HEPAP is meeting in Washington today, presentations available here. The idea of this regular meeting is for the US HEP community and the funding agencies to meet and plan for the future, something that’s not easily done in an environment where these agencies have no budget at all for the current year, just an authorization to spend money at last year’s rate that expires in a couple weeks from now. No one seems to be sure what funding prospects are for the next few months, much less the next few years. Fermilab is dealing with this situation by offering 600 of its staff incentives to quit or retire next month (see here). There’s a new DOE Committee of Visitors report out here, it contains the bizarrely familiar recommendation of all such reports: the US needs to fund more HEP theory students (they don’t explain why, or where the money should come from).
In dark matter news, Princeton this week hosted a workshop on the subject, talks available here. Still no results from the latest Xenon100 run. This week’s Nature has a nice review of the various searches for WIMP dark matter, with conclusion:
With the advent of the Large Hadron Collider at CERN, and a new generation of astroparticle experiments, the moment of truth has come for WIMPs: either we will discover them in the next five to ten years, or we will witness their inevitable decline.
(Update: a commenter points out that this article is also available on the arXiv here.)
One new astroparticle experiment that is supposed to look for evidence of dark matter is Sam Ting’s Alpha Magnetic Spectrometer, set to be launched in February, and described in a front-page New York Times article yesterday.
Ten days after first collisions, Alice already has two papers out (here and here) with experimental results on lead-lead collisions at an energy more than an order of magnitude higher than ever before. String theorists are very enthusiastic about this (see here and here), claiming that what is being observed is “properties of a type that can be nicely captured using string theory models”. I’d be quite curious to see any AdS/CFT based predictions that could be compared to these new results (or to forthcoming ones).
For the latest from the LHC, see here. Current plan is to have a proton-proton beam back around February 21, followed by at least 2 weeks of beam recommissioning. The proton run would end in November, followed by another ion run. First estimates for 2011 are that the run will be at 4 TeV/beam, and a “reasonable” estimate of total luminosity would be 2.2 inverse femtobarns, double the initial goal. Even more optimistically, the possible “ultimate reach” for next year would be a luminosity that would give a total of 7.2 inverse femtobarns if sustained over the hoped for 200 days of running. This kind of higher luminosity would allow the LHC to see evidence of a Higgs over the entire expected range, as well as allowing it to finally overtake the Tevatron in the Higgs race. The experiments so far are reporting results that match exactly the Standard Model, more announcements to come at the Winter Conferences early next year.
There’s an interesting trend of our LA-based theorist-blogger-media-stars starting to resist making dubious media appearances. A few months ago Sean Carroll described storming off the set of a TV pilot here. Now Clifford Johnson (whose media mishaps include appearing as a scientific expert on the question of how big women’s breasts need to be to crush beer cans, see here) tells us that Sometimes I Say No.
Regarding the heavy ion predictions: While the “low viscosity” discussion has generated a lot of publicity, it is somewhat unsuitable for quantitative comparisons: The number of free parameters and uncertainities is such that determining the viscosity to much better than an 100% error will be very difficult. Equally, determining stringy corrections to the “infinitely strongly coupled” value is somewhat controversial, especially in view that we do not,trivially live in a CFT world.
Thus, “AdS/CFT viscosity over entropy density=1/4pi” is a great publicity gimmick, but not really an experimentally verifiable prediction.
The best hope we have for the latter is the interactions heavy quark physics. Here, there will be very high quality data at the LHC, AND the strongly coupled theory might allow something of a systematic expansion whose results are _qualitatively_ different from the perturbation theory.
As a matter of fact, some of the “pioneers” on this live a few hundred meters from you:
http://arxiv.org/abs/0706.2336
http://arxiv.org/abs/0907.3062
http://arxiv.org/abs/1009.2286
Thus, “AdS/CFT viscosity over entropy density=1/4pi” is a great publicity gimmick, but not really an experimentally verifiable prediction.
Hasn’t it been verified already at RHIC, with an error of around 1/N^2=10%?
Not really,although there have been excellent tries (the latest effort is
http://arxiv.org/abs/1011.2783 ).
Baiscally, initial conditions in the transverse plane (currently controversial and well studied) give you an 100% or so error
(viscosity is really ~1/4pi for “Glauber” initial conditions but more like 2-3/4pi for “Color Glass condensate” ones).
That leaves controversial initial conditions which have NOT been studied:
How much flow forms BEFORE hydrodynamic expansion? How good is the longitudinal ansatz examined by the hydrodynamic calculations? What about corrections to Navier-Stokes?
These, together, could easily add another 100%.
Also, some observables do not fit the hydrodynamic theory at all (google “HBT puzzle”), which leaves some doubt that theorists have radically misunderstood the data. Its not impossible.
