Causes of loss of interest in String program

[PAllen]

I was just saying that most (all?) string theory papers appear in hep-th, and yes some get cross-listed to gr-qg. I remember some days when the section was full of lqg, that was when I stopped visiting it. And just when you get 1 or 2 LQG papers a day there it's still an overinflation when compared to the relative significance of the program.

The same is true for the "general physics" section. I certainly don't consider research in "general physics" to be worthless, but most papers in that section (last time I checked anyway) were pretty worthless. That's where all the crackpot papers are usually sent.

People have very limited time to check new papers, and this is one type of behavior I've often noticed, of which I'm of course not particularly proud. When a section is often polluted by meaningless garbage, you'll just find it inefficient to keep browsing it.

Another question: Do you all QG research other than string is irrelevant? For example, there is what I would call 'generic' QG research, neither loop nor string, example much of Steven Carlip's research? Just wondering how strongly you feel string is the only valid research direction in QG?

 

[negru]

Another question: Do you all QG research other than string is irrelevant? For example, there is what I would call 'generic' QG research, neither loop nor string, example much of Steven Carlip's research? Just wondering how strongly you feel string is the only valid research direction in QG?

It depends on the particular type of research. I certainly believe that the usual QFT approach to QG is quite valid. I'm not familiar with Carlip's work, but randomly skimming his recent stuff to get an idea I came across some sensible stuff, some less sensible eg

Is Quantum Gravity Necessary?
Authors: S. Carlip
(Submitted on 24 Mar 2008)
Abstract: In view of the enormous difficulties we seem to face in quantizing general relativity, we should perhaps consider the possibility that gravity is a fundamentally classical interaction.

This I don't agree with, and I don't even know why many physicists do. It's like people stopped learning physics sometime shortly before Wilson's renormalization ideas in the 70's or whenever it was. There are simply no "enormous difficulties" in quantizing gravity. We just don't know what the fundamental degrees of freedom are (I mean, we do know, they're strings, :P). We know from BH entropy that gravity needs some extra degrees of freedom, so it's no big surprise. Without the fundamental degrees of freedom of course you don't have a complete theory of QG. But there is nothing wrong with QFT QG per-se: we can compute eg the quantum correction to Newton's Universal Law of Attraction without much difficulty.

If you can point me to some specific or representative work he's done I'll take a look.As for other stuff, asymptotic safety, entropic gravity, horava, I don't think they're valid. At least I wouldn't go near them. The first one is sensible but again I feel fails to take into account everything we learned about gravity in the past decades. It's like Einstein ignoring QM developments and marching ahead blindly. I can't argue that string theory is the only valid approach, but I can argue that even if there is something else out there, it will have to redo everything string theory did anyway. Which is why I -personally- don't see much point in trying other approaches.

 

[atyy]

We just don't know what the fundamental degrees of freedom are (I mean, we do know, they're strings, :P).

Aren't you contradicting yourself here? Just a couple of posts ago, you were hoping they were twistors;)

 

[PAllen]

Is Quantum Gravity Necessary?
Authors: S. Carlip
(Submitted on 24 Mar 2008)
Abstract: In view of the enormous difficulties we seem to face in quantizing general relativity, we should perhaps consider the possibility that gravity is a fundamentally classical interaction.

This I don't agree with, and I don't even know why many physicists do. It's like people stopped learning physics sometime shortly before Wilson's renormalization ideas in the 70's or whenever it was. There are simply no "enormous difficulties" in quantizing gravity. We just don't know what the fundamental degrees of freedom are (I mean, we do know, they're strings, :P). We know from BH entropy that gravity needs some extra degrees of freedom, so it's no big surprise. Without the fundamental degrees of freedom of course you don't have a complete theory of QG. But there is nothing wrong with QFT QG per-se: we can compute eg the quantum correction to Newton's Universal Law of Attraction without much difficulty.

I'm sure he doesn't either. I would hope you can distinguish a 'speculative' paper, which has a distinguished history in physics. The purpose for the paper is to explore whether there is a feasible experiment to prove quantum gravity is necessary. No matter how much (almost) everyone already believes this, don't you think this would be nice? There aren't many (any?) experiments in this area so far.

