Thursday, September 12, 2013

Whatever happened to AdS/CFT and the Quark Gluon Plasma?

A decade ago, the AdS/CFT correspondence was celebrated as a possible description of the quark gluon plasma. RHIC measurements of heavy ion collisions at that time showed a surprisingly small viscosity that lead to a revision of the previous models. Excitingly, a small viscosity appears naturally in the gauge-theory dual of the AdS/CFT correspondence, nevermind that QCD is neither conformal nor supersymmetric. This development was all the more welcome as it served to demonstrate that string theory is not useless, as critics claimed, but that it can provide insights which improve our understanding of physical processes in the real world.

The gauge-gravity correspondence rapidly became a boom area in high energy physics. After the viscosity, people looked at other observables, notably the energy loss of particles going through the plasma. In highly energetic particle collisions, quarks are produced in pairs, but due to confinement individual quarks are never measured. What is measured instead are color-neutral hadrons that the quarks decay into and that are bundled into the direction of the original quarks. These bundles of hadrons are called jets and in the simplest case there are two of them with total momenta that are back-to-back correlated owing to their common origin from the quark pair.

In a heavy ion collision, one of the quarks may have to pass through the quark gluon plasma and thereby loses energy. This leads to what is known as ‘jet quenching’, a pair of back-to-back correlated jets where the total energy on one side is reduced. The energy loss in the plasma can and has been calculated in different models for heavy ion collisions. There are about a handful of such models, and in the days before the LHC all tried to get in their predictions for the jet quenching at LHC energies, the central question being how the energy loss scales with the increase in collision energy.

After the LHC heavy ion runs, it turned out the data do not agree very well with the scaling expected for energy loss from the AdS/CFT correspondence – in fact from all the models it was the worst prediction. As we discussed in an earlier post, AdS/CFT predicts too much energy loss, the plasma is too strongly coupled.

AdS/CFT confronts data. Image Credits: Thorsten Renk.
For details and references, please refer to this earlier post.

That the scaling doesn’t fit well with the data need not be too much of a worry because these scaling arguments were quite general and in reality the process of propagation through the quark gluon plasma isn’t quite as simple. But clearly the new data called on theoretical physicists working on AdS/CFT to study the observables and improve their model or to call it a failure and move on. Alas, nothing like that happened.

Since the LHC data came in, for two years or so, I’ve now been sitting through AdS/CFT talks that would inevitably be motivated by the low viscosity of the quark gluon plasma and the RHIC data, frog spawn picture and all. And every time I’d raise my hand at the end of the seminar and ask for the speaker’s opinion on the recent LHC data, expecting an update on the work on that matter and that there is no need to worry because the models can be improved to accommodate the data. Instead, it was like the LHC never happened. I don’t work in this field and don’t even follow the literature closely, but it seemed that I knew more about the problems with the LHC results than the people who got paid for talks motivated by yesterday’s data.

What they’d typically say is that nobody really expected AdS/CFT to make quantitative predictions. Alas, even the qualitative prediction, the mere slope of the curve, is wrong. The only prediction that is “qualitatively” correct is that there is some energy loss. Besides this, it’s all well and fine that a new model doesn’t make quantitative predictions, but that’s not a status that should become permanent.

It’s not that the data went entirely unnoticed. A few brave souls took on the issue. In this paper Ficnar, Norona and Gyulassy looked at the effects of higher derivative corrections to the gravity sector. It's somewhat ad-hoc, but apparently does reduce the energy loss. There is however no fit to the data and I’m not sure what this does to other observables. In another work, Ficnar also took into account a time-dependence of the configuration, but the conclusions with respect to the jet quenching and LHC data remain vague and amount to “a more thorough numerical analysis is needed.” In a recent paper, William Horowitz summarized the situation as follows:

“Despite significant efforts, AdS/CFT estimates for light quark and gluon energy loss are qualitative at best… it is difficult to imagine that a relatively sophisticated estimate of the suppression would be consistent with data.”

