Tuesday, May 04, 2010

Physics Bits and Bites

Here are three interesting and intriguing physics items I came across recently:
  • Last year, the American Association for the Advancement of Science (AAAS) had organized a symposium called "Quest for the Perfect Liquid: Connecting Heavy Ions, String Theory, and Cold Atoms". Perfect, low-viscosity liquids can be observed when there is a very strong interaction between the constituents of the fluid, as is the case for the quarks and gluons created in heavy ion collisions at RHIC, or clouds of ultracold lithium atoms in optical traps. The strongly coupled quark gluon plasma can be described using the AdS/CFT correspondence, which brings sting theory into play (see also this earlier post). At the AAAS symposium, physicist-blogger Clifford Johnson (from Asymptotia) and Peter Steinberg (from Entropy Bound) discussed this connection, and a write-up of their presentation has now come out as a feature article in the May 2010 issue of Physics Today, "What black holes teach about strongly coupled particles" (free access).

  • You may be aware of the ongoing quest for the densest possible packing of tetrahedra? The NYT wrote about this in January, and the articles mentions that a paper on the subject "prompted Paul M. Chaikin, a professor of physics at New York University, to buy tetrahedral dice by the hundreds and have a high school student stuff them into fish bowls and other containers." This project now resulted in a Physical Review Letter, with an experimentally determined volume fraction of 0.76±0.02 (The current theoretical "record" is at 0.856). Analysis of the experiment was done using Magnetic Resonance Imaging to look "into" the container crammed with tetrahedra, which shows that the packing is highly disordered. More background can be found in an article at "Physics", which also contains a free link to the PRL paper.

  • Also via Physics, I've learned about what is the fastest (and possibly smallest) analogue computer to perform Fourier transforms: a single iodine molecule. A iodine molecule consists of two iodine atoms, which can vibrate, realizing a tiny harmonic oscillator. During one period, a harmonic oscillator follows a circular trajectory in phase space, which means that the Wigner function describing the quantum state of the oscillator "switches" space and momentum coordinates every quarter period. Going from real space to momentum space corresponds to a Fourier transform, so when the wave function of the iodine molecule is prepared in real space, after quarter of a period, the wave function encodes the Fourier transform of the initial configuration. Using laser, it is possible to prepare the molecule in definite state, and to probe the state again later. This allows discrete Fourier transforms for four and eight elements, and all this within 145 femtoseconds, "which is shorter than the typical clock period of the current fastest Si-based computers by 3 orders of magnitudes." (Ultrafast Fourier Transform with a Femtosecond-Laser-Driven Molecule", PRL).


  1. Yummy, pretty much all the things that interest me at the moment. So much to write, but I'll pick one for now: tetrahedron packing.

    Looking at the simplest of the Five Platonic solids, good old Tetrahedron, and the 3rd simplest, the Octahedron, if you combine two tetrahedrons and one octahedron you'd have a rhomboid (technically: a parallelepiped).

    What is the volume fraction of that?

    I once had the silly idea that if I were to design a universe and make it as simple as possible, I'd build it that way. Of course the 2nd simplest Platonic solid, the cube, could pack with itself, but it could slip and slide too much. Too messy, and not very anthropic (good morning, Lenny). Rhomboids would hold each other together and as an extra added bonus, would naturally imply a handednessness or chirality to the universe, for what reason? I don't know, maybe to perplex a bunch of naked primates orbiting a very average star some 13.7 billion years after creation, maybe, when they're not scratching their ears as to how quantum mechanics, thermodynamics, and general relativity can exist at once.

    But I don't think that anymore. It's just a pleasant mathematical thought. It would also imply background-dependency, and that would just make Lee Smolin mad. I like Lee, so, no.

    Yes, we were all young and ignorant once, and I'm certainly no exception. Perhaps ignorance really is bliss?

  2. Hi Stefan,

    Thanks for all those happenings that have caught your attention as of late. I’m particularly intrigued by the one about the school kids packing tetrahedral dice into fish bowls and such to produce densities higher than current theoretical limits. It is indeed interesting that the higher density ones being very disordered and yet perhaps not to be unexpected.

    That is for mathematics at its very foundations what can be said about the ordering of the set of real numbers for instance? What I’m saying is most of us have this idea of numbers being very ordered, like as in the set of naturals as being 1,2.3.4 and so on, yet when you consider that the reals having their members dominated by the irrationals and transcendentals, whose internal structural ordering not being so straight forward, with many defying to be even algorithmically defined. I will definitely have to look at these papers when i have the time. Oh yes I was wondering if the researcher cited in his paper the child that managed the tightess packing, as it would seem only fair:-)



    P.S. I forgot to mention how nice it was to see you chiming in as I was wondering where you had gotten for a while:-)

  3. Before Mathematics there was Logic, Phil. From Logic grew two great fields of study: Mathematics, and Science (as Physics). Logic then went to the realm of Philosophy, where it stayed for millenia until Charles Babbage and others brought it back in the brand spanking new field of Computer "Science."