“… Clifford Johnson (whose media mishaps include appearing as a scientific expert on the question of how big women’s breasts need to be to crush beer cans, see here) …”
I believe this is a bona fide piece of research. Crushing cans flat makes recycling more efficient, because you can then fit more empty cans into recycle bins, which don’t then need to be emptied so often, thus reducing the carbon-footprint of the can recycling enterprize. It’s also good entertainment, after a few beers.
For those of us without a subscription to Nature, the article on dark matter is available at http://arxiv.org/abs/1011.3532
Peter,
On Dec 9, 2009, I sent a message to your blog regarding the
Hydrino Study Group, a forum which has since been discontinued. My
comments included the following:
“One of the regular posters to the HSG Forum, an
electrical engineer named John Barchak, frequently cites your blog as
evidence that quantum mechanics is hopelessly wrong.”
I would like to post a retraction of that statement. Mr. Barchak has
often quoted your blog on the HSG, and I think it is fair to say he is not
a fan of quantum theory, but in fact his quotations from your blog are
generally in support of his views regarding the Standard Model and String
Theory and the Higgs boson, and not directly in support of his views
regarding QM itself.
Thanks,
J.E. Connett
Thanks John. I’ve added that link to the posting.
Hi,
I would like to know your take on this article purposing a real life application of string theory:
http://www.scientificamerican.com/article.cfm?id=string-theory-tackles-strange-
Estrella,
I’m not a condensed matter theorist, so I really have no idea how significant this is. It doesn’t have anything to do with using string theory to get quantum gravity and unification. It’s plausible that AdS/CFT might lead to new approximate models that would have condensed matter applications. But, given the history of hype surrounding string theory, I’d like to hear about this from an expert.
Thanks for your opinion, Peter. 🙂
I am not an expert on the subjet either. I am just a Physics PhD student (on the Complex Systems area), so I am not an expert on String theory or Gravity either.
I just was curious about the subject.
BTW, I live in Montevideo, and I know people who works in an alternative to string theory unification, quantum loop gravity.
Do you have an opinion in this theory?
Estrella,
Search the blog for “loop quantum gravity” and “LQG”. Some of the posts (and comments) you find will include links to critical papers on the subject, as well as discussion of LQG and occasional cautious comments by Peter. For background you should look up some review articles, such as those at LivingReviews.org.
Estrella, since you live in Montevideo and know some LQG people, you have undoubtably heard of Rodolfo Gambini: a major figure in the field. His research group has come out with a number of interesting and creative papers over the past 10 years. Montevideo is the top LQG place in South America, and one of a handful of top places worldwide.
Another person at Montevideo who has contributed notably to the development of LQG is Michael P. Reisenberger. He collaborated with Carlo Rovelli around 1996-1998 on the first *spin foam* papers, an approach to LQG which has become increasingly important in recent years.
Thanks for the links Chris.
Yes, Marcus, I know Rodolfo Gambini and Michael Reisemberger. And I heard of their ideas on some talks they gave. Just curious what other people not related to them thought on their theories.
Moreover, as I said before, I am not an expert on that area, so I am just curious to hear all the bells.
By “Hear all the bells” I meant hear all the opinions, pro and con.
BTW, I am not an expert on Gambini or Reisemberger ideas either. I just asisted to some talks, but I don’t work with them or in their area.
Estrella,
*By “Hear all the bells” I meant hear all the opinions, pro and con.*
I understand and I think you are asking a good question, but Peter’s usual policy is to discourage us from discussing non-string quantum gravity here, because he doesn’t feel that he knows enough about Loop-and-allied approaches to be a good moderator.
Personally I would say that Loop (and related spinfoam) quantum gravity and cosmology have changed radically since 2006 and have made remarkable advances. To where phenomenologists begin to study how test (and even possibly to falsify). Relative to the size of the field a few years ago, there are a lot of young researchers, new energy, and even more job openings than before. So it is an exciting time.
One way to hear various opinions is to go to Physicsforums, this part of it: http://physicsforums.com/forumdisplay.php?f=66
and ask questions. Then people will sometimes point you to discussions that have already occurred—and sometimes, instead of that, when you ask a question they will begin immediately to argue among themselves.
Yes, please, enough about LQG right now. I have to keep reminding people this is not a general discussion board, I don’t want to manage such a thing.
I think there’s a lot interesting about LQG, but lack motivation to spend much time on quantum gravity theories that don’t unify with the rest of physics and tell us where the standard model comes from. I’m willing to believe that everyone who has a quantum gravity for sale may be right, which means that there are at least 10^500 of them….
Thanks for all the answers. 🙂
Estrella, here are 281 LQG papers from the two years 2009 and 2010 assembled by a Spires database search.
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+K+SPIN%2CFOAM+OR+DK+FIELD+THEORY%2C+GROUP+OR+DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3E+2008&FORMAT=www&SEQUENCE=
You can change the parameters as you wish–get the papers sorted by citations or in other ways, change the keywords, the timeframe. I have included spinfoam, group field theory, and loop quantum cosmology, which is the sector closest to being testable (by CMB observation).