 

[negru]

Oh sure you're probably right, I was just browsing the abstracts.

Regardless of Carlip however, I still think people should stop using those sort of phrases. Physics doesn't explode or anything when we combine QM and GR. It works where it's supposed to, and it doesn't where it's not.

 

[Sardano]

It is interesting to read "Loop vs Strings" if you want to read the discussion of Enrique Alvarez, who is a real expert in QG and a professional researcher (and to get rid of the incorrect monologue of Marcus, who is not).

 

[Sardano]

Marcus, I cannot believe it. You don't know or understand how to obtain GR from ST yet you are talking about the ST program, the relevance of ST papers and even talking about the KKLT model (which in light of this I am sure you don't understand a single word). How can be possible? I am serious about this. Why are you talking about things that you don't know at all? You are the biggest crackpot or you just have too much free time? (probably both of them)

 

[marcus]

It is interesting to read "Loop vs Strings" if you want to read the discussion of Enrique Alvarez, who is a real expert in QG and a professional researcher (and to get rid of the incorrect monologue of Marcus, who is not).

I remember reading Alvarez paper back in 2003 or 2004. At the time I thought it was a helpful and reasonably fair comparison (as things stood at the time.) Your tone is a bit ad hom, but I'm glad you mentioned the paper.

Too bad there isn't something more recent of that sort.

Loops versus strings
Enrique Álvarez (IFT UAM/CSIC, Madrid)
(Submitted on 21 Jul 2003)
"Two popular attempts to understand the quantum physics of gravitation are critically assessed. The talk on which this paper is based was intended for a general particle-physics audience."

 

[Sardano]

Too bad there isn't something more recent of that sort.

Thats due to the loss of interest in LQG program. There is no need for comparison nowdays.

 

[marcus]

Thats due to the loss of interest in LQG program. There is no need for comparison nowdays.

With so much over-the-top vituperation and animosity, it is hard to tell if you are kidding, Sardano.

 

[atyy]

Thats due to the loss of interest in LQG program. There is no need for comparison nowdays.

There's no loss of interest in it - condensed matter people are becoming interested in it.

http://books.google.com/books?id=VgO0dbjJchUC&dq=solvay+condensed+matter&source=gbs_navlinks_s, p230 has a story about one of Mattias Troyer's students finding some good tricks for tensor network calculations in LQG.

http://arxiv.org/abs/0907.2994 mentions LQG explicitly.

Also, from string theory, isn't it the case that theories without gravity can have gravity? So LQG may have gravity too;)

 

[fzero]

There's no loss of interest in it - condensed matter people are becoming interested in it.

http://books.google.com/books?id=VgO0dbjJchUC&dq=solvay+condensed+matter&source=gbs_navlinks_s, p230 has a story about one of Mattias Troyer's students finding some good tricks for tensor network calculations in LQG.

http://arxiv.org/abs/0907.2994 mentions LQG explicitly.

Also, from string theory, isn't it the case that theories without gravity can have gravity? So LQG may have gravity too;)

It's not an issue of whether gauge theories can describe gravity, it's that all known approaches to use gauge theory to describe canonical gravity fail nonperturbatively. This was the point Witten made in his "Three-Dimensional Gravity Revisited" paper. Two issues (not necessarily the most important ones) include:

* The gauge theories always include solutions where the vierbein is not invertible. In perturbation theory, if we start from an invertible vierbein, perturbations will never take us to a noninvertible vierbein, but there is no restriction on nonperturbative physics.

* The gauge theory only describes diffeomorphisms which are connected to the identity.

So it seems that any attempt to formulate quantum gravity as a gauge theory in which there is a canonical map between degrees of freedom is incomplete.

 

[atyy]

It's not an issue of whether gauge theories can describe gravity, it's that all known approaches to use gauge theory to describe canonical gravity fail nonperturbatively. This was the point Witten made in his "Three-Dimensional Gravity Revisited" paper. Two issues (not necessarily the most important ones) include:

* The gauge theories always include solutions where the vierbein is not invertible. In perturbation theory, if we start from an invertible vierbein, perturbations will never take us to a noninvertible vierbein, but there is no restriction on nonperturbative physics.