    AND gates. OR gates. NOR gates. It all comes down to that, hmm?

    But Logic developed AFTER Geometry. Geometry is truly the world's third oldest profession (ask the Egyptians), after pimping and prostitution, of course. :-p

    The wonder of our age of course is that we're tying all these wonderful things together now. What a beautiful time to be alive.

    Go quantumthermodynamicalgravity!

  4. Hi Steven,

    I understand your point about geometry perhaps being at the heart of it all and yet through the exploration of it logic was actually defined as to challenged to be what perhaps not as represented as being how we thought that it was; as the Pythagoreans discovered about the nature of even the simplest of geometric form. So I’m in the mind as Decartes was first to make note, that geometry and logic are perhaps merely different aspect of what it is we are struggling to express as to then have defined, with that being reality itself.

    “The long chains of simple and easy reasonings by means of which geometers are accustomed to reach the conclusions of their most difficult demonstrations, had led me to imagine that all things, to the knowledge of which man is competent, are mutually connected in the same way, and that there is nothing so far removed from us as to be beyond our reach, or so hidden that we cannot discover it, provided only we abstain from accepting the false for the true, and always preserve in our thoughts the order necessary for the deduction of one truth from another.”

    René Descartes - Discourse on The Method: of Rightly Conducting The Reason, and Seeking Truth in the Sciences (1637)



  5. Hi Bee,

    what is the ADS/CFT correspondence and how is it related to String theory ?

    Best, Kay

  6. Hi Kay:

    I'd recommend you read either one of the links in this post... Best,


  7. Hi Stefan, Thanks for the link. I should point out all the articles in the Physics Today May edition are about the subject. My article with Peter leads off (and readers can learn a bit about how the computations work there - see e.g. my blog for more) but it is followed by two articles by Peter and Barbara Jacak, and by John Thomas, that go in depth on the experimental side of things. (We all presented at that AAAS event.)

    See: here, and links within and here for a description of the AAAS event.



  8. A pair of pseudotetrahedra fused base to base with concave faces, the three-armed spirallohedron, is exactly space-filling,

    Symmetry: Culture and Science 11[1-4] 293 (2000)

    Physical theory is obsessed with fundamental intrinsic (intensive) properties initially possessing the highest symmetries and existing independent of local or global aggregation. Physics determinedly ignores extrinsic (extensive) emergent-scale properties. Perturbation theory cannot predict emergence. String theory can be both rigorously derived and wrong.

    Chirality is an extrinsic, extensive, emergent property. Do opposite shoes vacuum free fall identically? Physics is a fool for not looking.


  9. The most important thing is to be motivated by your own intellectual curiosity.KIP THORNE

    I was visiting Clifford's blog posting article the night before you posted Stefan.:)

    This topic has always been of interest to me, as I can attest by my presence at Clifford's postings in this regard. All research material I have done over the years lead me to this topic.

    There is "a plate" in mind that Kip Thorne produced that exemplifies the question I have about the information we are getting by Fermi in context of all other data we are receiving.

    Just focusing on Fermi for a minute please consider the following...

    Physicists theorize that the omnipresent Higgs field slows some particles to below light speed, and thus imbues them with mass. Are We There Yet?

    If we are seeking computerized data, how is this taken from events not only in cosmological data, but in the LHC itself, as a discrete matter away from symmetry?

    The QGP has to be important in this respect as we surmise supernova explosions and the massless particles in context of gravitational waves, neutrons, and photons that we are receiving as descriptors of the event?

    The singularities, as QGP origins? Just, after the explosion. This is the closest to it's beginnings?

    Please for sure correction on questions.

  10. Hi Phil,

    I’m particularly intrigued by the one about the school kids packing tetrahedral dice into fish bowls and such to produce densities higher than current theoretical limits.

    Indeed - it's a bit of a pity that the high school kids didn't make it on the list of authors of the PRL - but it seems they are acknowledged in the paper. Anyway, this is a fascinating problem, as it is easy to state and understand, and of a certain practical relevance, as tetrahedral packing plays a role in the structure of glasses, for example.

    Hi Clifford,

    thanks for looking in! The "experimental" articles by John E. Thomas on the "The nearly perfect Fermi gas" and Barbara Jacak and Peter Steinberg on "Creating the perfect liquid in heavy-ion collisions" require subscription, though, so I didn't mention them. They are definitely worth a look, if you have access to Physics Today. BTW, the BNL web page of the symposium has links to the slides of the talks.

    Cheers, Stefan

  11. In more cordial days:)

    Wiping away some discussion comments is a common practise with some blog hosts "after the fact" to keep some clean lines.:)

    I am sure some remember Walter and Peter's final say on the topic of microscopic blackholes. Sorry if it's brought up again, but it was part of the idea behind the dissipation of cosmic particles in collision.Did they ever produce QGP, same? That's question.

    Does String Theory explain Heavy Ion Physics?