I was thus thrilled when I heard a talk by Stephen Gubser (about recent work with Ficnar) at a conference in Frankfurt this July, because he spoke about a possibility to improve the AdS/CFT model to accommodate the LHC data. Unfortunately, Gubser and collaborators don’t have a paper about this on the arXiv yet, so all I can do is refer you to the slides. My vague recollection is that he said one needs to take into account the momentum on the endpoints of the strings and that this does improve the scaling of the energy loss and fits considerably better with the LHC measurements. Though, if I recall correctly, getting the slope to match the data requires pushing the parameter into a range where one actually shouldn’t trust the model anymore. So in the end this might not solve the problem either.

If that explanation sounds like I don’t really understand the details it’s because I don’t really understand the details. I didn’t take notes, and two months later that’s as much as I can recall when looking at the slides and the Princeton professor has not been very communicative upon my inquiry. I thus just want to draw your attention to this development – if you’re interested in the topic, I recommend you have an eye on Ficnar and Gubser’s next arXiv uploads. For all I can tell, these guys are the only ones who take the issue seriously and so far it doesn’t sound too promising to me. If I’m missing some references, please let me know.

I don’t know enough about the topic to tell how likely it is that the AdS/CFT model can be improved to fit the data, and personally I find the applications to condensed matter systems better motivated. What annoys me about this situation is that people working in the field continue to decorate themselves with false achievements when they use the viscosity of the quark gluon plasma to justify the relevance of their own work and that of string theory by large.

It’s time the community comes clean and draws a conclusion. Either AdS/CFT cannot describe the quark gluon plasma, then please bury this episode in the history books and move on. Or it can, and then I expect to see a curve that fits on the LHC data. At the very least I want to hear it’s on the to-do list. Yes, the LHC really happened.


  1. Pity the poor layman that has no clue, about anything but especially that AdS/CFT means "anti-de Sitter/conformal field theory correspondence" and what it means, like Einstein talking to his grandmother. Yes I Googled it but I think great Science outreach writing explains this sort of thing without pointing out that the reader is ignorant even if he is ☺.

  2. I do pity the poor layman and recommend he or she reads this :)

  3. I am quite impressed with the topic and your evaluations over time with these concerns.

    We laymen can pity those who do the ground work who long for what so many say the arrival of say another Einstein which really does disservice to our minds other than perhaps to inspire someone to try to reach new heights.

    Now, in an earlier state of theory why do we think we can find the ends of such "strings" when in the proton three are involved and one presumably relativistic heeding asymptotic freedom? Where is the zero point of such a quark-gluon plasma?

    The anti-DeSitter idea in relation to gravity certainly may be part of the general picture.

    We use common notions like pressure, viscosity and so on to find the way to make communication of this esoteric physics more intelligible- but are they deep enough as metaphors? Are we still on a liquid drop model or something that ends at some minimum scale?

    I simply do not feel the idea of a trivial integral spacing of gluons is the fact and not part of a general picture reduced to this simple grounding from more complicated levels of vacua.

    Constants may change partly and even sync with statistics like any jets observed and measured- although within a reasonable depth of field or bandwidth. I mean why in inference patterns do we not count the zero in condensing geometry for entanglement of reduced superimposed bits?

    Oh, thanks for Modest Mouse - my kids make fun that I like such groups. The generations should be more adaptable if it can be a restrained taste of new memories and ideas.

  4. Been following subject correlation for a long time. Wanna burst my bubble go ahead.:)

    There are certain classes of researchers, regardless of how you might want to bury correspondence once and for all who will still retain AdS/CFT perspective when it comes to Black hole gazing. You are never going to be able to dispense with this.

    It would be like saying, all other researchers in theoretic of black hole should give up their thought experiments?:) Go ahead tell Lenny to give up Firewall considerations. Or Lee's description of a thing from the horizon, or, Bekenstein's good image descriptor.

    It is intuitively leading that research will continue because we truly want to understand what is dissipative in the microscopic sense might be helping to describe what is happening on a larger scale as we look at the cosmos over time.

    How about the exchange of information from one universe to the next? Does this not seem appealing in that information that never dies can some how be transported to instill motivation for the expression of the universe from one to the next. That black holes are all interconnected?

