactions during the travel. Another critical assumption is a uniformly distributed birefringence over cosmological distances... In contrast to the astrophysical methods, an accelerator Compton experiment is sensitive to the local properties of space at the laser-electron interaction point and along the scattered photon direction."

He leaves the reader to wonder then what model he wants to test. One in which the vacuum birefringence just so happens to be 15 orders of magnitude larger at the collision point than anywhere else in space where particles from astrophysical sources might have passed through? Sorry, but that's a poor way of claiming to test a "new" regime. At the very least, I would like to hear a reason why we should expect an effect so much larger. Space-time here on Earth as well as in interstellar space is, for what quantum gravitational effects are concerned, essentially flat. Why should the results be so dramatically different?

I usually finish with a sentence saying that it's always good to test a new parameter regime, no matter how implausible the effect. In this case, I can't even say that, because it's just not testing a new parameter regime. The only good thing about the paper is that it drives home the point that we can test Planck scale effects. In fact, we have already done so, and Lorentz-invariance violation is the oldest example of this.

Here's one of the publication criteria that PRL lists on the journal website:

"Importance.
Important results are those that substantially advance a field, open a significant new area of research or solve–or take a crucial step toward solving – a critical outstanding problem, and thus facilitate notable progress in an existing field."

[x] Fails by a large amount.

Thanks to Elangel for the pointer.

Towards an understanding of the Sun's Butterfly Diagram

The layered structure of the sun.
Click to enlarge. Image credits: NASA

It's hot, round, and you're not supposed to stare at it: The Sun has attracted curiosity since we crawled out of the primordial pond. And even though we now have a pretty good idea of how the Sun does its job, some puzzles stubbornly remain. One of them is where sunspots form and how their location changes with the solar cycle. A recent computer simulation has now managed to reproduce a pattern that brings us a big step closer to understanding this.

The Sun spins about a fixed axis, but since it's not solid its rotation frequency is not uniform: At the visible surface, the equator rotates in about 27 days whereas close by the poles it takes 35 days. The plasma that forms the Sun is held together by its own gravitational pull with a density that is highest in the center. In this high density core, the sun creates energy by nuclear fusion. Around that core, there's a layer, the radiative zone, where the density is already too small for fusion, and the heat created in the core is just passed on outwards by radiative transfer. Further outside, when the density is even lower, the plasma then passes on the heat by convection, basically cycles of hot plasma moving upwards and cooler plasma moving downwards. Even further outside, there's the photosphere and the corona.

The physics of the convection zone is difficult because the motion of the plasma is turbulent, so it's hard to understand analytically and numerical simulations require enormous computing power. Some generic features are well understood. For example the granularity of the sun's surface comes about by a mechanism similar to Rayleigh–Bénard convection: In the middle of the convection cell there's the hot plasma rising and towards the outside of the cell there's the cooler plasma moving down again.


It also has been known since more than a century that sunspots are not only colder than the normal surface of the sun, but are also regions with strong magnetic fields. They arise in pairs with opposite magnetic polarity. Sunspot activity follows a cycle of roughly 11 years, after which polarity switches. So the magnetic cycle is actually 22 years, on the average.

A big puzzle that has remained is why sunspots are created predominatly in low latitudes (below 30°N/above 30 S) and, over the course of the solar cycle, their production region moves towards the equator. When one plots the latitude of the sunpots over time, this creates what is known as the "Butterfly diagram", shown below

You can find a monthly update of the butterfly diagram on the NASA website. The diagram for the magnetic field strength follows the same pattern, except for the mentioned switch in polarity, see for example page 54 of this presentation. On the slide, note that in the higher latitudes the magnetic fields move towards the poles rather than towards the equator.

Numerical simulation of the convection zone have been made beginning already in the early 80s, but so far something always left the scientists wanting. Either the sunspots didn't move how they should or the rotation wasn't faster towards the equator, or the necessary strong and large-scale magnetic fields were not present, or something else just didn't come out right.

At Nordita in Stockholm, there's a very active research group around Axel Brandenburg, which has developed a computer code to simulate the physics of the convection zone. It's called the "pencil code" and is now hosted by Google code, for more information see here. Basically, it's an integration of the (non-linear) hydrodynamics equations that govern the plama with magnetic fields added. In the video below you see the result of a very recent simulation done with his collaborators in Helsinki:


The colors show the strength of the magnetic field (toroidal component), with white and blue being the strongest fields, blue for one polarity and white for the other. Two things you should be able to see in the video: First, the rotation is faster at the equator than at the poles, second, the spots of strong magnetic fields in low latitudes migrate towards the equator. One can't see it very well in the video, but in the higher latitudes the magnetic fields do move towards the poles, as they should. In the time-units shown in the top-left corner, about 600 time steps correspond to one solar cycle. A computation like this, Axel tells me, takes several weeks, run on 512 to 2048 cores.

Details on how the movie was made can be found in this paper

Cyclic magnetic activity due to turbulent convection in spherical wedge geometry
Petri J. Käpylä, Maarit J. Mantere, Axel Brandenburg
arxiv: 1205.4719

The model has six parameters that quantify the behavior of the plasma. For some of these parameters, values that would be realistic in the sun are too large to be possible to simulate. So instead, one uses different values and hopes to still capture the essential behavior. The equations and boundary conditions can be found in the paper, see eqs (1)-(4) and (6)-(11).

The calculation doesn't actually simulate the whole convection zone, but only a wedge of it with periodic boundary conditions. In the video this wedge is just repeated. The poles are missing because there the coordinate system becomes pathological. In the part that they simulate, they use 128 x 256 x 128 points. A big assumption that goes on here is that the small scales, scales too small to be captured at this resolution, don't matter for the essential dynamics.

If you found the video was too messy, you can see the trend of the magnetic fields nicely in the figure below, which shows the average strength of the magnetic fields by latitude as a function of time.

Fig 3 from arxiv:1205.4719.

Not all is sunny of course. For example, if you gauge the timescale with the turnover time in the convection zone which can be inferred from other observatons, the length of the magnetic solar cycle is about 33 years instead of 22. And while the reason for the faster rotation towards the equator can be understood from the anisotropy of the turbulence (with longitudinal velocity fluctuations dominating over latitudinal ones), the butterfly trend is not (yet) analytically well understood. Be that as it may, I for certain am impressed how much we have been able to learn about the solar cycle despite the complicated turbulent behavior in the convection zone.

The original movie (in somewhat better resolution) and additional material can be found on Petri's website. Kudos to Axel and Amara for keeping me up to date on solar physics.