* The gauge theory only describes diffeomorphisms which are connected to the identity.

So it seems that any attempt to formulate quantum gravity as a gauge theory in which there is a canonical map between degrees of freedom is incomplete.

But isn't gauge theory supposed to contain quantum gravity non-perturbatively by gauge/gravity duality (which is what I had in mind when saying that theories without gravity contain gravity)?

 

[fzero]

But isn't gauge theory supposed to contain quantum gravity non-perturbatively by gauge/gravity duality (which is what I had in mind when saying that theories without gravity contain gravity)?

Yes, but in AdS/CFT the gauge connection is not the vierbein and spin connection. One can probably connect the absence of singular vierbeins with the absence of null states in the CFT.

 

[atyy]

Yes, but in AdS/CFT the gauge connection is not the vierbein and spin connection. One can probably connect the absence of singular vierbeins with the absence of null states in the CFT.

Yes, I didn't intend to imply otherwise.

 

[marcus]

There was a fascinating nuanced exchange on Woit's blog, between the blogger and Mitchell Porter. It points to what I would call not a loss or shift of interest, but a qualitative change in the kind of interest. ( Something is going on which I think a number of us would like to understand better.)

==quote==

Mitchell Porter says:
May 15, 2011 at 2:36 am
Peter wrote:

“The hot topic these days is not string theory, but gauge theory amplitudes, using twistors.”

But these aren’t separate topics! It started with Witten’s twistor string, and the theories being studied have string duals in AdS space.

===================

Peter Woit says:
May 15, 2011 at 12:10 pm

Mitchell Porter,
Just because you can find some connection between a topic and string theory, that doesn’t mean the topic is string theory.

Nati Seiberg of course predicted this years ago, when he said that no matter what replaced string theory, string theorists would “call it string theory”.

===================

Mitchell Porter says:
May 15, 2011 at 8:35 pm

Peter – d=4 N=4 Yang-Mills theory, which is at the center of the twistor/gauge enthusiasm, is *equivalent* to Type IIB superstring theory on a certain background. (Or if, against all the evidence, it *is* inequivalent, then it is so close that the difference consists of a very subtle deformation.) And Type IIB is, uncontroversially, old-school string theory, it’s not some new topic which has been adventitiously appropriated by string theorists in order to remain relevant. So string theory was rediscovered in an unexpected place.

It *is* remotely conceivable that the string description will recede into the background conceptually, and people will prefer to think in terms of twistors, but I doubt it. A more reasonable question might be, does this mean that strings “mean” something different to what people thought in the 1980s? What I mean is that from the d=4 field-theoretic perspective, the AdS dimension, the compact dimensions, and the extended objects (strings and branes) all emerge from renormalization group flow and the structure of moduli space. It might be argued that strings and branes should therefore be conceived as abstract in some way, and one might wish to reserve the notion of physicality proper for the fields in four dimensions. I think *that* is a debate with a future. But if string theory is truly irrelevant to reality, then so is the twistor/gauge revolution.

=======================

Peter Woit says:
May 15, 2011 at 9:33 pm

Mitchell,
As far as I can tell, the reasons twistors are useful in studying perturbative gauge theory amplitudes have little to nothing to do with string theory. But it’s an evolving story, we’ll see what the final result is when people really understand how to formulate these theories in twistor space. Maybe strings will play a central role, we’ll see. Until then, I think continually hyping the importance of strings in cases where they aren’t the center of attention is PR, not science.

==endquote==

 

[suprised]

Maybe strings will play a central role, we’ll see. Until then, I think continually hyping the importance of strings in cases where they aren’t the center of attention is PR, not science.
==endquote==

Well, it's funny how Woit invokes something as not being science, himself not being a scientist either. As if he could judge!

 

[atyy]

Well, it's funny how Woit invokes something as not being science, himself not being a scientist either. As if he could judge!

