Thursday, November 27, 2008

Stephen Hawking to Visit Perimeter Institute

I just recieved the following email:

Professor Stephen Hawking to Regularly Visit Canada's Perimeter Institute as Distinguished Research Chair

Waterloo, Ontario, Canada, November 27, 2008 - Dr. Neil Turok, Director of Canada's Perimeter Institute for Theoretical Physics (PI), is pleased to announce the appointment of internationally renowned scientist Professor Stephen Hawking to the position of PI Distinguished Research Chair.

Prof. Hawking will conduct regular stays at PI in coming years, beginning in the summer of '09, and says, "I am honoured to accept the first Distinguished Research Chair at the Perimeter Institute. The Institute's twin focus, on quantum theory and gravity, is very close to my heart and central to explaining the origin of the Universe. I look forward to building a growing partnership between PI and our Centre for Theoretical Cosmology, at Cambridge. Our research endeavour is global, and by combining forces I believe we will reap rich rewards."

In announcing that Prof. Hawking will visit PI for extended periods each year, PI Director Neil Turok said, "The appointment marks a new phase in our recruitment that will see leading scientists from around the world establish a second 'research home' at Perimeter Institute. I am delighted that Stephen has agreed to accept the first of a projected 40 such visiting Chairs. We look forward to hosting Stephen in Waterloo, Ontario, to benefiting from his wise mentorship and guidance which has been so successful in Cambridge, and to the many stimulating scientific collaborations which will undoubtedly emerge."

About Prof. Hawking

Prof. Stephen Hawking is possibly the world's most famous living physicist, having made several extraordinary contributions to fundamental theoretical physics, especially in establishing the classical and quantum properties of black holes and in building quantum gravitational theories of the origin of the Universe and structures within it. His most celebrated work was the theoretical prediction that black holes should emit radiation, known as Hawking radiation. Prof. Hawking is presently the Lucasian Professor of Mathematics at Cambridge University, a position once held by Isaac Newton. He has authored many popular books, ranging from A Brief History of Time (1988) to George's Secret Key to the Universe (2007). Additional information can be found here.

About Perimeter Institute

Canada's Perimeter Institute is an independent, non-profit, scientific research and educational outreach organization where international scientists push the limits of our understanding of physical laws and develop new ideas about the very essence of space, time, matter and information. The centre provides a multi-disciplinary environment to foster scientific collaboration in research areas of cosmology, particle physics, quantum foundations, quantum gravity, quantum information, superstring theory, and related disciplines. The Institute also provides outreach resources and public lectures for students, teachers and the general public in order to share the joy of scientific research, discovery and innovation. In partnership with the Governments of Ontario and Canada, PI continues to be a successful example of private and public collaboration in science research and education. A full history is available at

See also: Globe and Mail: Waterloo lures Hawking

Wednesday, November 26, 2008

Galileo and the Discovery of a New World

2009 will be the International Year of Astronomy, commemorating the 400th anniversary of Galileo Galilei's groundbreaking astronomical discoveries with the then new telescope.

It's in this context that the University Heidelberg is organising a series of public lectures, Galilei's first glimpse through the telescope and its consequences today. So, a few days ago I spent a very entertaining evening in the magnificent "Alte Aula" of the university (photo here), listening to a talk by historian of science William Shea of the Cattedra Galileiana di Storia della Scienza, Università degli Studi di Padova, on Galileo and the Discovery of a New World.

Shea explained the main astronomical discoveries of Galileo, and also told quite a few entertaining side notes. For example, Galileo had no real understanding of the detailed workings of his telescope. On the other hand, he was an accomplished artist, who composed his famous drawings of the moon from partial views of the moon disc, as his telescope didn't show the whole moon at once.

If you are interested in a compact and entertaining introductory lecture about Galileo the astronomer, you might want to check out Shea's talk (it's in English, contrary to all the German text on the web page).


Tuesday, November 25, 2008

Dancing Droplets and Spherical Harmonics

My first encounter with Spherical Harmonics must have been in the course on electrodynamics, when these intimidatingly looking functions showed up in series expansion of the Coulomb potential and in the multipole expansions of charge distributions. Half a year later, they appeared again, in the solution of the hydrogen problem in the quantum mechanics class. Here, at least, they were used to produce nice figures of electron orbitals.