    Oops lost it for a second there;)



  5. Isn't adjusting the model to better fit the data sort of a Ptolemaic approach to doing science?

  6. Bee,

    It was in inevitable that correlation be found in high energy collisions with what started way back when. The LHC is a very larger confirmation tool. I would have taken the subject for granted given the quest to understand and find meaning to Higgs.


  7. Heavy Ion Collisions: A Few CMS Results

    Thanks goodness there are people still working to inform on this.

    "Even the famous helium-3, which can flow out of a container via capillary forces, does not count as a perfect fluid.What black holes teach about strongly coupled particles by Clifford V. Johnson and Peter Steinberg....May of Last Year."

  8. Hi Sabine,

    To tell you the truth I'm not following closely the ADS/QCD developments but overall there is a great confidence in ADS/CFT in general.

    It has passed so many non-trivial tests that for me not to be true is almost an impossibility (and I'm not even sure about the "almost":-))

    Maybe this overall justified confidence is affecting people's reaction to the specific issue too.

  9. "AdS/CFT correspondence...was the worst prediction." "served to demonstrate that string theory...can provide insights which improve our understanding of physical processes in the real world." It elegantly must be - and more so when it empirically isn't.

    A Euclidean cube's volume is (abc)sqrt[(1 - cos^2(alpha) - cos^2(beta) - cos^2(gamma) + 2cos(alpha)cos(beta)cos(gamma)] outside the trivial case. 2-D CFTs are chiral, Witt algebra invariant with respect to the full infinitesimal conformal group. Higher-dimensional CFTs demand extended supersymmetry. They fail. Theory fundamentally mirror-symmetric toward matter is empirically wrong outside the trivial case. Geometric Eötvös experiments oppose one substance as single crystal test masses in enantiomorphic space groups to confirm: alpha-quartz, berlinite, gamma-glycine, cinnabar, tellurium, benzil, etc. Do it.

  10. I'm sure that AdS/CFT is a piece of neat math, but for a physicist these are the most important things to know:

    1. AdS is unphysical. The cosmological constant is positive.

    2. CFT is unphysical. Massive particles exist.

    3. AdS/CFT really only works in the presence of supersymmetry, which is unphysical (ruled out by the LHC).

    PS. Was a Kungsträdgården on Sept. 7, but before the boots opened. Had to catch an early Waxholm boat to our summer house.

  11. A few comments, since this is a topic dear to my heart:

    1) The work Steve talked about at FIAS came out in June, 1306.6648 on the arxiv. They do promise a more detailed comparison to experiment in the future.

    2) We know that at sufficiently high energies perturbative QCD (pQCD) is the correct description for energy loss. That's guaranteed by the asymptotic freedom of QCD. So trying to apply holographic toy models at all energies is and has always been a pointless task and certainly not something anyone would have advertised doing. One interesting question is what is "sufficiently high". One not unreasonable interpretation of the LHC data is that the jet energies probed at the LHC, in fact, starts being sufficiently high in this sense. In that case, trying to apply holography to LHC data is pointless and counterproductive.

    3) This does not answer the question whether at lower jet energies there is a regime where energy loss behaves qualitatively different - strong coupling makes itself known. One thing holography has been used for is to understand how different energy loss in some strongly coupled systems can be - even the scaling exponents that tell us how energy loss depends on distance traveled can change from their pQCD values.

    4) Recent experimental evidence from RHIC gives strong indication that indeed such a regime of jet energies in which naive pQCD fails does exist. A nice review of the data you can find in a paper by Betz and Gyulassy from this May, 1305.6458. They clearly show that at RHIC energies one needs modified scaling exponents to match the jet data. Holography is not the only model that gives modified scaling exponents, they also compare "pQCD" inspired models with modified exponents that do just as good a job as holography - jet data in the RHIC energy regime can not tell them apart. But please note that neither of their pQCD inspired models is real pQCD either. There clearly is a window in which jet energy loss requires some modification of the theoretically well grounded pQCD framework.