Well, Woit hasn't lost intrerest in string theory - he's still blogging about it;)

 

[marcus]

Hi Super,

What is more new and interesting here, for me, is what Mitchell says. It is similar in a sense to what you said one time which suggested there was a better way to view SST. (a more sophisticated way of regarding the compactified xd's and so forth). You indicated, as I recall, that many researchers had already adopted the more sophisticated viewpoint. Of course I may have misunderstood...

Here is a link to Mitchell's post, which I think contains the key idea of the exchange:
http://www.math.columbia.edu/~woit/wordpress/?p=3689&cpage=1#comment-90707
================

A sample illustrative comment (mathematicians discussing something unrelated to sst):
http://math.stackexchange.com/questions/25794/factorial-of-0-a-convenience
the virtue of a particular math scheme or definition is that it is convenient.
================

Mitchell: "...It might be argued that strings and branes should therefore be conceived as abstract in some way, and one might wish to reserve the notion of physicality proper for the fields in four dimensions. I think *that* is a debate with a future..."

 

[Haelfix]

The reason Nima, amongst others, got into the gauge theory amplitude business, is to try to remove manifest locality from the rules of quantum field theory. The underlying thought being that it would eventually be necessary for a proper treatment of gravity and cosmology in spacetimes where the boundary is hard to define (for instance De Sitter space) and for use in understanding eternal inflation etc

So, the point being once you have a formalism where locality is not manifest, you can imagine generalizing it to cases where it is absent and only recovered in some sort of low energy limit.

The incredible thing is that it is working and in fact the desire for manifest locality was obscuring huge symmetry groups that were just sitting there, under everyones noses, waiting to be found. These same symmetry groups were originally identified in part by Maldacena.

So once again we have a huge theoretical coup, where string theory was in some sense the originator of the idea (both in the motivation side, as well as the technical details). Of course certain scientists can stick their heads in the sand for the umpteenth time and argue (perhaps even convincingly_ that this is just math, and its all coincidence. But really it begins to stretch credulity.

 

[marcus]

The reason Nima, amongst others, got into the gauge theory amplitude business, is to try to remove manifest locality from the rules of quantum field theory. The underlying thought being that it would eventually be necessary for a proper treatment of gravity and cosmology in spacetimes where the boundary is hard to define...

...Of course certain scientists can stick their heads in the sand for the umpteenth time and argue (perhaps even convincingly_ that this is just math, and its all coincidence. But really it begins to stretch credulity.

I like the substantive thing you say about "remove manifest locality from the rules of quantum field theory".

But part of the discussion also seems to be about interpretation and nuance. There was what Mitchell said:

"...A more reasonable question might be, does this mean that strings “mean” something different to what people thought in the 1980s? What I mean is that from the d=4 field-theoretic perspective, the AdS dimension, the compact dimensions, and the extended objects (strings and branes) all emerge from renormalization group flow and the structure of moduli space. It might be argued that strings and branes should therefore be conceived as abstract in some way, and one might wish to reserve the notion of physicality proper for the fields in four dimensions. I think *that* is a debate with a future..."

And I noticed the interesting wording of a U Toronto physics prof's webpage statement of interest. This is Erich Poppitz, who does a mix of 4D QFT and also string-looking research. You would have to look at his pubs and judge for yourself.
http://www.physics.utoronto.ca/~poppitz/epoppitz/Erich_Poppitz.html
His faculty webpage says:
==quote==
Research

I am interested in physics beyond the standard model. I also study general quantum field theories and their non-perturbative dynamics, using a variety of tools, from supersymmetry, branes, and dualities, to lattice field theory and Monte-Carlo simulations.

==endquote==

Taking Poppitz as an example of "certain scientists" I do not think he has his head in sand, on the other hand I think he would probably be too sophisticated to get into argument about whether suchandsuch actually physically exist. His statement of research interest refers to branes dualities etc as tools for doing (4d?) QFT.

 

[Haelfix]

The question of what string theory actually is, and the philosophy behind it, is of course still widely open. And yes, since the 90s people have realized that its less about fundamental strings and more about a much bigger object called 'M theory' or 'string theory' where the various degrees of freedom: Strings, D Branes, etc morph into each other under continuous deformation of the parameters of the theory.