But I did miss out on one of the most elementary occurrences of Spherical Harmonics.

Spherical Harmonics Ym(θ, φ) describe the angular part of the solution to Laplace's equation in spherical coordinates. As such, they are ubiquitous in physical problems with a spherical symmetry. Thus, they describe not only the behaviour of the electron in the hydrogen atom, but also the wobbling deformations of an oscillating, elastic sphere. What sine and cosine are for a one-dimensional, linear string, the Spherical Harmonics are for the surface of sphere.

Deformation modes of a bouncing oil droplet (radius R = 0.765 mm) described by the Spherical Harmonics Y20, Y30 and Y40, as observed with a high-speed camera. From S. Dorbolo et al.: Resonant and rolling droplet, New J. Phys. 10 (2008) 113021.

This has been demonstrated very nicely in a paper by S. Dorbolo, D. Terwagne, N. Vandewalle and T. Gilet just published in the New Journal of Physics, Resonant and rolling droplet. In the experiment, a tiny oil droplet is placed on an oil bath which is set into vertical vibrations to prevent coalescence of the droplet with the bath. The droplet, which at rest would have a spherical form due to surface tension, bounces periodically on the bath. At the right frequencies of the vibrating surface, the droplet oscillates in resonance – and deforms according to spherical harmonics!

A movie (Quicktime, 11.0 MB – someone should explain to the NJP how to upload these movies to YouTube ... ) shows the oscillations of the drop and the corresponding calculations using Spherical Harmonics Ym with ℓ = 2, 3, 4 and m = 0. "Magnetic quantum number" m = 0 means rotational symmetry of the wobbling around the vertical axis. For m ≠ 0, deformations are not symmetric with respect to the vertical, and in this case, the droplet starts to move around on the oil bath. This can be seen in a second movie (QuickTime, 5.6 MB).

That's a beautiful example of Spherical Harmonics in action I would like to have known when I was struggling for the first time with multipole expansions!

The first application of Spherical Harmonics to describe the wobbling of a droplet was by Lord Rayleigh, in the appendix of a paper On the Capillary Phenomena of Jets, Proceedings of the Royal Society of London 29 (1879) 71-97. You can check out his calculation - the PDF (2.5 MB) is available for free.

Monday, November 24, 2008

Backreacting Personality

Via David Berenstein, via Clifford Johnson, I've piped our blog into the Typealyzer, which allegedly “is able to guess which personality type a text represents” based on a statistical analysis of words and sentences. Here is the result:

INTJ - The Scientists

The long-range thinking and individualistic type. They are especially good at looking at almost anything and figuring out a way of improving it - often with a highly creative and imaginative touch. They are intellectually curious and daring, but might be pshysically hesitant to try new things.

The Scientists enjoy theoretical work that allows them to use their strong minds and bold creativity. Since they tend to be so abstract and theoretical in their communication they often have a problem communcating their visions to other people and need to learn patience and use conrete examples. Since they are extremly good at concentrating they often have no trouble working alone.


This show what parts of the brain that were dominant during writing.

Which is quite good actually, my personality type is inded INTJ. I can assure you however, that I am not “pshysically hesitant to try new things”.

Sunday, November 23, 2008

Chocolate Promises

Back then, in my days as a fresh postdoc who just moved to the USA, Dove turned out to be the only readily available and eatable chocolate option. So I got used to the Dove 'Promises': little messages in the wrappers. They would read “Be true to yourself,” “Live your dreams,” or “Little things can make big differences.” (You find some collected on this website.) Goes well with a glass of red wine.

Last year Hershey's finally discovered chocolate. (Yes, capitalism works - sometimes.) They call it Hershey's Bliss, it seems indeed to contain cacao, and is strikingly similar to Dove - minus the messages (some people might appreciate that). Since Hershey is omnipresent and I dislike monopolies, these days I sometimes buy Dove chocolate for nostalgic reasons. However, the promises I find now read “Get a manicure,” “Wear high heels,” or “Use a good hand moisturizer.” The latter in particular makes one wonder about the relation of Dove to Dove. We are one step away from “Bleach your teeth,” “Call your mother," or “File in the tax-return.”