ESQG 2012 Update

Our conference on "Experimental Search for Quantum Gravity" now has the schedule online. As you can see, this year's format is somewhat different from the previous installations. Based on Astrid's suggestions, we have only a few long talks and otherwise many discussions with short (10-15 min) contributions. I'm curious to see how this goes.

Personally, I find discussion sessions to be of limited use. Participants usually to like them for the social touch, but in my experience they tend to be dominated by always the same people who say always the same things. And I guess I just prefer prepared talks for they are usually better structured and convey information better. Which is why, if I add discussion sessions to a conference I'm organizing, I do my best to encourage participants and esp the discussion leaders to prepare some questions and arguments in advance. Maybe mixing discussions with the short contributions is a good way to avoid these pitfalls. Either way, I think it is worthwhile to try a different format.

Clearly foggy

"I am ... rather skeptical about "popular" science in general, in particular when I bump into those books pretending to address in "popular" language formidable mathematical conjectures, or esoteric concepts such as black holes, superstrings, and dark matter. Quite often, skimming through their first chapters, the non-professional reader gets the impression that everything is as clear as day, to realize well before the end that it is in fact quite a foggy day."

~Roberto Piazza, Politecnico di Milano

Book review: “The Universe Within” by Neil Turok

The Universe Within: From Quantum to Cosmos (CBC Massey Lecture)
By Neil Turok
House of Anansi Press (October 2, 2012)

Neil Turok is director of Perimeter Institute and founder of the African Institute for Mathematical Sciences. His research is mostly in theoretical cosmology, and he has written a pile of interesting papers with other well-known physicists. Some weeks ago, I found a free copy of Turok’s new book “The Universe Within” in my mail together with a blurb praising it as “the most anticipated nonfiction book of the season” and a “personal, visionary, and fascinating work.” From the back cover, I expected the book to be about the relevance of basic research, physics specifically, and the advances blue sky research has brought to our societies.

You know me for arguing that we need knowledge for the sake of knowledge and it’s a mistake to justify all research by practical applications. To advance my own arguments, I thought I should read Turok’s book.

The book is to accompany the 2012 Massey Lectures that will be broadcast in November 2012.

Turok starts with the old Greeks, then writes about Leonardo da Vinci and Galileo, and lays out the development of the scientific method. He spends some time on Newton’s laws, electrodynamics, special relativity and general relativity. Since Turok’s own work is mostly in cosmology, it is not surprising that quite some space is dedicated to this. The standard model of particle physics appears here and there, and the recent discovery of the Higgs is mentioned. He goes to some length to explain path integrals with the action of the standard model coupled to general relativity, the one equation appearing in the book (without the measure), a courage that I think should be applauded. Turok makes clear he is not a fan of the multiverse. In the final chapter, he goes on to a general praise of basic research.

His explanations about physics are interwoven with his own experiences, growing up in South Africa, the challenges he faced, and the research he has done. This is all content well intentioned and sounds like a good agenda. Unfortunately, the realization of this agenda is poor.

The introductions into the basic physical concepts will be difficult to understand if one doesn’t know already what he is talking about. For example, he talks about inflation before he speaks about general relativity. He talks about the Planck length and the Hubble length without explaining the relevance. To make contact to Euclidean space, Turok wants to explain Minkowski-spacetime by using the “ict” trick that nobody uses anymore and will leave many readers confused. They will be left equally confused about the question how the wavefunction and the path integral is related to actually observable quantities. The reader should also better previously have heard about the multiverse, because that’s only mentioned in the passing to get across the author’s opinion.

The book has several photos and illustrations in color, including the “formula that summarizes all the known laws of physics”, but these are not referenced in the text. You better look at them in advance to know where they belong, or you have to guess while reading that there might be an image belonging to what you read.

The book is also repetitive in several places, where concepts that were introduced earlier, for example extra dimensions, reappear. “As I explained earlier” or similar phrases have been added in some instances, but the overall impression I got is that this book was written in pieces that were later put together sloppily. The picture presented is incoherent at best and superficial at worst. Rather than making a solid case for the relevance of basic research, Turok has focused on introducing the basics of modern physics with some historical background, and then talks mostly about cosmology. Examples of unpredictable payoff appear, in the form of electrodynamics, the transistor, and potentially quantum computing. But the cases are not well made in the sense that he doesn’t drive home the point that none of that research was aimed at producing the next better computer. And they’re not exactly very inspired choices either.

Turok’s argumentation is sometimes just weird or not well thought through. For example, to explain the merits of quantum computers, he writes:

“Quantum computers may also transform our capacities to process data in parallel, and this could enable systems with great social benefit. One proposal now being considered is to install highly sensitive biochemical quantum detectors in every home. In this way, the detailed medical condition of every one of us could be continuously monitored. The data would be transmitted to banks of computers which would process it and screen for signs of any risk.”

He does not add as much as one word on the question if this was desirable. This is pretty bad imo, because it suggests the image of a scientist who doesn’t care about ethical implications. (I mean: the question whether you want information about potentially uncurable diseases is already a topic of discussion today.) Another merit of quantum computers is apparently:

“With a quantum library, one might… be able to search for all possible interesting passages of text without anyone having had to compose them.”

Clearly what mankind needs. And here’s what, according to Turok, is the purpose of writing:

“Writing is a means of extracting ourselves from the world of our experience to focus, form, and communicate our ideas.”

One might maybe say so about scientific writing, at least in its ideal form. But the scientist in the writer seems to have taken over here. Another sentence that strikes me as odd is “I have been fascinated by the problem of how to enable young people to enter science, especially in the developing world.” I’m not sure “fascinating problem” is a particularly emphatic choice of words.

Other odd statements: “M-theory is the most mathematical theory in all of physics, and I won’t even try to describe it here.” He does anyway, but I’m left wondering what “most mathematical” is supposed to mean. Is it just an euphemism for “least practical relevance”? Another fluff sentence is “We are analog beings living in a digital world, facing a quantum future.” Turok also adds a sentence according to which one day maybe we’ll be able to harness dark energy. I can just see his inbox being flooded with proposals on exactly how to do that.