    Why the Quark Gluon Plasma is a Banana

    While Cerenkov was produced in faster then light medium, did this ever provide the opportunity for such examples like muons and Gran Sasso experiments while looking at Cosmo correlations?

  12. For some of your readers here is some info to help them along.

    Article From New York Times and More

  13. Hello Stefan,
    is that Prof. Paul M. Chaikin in theoretical
    What he did (or better let do by
    some innocent children) is a kind of
    experimental work, isn't it?
    Archimedes as a young man made some
    half-spheres, a cylinder and cones
    from wood with equal ground plane and height on a lathe and demonstrated
    to the Academy of Alexandria the
    relation of Volumes 1 : 2 : 3 of cone,
    half-sphere and cylinder with the aid of a balance.
    After that, the tale ends, Archimedes was
    kicked out of Academia for violating pure science by use of
    What will be the fate of
    Prof. Paul M. Chaikin?

  14. Hi Bee,

    thank you, I've red the article of "Physics Today". I didn't understand everything. However I understood the basics, I guess.

    Best, Kay

  15. Hello Georg,

    I think Paul Chaikin is an experimentalist, but with a strong connection to theory - or the other way round ;-). Anyway, he is one of the authors of "Principles of Condensed Matter Physics", a really great textbook on modern condensed matter physics.

    Cheers, Stefan

  16. Going from real space to momentum space

    Define "momentum space", please Stefan. I know what it is, but many of your readers who find you fascinating, don't. Thanks.

  17. Surely all the readers who find my husband so fascinating are able to use Google?

  18. Hi Kay,

    Excellent :-) There's many things I don't understand either, but if I can be helpful, let me know. Best,


  19. Hi Steven,

    Momentum space is but one of the many spaces in physics which provides a place that affords physicists some room for their thoughts to exist as to have certain aspects of nature considered.. Difficulty in their conception only arises when they or others take these spaces more seriously than has been demonstrated to be warranted by reality :-)



  20. Hi Bee,

    so a perfect fluid has a negligible shear viscosity and is its constituents are strongly coupled. When quarks and gluons are not in asymtotic freedom they are strongly coupled. Physicists assumed that when temperatures are high enough quarks and gluons are separated from themselves and form the quark gluon plasma (QGP). The QGP has a very low shear viscosity. Physicists say because of some effect called jet quenching and the low shear viscosity it is a strongly coupled system.

    What is jet quenching ?

    Best, Kay

  21. Hi Kay,

    A jet, usually a di-jet, are two showers of secondary particles that are produced from QCD scattering processes. The particles participating in the elementary scattering process can't be observed in the detector because of confinement. What happens is that they fragment into color-neutral hadrons, and these are then measured.

    Because of energy and momentum conservation, when you add up the total momentum of the outgoing particles of the shower in each direction they should be the same. In practice of course there are some losses and uncertainty. Also, one typically measures the transverse momentum, but that's not so relevant to understand the main feature.

    Now if a jet is produced close by some dense soup of particles (eg the quark gluon plasma) then generically one half of the jet goes through the medium and experiences in-medium loss of energy. If you now go and measure the energy (rspt transverse momentum) of both sides of the jet's showers, you'll find that it's no longer symmetric but one side seems suppressed. That's the so-called "jet quenching." It's an interesting observable because it carries information about the medium that the jet has passed through. Best,


  22. Hi Steven,

    Define "momentum space", please Stefan. ...

    While writing the post I was painfully aware that there are plenty of technical terms in all three items which I just had to presume to be known. (Though I did delete a quote from the abstract of the PRL on tetrahedron packing about the "translational and orientational correlation functions which decay as soon as particles do not touch" ;-).)

    But of course, everyone is invited, and welcome, to ask for further explanations when I was to sloppy, or to brief.

    Hi Kay,

    What is jet quenching ?

    as Sabine has explained, this means quite literally that a jet (or a "bundle") of particles is attenuated, because it loses energy and momentum when going through the hot and dense quark-gluon plasma.

    Cheers, Stefan

  23. Hi Stefan, hi Bee,

    thank you for explaining. Best, Kay

  24. Hi Stefan, hi Bee,

    do you know, what thermodynamic and transport properties of a strongly coupled QFT are related to properties of the black hole geometry ?

    I found this in the article by Klebanov and Maldecena.

    Best, Kay

  25. Hi Kay,

    these "thermodynamic and transport properties" (at least in the context of QCD and heavy ion collisions) mean properties such as shear and bulk viscosity, thermalization time, and drag force on quarks (which is related to the jet quenching, because it implies dissipation of energy and momentum).

    I do not know much more about these topics- maybe you will find these two papers helpful: "Heavy ion collisions and black hole dynamics" by Steven Gubser (PDF), and "From gauge-string duality to strong interactions: a Pedestrian's Guide" by Steven Gubser and Andreas Karch (arXiv:0901.0935v2).

    Cheers, Stefan


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