This made me wonder what message I'd want in the wrappers were I to distribute chocolate among my colleagues? “Read your notes upside down,” “Smile at your postdoc,” or “Just tell him what you really think.” Leave your suggestions in the comments.

Another thing I had to learn from these wrappers is that the French translation of “Read a trash novel” is supposedly “Perdez votre temps.” Which I think severely underestimates the ego-boost one gets from reading a really bad novel that got published. Anyway, one of the nicer messages was “Write a real letter, not just an email.” Here is the result, tentatively titled “Faster than the speed of light”:

Thursday, November 20, 2008

A town rips up

I just wanted to share with you an article I read in the German magazine Spiegel because I found it as spooky as fascinating. It is in German, so here is a rough and partial translation. For those of you who speak German, the full original article can be found at

and photos are here.

After Geothermal Drilling: A town rips up

Exemplary into disaster: The idea was to heat the town-hall in Staufen with geothermal energy. But briefly after the drilling the horror began. Everywhere in the town, cracks and crevices started to appear. Nobody knows what else is to expect - and who is to blame.

Staufen in Breisgau: A small, quiet town near the Black Forest. 7800 people live here, where the world is still all right. More precisely: Where the world was still all right. Then last fall, the disaster started to happen...

It started with a worthily idea. One wanted to heat the historical town hall with climate-friendly geothermal heat. An Austrian company was hired, seven drillings were made below the town-hall, 140 meters deep.

Briefly after this, the first cracks appeared in the historical building. At first one was not really worried. Mayor Michael Benitz spoke of “cosmetic damage”. “In the beginning the movement was in the millimeter range,” he says. But it didn't stay that way: Millimeters grew to centimeters, and the cosmetic damage grew to a catastrophe. These are at least the words Mayor Benitz uses when he talks about the uncanny events in his town.

The cracks in the town-hall began to grow, spread to the surrounding houses, and became longer and deeper. Like monster from inside the earth, they gnaw on the town. After only one year, more than a hundred houses show cracks. Sometimes they are so deep you can reach into them.

Something is going on below Staufen. The whole town has raised. And that on scales that are enormous in a geological context. We are talking about several centimeters per month.

What is going on?

Geologists were asked for advice. They should clarify if - and if so, how - the mysterious cracks were caused by the drilling. Scientists from the Technical University (TU) Darmstadt have a theory. Ingo Sass, geological engineer at the TU Darmstadt and expert for geothermal drilling, suspects [...] that the following happened: “One started drilling below the town-hall and broke through the gypsum-keuper-layer, under which there is groundwater under high pressure.”

Keuper is an anhydride, a calcium sulfat. In contact with water, if forms gypsum. And that gypsum expands. When the groundwater layer below the Keuper was drilled into, water rose through the drilling and came in contact with the anhydrite. This caused a chemical reaction. The volume growth in this process can be up to 60 percent. [For details, see e.g. this paper.]

The people in Staufen are desperate [...] Presently it is checked whether it is still save to enter the town-hall at all [...]

Sass further says: “This can go on like this for years, depending on how fast the water raises.” He is even afraid the worst is yet to come. The plaster could partly resolve again the water, causing hollow spaces below the city. “I can not exclude this situation won't become dangerous.” Because then, there could be sudden collapses. “Something needs to be done urgently,” Sass says. “The water contact needs to be stopped." But that will be expensive.


But as long as the question of responsibility is not clarified, no insurance company will pay. A report was alread conducted to bring clarity.

Geotechnicians took temperature profiles in the drilling holes and at 30 other places in the city center, and measured the vertical motion. In the end however, nothing could be said with clarity. The drilling might have caused the problem. Or maybe not. It could also have a natural cause.

“Staufen is a tectonically active area,” says Sass. “Of course it is possible that the layers moved tectonically against each other which changed the water flow and caused the reaction.” But: He doesn't consider this to be very probable.

That the start of the events coincides with the drilling is a strong indicator against natural causes. Why would this weird raise of the ground start now, so briefly after the drilling. Most of the inhabitants of Staufen do not believe in theoretically possible natural geological processes [...]