    In summary, I think your conclusion that either AdS/CFT works or doesn't and if it works it got to address LHC data is oversimplified. We know N=4 SYM is not QCD. The question is whether there is a kinematical regime in which AdS/CFT does a better job in describing data than pQCD. The LHC data on jets gives us a good idea of where AdS/CFT certainly does not work. The task is not to massacre AdS/CFT to make it fit to data that is better described by pQCD. The question is whether AdS/CFT can tell us something interesting about the regime where pQCD may fail (and where that regime is).

  12. Two quick comments:

    1) Strongly coupled N=4 SUSY Yang Mills theory is in a plasma phase, and we can compute the viscosity of the plasma. However, the theory does not have jets (it is strongly coupled on all scales), and it is far from obvious how jet energy loss should be computed. The fact that comparison with data works better for fluid properties than for energy loss is not exactly surprising.

    2) The statement that the data rules out strongly coupled AdS/CFT-inspired models would be more convincing if the data agreed with weak coupling pQCD calculations. But that is not the case. The model that is closest to a straight pQCD calculation is labeled ASW and fails just as badly as AdS/CFT.


  13. Neil Turok sees the light.

    Better late than never.

  14. Yes, the LHC happened, but you have not explained why you think that it is more relevant than the RHIC data. As Prof. Karch says, the LHC is going into regions of the phase diagram where pQCD and lattice methods work rather well: we don't need AdS/CFT there. The more interesting experiment for AdS/CFT is the RHIC beam scan currently going on.

    I don't quite understand why you are so "annoyed" about this. There are a lot of people [not me] who get "annoyed" by many of the things said by people in your field. Is that OK by you?

  15. Remember, AdS/CFT is not supposed to be the ultimate fundamental description but (only) an effective theory that describes certain regimes. I tried to explain this in for the condensed matter applications (but the same holds true here) in my blog a while ago

  16. Andreas,

    Thanks for your comment. Yes, of course it's oversimplified. To paraphrase Bismark: fits in heavy ion physics are like sausages.

    What I'm saying is that I find it somewhat strange that before the LHC people working on AdS/CFT would go about and talk about the QGP viscosity and how great string theory is, and after the LHC... they're still doing that, even though it's unclear whether or not it's actually a good description of the physics.

    Yes, we want to know whether it captures an interesting piece of physics. Or so you'd think. But then why do I get the blank stare if I ask people who spend day-in day-out working on AdS/CFT what they think about the data. I can't shake off the feeling that the biggest part of this community has absolutely zero interest in making contact to the real world. That by itself wouldn't bother me, I have a lot of sympathy for pure mathematics and even philosophy. But I don't want them to pretend they're doing physics when in fact they don't even look at the physics.

    Regarding your 1st point. Yes he said in the talk there's a paper to follow, which will be interesting, thus the pointer in my post.

    I agree on the other points. I had looked at the Betz paper (or so I believe), but not read it very closely.



  17. Rastus,

    I'm not saying the LHC data is more relevant than the RHIC data. I'm saying there's now more data and thus the demands on what a model must successfully describe have risen. AdS/CFT did okay with the RHIC data is my understanding, or at least not worse than other models. But at least the simplest AdS/CFT model does not do very well if the LHC data is taken into account. Best,


  18. Hi Giotis,

    It's one thing to believe in the truth of a mathematical relation, and I share your impression on this. It's another thing to pretend that you're working on a model that describes some physics in the real world and not even care about the evidence. If somebody calls themselves a physicist, I expect that they pay attention to the data.

    Really, it isn't hard to tell why I'm pissed off. Because hep-ph seems to be run over by people who do AdS/CFT and claim it's physics while at the same time they give a shit about the physics. And these are the people who end up being hired for their great achievements. This just makes me want to quit and turn into one of these cynic blog commenters who constantly complain that the end is nigh. Getting there, getting there :p Best,


  19. I think you're right to feel dissatisfied Sabine. IMHO if you were to look into the Percy Hammond stuff and GR inhomogeneous vacuum you'd end up feeling even more dissatisfied.

  20. So I am stuck in 2010

    So you keep theoretic in one pocket and experimental procedures in another and see where the two shall meet.

    PI director Neil Turok’s welcome speech Make up your own mind.