The last chapter of the book starts out quite promising, as it attempts to take on the question of what is the merit of knowledge for the sake of knowledge. Then I got distracted by a five pages long elaboration on “Frankenstein”. (He somehow places the origin of this novel in Italy, and forgets to mention that the Castle of Frankenstein is located in Germany, I pass by every time I visit my parents.) Then Turok seems to recall that the book is to appear with a Canadian publisher and suddenly adds a paragraph to praise the country:

“[T]oday’s Canada… compared to the modern Rome to its south, feels like a haven of civilization. Canada has a great many advantages: strong public education and health care systems; a peaceful, tolerant, and diverse society; a stable economy, and phenomenal natural resources. It is internationally renowned as a friendly and peaceful nation, and widely appreciated for its collaborative spirit and for the modest, practical character of its people.”

It’s not that I disagree. But it makes me wonder what audience he is writing for. The member of parliament who might have to sign in the right place so cash keeps flowing? But what bugs me most about “The Universe Within” is that Turok expresses his concerns about the current use of information technology, and then has nothing to add in terms of evidence that this really is a problem or any idea what can or should be done about it:

“Our society has reached a critical moment. Our capacity to access information has grown to the point where we are in danger of overwhelming our capacity to process it. The exponential growth in the power of or computers and networks, while opening vast opportunities, is outpacing our human abilities and altering our forms of communication in ways that alienate us from each other.”

Where is the evidence?

“We are being deluged with information through electric signals and radio waves, reduced to a digital, super-literal form that can be redistributed at almost no cost. The technology makes no distinction between value and junk.”

This isn’t a problem of technology, this is a problem of economy.

“The abundance and availability of free digital information is dazzling and distracting. It removes us from our own nature as complex, unpredictable, passionate people.”

According to Turok, the solution to this problem has something to do with the “ultraviolet-catastrophe”, I couldn’t quite follow the details. From a scientist, I would have expected a more insightful discussion. Not too long ago, Perimeter Institute had a really bright faculty member by name Michael Nielsen, who thought about the challenges and opportunities of information technology for science and what can be done about it. Turok does not only not explain what evidence it is that has him worried, he also doesn’t comment on any recent developments or suggestions. Maybe he should have spent some time talking to Nielsen.

So in summary, what can I say? This book strikes me as well intentioned, but sloppy and hastily written. If you are looking for a good introduction to the basic concepts of modern physics and cosmology, better read Sean Carroll’s book. If you are looking for a discussion of the challenges science and our societies are facing by rapid information exchange, better read Jaron Lanier’s book, or even Maggie Jackson’s book. If you want to know what the future of science might look like and what steps we should take to advance knowledge discovery, read Michael Nielsen’s book. And if you want to know how our societies economically benefit from basic research, read Mark Henderson’s book because he lists facts and numbers, even if they’re very UK-centric.

Neil Turok’s book might be interesting for you if you want to know something about Neil Turok. At least I found it interesting to learn something about his background, but it’s only a page here or there. I would give this book two out of five stars. That’s because I think he should be thanked for making the effort and taking the time. I hope though next time he gets a better editor.

10 effects you should have heard of

1. The Photoelectric Effect
   
   Light falling on a metal plate can lead to emission of electrons, called the "photoelectric effect". Experiments show for this to happen the frequency of the light needs to be above a threshold depending on the material. This was explained in 1905 by Albert Einstein who suggested that the light should be thought of as quanta whose energy is proportional to the frequency of the light, the constant of proportionality being Planck's constant. Einstein received the Nobel Prize in 1921 "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect."
   
   Recommended reading: Our post on the Photoelectric Effect and the Nobel Prize speech from 1921.



2. The Casimir Effect
   
   This effect was first predicted by Hendrik Casimir who explained that, as a consequence of quantum field theory, boundary conditions that may for example be set by conducting (uncharged!) plates, can result in measurable forces. This Casimir force is very weak and can be measured only at very small distances.
   
   Recommended reading: Our post on the Casimir Effect and R. Jaffe's The Casimir Effect and the Quantum Vacuum.



3. The Doppler Effect
   
   The Doppler effect, named after Christian Doppler, is the change in frequency of a wave when the source moves relative to the observer. The most common example is that of an approaching ambulance, where the pitch of the signal is higher when it moves towards you than when it moves away from you. This does not only happen for sound waves, but also for light and leads to red- or blueshifts respectively.
   
   Recommended reading: The Physics Classroom Tutorial.



4. The Hall Effect
   
   Electrons in a conducting plate that is brought into a magnetic field are subject to the Lorentz force. If the plate is oriented perpendicular to the magnetic field, a voltage can be measured between opposing ends of the plate which can be used to determine the strength of the magnetic field. First proposed by Edwin Hall, this voltage is called the Hall voltage, and the effect is called the Hall effect. If the plate is very thin, the temperature low, and the magnetic field very strong, a quantization of the conductivity can be measured, which is also known as the quantum Hall effect.
   
   Recommended reading: Our post on The Quantum Hall Effect.



5. The Meissner-Ochsenfeld Effect
   
   The Meissner-Ochsenfeld effect, discovered by Walther Meissner and his postdoc Robert Ochsenfeld in 1933, is the expulsion of a magnetic field from a superconductor. Most spectacularly, this can be used to let magnets levitate above superconductors since their field lines can not enter the superconductor. I assure you this has absolutely nothing to do with Yogic flying.
   
   Recommended watching: Amazing Physics on YouTube.



6. Aharonov–Bohm Effect
   
   A charged particle in an electromagnetic field acquires a phase shift from the potential of the background field. This phase shift is observable in interference patterns and has been experimentally confirmed. The relevant point is that it's the potential that causes the phase, not the field. Before the Aharonov–Bohm effect one could question the physical reality of the potential.



7. The Hawking Effect
   
   Based on a semi-classical treatment of quantum fields in a black hole geometry, Stephen Hawking showed in 1975 that black holes emit thermal radiation with a temperature inverse to the black hole's mass. This emission process of the black hole is called the Hawking Effect. This result has lead to a great progress in understanding the physics of black holes, and is still subject of research, see recent post at Cosmic Variance.
   
   Recommended reading: Black Hole Thermodynamics by David Harrison and P.K. Townsend's lecture notes on Black Holes.



8. The Zeeman Effect/Stark Effect
   
   In the presence of a magnetic field, energy levels of electrons in atomic orbits that are usually degenerated (i.e. equal) can obtain different values, depending on their quantum number. As a consequence, spectral lines corresponding to transitions between these energy levels can split into several lines in the presence of a static magnetic field. This effect is named after the Dutch physicist Pieter Zeeman, who was awarded the 1902 physics Nobel prize for its discovery. The Zeeman effect is an important tool to measure magnetic fields in astronomy. For some historical reasons, the plain vanilla pattern of line splitting is called the Anomalous Zeeman effect.
   
