Friday, December 21, 2012 ... Deutsch/Español/Related posts from blogosphere

Subir Sachdev on AdS/CMT

Yes, it's the date of another major failed end of the world ;-)

My ex-colleague and fellow superhero, condensed matter physicist Subir Sachdev wrote a neat article for a mostly bad magazine called Scientific American,

Strange and Stringy
It does a good job in explaining one skill of string theory from a viewpoint of someone who was definitely not trained as a string theorist. In condensed matter physics, there are various phases of matter displaying numerous kinds of behavior (and critical behavior) and things can get very complicated. However, under somewhat general circumstances, when the complexity becomes really extreme, there is another, alternative description of the situation that becomes easy, at least once you know its formalism.

So like any proper solid state physicist, Sachdev doesn't care about the right theories at the Planck scale – or any other scale that is more fundamental than the characteristic scale of the phenomena in the common materials, for that matter. But even in this seemingly mundane realm that looks as non-fundamental as Radiohead, one may apply relationships that were found by physicists who analyzed a consistent description of quantum gravitational phenomena – who studied string theory in its familiar regime.

Sachdev makes some provoking points – e.g. that he had to explain basics of condensed matter physics to some string theorists using the same caricatures as he's using, approximately speaking, for the kids in the kindergarten. ;-)

I have some doubts whether the dual AdS-like description of condensed matter physics and related problems may ever be considered an "ultimate reliable description". But string theory surely gives us a new perspectives from which one may look at various physical situations and Subir Sachdev is among those who are exploiting these new opportunities very often.

Incidentally, "Large extra dimensions not dead yet" at a Western European physics blog reviews some at least superficially clever attempts by Cliff Burgess and others to solve the cosmological constant problem within the large extra dimensions scenario. A cosmic string – or, more generally, a co-dimension-2 brane – induces a deficit angle in the surrounding spacetime but leaves the cosmic string essentially undisturbed. Such co-dimension-2 branes on a sphere may conspire to produce a rugby ball geometry which adjusts itself so that the effective 4D curvature seems to be (nearly?) zero.

Off-topic: For her 60th anniversary of reign, Queen Elizabeth received a chunk of Antarctica and a new rendition of the royal anthem (the video above).

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reader Peter F. said...

Re: "I have some doubts whether the dual AdS-like description of condensed matter physics and related problems may ever be considered an "ultimate reliable description"."

I really wish our favorite humble correspondent never become wholly humble - maybe you have just mellowed a little because it is so close to Xmas! Anyhow, I hope you Lubos have a good one!

IMO is better than a merry one.

P.S.I have spoken to my almost country-man Tomten and told him you have been good, yet again! ;-)

reader Dilaton said...

... exactly that quote gave me quite a pause too...

I mean did Lumo really say that the AdS/something or just the AdS/condensed matter business is probably no good ... ?

reader Luboš Motl said...

Dear Dilaton, I surely didn't say anything of the sort. What I said was

I have some doubts whether the dual AdS-like description of condensed matter physics and related problems may ever be considered an "ultimate reliable description".

which is something entirely different than what you wrote. After all, any other effective description used in condensed matter physics or any other low-energy physics fails to be the "ultimate reliable description" of the system as well, so the AdS description is in no way different.

The only "ultimate reliable description" of similar systems is relativistic quantum field theory and, when we want all the quantum gravity details to be incorporated as well, string theory in the high-energy sense.

reader Peter F. said...

This is unrelated to what you wrote:
We visited Hamburg 1.5 year ago and very much liked what we saw and the people we casually interacted with. I just felt like letting you know since I've gathered you live there. :-)

reader Dilaton said...

Ah thanks for this clarification Lumo, now I see what you mean by "ultimate reliable describtion"...

After having been worried and confused, I am now happy again :-)


reader Dilaton said...

Hi Peter,

Huh, do you mean you have actually seen me in Hamurg ... :-D?
That can not be the case ha ha, you are certainly joking :-P?

I too think that people in Hamburg and other Nothern Germany are quite nice, that's why I'm planning to stay a bit here :-)


reader Luboš Motl said...

That's nice. It's been a much longer time when I visited Hamburg and frankly speaking, I only remember the red light district, a street over there, and some interiors that were somewhat high tech when I tried. ;-)

reader Shannon said...

1) It is the 21 Dec all day. Let's wait until midnight.

2) The "strange metal" is it plasma like ? Sachdev's article is awesome. He's able to draw a simple picture of ST at large. I'm now going to read The Illusion of Gravity. I like gravity. It makes me feel down to Earth ;-)

reader Physics Junkie said...

I have been wondering for some time about a similar link, the one between Higgs fields and BCS theory of superconductivity. Since the Higgs model was inspired by BCS theory, I was wondering if anyone has tried modelling the vacuum as a superconductor, or maybe it already has? Maybe experiments could be done using solid state materials that could mimic the transition at the electroweak scale. Such experiments might lend some insight onto the theoretical side of the electroweak transition.

reader Rezso said...


"one between Higgs fields and BCS theory of superconductivity"

Just a little clarification. The analogy holds between Ginzburg-Landau theory and the Higgs mechanism. In BCS theory, the Ginzburg-Landau wavefunction arises as a composite field. But the standard model contains an elementary Higgs, so the analogy between BCS theory and the standard model Higgs is not perfect.

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