  21. The AdS/CFT correspondence is alive and well. We can see its evidence on the sky at many places, for example in similarity of geometry of Higgs field and CMBR field. Of course this symmetry is broken heavily, because it's low dimensional correspondence, so it can be observed at the low-dimensional portions of our Universe.

  22. In my opinion the AdS/CFT correspondence works better for lower energies (these achieved ad RHIC), until the system will not become so hyperdimensional. At the higher energy density of collision the nested condensation will occur and the AdS/CFT correspondence will get broken. It will not disappear completely but it will less significant in data.

    We even discussed this problem before year here and Bee opposed me...;-)

  23. Is there some sort of universality argument why AdS/CFT might get the viscosity right, but not other parameters, analogous to how critical exponents can be calculated using any model in the same class, but not other quantities such as the critical temperature?

  24. /*..but it seemed that I knew more about the problems with the LHC results than the people who got paid for talks motivated by yesterday’s data...*/

    ..;-) I've the very same feeling about many specialized deductions of yours here. This is general attitude of all outsiders: they can see the stuffs of experts from more distant - still shallower and subtler - but more general perspective. They can simply see the forest through the woods.

    Because we are living inside of galaxy, we can perceive only the movement of the nearby stars - all the rest appears too random and chaotic for us.

    But from sufficient distance the coherent internal motion inside of galaxy becomes suddenly quite apparent. In brief, sometimes it's simply better to remain half-educated layman, unloaded with professional blindness.

  25. /* there some sort of universality argument why AdS/CFT might get the viscosity right, but not other parameters */

    IMO it is. As I told already, the reason of AdS/CFT breaking during too energetic LHC collisions is, that the QG plasma forms the nested density fluctuations, which do propagate as a rigid bodies inside of it. The actual macroscopic flow of plasma is limited to the surface "laminar" zone of these fluctuations, where the AdS/CFT duality still applies in most pronounced way (just see my animation above). The interior of these fluctuations is already highly viscous, but this interior doesn't contribute to the "macroscopic" flow of the plasma as a whole.

    So - at the end the behavior of extreme forms of matter remains quite analogous to behavior of particle systems at the human scale, which is sorta great - we are still in our familiarly known Universe.

  26. Zephir, I don't even have to "oppose" you because your nonsensical babble has made yourself your own worst enemy.

  27. Andrew,

    Not that I know of. I would be surprised if one could make such an argument here because there are many aspect to heavy ion collisions and only one of them is the AdS/CFT input on energy loss. Best,


  28. Robert,

    Models are adjusted all the time to better fit the data. You have a confusion here about what is the purpose of model building. You're trying to describe observations to extract the underlying physical concepts. If new observations don't fit the model, you go and revise it. Nothing wrong with that. What you should not do is to take 'revision' to mean you're adding arbitrarily many unmotivated parameters, because then you can fit anything and everything. This isn't a theory of everything people are working on here. It's heavy ion physics. There are many aspects that play a role to describe the data and if you didn't get it right the first time you go back and ask if you've forgotten something. Best,


  29. Bee, thanks for the response. I was thinking about statements I've read that the shear viscosity to entropy density ratio is universal in a class of theories, whereas other transport coefficients aren't (eg. DeWolfe et al arXiv:1304.7794 say something like this around their Eq 136-137). Are you saying that if other predictions fail, then it isn't justified to use AdS/CFT to understand the shear viscosity to entropy density ratio?

  30. Why you are calling it a Mathematical relation? AdS/CFT is quite physical; it’s a duality between two physical theories, a UV complete theory of QG (i.e. String theory) in the bulk and a conformal field theory on the boundary.

    In my view AdS/CFT is the stringy realization of a fundamental property of Nature i.e. the Holographic principle, and has given us in a remarkable way, valuable insights for the theory of QG (holographic principle is now widely admitted as a benchmark for any candidate theory of QG). Now using it to do heavy ion physics calculations is like using a shotgun to kill ants, it can only provide qualitatively results, meaning we can only demonstrate that a shotgun indeed can kill ants but it’s not very effective for this low value task if I dare to say :-).