It is conceivable that there is some sort of generalized object that supercedes both of them (something new) and can act like both of them in some sort of limit, or perhaps it is just some large disconnected theory where 'God' twiddles switches and knobs and dictates what is fundamental or not. Or perhaps you could think of it like Mitchell does, where you have this huge theoretical artifice acting a bit like the aether wind, and the fundamental observable objects (quantum fields) are dictated by the action of this thing.

In any event, what is just not goign to happen is for it to go away. It is very much a part of the rules and theoretical structure of our world (gravity, quantum field theories, etc) and what is left to decide is the specific details and the philosophy will go where the philosophy will go.

Incidentally, Its a bit like trying to build a hydrogen atom out of electrons and protons, and then finding out that you could build up electrons and protons out of hydrogen atoms. Its very weird, but that pattern has shown up again and again in many different guises.

 

[marcus]

...

In any event, what is just not goign to happen is for it to go away...

At the moment the historical analogy that suggests itself is "Lie groups". Lie groups are a general math toolkit, not a specific model of physics. To get specific you have to specify which groups and what other structure. And they are human artifacts--something exactly like a Lie group might not exist in nature.

But Lie groups are not going to go away. In fact their role in physics has increased in importance with time.

Again it reminds me of how Erich Poppitz described his research interests. He would not be one to argue, I think, about whether "Lie groups" is something that actually exists in nature or is, instead, merely a convenient mathematical device of description which will not go away.

... interesting wording of a U Toronto physics prof's webpage statement of interest. This is Erich Poppitz, who does a mix of 4D QFT and also string-looking research. You would have to look at his pubs and judge for yourself.
http://www.physics.utoronto.ca/~poppitz/epoppitz/Erich_Poppitz.html
His faculty webpage says:
==quote==
Research

I am interested in physics beyond the standard model. I also study general quantum field theories and their non-perturbative dynamics, using a variety of tools, from supersymmetry, branes, and dualities, to lattice field theory and Monte-Carlo simulations.

==endquote==

... I think he would probably be too sophisticated to get into argument about whether suchandsuch actually physically exist. His statement of research interest refers to branes dualities etc as tools for doing (4d?) QFT.

BTW Erich P. keeps track of the job situation for HEP theorists---first-time faculty hires at places in the Usa & Canada, of people in particle theory. It might be of interest--I'll fetch the link. The URL gives the impression it only goes to 2008 but the data goes up through 2010, so it's fairly current.
http://www.physics.utoronto.ca/~poppitz/Jobs94-08

Thanks to Erich P. we have data of this sort (for Usa and Canada, from the particle theory rumor mill).

First time faculty hires in string
2002-2004 23
2005-2007 18
2008-2010 7

The decline in string jobs that Poppitz charts for us may have some relation to the shifts or changes in interest that we've been discussing. Or perhaps some completely independent explanation, as so often happens.

 

[negru]

"Lie groups are a general math toolkit, not a specific model of physics."

Right, and what's the difference between eg compactifying on a Calabi -Yau to get the SM and putting the strings in AdS to describe YM? Or using strings in a different context to study some other QFT like maybe Poppitz does? You still impose some external conditions etc.

These questions of whether string theory is a "physical model" or a "toolkit" are the kind of useless and irrelevant epistemological questions that should be left to physics drop-outs who switch to philosophy or people like Woit. What scientists are interested in is getting new answers, results about the world, by whatever means necessary, not deciding what the nature of their tools is.

 

[Demystifier]

Well, it's funny how Woit invokes something as not being science, himself not being a scientist either. As if he could judge!

According to one definition, science is what scientists do. :tongue2:

 

[mitchell porter]

what's the difference between eg compactifying on a Calabi -Yau to get the SM and putting the strings in AdS to describe YM?

It has to be significant that AdS geometry arises in the study of RG flow. There's a hint of the same phenomenon in the vanishing of worldsheet beta functions for string theory in a flat space, too, though it's hard to make the analogy precise. The position I was describing - and not advocating, by the way, though I have considered it - would be one according to which string theory is what you get when you project "real physics" into the "space" of energy scales, and try to describe physics as occurring in that second space. It's like saying that the boundary is the only real part of the hologram, and the bulk is a construct. This is the reverse of https://www.physicsforums.com/showthread.php?t=459744#6" might be to attach reality to classical limits wherever they exist.