   A related effect, the splitting of spectral lines in strong electric fields, is called the Stark Effect, after Johannes Stark.
   
   Recommended reading: HyperPhysics on the Zeeman effect and the Sodium doublet.



9. The Mikheyev-Smirnov-Wolfenstein Effect
   
   The Mikheyev-Smirnov-Wolfenstein effect, commonly called MSW effect, is an in-medium modification of neutrino oscillation that can for example take place in the sun or the earth. It it a resonance effect that depends on the density of the medium and can significantly effect the conversion of one flavor into another. The effect is named after Stanislav Mikheyev, Alexei Smirnov and Lincoln Wolfenstein.
   
   Recommended reading: The MSW effect and Solar Neutrinos.



10. The Sunyaev-Zel'dovich Effect
    
    The Sunyaev-Zel'dovich effect, first described by Rashid Sunyaev and Yakov Zel'dovich, is the result of high energy electrons distorting the cosmic microwave background radiation through inverse Compton scattering, in which some of the energy of the electrons is transferred to the low energy CMB photons. Observed distortions of the cosmic microwave background spectrum are used to detect the density perturbations of the universe. Dense clusters of galaxies have been observed with use of this effect.
    
    Recommended reading: Max Planck Society press release Crafoord Prize 2008 awarded to Rashid Sunyaev and The Sunyaev-Zel'dovich effect by Mark Birkinshaw.



11. Bonus: The Pauli Effect
    
    Named after the Austrian theoretical physicist Wolfgang Pauli, the Pauli Effect is well known to every student of physics. It describes a spontaneous failure of technical equipment in the presence of theoretical physicists, who should therefore never be allowed on the vacuum pumps, lasers or oscilloscopes.
    
    Recommended reading: Our post Happy Birthday Wolfgang Pauli.

[This is a slightly updated and recycled post that originally appeared in March 2008.]

Interna

Seems I've been too busy to even give you the family update last month, so here's to catch up.

Lara and Gloria can meanwhile climb up and down chairs quite well, which makes life easier for me, except that they often attempt to climb upwards from there. They can now reach the light switches, and last week they learned to open doors so it's difficult now to keep them in a room. Their favorite pastime is presently hitting me with empty plastic bottles, which seems to be infinitely entertaining. They also have developed the unfortunate habit of throwing their toys in direction of my laptop screen.

The girls have increased their vocabulary with various nouns and can identify images in their picture books. They still haven't learned a single verb, though Stefan insists "cookie" means "look."

Gloria is inseparable from her plush moose, Bo. She takes him everywhere and sleeps with him. Since I'd really like to wash it on occasion, I've now bought a second one and we're doing our best to avoid she sees both at once. (We also have to maneuver carefully around the Arlanda Duty Free shop, where there sits a whole pile of them.) Gloria has developed a bad case of motion sickness in which she'll be sick after ten minutes on the road. We now got some medication from our pediatrician that seems to help, so our mobility radius has expanded again. Lara meanwhile is squinting and we'll have to do something about this.

Right now, they're sitting behind me with their Swedish-English picture book. I am often amazed how well they understand what we say, especially because Stefan and I don't speak the same accent and we both mumble one way or the other. I guess it's because I judge their progress by my lack of progress in learning Swedish. Last week I took a taxi in Stockholm, and this was the first time I had a taxi driver who was actually Swedish. Ironically I noticed that because he spoke British English that was at least to my ears basically accent free. He didn't even try to address me in Swedish. When I asked him about it he said, well, there's so few people on the planet for whom Swedish is useful that they don't expect others to speak it. The Swedes are just so damned nice to immigrants.

We were lucky to get two daycare places starting in January. It's a half-day place, but this will be quite a change for all of us.

The organization of the PI conference on Experimental Search for Quantum Gravity is going very well, thanks to Astrid Eichhorn who has done a great job. We now have a schedule that should appear on the website within the next days. We'll probably have most of the talks recorded, so it's something for all of you. The organization of the November program on Perspectives of Fundamental Cosmology is running a little behind, but it seems everything is slowly falling into place there too.

Besides this, I have been trying to convince my colleagues at Nordita to engage more in public outreach, as I think we're behind in making use of the communication channels the online world has to offer. I'm happy to report that we did get some funding approved by the board last week. Part of this will go into a few videos, another part will go to a workshop for science writers - an idea that goes back to a discussion I had with George Musser earlier this year. I'll let you know how this goes, and I'm open to suggestions for what else we could do. I think I don't have to explain you my motivation for doing this - I'd be preaching to the choir. So let me instead say that it can be difficult to get scientists to make a time commitment to anything that's not research, so the biggest constraint on the matter is personnel.

Quantum Gravity in Tritium Decay?

If you've been working in a field for some while there comes the moment when you feel like you've heard it all before. So I was surprised when the other day I came across an idea to test the phenomenology of quantum gravity that I had not heard about before - and the paper is three years old already:

Hypersharp Resonant Capture of Neutrinos as a Laboratory Probe of the Planck Length
R. S. Raghavan
Phys. Rev. Lett. 102:091804 (2009).
arxiv:0903.0787

Time-Energy Uncertainty in Neutrino Resonance: Quest for the Limit of Validity of Quantum Mechanics
R. S. Raghavan
arXiv:0907.0878

In a nutshell, the idea is as follows. We previously discussed that the Planck length is expected to play the role of a minimal length. It takes high energies to resolve short distances, and once you reach the Planck scale, this creates large fluctuations of space-time which prevents a better resolution. This idea can be captured in what has become known as the "generalized uncertainty principle", a research direction that has recently become quite popular.

This all goes back, essentially, to Mead's idea which we discussed in the earlier post. Mead however had more to say about this: He wrote another paper, "Observable Consequences of Fundamental-Length Hypotheses" Phys. Rev. 143, 990–1005 (1966), in which he argued that such a Planck scale limit should, in principle, lead to a lower limit on the width of atomic spectral lines; it should create a fundamental blurring that can't be removed by better measurement. Raghavan in his paper now wants to test this limit. Rather than using photon emission though, he suggests to use tritium decay.

Tritium makes a β-decay to Helium and in this emits an electron and anti-electron neutrino. Normally the electron flies off and the energy spread of the outgoing neutrino is quite large, but Raghavan lays out some techniques by which this spread can be dramatically reduced. The starting point is that some fraction of the tritium the electrons doesn't fly off but is instead captured in a bound orbit around the Helium. Now if the tritium, normally a gas at room temperature, can be embedded in a solid, then the recoil energy can be very small; this is essentially the Mössbauer effect, just with neutrino emission, and this gives a hypersharp neutrino line. The first some slides of this pdf are a useful summary of the recoilless bound-state β-decay.