    Besides that AdS/CFT is a weak/strong coupling duality and thus it can be used to perform calculations for the strongly coupled field theory on the boundary only in the coupling regime where the Supergravity in the bulk is completely reliable for such task. Moreover in order to have a field theory on the boundary which only resembles a QCD like theory we must first break conformal invariance and all the SUSY and we still don’t get a real quarkless QCD. So it’s quite a delicate procedure and not surprisingly they don’t get everything quantitative right.

    Having said that I must admit that if indeed some people have as a goal of their life to use AdS physics to study the glueballs in a quantitative way, then indeed they must incorporate in their study the latest data.

    For my taste the qualitative agreement of AdS/QCD is just fine (even if it demonstrated only confinement and a mass gap) since it serves as another indication that AdS/CFT is right.

  31. Giotis, I think you are just blind to Bee's argument here, i.e., that Ads/CFT estimates have begun to veer from the experimental results from the LHC. As Jack Nicholson would say "Son, you can't handle the truth."

    Couldn't resist. Also I read a good book recently, The Righteous Mind. It's about the ability to discern the truth and how it gets all mixed up with morals. It turns out that ones affinity group and its values controls more about how you evaluate data than the data itself. You should think about that.

    Also - a remarkable fact... High intelligence does not predispose one to seeing the facts more clearly than having an average intelligence. What it does instead is allow one to come up with more arguments in favor of your affinity group's position on the issue than someone with average intelligence. In fact, it is often better to just be bright rather than extremely bright.

    A poignant example: I'm sure Lubos' IQ is higher than 125. Yet Feynman's IQ was only 125. I would be any amount of money on which one produced more permanent and established results in physics and which one just all his energy going on diatribes against his enemies. Self deception is a powerful force, and all the more so in the extremely intelligent.


  32. Bee,

    You say: "What you should not do is to take 'revision' to mean you're adding arbitrarily many unmotivated parameters, because then you can fit anything and everything."

    But if we are candid and unbiased, then we have to admit that a boat-load of ad hoc "fixes" have been added to many of the models that have dominated physics for the last 4 decades.

    Model-building is needed for provisional working models when we are theoretically or empirically stuck. Such models are not to be confused with Theories Of Principle. Nor are they to be treated as anything more than provisional.

    If we keep adding bells and whistles to failing models, then we end up with increasingly bad-smelling garbage. Calling it an acquired taste that can only be appreciated by aficionados is becoming less hype-able. It stinks! And more people are beginning to speak out about it.

    We can do better. We can demand definitively testable Theories Of Principle.

  33. /* AdS/CFT is quite physical; it’s a duality between two physical theories, a UV complete theory of QG (i.e. String theory) in the bulk and a conformal field theory on the boundary */

    But are these theories physical? So far the string theory has been refused with all experiments and I'm not even talking about "conformal field theory on the boundary". Such a theory is just a pure math in this moment.

  34. "AdS/CFT is quite physical; it’s a duality between two physical theories, a UV complete theory of QG (i.e. String theory) in the bulk and a conformal field theory on the boundary. "

    This is a mathematical, not physical truth; and it is not a rigorous mathematical truth either (I.e., closer to the Babylonian than the Greek understanding of Pythagoras' theorem).

  35. List #1: Gnomes, yousie, elves, veelas, faeries, imps, sprites, unicorns, leprechauns, wights, halflings, merlions, trolls, kelpies, silkies, pixies, gremlins, nymphs, dwarves, kobolds, banshees, paladins, genies, boggarts, timte, goblins, valkyries, dragons, oberons, golems, wraiths, wendigos, buraqs, nagas, undines, cecaelia...

    (Tip o' the hat to Robert Oldershaw)

    List #2: dark matter, string/M-theory, quantum gravitation, solar axions, SUSY, extended SUSY, SUGRA, proton decay, MSSM, string/brane exotica, sparticles, leptoquarks, lazy photons, WIMPs, supersymmetry exotica, extra-dimensions, magnetic monopoles, mini-black holes, Randall-Sundrum 5-D phenomena (gravitons, K-K gluons, etc.), evidence for ADS/CFT duality, colorons, fractionally charged particles...