One problem with saying that the bulk (and the strings and branes that inhabit it) is not fully real, is that ordinary phenomenal d=4 space-time - the space where we think we live - may be the bulk space in some cosmological form of dS/CFT (with time emerging from a primordial Euclidean CFT). Also, giving ontological priority to the boundary raises the question, exactly which surfaces are holographic surfaces? I know Bousso and possibly Banks have a maximal interpretation of this - every lightlike surface, I think - whereas I tend to the other extreme, but maybe that's just caution: I can see how holography works for AdS/CFT and for flat space (the in/out states of the S-matrix are defined on the conformal boundary), but I don't see how it works for an arbitrary surface. dS/CFT is an interesting test case for me. I am skeptical of the extension of Susskind's black hole complementarity to cosmological horizons, on the grounds that they are observer-dependent whereas an event horizon is an objectively distinguished surface. So I tend to think of dS/CFT as once again defined on the conformal boundary of de Sitter space, rather than on the observer horizons... And maybe this approach can even deal with compact spaces in general - i.e. one has to look at past and future conformal boundaries, to find the holographic dual.

 

[marcus]

I was looking at the Particle Theory Jobs Rumor Mill yesterday and noticed something that makes me more watchful of Erich Poppitz, the U Toronto physics prof who uses string (among other) techniques. To recall, here's what I said earlier:

... interesting wording of a U Toronto physics prof's webpage statement of interest. This is Erich Poppitz, who does a mix of 4D QFT and also string-looking research. You would have to look at his pubs and judge for yourself.
http://www.physics.utoronto.ca/~popp...h_Poppitz.html
His faculty webpage says:
==quote==
Research

I am interested in physics beyond the standard model. I also study general quantum field theories and their non-perturbative dynamics, using a variety of tools, from supersymmetry, branes, and dualities, to lattice field theory and Monte-Carlo simulations.

==endquote==

... I think he would probably be too sophisticated to get into argument about whether suchandsuch actually physically exist. His statement of research interest refers to branes dualities etc as tools for doing (4d?) QFT.

BTW Erich P. keeps track of the job situation for HEP theorists---first-time faculty hires at places in the Usa & Canada, of people in particle theory. It might be of interest--I'll fetch the link. The URL gives the impression it only goes to 2008 but the data goes up through 2010, so it's fairly current.
http://www.physics.utoronto.ca/~poppitz/Jobs94-08

Thanks to Erich P. we have data of this sort (for Usa and Canada, from the particle theory rumor mill).

First time faculty hires in string
2002-2004 23
2005-2007 18
2008-2010 7

What I noticed yesterday is that he has recently (since 2009) published six papers co-authored with Mithat Unsal. Why is that interesting?
http://inspirebeta.net/search?p=find+a+Unsal,+M
Of course Poppitz has a big pub track record but it's interesting he should be recently collaborating as senior author with Unsal, because Unsal was one of the few string theorists offered a first-time faculty job this year. In Usa+Canada, I mean, according to the rumor mill:
http://particle.physics.ucdavis.edu/rumor/doku.php?id=current

Of the HEP people listed here as getting firsttime offers this year, I'd classify Cheung as cosmo. Profumo is another cosmo/astro. Sandick looks like astrophysics. Yavin, Essig and Kilic would be pheno/dark matter. Hoeche is numerical LHC pheno. Paz is pheno (shading over to experimental physics).
But Bringoltz and Unsal both look string to me.

It suggests that Poppitz might be an alert realist, a good person to work with. Pursuing his lines of research interest might correlate with chances of a faculty hire later on down the road. A vague idea that needs to be seen in perspective. You see from the previous table that first time faculty hires in string are currently about 2 per year. This is for Usa + Canada. Assume for argument sake that continues level. So if you enter a string PhD program this year you join a cohort for which there are two firsttime faculty jobs waiting--on average. It is from that perspective that I notice the associations of the people listed.