Tuesday, November 18, 2008

Peer Review V

Occasionally, I come across these people who say things like “The peer review process is severely broken,” as Virginia Hughes at Seed Magazine echos in a recent article titled “”. Most of the article however is about open access instead, two issues that she happily mixes up:
“The journal-operated system of peer-review, Lisi says, "is severely broken." On this point, he couldn't find a stronger ally than the science blogosphere. Most of the ScienceBloggers are unwavering advocates of the Open Access (OA) movement, and two of them—Bora Zivkovic, of PLoS ONE, and John Wilbanks, of Science Commons—devote all of their time to it.”

At least she mentions “Most OA advocates are quick to point out that open-access doesn't necessarily mean the end of publishers or peer-review.” Indeed. So that then leaves me to wonder what kind of allies on exactly what does Garrett find in the science blogosphere?

There are three reasons why statements like this upset me: they are a) unverified b) self-fulfilling and c) unconstructive. Let me elaborate:

    a) I actually find the peer review process useful, and I also think it is necessary. There are many people who otherwise would not get any qualified feedback on their work. I am lucky to have colleagues to discuss with, who I can ask for opinions, references, or keywords. But not everybody is that lucky. I certainly agree that peer review can be quite painful, and I have received my share of completely nonsensical reports by referees who evidently didn't read more than the abstract. On other occasions however referees have pointed out important issues, and made suggestions for improvement, and even for further studies. So where are all these people who allegedly think the peer review process is broken?

    b) I frequently referee papers. I do my best trying to understand the author's work, and to write a useful review. This takes time, time I don't have for my own work, and the only thing I get for it is an automated Thank-you email from the publisher. I do it because I believe that peer review is an essential part of the organization of scientific knowledge and important for progress, but it only works if enough people participate constructively. What we'd need is to encourage people to take it more seriously, and not proclaim it is 'broken'.

    c) What are the alternatives? Some people like to advocate 'open peer review,' which seems to mean you put your paper somewhere on the web and hope you'll get comments. This, excuse me, is hopelessly naive. The vast majority of papers would never get any comments. Heck, the vast majority of papers probably wouldn't even get read if it wasn't for peer review. Do me the favour and think two steps ahead. We would be running into a situation in which the well-known people and the well-established topics receive a lot of 'reviews' and a lot of attention, whereas the vast body of work will never get the necessary stamp of having been critically read by somebody with an adequate education. As a consequence, a large fraction of serious researchers would step down on the same level with all the weirdos and their backyard theories that never get published. Sorry, but I really don't want to be a scientist under such circumstances.

That having been said, I certainly don't think peer review works very well. My largest frustation is that people don't take it seriously. It has happened in many instances that I wrote a long report on a flawed paper and recommendend rejection, only to see later that the paper got published in a different journal in exactly the same version. Evidently, the authors were not even remotely interested in improving their work. The biggest problem however is just that we are writing way too many papers. Obviously, the more papers we write, the less time we have to read and comment on other people's papers. If you want to fix the peer review process there's then two easy things to do:

1) Lower pressure on researchers to produce papers.

2) Encourage refereeing e.g. by pointing out its relevance or by providing incentives.

Related: See my comment on the paper “Why Current Publication Practices May Distort Science” in which the role of publishing as a branding process was studied, and my posts Peer Review IV, Peer Review III, Peer Review II.

Sunday, November 16, 2008

Revenge of the Nerds

Yesterday, I spent some hours in a cafe, scribbling on a notepad. Next to me a guy was browsing a shiny brochure. From the corner of my eye I read “So what, you may be asking, do they actually do in that ominous building beside Waterloo Park?” Yeah, I wondered. What do they do there? More interestingly, what do people think we do there?

The guy left behind the brochure on the table, and it turned out to be the fall/winter 2008 issue of “Waterloo Revealed”. They list a website that however is under construction, neither does it seem to be cached, so I indeed hat to retype it (!).

The brochure features an article with “Revenge of the Nerds” by Marc Cameron about Perimeter Institute. The author seems to confuse Quantum Foundations with Quantum Gravity and Quantum Information, but otherwise his writing is a nice laudatio on fundamental research, and PI's outreach and art program:

“Researchers at PI, a self-proclaimed “Independent, non-profit, scientific research and education outreach organization,” operate under the auspices of what many might consider “pure research”. It's the kind of thing that some fear may be going out of style in corporate laboratories and universities: the notion of research for research's sake.