    Reality is what remains after faith fails.

  36. /* dark matter, string/M-theory, quantum gravitation, solar axions, SUSY, extended SUSY, SUGRA, proton decay, MSSM, string/brane exotica, sparticles, leptoquarks, lazy photons, WIMPs, supersymmetry exotica, extra-dimensions, magnetic monopoles, mini-black holes, Randall-Sundrum 5-D phenomena (gravitons, K-K gluons, etc.), evidence for ADS/CFT duality, colorons, fractionally charged particles..*/

    You forget the scalar field, quintessence, mirror matter, axions, dilatons, inflatons, heavy and dark photons, dark atoms, fat strings and gravitons, anapoles, sterile neutrinos, chameleon particles, dark fluid and dark baryons, fotinos, gluinos, gauginos, gravitinos and WIMPs, SIMPs, MACHOs, RAMBOs, DAEMONs...

  37. Ist das ist nicht nur nicht richtig?
    Ja das ist nicht nur nicht richtig!
    Ist das nicht Herr Jürgen Würgen?
    Ja das ist Herr Jürgen Würgen!

    Nur nicht richtig, Jürgen Würgen.
    Oh du schone, oh du schone, oh du schone Schnitzelbank!

    Ist das ist nicht einmal falsch?
    Ja das ist nicht einmal falsch!
    Ist das nicht ein Dunkelbumser?
    Ja das ist ein Dunkelbumser!

    Nicht einmal falsch, Dunkelbumser.
    Oh du schone, oh du schone, oh du schone Schnitzelbank!

    (Bee - delete if this offends delicate sensibilities)

  38. Der denkende Mensch hat die wunderliche Eigenschaft, dass er an die Stelle, wo das unaufgelöste Problem liegt, gern ein Phantasiebild hinfabelt, das er nicht loswerden kann.
    - Johann Wolfgang von Goethe -

  39. It is important that our views are pointed in the right direction. Theoretically this implies "direction" in your model, yes?

    So understanding matter creation in the early universe is an important property of any theoretical observation created to help see how that universe came into being.

    Pointing to microscopic examinations help to reveal decay chains that are being detect against the backdrop of other experimental measures. Are Calibrated by cosmic particles currently bombarding earth.

    Properties that will help extend our views with regard to present examinations already verified in the experimental models currently used?

    With this track record there is no amount of displeasure for which consideration of reality forming is as a loose structure for the desire of further examinations.

    Condense matter theory is already developing along with reductionism, to help align existing views. These theoretical processes were nurtured along side of those theoretical views.

    Examination of a bulk space from the horizon with conformal field theory and to suggest that such examination is not necessary from the boundary is how shall I say throwing the baby out with the bath water?:)

    Business as usual.:)

  40. Hi Bee,

    Thanks for the update on all this. So as you point out all is not going so well for AdS/CFT in relation to having quark soup understood and thus a new recipe may be needed. There’s an old adage that too many cooks spoil the broth, yet in this case it seems there to be a scarcity of them. Also liked the theme music you picked for this post and yet would have to admit when I was reading through it had another tune ringing in my head :-)

    Beat Regards,


  41. Giotis,

    To me it's 'physical' if it's a description of a real world system. Now we can debate to which accuracy this has to work to be called physical, I'm not saying it's a sharp boundary, but at least presently the AdS/CFT description for the qgp doesn't quite cut it. You just seem to mean something else with 'physical.' Best,


  42. Robert,

    "If we keep adding bells and whistles to failing models, then we end up with increasingly bad-smelling garbage."

    Again, I think you're entirely misjudging the subject matter here. Heavy ion physics is not g-2. There's lots of factors going in that are presently not very well understood for not to even mention the unknown unknowns. It is very hard to tell whether and why a model is failing.