Raghavan estimates ΔE/E to be as small as 10^-29. The average lifetime of tritium is about 12 years. There are a lot of techniques involved in this estimate that I don't know much about, so I can't tell how feasible the experiment he proposes is. It sounds plausible to me though, give or take some orders of magnitude.

He then speaks in his paper about the energy-time uncertainty relation and its Planck scale modifications. Now it is true that if you have a generalized uncertainty for spatial spread Δx and momentum spread Δp, you expect there to be also one for ΔEΔt. Yet, normally the deviations from the usual Heisenberg uncertainty scale with the energy over the Planck mass. And for the emitted neutrinos with an average energy of some keV this a ridiculously small correction term.

So here then comes the input from Mead's paper. Mead argues that the ratio ΔE/E is, in the most conservative model, actually proportional to the Planck length over the size of the system l_Pl/R, which he takes to be the size of the nuclei. This is quite puzzling, because if you take the Planck length bound on a wavelength and make an error propagation to the frequency, what you'd get is actually ΔE/E larger or equal to l_PlE which is about 4 orders of magnitude smaller in the case at hand. The reason for this mismatch is that Mead in his argument speaks about the displacement of elementary particles in a potential. Now if the wavelength of the particles is larger than the typical extension of the potential this doesn't make much sense.

That having been said, one can of course consider the proposed parameterization as a model that is to be constrained, but this leaves the question how plausible it is that there be such a modification from quantum gravity. At first sight, I'd have said a low-energetic system like an atom is a hopeless place to look for quantum gravity, but then the precision of the suggested measurement would be amazing indeed. If it works that is. I'll have to do some more thinking to see if I can make sense of the argument for the scaling of the effect. Either way however, an experiment like the one Raghavan discusses, watching the decay of tritium under suitable conditions, would test a new range of parameters, which is always a good thing to do.

Research Areas and Social Identity

Last year, when I was giving the colloquium in Jyväskylä, my host introduced me as "leading the quantum gravity group at Nordita." I didn't object since it's correct to the extent that I'm leading myself, more or less successfully. However, the clustering of physicists into groups with multiple persons is a quite interesting emergent feature of scientific communities. Quantum gravity for example is usually taken to mean quantum gravity excluding string theory, a nomenclature I complained about earlier.

In the literature on the sociology of science it is broadly acknowledged that scientists, as other professionals, naturally segregate into groups to accomplish what's called a "cognitive division of labor": an assignment of specialized tasks which allows the individual to perform at a much higher level than they could achieve if they had to know all about everything. Such a division of labor is often noticeable already on the family level (I do the tax return, you deal with the health insurance). Specialization into niches for the best use of resources can also be seen in ecosystems. It's a natural trend because it's a local optimization process: Everybody dig a little deeper where you are and get a little more.

The problem is of course that a naturally occurring trend might lead to a local optimum that's not a global optimum. In the case of scientific communities the problem is that knowledge which lies at the intersection of different areas of specialization is not or not widely known, but there is a potential barrier preventing the community from making better use of this knowledge. This is unfortunate, because information relevant to progress goes unused. (See for example P. Wilson, “Unused relevant information in research and development,”. Journal of the American Society for Information Science, 45(2), 192203 (1995).)

So this is the rationale why it's necessary to encourage scientists to look out of their box, at least on occasion. And that takes some effort because they're in a local optimum and thus generally unwilling to change anything.

This brings me back then to the grouping of researchers. It does not seem to me very helpful to reach a better global optimum. In fact, it seems to me it instead that it makes the situation worse.

Social identity theory deals with the question what effect it has to assign people to groups; a good review is for example Stryker and Burke “The Past, Present, and Future of an Identity Theory”, Social Psychology Quarterly, Vol. 63, No. 4 (Dec., 2000), pp. 284-297. This review summarizes studies that have shown that the mere act of categorizing people as group members changes their behavior: When assigned a group, one that might not even be meaningful, they favor people in the group over people outside the group and are trying to fit in. The explanation that the researchers put forward is that "after being categorized of a group membership, individuals seek to achieve positive self-esteem by positively differentiating their ingroup from a comparison outgroup."

This leads me to think, it cannot be helpful to knowledge discovery to assign researchers at an institute to a handful of groups. It is also very punched-paper in the age of social tagging.

A suggestion that I had thus put forward some years ago at PI was to get rid of the research groups altogether and instead allow researchers to chose keywords that serve as tags. These tags would contain the existing research areas, but also cover other interests, that might be black holes, networks, holography, the arrow of time, dark matter,  phase transitions, and so on. Then, one could replace the groups on the website with a tag cloud. If you click on a keyword, you'd get a list of all people who've chosen this tag.

Imagine how useful this would be if you were considering to apply. You could basically tell with one look what people at the place are interested in. And if you started working there, it would be one click to find out who has similar interests. No more browsing through dozens of individual websites, half of which don't exist or were last updated in 1998.

I was thinking about this recently because Stefan said that with better indexing of abstracts, which is on the way, it might even be possible in the not-so-far future to create such a tag-cloud from researcher's publication list. Which, with an author ID that lists institutions, could be mostly automatically assembled too.

This idea comes with a compatibility problem though, because most places hire applicants by group. So if one doesn't have groups, then the assignment of faculty to committees and applicants to committees needs to be rethought. This requires a change in procedure, but it's manageable. And this change in procedure would have the benefit of making it much easier to identify emerging areas of research that would otherwise awkwardly fit neither here nor there. Which is the case right now with emergent gravity and analogue gravity, just to name an example.

I clearly think getting rid of institutional group structures would be beneficial to research. Alas, there's a potential barrier that's preventing us from making such a change, a classic example of a collective action problem. However, I am throwing this at you because I am sure this restructuring will come to us sooner or later. You read it here first :o)

Book Review “The Geek Manifesto” by Mark Henderson

The Geek Manifesto: Why Science Matters
By Mark Henderson
Bantam Press (10 May 2012)

Henderson’s book is a well-structured and timely summary of why science, both scientific knowledge and the scientific method, matters for the well-being of our societies. Henderson covers seven different areas: why science matters to politics, the government, the media, the economy, education, in court, in healthcare and to the environment. In each case, he has examples of current problems, mostly from the UK and to a lesser extent from the USA, that he uses to arrive at recommendations for improvement.