So what, you may be asking, do they actually do in that ominous building beside Waterloo Park? The research done there in areas like Cosmology, Particle Physics, and Superstring Theory improve our scientific understanding of the universe (once it trickles down from the halls of academe), but they also contribute to the pioneering of new technologies. It's hard to predict how scientific breakthroughs and new theories will impact technological advances, but fundamental discoveries - like Einstein's reckoning of light as a particle - lead to new ways of understanding the basic parts of the physical universe which allows for improvements in quality of life through technology for people everywhere.”

The last sentence suspiciously sounds as if it came from our PR department, but anyway. Einstein of course has to be mentioned when it comes to nerds and theoretical physics. About PI's outreach program Cameron writes:
“While theoretical physics bears the stigma of nerd-dom, PI goes to great length to bring physics to the people through numerous public and education outreach programs. Their (free!) public lecture series is probably the most well-known of PI's offerings to the community [...] The lectures have been televised on Rogers Cable channels in many Ontario markets on the program Celebrating Science, as well as special episodes of TVOntario's Big Ideas. Starting this fall, select PI public lectures will also be airing on Discovery Channel.”

The latter was news to me. But the upshot of the article is this highlighted paragraph:
“Science they say, is the new religion. For certain it's a belief system and a philosophy about life and the rhythms of the universe. When it comes down to it, religion and science are each ways of asking questions about the intangible. If the architecture of the PI building is any indication, Waterloo has its own Cathedral of Theoretical Physics. And, like most Holy sites, they open up their doors to share freely what they have with the scientific layperson, like you or me, not because they'd like to convert us, but because they've found something exciting that maybe, just maybe, could make life a little better for all of us.”

Well. One would have hoped that after all the public outreach the message would have gotten across that science is the very antithesis of a belief system. You'd better call it a 'doubt system'.

The title of the article is btw completely unmotivated. Maybe however it's indeed time for the revenge of the nerds.

Saturday, November 15, 2008

It's a man's world...

I recently stumbled across the GenderAnalyzer, a text classifier that according to their description “has been trained on blogs written by men and women” and “uses Artificial Intelligence to determine if a homepage is written by a man or woman”.

So, I piped in some links from my blogroll. Here are the results, sorted by male-ness:

And here is the absolute high-score of male-ness:


Sorry Christine.

Having come so far I concluded that writing about science generally must count as an indicator for male-ness, and I discarded the 'GenderAnalyzer' as crap.

My homepage btw, is "quite gender neutral".

Friday, November 14, 2008

This and That

Thursday, November 13, 2008

Chaos, Solitons and Self-Promotion

Recently, our attention was drawn to the Elsevier Journal Chaos, Solitons & Fractals, and its Editor-in-Chief M. S. El Naschie. Over the course of the years, El Naschie himself published about 300 mostly single authored papers in this journal, with abstracts of the kind:
“Von Neumann’s continuous geometry has been considerably developed by Connes and is characterized by two fundamental concepts. First it is formulated without any direct reference to points and second it possesses a dimensional function. The present work explores the relevance of these two points to string theory as well as E-infinity theory. In particular we show that point-lessness and dimensional function implies fractality. In turn fractality leads to the concept of average or fuzzy symmetry and the elimination of gauge anomalies.”

Now neither of us in an expert in Solitons or Fractals. So we instead want to ask the completely unrelated questions whether being an editor at Elsevier allows one to circumvent peer review. In case you are suspicious about the scientific merit of El Naschie's work, you are not alone. John Baez gave it a closer look in his recent post The Case of M. S. El Naschie and finds the result wanting.

The reason we got interested in this topic is that El Naschie lists himself on his website as a “distinguised Fellow of the Physics Institute of the Johann Wolfgang Goethe University, Frankfurt” - the Institute where we both made our PhD. However, this “Fellowship” has not been awarded by the physics department, but by a private association, called the “Frankfurter Förderverein für physikalische Grundlagenforschung” (Frankfurt association for the support of basic research in phyiscs). Gossip that we would never spread says the guy has money. Zoran Škoda wrote in an earlier comment:
“I was told that there is an investigation about using this affiliation now. I contacted some of the associate editors, most of whom did not respond to my question how such a behaviour is allowed. Two of them told me that they will quit from the editorial board, and one that his name was put on the editorial page without his consent!”