    Forget about AdS/CFT for a moment because I think you have some issue with that. Take solar physics. People have tried to explain the solar cycle since decades with various means, both analytical and numerical. They get some things right, yet other things don't quite work (eg, the 22-year cycle seems to be very hard to get right), and every time there's a new measurment method and every time there's new data and every time there's a new sunspot peak they know a little more and update their models and the ones who were close to the data are cheerful and the other ones work hard. There's nothing wrong with that. Of course you hope that at some point they have all the observations needed to come up with a model that's good for all future predictions and discard the rest or find out that they're equivalent. But it's very hard, if possible at all, to tell just when that will be the case. Best,


  43. The difference Sabine, is that de Sitter space is "a cosmological model for the physical universe" but anti-de Sitter space remains hypothetical. And in physics we have h, and electrons that come in one size only, so quantum field theory is not scale invariant. So conformal field theory is going to remain hypothetical too. And AdS/CFT correspondence is "a conjectured relationship between two kinds of physical theories". Both of which are hypothetical. Then we're into the holographic principle, about which I will not comment. It's not much like solar physics.

  44. John,

    The qgp doesn't care at all if the measured value of the cc is positive. Look, it's a model and you can use it to describe a physical system, in this case a heavy-ion collision, and the question is how well it works. Now you might question that it's a well-motivated model, which is what you seem to be saying, but that's another question. Best,


  45. Qgp might not care Sabine, but I do, as does Thomas Larsson and other. I've just re-read your blog and the comments, and it's kind of like I agree with you and then some. Especially since the AdS/CFT predicted result was so close to the straight pQCD prediction. That reminds me of "guess the weight" where you go one gram under the other guy. And then you retrofit your unfounded theory to match the actual result? Hmmmn.

    By the way, I thought this old physicsworld article was interesting. See this bit: "Any such particles travelling through this plasma are halted in a short distance and become part of the soup. This quenches the characteristic signal used to detect their emission, effectively causing them to go 'missing'". See how the word soup is used? Have you ever had pea soup? And have you noticed that there ain't no peas in it? Oh and see this: "Unlike photons, which are more or less oblivious to one other, gluons interact with each other as well as with quarks – a process known as gluon self-interaction". That's wrong!

  46. John,

    Sorry you lost me on the peas. I think you didn't understand my reply, maybe re-read it, we do not live in the AdS-space of AdS/CFT that is used to describe the gqp. Also, the sentence that you believe to be wrong just says that qcd, unlike qed, is non-abelian. We've now had a few exchanges on this blog and frankly it seems to me that your physics background is not the best. Unfortunately, you blame this lack of understanding on the physics instead of looking for helpful information. Best,


  47. Then perhaps you could provide some helpful information on this Sabine. I've tried to find an answer elsewhere but have been unable to do so.

    The Wikipedia two-photon physics article concerns gamma-gamma pair production, and it says this: "A photon can, within the bounds of the uncertainty principle, fluctuate into a charged fermion-antifermion pair, to either of which the other photon can couple". That seems to be saying pair production occurs because pair production occurs. And that a 511keV photon spends its time constantly morphing into a 511keV electron and a 511keV positron, which then magically morph back into a SINGLE 511keV photon, which nevertheless manages to keep on going at c.

    That doesn't sound right on a number of counts. Perhaps I've misunderstood something there. If you could explain what, I'd be most grateful. But it is a little tangential to qgp, this is no longer your latest entry, and I wouldn't want to take up too much of your time. Perhaps you might address this in a future blog entry sometime?

  48. Thanks @Andreas Karch for this very enlightening comment that shows what is going on and why it is not reasonable to make the AdS/CFT description fit the data in domains where it has never been assumed to be relevant.

    That nicely answers the question brought up in this article why people are not trying to do this.

  49. John,

    Please read our comment rules. I'm not an ask-the-expert forum, I don't have time for this. Please use a crowd-sourced website like the physics stack exchange or physics forums for that. About the Wikipedia quote. First, while Wikipedia can supplement a textbook, it cannot replace one. Second, I'm guessing it's a verbal description of a fermion-loop correction to the photon propagator. You should not take this verbal description literally and over-interpret it. It's just that: words that very insufficiently replace a mathematical expression. On that level, it seems accurate to me however. In any case, as I said, please take these questions elsewhere, my time is limited. Best,



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