The book is quite impressive in the breadth of topics covered. The arguments that Henderson leads are well thought through and he has hands-on suggestions for what can be done, for example how and why scientists should take the time to correct journalists, how and why to communicate their concerns to members of the parliament, why random controlled trials matter not only in health care but also for general policies and educational practice, and so on.

“The manifesto’s aim is to win your broad support for its central proposition: that a more scientific approach to problem-solving is applicable to a surprisingly wide range of political issues, and that ignoring it disadvantages us all.”

That having been said, the book is clearly addressed at people who know the value of and apply the scientific method, people he refers to as “geeks.” I’ll admit that I’m not very fond of this terminology. If I hear “geek” I think of a guy who can fix a TV with a fork and salt, and who can recite Star Wars backwards in Klingon. What’s wrong with “scientists”, I am left to wonder?

There’s some more oddities about this book. To begin with it’s set in Times, and the text is in several places broken up with large quotes that repeat a sentence from the page. You see this very frequently in magazines these days, with the idea to get across at least a catchy sentence or two, but it doesn’t make any sense whatsoever to do this in a book every 30 pages or so. It’s just plainly annoying one has to read the same sentence twice.

I’ll also admit that I’m not following British politics whatsoever and most of the names that are being dropped in this book don’t tell me anything. It’s a strangely UK-centric vision of what is a much broader issue really. Plenty of twists and turns of UK politics did not make a compelling read to me. That’s really unfortunate, because Henderson has a lot of good points that are relevant beyond the borders of his country.

Basically, Henderson’s message can be summarized as urging “geeks” to become more active and more vocal about their frustration with how scientific evidence and methods are being treated in various realms of our society. As a call to action however the book is far too long and, being addressed to readers who are fond of science already, it’s preaching to the choir. Thus, it’s a good book, by all means: well-argued, well-referenced, well-written – but I doubt it’ll achieve what its author hopes for.

I have to add however that it is good to see somebody is at least working into the direction of addressing this systemic problem that I’ve been writing about for years. I think that the root of our global political systems is that scientific knowledge and thinking is not, at present, well-integrated into our decision making processes. Instead we have an unfortunate conflation of scientific questions and questions of value when it comes to policy decisions. These really should be disentangled. But I’m preaching to the choir...

You may like “The Geek Manifesto” if you have an interest in how science is integrated into our societies, and what the shortcomings are with this integration. I’d give this book three out of five stars, which is to say I had to fight the repeated desire to skip over a few pages here and there.

What are you, really?

Last month, I reviewed Jim Holt’s book “Why does the world exist?” This question immediately brings up another question: What exists anyway? Holt does not seem to be very sympathetic to the idea that mathematical objects exist, or at least he makes fun of the idea:

“A majority of contemporary mathematicians (a typical, though disputed, estimate is about two-thirds) believe in a kind of heaven – not a heaven of angels and saints, but one inhabited by the perfect and timeless objects they study: n-dimensional spheres, infinite numbers, the square root of -1, and the like. Moreover, they believe that they commune with this realm of timeless entities through a sort of extra-sensory perception.”

There’s no reference for the mentioned estimate, but what’s worse is that referring to mathematical objects as “timeless” implies a preconceived notion of time already. It makes perfect sense to think of time as a mathematical object itself, and to construct other mathematical objects that depend on that time. Maybe one could say that the whole of mathematics does not evolve in this time, and we have no evidence of it evolving in any other time, but just claiming that mathematics studies “timeless objects” is sloppy and misleading. Holt goes on:

“Mathematicians who buy into this fantasy are called “Platonists”… Geometers, Plato observed, talk about circles that are perfectly round and infinite lines that are perfectly straight. Yet such perfect entities are nowhere to be found in the world we perceive with our sense… Plato concluded that the objects contemplated by mathematicians must exist in another world, one that is eternal and transcendent.”

It is interesting that Holt in his book comes across as very open-minded to pretty much everything his interview partners confront him with, including parallel-worlds, retrocausation and panpsychism, but discards Platonism as a “phantasy.”

I’m not a Platonist myself, but it’s worth spending a paragraph on the misunderstanding that Holt has constructed because this isn’t the first time I’ve come across similar statements about circles and lines and so on. It is arguably true that you won’t find a perfect circle anywhere you look. Neither will you find perfectly straight lines. But the reason for this is simply that circles and perfectly straight lines are not objects that appear in the mathematical description of the world on scales that we see. Does it follow from that they don’t exist?

If you want to ask the question in a sensible way, you should ask instead about something that we presently believe is fundamental: What’s an elementary particle? Is it an element of a Hilbert space? Or is it described by an element of a Hilbert space? Or, to put the question differently: Is there anything about reality that cannot be described by mathematics? If you say no to this question, then mathematical objects are just as real as particles.

What Holt actually says is: “I’ve never seen any of the mathematical objects that I’ve heard about in school, thus they don’t exist and Platonism is a phantasy. “ Which is very different from saying “I know that our reality is not fundamentally mathematical.” With that misunderstanding, Holt goes one to explain Platonism by psychology:

“And today’s mathematical Platonists agree. Among the most distinguished of them is Alain Connes, holder of the Chair of Analysis and Geometry at the College de France, who has averred that “there exists, independently of the human mind, a raw and immutable mathematical reality.”… Platomism is understandably seductive to mathematicians. It means that the entities they study are no mere artifacts of the human mind: these entities are discovered, not invented… Many physicists also feel the allure of Plato’s vision.”

I don’t know if that’s actually true. Most of the physicists that I asked do not believe that reality is mathematics but rather that reality is described by mathematics. But it’s very possibly the case that the physicists in my sample have a tendency towards phenomenology and model building.

Most of them see mathematics as some sort of model space that is mapped to reality. I argued in this earlier post that this is actually not the case. We never map mathematics to reality. We map a simplified system to a more complicated one, using the language of mathematics. Think of a computer simulation to predict the solar cycle. It’s a map from one system (the computer) to another system (the sun). If you do a calculation on a sheet of paper and produce some numbers that you later match with measurements, you’re likewise mapping one system (your brain) to another (your measurement), not some mathematical world to a real one. Mathematics is just a language that you use, a procedure that adds rigor and has proved useful.

I don’t believe, like Max Tegmark does, that fundamentally the world is mathematics. It seems quite implausible to me that we humans should at this point in our evolution already have come up with the best way to describe nature. I used to refer to this as the “Principle of Finite Imagination”: Just because we cannot imagine it (here: something better than mathematics) doesn’t mean it doesn’t exist. I learned from Holt’s book that my Principle of Finite Imagination is more commonly known as the Philosopher’s Fallacy.