It is thus good to read that Herman van Campenhout, Elsevier CEO Science & Technology, writes in the Publishing Ethics Resource Kit: “Monitoring Publishing Ethics is a major aspect of the peer-review process, and as such lies within the area of responsibility of the Editor-in-Chief [].” And, he adds, “Fortunately, the area of science publishing is reasonably good at self-correcting, albeit sometimes later rather than earlier.”

Tuesday, November 11, 2008


99TcWhen nuclear physics hits the headlines, it's usually in unpleasant contexts, such as leakage of radioactive substances from reactors, the unsolved problem of disposal of nuclear waste, or the proliferation of nuclear weapons.

So, I was surprised by I story I had heard on the radio a few weeks ago, and read about again a while later: It was about the temporary shortage in the supply of a radioactive isotope heavily used in medicine, Technetium-99.

Technetium-99, a nucleus made up of 43 protons and 56 neutrons, has an excited state which decays with a half-life of about 6 hours. Similar to an excited atom emitting a photon of visible light when converting back to the ground state, the decay of the exited nucleus comes along with the emission of a γ photon. This γ photon has an energy of 140 keV – about 100.000 times the energy of a photon of red light. Here is schematic representation of the energy levels and the transitions involved:

To create nuclei of Technetium-99 in the excited state – also called Technetium-99m, where "m" stands for "metastable" –, one resorts to another isotope, Molybdenum-99. This isotope undergoes a β decay with a half-life of 66 hours, thereby ending up as Technetium-99 in the excited state. Like all isotopes of Technetium, Technetium-99 isn't stable either and finally ends up, following another β decay, as Ruthenium-99.

Technetium-99 thyroid uptake scans. Scan (A) shows the normal, healthy result. (from Petros Perros: Thyrotoxicosis and Pregnancy, PLOS Medicine 2(12): e370)
Now, what is this good for? As it came out from investigations at the Brookhaven National Laboratory done in the 1960s, the decay reaction of Technetium can be adapted as a very elegant and practical tool for medical diagnosis. To this end, "freshly produced" Tc-99m is extracted chemically from a probe of Mo-99, bound to suitable large molecules, and administered intravenously to the blood circuit. Then, the 140 keV γ photons emitted at the decay of Tc-99m map from inside the body the distribution of blood. They trace regions of lacking blood supply, for example after a stroke, or highlight spots with enhanced metabolisms, which could be tumours. Energy of the γ photon and lifetime of Tc-99m are just so that such an exploration does not produce to high a radiation exposure, and can be done in a very reasonable time.

To use this technique, Molybdenum-99 is needed, and this is where the current shortage comes from: Molybdenum-99 is created in nuclear reactions, either by bombarding more common isotopes with neutrons, or by fissioning of U-235 in highly enriched uranium targets. This second source, which is the most important one, is of course highly linked to weapon-grade stuff, so there are only a handful of civilian reactors in the world that produce Molybdenum-99. In Europe, the main source is a reactor in Petten in the Netherlands, which is currently shut down for maintenance and inspections. It seems, however, that the consequential shortage of Molybdenum-99 and Technetium-99m for medical purposes is not critical.

While trying to get some background on this news story, I realised that the decay scheme of Molybdenum-99 and Technetium-99m involves a few interesting questions:

Why does the decay of Mo-99 not end up in the ground state of Tc-99? Why is the lifetime of the γ decay of Tc-99m so long? Usually, γ transitions happen within fractions of a second. And finally, what a strange element is technetium in the first place, as without stable isotopes, it marks a gap in the middle of the periodic table? And as it comes out, the answers to these questions touch upon a few concepts very central to nuclear physics.

But this will be the stuff of another post.

Monday, November 10, 2008

Bullshit with Equations

    “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, at PI's recent public lecture

via Sundance Bilson-Thompson, thanks :-)

Sunday, November 09, 2008

Thursday, November 06, 2008

Gallery of Fluid Motion

The motion of fluids can be surprising, beautiful, and sometimes just funny to watch. At its annual meetings, the Division of Fluid Dynamics of the American Physical Society organizes exhibits with stunning photographs and videos of fluid. Each year, awards are assigned to "photographs and videos [that] illustrate both experimental and numerical investigations of a wide variety of flow phenomena. Judged by a distinguished international panel of referees, winning entries were selected based upon criteria of scientific merit, originality, and artistry/aesthetic appeal."