@Peter Woit: You’ve called for hep-th community to diversify, and they did, but it seems that you’re not impressed by any of the following: susy, string theory, LQG, Horava’s theory, Verlinde’s theory, Lisi’s theory… So what exactly is the “diversity” that you long for? You’re only impressed with stuff along the line of “elucidating the mathematical structure of non-supersymmetric QFT”. If everyone is doing this, I’m sure the community will be truly diverse!
Anonymous,
Susy and string theory are still by far the dominant research areas in the subject. LQG and Horava’s theory also get attention, which is great. Verlinde’s theory doesn’t seem to me to be a theory at all, but maybe I’m missing something. Lisi’s theory is being worked on by, well, Lisi. That’s still not a whole lot of diversity.
You’re right that if everyone was working on better understanding non-perturbative QFT using new mathematical methods, that would not be diverse. I think we’re a long way however from having to worry about that particular danger right now….
@Peter Woit
If you ever comment on Penrose Conformal cyclic cosmology, could you put the links again? There’s a 6σ claim going on:
http://fr.arxiv.org/ftp/arxiv/papers/1011/1011.3706.pdf
Loco,
My only comment about that claim is that I’m not a cosmologist and have no way to evaluate it. If someone else can point to somewhere an expert in the subject has commented on this, that would be interesting.
Responding to
”Thus, “AdS/CFT viscosity over entropy density=1/4pi” is a great publicity gimmick, but not really an experimentally verifiable prediction.”
Perhaps I can offer some perspective (I work in this field). I would not say that
1/4pi is a publicity gimmick. The importance of the AdS/CFT
result is that there exsist field theories (in any theory!)
where is \eta/s is as low as 1/4\pi. Before this calculation
in the AdS/CFT it seemed extreme to imagine that QCD
would have \eta/s less than 1.
The other important point is that the gradient expansion
which underlies the hydrodynamic results at RHIC would
not converge (for typical initial) conditions for \eta/s > 0.4.
For say $\eta/s$ less than $0.3$ the gradient expansion
does clearly converge, i.e. ideal hydrodynamics provides
the baseline result, the navier stokes theory provides a correction,
and the second order corrections are small.
Thinking about hydrodynamics in AdS/CFT led to a precise
formulation of second order corrections in hydrodynamics.
To date I found only one comment which seems interesting.
http://www.physicsforums.com/showthread.php?p=3003554
And back to your original blog posting, re “an interesting trend of our LA-based theorist-blogger-media-stars starting to resist making dubious media appearances,” check out the latest Abstruse Goose:
http://abstrusegoose.com/321
Casey
Derek… I do not disagree that 1/4pi is a very important result from a theoretical point of view which spurred quite a lot of interesting work.
It is however wrong to claim that “Before this calculation
in the AdS/CFT it seemed extreme to imagine that QCD
would have \eta/s less than 1”. A “lower limit” on viscosity in a quantum field theory was argued for in the ’80s, in the context of heavy ion collisions, from back-of-the-envelope arguments stemming from the uncertainty principle, see
Phys.Rev.D31:53-62,1985
(the limit is surprisingly similar to 1/4pi!).
So its not quite correct that the AdS/CFT result is the first result suggesting that a quantum field theory can exhibit hydrodynamical behavior at microscopic scales.
In any case, by “publicity gimmick” I mean that, while there have been a lot of popular science implying that string theory calculations can be quantitatively tested in heavy ion collisions, this has simply not been the case: The phenomenological uncertainity in hydrodynamic simulations, and the lack of knowledge of how to relate infinitely strongly coupled N=4 Nc=infinity SYM to not-quite-infinite-coupled N=0 Nc=3 QCD prevents any kind of real comparison at present.
I am not saying this comparison is impossible in the future, but at the moment it can not be done.
It of course does not mean this work is a waste of time! The Sine-Gordon model was also very important for field theory which led to important theoretical developments of QCD, but it would be a “publicity gimmick” to say it can be used as a quantitative test for anything.
Luny,
The calculation you refer to was a extrapolation of weak
coupling results where $eta/s >> 1$ deap to a regime where it is not valid.
So it was terribly unclear wether such field theories actually
exsist. The only thing which was clear from such extrapolations
was that when $eta/s \sim 1$ something must happen.
The 1/4\pi showed that there exsist field theories (where you
can calculate at strong coupling) . This result gave a kind of
reason to suggest that hydrodyamics (as opposed to alternatives which don’t seem to hang together anyway)
was actually responsible for the observed elliptic flow
You write,
” In any case, by “publicity gimmick” I mean that, while there have been a lot of popular science implying that string theory calculations can be quantitatively tested in heavy ion collisions, this has simply not been the case ”
This is true. Last comment, the heavy quark results you quote above
are really no better in this regard