“[T]he philosopher’s fallacy: a tendency to mistake a failure of the imagination for an insight into the way reality has to be.”

Though Googling "philopher's fallacy" brings up some different variants, so maybe it's better to stick with my nomenclature.

Anyway, this has been discussed since some thousand years and I have nothing really new to add. But there’s always somebody for whom these thoughts are new, as they once were for me. And so this one is for you.

xkcd: Lucky 10000.

Public Attitudes to Science

"Public Attitudes to Science" is a survey that has been conducted in the UK every couple of years since 2000, most recently 2011. It's quite interesting if you're interested in how scientific research is perceived by the public; you can download the full survey results here. Let me just show you some of the figures that I found interesting.

First, here's where people hear or read about new scientific research findings most often. TV and print newspapers are the dominant sources with 54% and 33%, followed by internet excluding blogs. Science blogs come in only at 2% (I don't know what the asterisk means, I took the number from the text to this figure).

Next, a somewhat odd question. People were asked how much they agree or disagree with the statement "The information I hear about science is generally true." It's beyond me how anybody can agree with a statement like that. Anyway, 9% disagree or strongly disagree and an amazing 47% agree or strongly agree.

What's more interesting is that those who agreed or disagreed were asked for their reasons in an unprompted reply. Here's the most frequently named reasons for agreeing that "information I hear about science is generally true." The top answer (no reason to doubt it) means to me essentially they're generally trusting or didn't think very much about their answer. More telling are the subsequent reasons: It's checked by other scientists, science is regulated, it comes directly from scientists, it's checked by someone, checked by journalists. Don't laugh, this is serious.

And here are the top reasons to disagree that scientific information s generally true. The first two replies are variants of why should I believe it. Followed by it's not checked by anyone, not checked by other scientists, not checked by journalists, does not come directly from scientists, and a general mistrust in mass media. This reply is interesting because science blogs can alleviate this trust issue very much, yet, as we have seen above, only very few people seems to use them as a source of information.

This becomes even clearer if you look at the replies to the next question, that is what could increase people's trust in the finding of scientific studies:

I am as shocked as amazed that 47% of people say they would trust information more if it was repeated. Though that shouldn't come as a surprise to me because it's a well-known effect that Kahneman in his book elaborates on for a while. The same goes for the reply that information fitted nicely with what they already new. If you really needed evidence that the human brain easily falls for confirmation bias, here it is. And that's only the people who admitted it! But on the more hopeful side are the replies that ask for review by other scientists and publication in a scientific journal. One might add that at least a proper reference our source would greatly help. I think science blogs do much better in terms of referencing and they're a source of review by other scientists in themselves. So, I come to conclude the world would be a better place if people would read more science blogs. Though that might be a case of confirmation bias ;o)

Questioning the Foundations

The submission deadline for this year’s FQXi essay context on the question “Which of Our Basic Physical Assumptions Are Wrong?” has just passed. They got many thought-provoking contributions, which I encourage you to browse here.

The question was really difficult for me. Not because nothing came to my mind but because too much came to my mind! Throwing out the Heisenberg uncertainty principle, Lorentz-invariance, the positivity of gravitational mass, or the speed of light limit – been there, done that. And that’s only the stuff that I did publish...

At our 2010 conference, we had a discussion on the topic “What to sacrifice?” addressing essentially the same question as the FQXi essay, though with a focus on quantum gravity. For everything from the equivalence principle over unitarity and locality to the existence of space and time you can find somebody willing to sacrifice it for the sake of progress.

So what to pick? I finally settled on an essay arguing that the quantization postulate should be modified, and if you want to know more about this, go check it out on the FQXi website.

But let me tell you what was my runner-up.

“Physical assumption” is a rather vague expression. In the narrower sense you can understand it to mean an axiom of the theory, but in the broader sense it encompasses everything we use to propose a theory. I believe one of the reasons progress on finding a theory of quantum gravity has been slow is that we rely too heavily on mathematical consistency and pay too little attention to phenomenology. I simply doubt that mathematical consistency, combined with the requirement to reproduce the standard model and general relativity in the suitable limits, is sufficient to arrive at the right theory.

Many intelligent people spent decades developing approaches to quantum gravity, approaches which might turn out to have absolutely nothing to do with reality, even if they would reproduce the standard model. They pursue their research with the implicit assumption that the power of the human mind is sufficient to discover the right description of nature, though this is rarely explicitly spelled out. There is the “physical assumption” that the theoretical description of nature must be appealing and make sense to the human brain. We must be able to arrive at it by deepening our understanding of mathematics. Einstein and Dirac have shown us how to do it, arriving at the most amazing breakthroughs by mathematical deduction. It is tempting to conclude that they have shown the way, and we should follow in their footsteps.

But these examples have been exceedingly rare. Most of the history of physics instead has been incremental improvements guided by observation, often accompanied by periods of confusion and heated discussion. And Einstein and Dirac are not even good examples: Einstein was heavily guided by Michelson and Morley’s failure to detect the aether, and Dirac’s theory was preceded by a phenomenological model proposed by Goudsmit and Uhlenbeck to explain the anomalous Zeeman effect. Their model didn’t make much sense. But it explained the data. And it was later derived as a limit of the Dirac equation coupled to an electromagnetic field.

I think it is perfectly possible that there are different consistent ways to quantize gravity that reproduce the standard model. It also seems perfectly possible to me for example that string theory can be used to describe strongly coupled quantum field theory, and still not have anything to say about quantum gravity in our universe.

The only way to find out which theory describes the world we live in is to make contact to observation. Yet, most of the effort in quantum gravity is still devoted to the development and better understanding of mathematical techniques. That is certainly not sufficient. It is also not necessary, as the Goudsmit and Uhlenbeck example illustrates: Phenomenological models might not at first glance make much sense, and their consistency only become apparent later.

Thus, the assumption that we should throw out is that mathematical consistency, richness, or elegance are good guides to the right theory. They are desirable of course. But neither necessary nor sufficient. Instead, we should devote more effort to phenomenological models to guide the development of the theory of quantum gravity.

In a nutshell that would have been the argument of my essay had I chosen this topic. I decided against it because it is arguably a little self-serving. I will also admit that while this is the lesson I draw from the history of physics, I, as I believe most of my colleagues, am biased towards mathematical elegance, and the equations named after Einstein and Dirac are the best examples for that.