Here is a winning entry from the Gallery of Fluid Motion 2008, chosen from the exhibition at the Annual Meeting of the APS Division of Fluid Dynamics in Salt Lake City last November (click on the still to get to the movie, requires some patience and Quicktime):

"BLACK HOLE" NUCLEATION IN A SPLASH OF MILK, by Laurent Courbin, James C. Bird, Andrew Belmonte, and Howard A. Stone: This video shows the impact dynamics of a millimeter-size drop of milk onto a superhydrophobic substrate that is spinning at a constant rate. (explanation as PDF file).

And here, a winning entry from the Gallery of Fluid Motion 2007 (Bee's absolute favourite):

CREEPING, WALKING AND JUMPING DROP by A. Renaudin, E. Galopin, V. Thomy, C. Druon, and F. Zoueshtiagh: This video shows the movement of a deionized water drop provoked by surface acoustic waves. (explanation as PDF file)

Don't be put off by the lengthy, silent-picture style explanations of the experimental setup at the beginning of the clips.

To see the amazing behavior of these drops rewards a little patience - enjoy!

Wednesday, November 05, 2008

Congratulations, Obama!

German Chancellor Angela Merkel
“My heartfelt congratulations on your historic victory in the presidential elections.

At the beginning of your administration, the world faces momentous challenges. I am convinced that, with closer and more trusting cooperation between the US and Europe, we can resolutely confront the novel challenges and dangers facing us [...] You can be sure that my government is fully aware of how important the trans-Atlantic partnership is for our futures.

It is my pleasure to invite you to visit Germany in the near future.”

French President Nicolas Sarkozy
“With the world in turmoil and doubt, the American people, faithful to the values that have always defined America's identity, have expressed with force their faith in progress and the future. At a time when we must face huge challenges together, your election has raised enormous hope in France, in Europe and beyond.”

European Commission President Jose Manuel Barroso
“We need to change the current crisis into a new opportunity. We need a new deal for a new world. I sincerely hope that with the leadership of President Obama, the United States of America will join forces with Europe to drive this new deal - for the benefit of our societies, for the benefit of the world.”

British Prime Minister Gordon Brown
“It has been an important election. I think the most important thing that follows from it is that America and Europe will have to work together to deal with the international problems we face, not just the financial crisis, but also stopping protectionism, making sure we work for stability and particularly peace in the Middle East.”

Dutch Prime Minister Jan Peter Balkenende
“The necessity for cooperation between Europe and the United States is bigger than ever. Only by close trans-Atlantic cooperation can we face the world's challenges.”

Chinese President Hu Jintao
“The Chinese Government and I myself have always attached great importance to China-US relations. In the new historic era, I look forward to working together with you to continuously strengthen dialogue and exchanges between our two countries.”

Indian Prime Minister Manmohan Singh
“Your extraordinary journey to the White House will inspire people not only in your country but also around the world.”

Afghanistan President Hamid Karzai
“I applaud the American people for their great decision and I hope that this new administration in the United States of America, and the fact of the massive show of concern for hhuman beings and lack of interest in race and color while
electing the president, will go a long way in bringing the same values to the
rest of the world sooner or later.”

Australian Prime Minister Kevin Rudd
“Senator Obama's message of hope is not just for America's future, it is also a message of hope for the world as well. A world which is now in many respects
fearful for its future.”

Japanese Prime Minister Taro Aso
“The Japan-US alliance is key to Japanese diplomacy and it is the foundation for peace and stability in the Asia-Pacific region. With President-elect Obama, I will strengthen the Japan-U.S. alliance further and work towards resolving
global issues such as the world economy, terror and the environment.”

Israeli Foreign Minister Tzipi Livni
“Israel expects the close strategic cooperation with the new administration, president and Congress will continue along with the continued strengthening of the special and unshakeable special relationship between the two countries.”

Former PI postdoc representative Sabine Hossenfelder
“Please don't switch off your brain the moment you move into the White House.”