 

[atyy]

I was looking at the Particle Theory Jobs Rumor Mill yesterday and noticed something that makes me more watchful of Erich Poppitz, the U Toronto physics prof who uses string (among other) techniques. To recall, here's what I said earlier:


What I noticed yesterday is that he has recently (since 2009) published six papers co-authored with Mithat Unsal. Of course Poppitz has a big pub track record but it's interesting he should be recently collaborating as senior author with Unsal, because Unsal was one of the very few young researchers offered a faculty job this year. In high energy theory, I mean.
http://inspirebeta.net/search?p=find+a+Unsal,+M

This could be interesting, since there is some duality between spin foams and lattices. The other duality is between spin foams and GFTs. I don't know what the exact statements of these are though.

Can all lattices be formulated as spin foams?
Can all spin foams be formulated as lattices?
Can all spin foams be formulated as GFTs?
Can all GFTs be formulated as spin foams?

Here is some LQG work that I'd love to know if there's any connection with Unsal's supersymmetric lattice stuff:
http://arxiv.org/abs/1103.6264
http://arxiv.org/abs/1004.0672

 

[marcus]

Probably everybody saw Ordered_Chaos's pointer to the blog post reporting zero first-time faculty job offers to string program theorists this year.

http://www.math.columbia.edu/~woit/wordpress/?p=3715

Woit just blogged on this question.

This was post #2 in a thread that was here in Beyond forum for a week or so (25-31 May) and then moved to Career. I had earlier looked at the same Rumor Mill page and thought I saw TWO offers to people that some here might classify as string. Maybe someone would like to comment. Apparently one of those who looked a bit string-minded to me was really a "lattice gauge theorist" for the most part. But it's trifling, just how different people count.

Could there be any underlying physics reasons for this change or is it all explainable by irrelevant factors?

This goes back to an earlier post of mine, where I noted the decline in faculty job offers and quoted the research interest statement of a U Toronto professor Erich Poppitz which I thought was suggestive of how String is starting to be seen in a different light.

...part of the discussion also seems to be about interpretation and nuance. There was what Mitchell said:

"...A more reasonable question might be, does this mean that strings “mean” something different to what people thought in the 1980s? What I mean is that from the d=4 field-theoretic perspective, the AdS dimension, the compact dimensions, and the extended objects (strings and branes) all emerge from renormalization group flow and the structure of moduli space. It might be argued that strings and branes should therefore be conceived as abstract in some way, and one might wish to reserve the notion of physicality proper for the fields in four dimensions. I think *that* is a debate with a future..."

... I noticed the interesting wording of a U Toronto physics prof's webpage statement of interest. This is Erich Poppitz, who does a mix of 4D QFT and also string-looking research. You would have to look at his pubs and judge for yourself.
http://www.physics.utoronto.ca/~poppitz/epoppitz/Erich_Poppitz.html
His faculty webpage says:
==quote==
Research
I am interested in physics beyond the standard model. I also study general quantum field theories and their non-perturbative dynamics, using a variety of tools, from supersymmetry, branes, and dualities, to lattice field theory and Monte-Carlo simulations.
==endquote==...

BTW Erich P. keeps track of the job situation for HEP theorists---first-time faculty hires at places in the Usa & Canada, of people in particle theory. It might be of interest--I'll fetch the link. The URL gives the impression it only goes to 2008 but the data goes up through 2010, so it's fairly current.
http://www.physics.utoronto.ca/~poppitz/Jobs94-08

Thanks to Erich P. we have data of this sort (for Usa and Canada, from the particle theory rumor mill).

First time faculty hires in string
2002-2004 23
2005-2007 18
2008-2010 7

The decline in string jobs that Poppitz charts for us may have some relation to the shifts or changes in interest that we've been discussing...