Quantum Gravity and Taxes

The other day I got caught in a conversation about the Royal Institute of Technology and how it deals with value added taxes. After the third round of explanation, I still hadn’t quite understood the Swedish tax regulations. This prompted my conversation partner to remark Swedish taxes are more complicated than my research.

The only thing I can say in my defense is that in a very real sense taxes are indeed more complicated than quantum gravity.

True, the tax regulations you have to deal with to get through life are more a matter of available information than of understanding. Applying the right rule in the right place requires less knowledge than you need for, say, the singularity theorems in general relativity. In the end taxes are just basic arithmetic manipulations. But what’s the basis of these rules? Where do they come from?

Tax regulations, laws in general, and also social norms have evolved along with our civilizations. They’re results of a long history of adaption and selection in a highly complex, partly chaotic, system. This result is based on vague concepts like “fairness”, “higher powers”, or “happiness”, that depend on context and culture and change with time.

If you think about it too much, the only reason our societies’ laws and norms work is inertia. We just learn how our environment works and most of us most of the time play by the rules. We adapt and slowly change the rules along with our adaption. But ask where the rules come from or by what principles they evolve, and you’ll have a hard time coming up with a good reason for anything. If you make it more than five why’s down the line, I cheer for you.

We don’t have the faintest clue how to explain human civilization. Nobody knows how to derive the human rights from the initial conditions of the universe. People in general, and men in particular, with all their worries and desires, their hopes and dreams, do not make much sense to me, fundamentally. I have no clue why we’re here or what we’re here for, and in comparison to understanding Swedish taxes, quantizing gravity seems like a neatly well-defined and solvable problem.

How to beat a cosmic speeding ticket

xkcd: The Search

After I had spent half a year doing little more than watching babies grow and writing a review article on the minimal length, I got terribly bored with myself. So I’m apparently one of the world experts on quantum field theories with a minimal length scale. That was not exactly among my childhood aspirations.

As a child I had a (mercifully passing) obsession with science fiction. To this day contact to extraterrestrial intelligent beings is to me one of the most exciting prospects of technological progress.

I think the plausible explanation why we have so far not made alien contact is that they use a communication method we have no yet discovered, and if there is any way to communicate faster than the speed of light, clearly that’s what they would use. Thus, we should work on building a receiver for the faster-than-light signals! Except, well, that our present theories don’t seem to allow for such signals to begin with.

Every day is a winding road, and after many such days I found myself working on quantum gravity.

So when the review was finally submitted, I thought it is time to come back to superluminal information exchange, which resulted in a paper that’s now published

Quantum superpositions of the speed of light
arXiv:1207.1002

The basic idea isn’t so difficult to explain. The reason that it is generally believed nothing can travel faster than the speed of light is that Einstein’s special relativity sets the speed of light as a limit for all matter that we know. The assumptions for that argument are few, the theory is extremely well in agreement with experiment, and the conclusion is difficult to avoid.

Strictly speaking, special relativity does not forbid faster-than-light propagation. However, since in special relativity a signal moving forward in time faster than the speed of light for one observer might appear like a signal moving backwards in time for another observer, this can create causal paradoxa.

There are three common ways to allow superluminal signaling, and each has its problems:

First, there are wormholes in general relativity, but they generically also lead to causality problems. And how creation, manipulation, and sending signals through them would work is unclear. I’ve never been a fan of wormholes.

Second, one can just break Lorentz-invariance and avoid special relativity altogether. In this case one introduces a preferred frame and observer independence is violated. This avoids causal paradoxa because there’s now a distinguished direction “forward” in time. The difficulty here is that special relativity describes our observations extremely well and we have no evidence for Lorentz-invariance violation whatsoever. There is then explaining to do why we have not noticed violations of Lorentz-invariance before. Many people are working on Lorentz invariance violation, and that by itself limits my enthusiasm.

Third, there are deformations of special relativity which avoid an explicit breaking of Lorentz-invariance by changing the Lorentz-transformations. In this case, the speed of light becomes energy-dependent so that photons with high energy can, in principle, move arbitrarily fast. Since in this case everybody agrees that a photon moves forward in time, this does not create causal paradoxa, at least not just because of the superluminal propagation.

I was quite excited about this possibility for a while, but after some years of back and forth I’ve convinced myself that deformed special relativity creates more problems than it solves. It suffers from various serious difficulties that prevent a recovery of the standard model and general relativity in the suitable limits, notoriously the problem of multi-particle states and non-locality (which we discussed here).

So, none of these approaches is very promising and one is really very constrained in the possible options. The symmetry-group of Minkowski-space is the Lorentz-group plus translations. It has one free parameter and that’s the speed of massless particles. It’s a limiting speed. End of story. There really doesn’t seem to be much wiggle room in that.

Then it occurred to me that it is not actually difficult to allow several different speeds of lights to be invariant, as long as can never measure them at the same time. And that would be the case if one had particles propagating in a background that is a superposition of Minkowski-spaces with different speeds of light. Because in this case then you would use for each speed of light the Lorentz-transformation that belongs to it. In other words, you blow up the Lorentz-group to a one-parameter family of groups that acts on a set of spaces with different speeds of lights.

You have to expect the probability for a particle to travel through an eigenspace that does not belong to the measured speed of light to be small, so that we haven’t yet noticed. To good precision, the background that we live in must be in an eigenstate, but it might have a small admixture of other speeds, faster and slower. Particles then have a small probability to travel faster than the speed of light through one of these spaces.

If you measure a state that was in a superposition, you collapse the wavefunction to one eigenstate, or let us better say it decoheres. This decoherence introduces a preferred frame (the frame of the measurement) which is how causal paradoxa are avoided: there is a notion of forward that comes in through the measurement.

In contrast to the case in which Lorentz invariance is violated though, this preferred frame does not appear on the level of the Lagrangian - it is not fundamentally present. And in contrast to deformations of special relativity, there is no issue here with locality because two observers never disagree on the paths of two photons with different speeds: Instead of there being two different photons, there’s only one, but it’s in a superposition. Once measured, all observers agree on the outcome. So there’s no Box Problem.

That having been said, I found it possible to formulate this idea in the language of quantum field theory. (It wasn’t remotely as straight forward as this summary might make it appear.) In my paper, I then proposed a parameterization of the occupation probability of the different speed of light eigenspaces and the probability of particles to jump from one eigenstate to another upon interaction.

So far so good. Next one would have to look at modifications of standard model cross-sections and see if there is any hope that this theoretical possibility is actually realized in nature.

We still have a long way to go on the way to build the cell phone to talk to aliens. But at least we know now that it’s not incompatible with special relativity.