Sunday, November 02, 2008

Infinity Really is Different

After a couple of crazy weeks, I finally had the time to read some of the papers on my desk, and that's where this article reappeared

    More Really is Different
    By Mile Gu, Christian Weedbrook, Alvaro Perales, Michael A. Nielsen
    arXiv:0809.0151v1 [cond-mat.other]

    Abstract: In 1972, P.W.Anderson suggested that `More is Different', meaning that complex physical systems may exhibit behavior that cannot be understood only in terms of the laws governing their microscopic constituents. We strengthen this claim by proving that many macroscopic observable properties of a simple class of physical systems (the infinite periodic Ising lattice) cannot in general be derived from a microscopic description. This provides evidence that emergent behavior occurs in such systems, and indicates that even if a `theory of everything' governing all microscopic interactions were discovered, the understanding of macroscopic order is likely to require additional insights.

Since Stephen Luttrell asked last week what I think about the paper, I thought I should come back to it.

The paper is really neat. Here is a quick summary. The authors consider a 2-dimensional spin lattice with nearest neighbor interaction. We thus have a lattice of ups and downs that can influence the other ups and downs around them according to some rule given by the Hamiltonian of the system. On this lattice, the authors put certain “designer Ising blocks” with an associated Hamiltonian, composed of several spin states. These blocks have the property that if they are in the ground state (the state of lowest energy), and one forces the spins on one side to be in a certain pattern of ups and downs by applying a field, then the other side will produce a certain output. They give specific examples in the appendix.

If one covers a 2-dimensional semi-infinite plane with these blocks and has an input on one side of the first row, the spin-spin interactions give a rule determining what is on the other side of that row, which is the input for the second row. And so on. Thus, the ground state of the system is fully determined. But what can we say about this ground state?

Now here is the clue of the paper. The authors show that with the appropriate initialization and designer blocks, one can map a cellular automaton to this spin-system. A cellular automaton operates on a one dimensional input line according to a specific rule. This rule crates a new state, on which the rule is applied again etc. This is commonly shown in a diagram with all the so created states below each other, each corresponding to a certain time step. In the spin-lattice, there are no time steps, but the ground state would be a picture of these states of the cellular automaton. Note however that for the spin-lattice this is not a time-dependent realization of this state. The ground-state just is specified according to some rules.

However, there exists cellular automata for which it can be proven that no non-trivial questions can be answered about their evolution, without actually running them and looking, thus one can never say anything about the total evolution. Because of the correspondence to the spin-lattice this then means there are questions about its ground state that can't be answered either. An example for such a question would be what the overall magnetization is of the system. There is thus no way to derive this quantity from the Hamiltonian, the question is undecidable.

It should be noted that it is important for this conclusion the spin-lattice is indeed infinite. The approximation that a system is infinite is very common in physics and often used to simplify computations. What this argument thus shows is that in this limit, there can remain questions open that fundamentally can not be answered about the whole system.

The title of the paper is a reference to Anderson's paper “More is Different,” an argument against reductionism, claiming that not every system can be understood by merely analysing its parts. Gu et al's paper provides an explicit example for which it can be proved that it indeed is not possible to understand the whole system from the behavior of its constituents. For this argument to hold however “more” isn't enough, it has to be infinitely more.

On the risk of merely expressing my utter ignorance, this doesn't surprise me much. What the authors have shown in the paper is a map from a cellular automata, commonly run on a computer, to a 2-d spin lattice. This lattice is a physical realization of a computer code and thus similar conclusions hold for both. As far as I am concerned, if I run the code and visualize it on my screen (for an infinitely long time of course) this is also a physical realization of the code, it is a state my computer's hardware is in. However, the map to the spin system is without doubt much cleaner and better to analyze.

It would be interesting to see whether one could find a possibly weaker statement for large, but finite systems.

For more on the topic, see also my post Emergence and Reductionism, NewScientist's article Why nature can't be reduced to mathematical laws, or check out Stuart Kauffman's last week talk The Open Universe: Toward a Post-Reductionist Science, PIRSA:08100058.

Mile Gu, Christian Weedbrook, Alvaro Perales, Michael A. Nielsen (2008). More Really is Different arXiv