So the Usa-Canada stringy hires-per-year goes like this, 2002-2010 according to Poppitz, and 2011 according to Woit's reading of the current Rumor Mill:

[U]First time faculty hires in string[/U] 
2002-2004      8 jobs per year (avg.)
2005-2007      6 jobs per year
2008-2010      2 jobs per year
2011           0 jobs per year

In case anyone is interested, here are Poppitz's totals for all high-energy theory hires. I haven't bothered to average over 3-year periods, since not a lot of fluctuation.
First time faculty hires in HEP theory as a whole
2002 25
2003 23
2004 25
2005 19
2006 21
2007 28
2008 15
2009 9
2010 14

 

[marcus]

I think what we are seeing here (e.g. looking at what Mitchell said and also at Poppitz statement of research interest) is not a simple decline of interest but a change in the kind of interest that the theory community has in string.

It is increasingly seen as one of a number of different methods usable to explore and unravel nature.

I think this also fits in with the rather cool-headed sober assessment given by Steve Giddings (erstwhile string stalwart) in his recently posted essay "Is String Theory a Theory of Quantum Gravity?" see https://www.physicsforums.com/showthread.php?t=503240

There is less tendency now (than say back in 2005) to repeat the formula about "our one best hope" for a be-all end-all theory.

I'm struck by Erich Poppitz description of his research:
==quote==
I am interested in physics beyond the standard model. I also study general quantum field theories and their non-perturbative dynamics, using a variety of tools, from supersymmetry, branes, and dualities, to lattice field theory and Monte-Carlo simulations.
==endquote==

So, in a sense, you might argue for just as much interest as, say, in 2005, but with a nuanced self-redefiniition and shift in categories.

 

[marcus]

The kind of talks at the annual conference gives us one way to gauge what is happening in the String program. The conference takes place at the end of this month, some of the talk titles are posted:Niklas Beisert (AEI Potsdam) "Counterterms and E7 Symmetry in N=8 Supergravity"

Henriette Elvang (University of Michigan) review talk "Recent progress on amplitudes"

Rajesh Gopakumar (Harish-Chandra Research Institute, Allahabad) "Holographic Minimal Models"

David Gross (KITP, Santa Barbara) opening talk

Jeff Harvey (University of Chicago) summary talk

Andrei Linde (Stanford University) "Chaotic inflation in supergravity"

Marcos Mariño (University of Geneva) "Exact results and stringy effects in ABJM theory"

Liam McAllister (Cornell University) review talk "String cosmology"

Greg Moore (Rutgers University) review talk "The Recent Role of (2,0) Theories in Physical Mathematics"

Subir Sachdev (Harvard University) review talk "Quantum matter and gauge-gravity duality: quantum criticality, superconductivity, and Fermi surfaces"

Nathan Seiberg (IAS, Princeton) review talk "Recent advances in SUSY"

Tadashi Takayanagi (IPMU, the University of Tokyo) "Holographic Entanglement Entropy and its New Developments"

Frank Wilczek (MIT) "Three Ways Beyond the Standard Model"

Edward Witten (IAS, Princeton) "Chern-Simons theory from four dimensions"

I don't see that one can draw any conclusion from this as yet. Here is the link:
http://www-conference.slu.se/strings2011/programme_NEW.html
We can watch this to see titles of more of the talks as they are posted.

 

[Lt_Dax]

I'm not at all surprised that String researchers are slowly tranforming what they study into something more involved with cosmology, or as part of AdS/CFT. Even though something can be science even if it is untestable (we may be able to test it in the future), let's be honest - we don't want to forever be equation manipulators becoming ever more detached from the so-called experimental physics community. We want to see our ideas validated. It's no use being the world's greatest bus driver if you're driving in the wrong direction (and with regards to the String community, I have nothing but admiration for their bus driving skills, which in many cases are second to none).

Of course, my own views on this have been made plain in the past. We have to very careful that the ideas we put forward are themselves guided by physical intuition derived from experiment. Physics is an experimental science by definition. I say this as a theorist. I am under no illusions about the role of my work and I enjoy this subservience to observation and experiment. Science advances by incremental steps in theory and experiment with experiment leading the way, and physics is not exempt from this just because a large portion of the theoretical physics community imagine that the methods of Faraday, Maxwell and (early) Einstein are too primitive and old-fashioned to work.

 

[mitchell porter]

The possible observation of a Z' boson at CERN, if it holds up, will lead to a lot of string phenomenology papers, because a Z' is a standard feature of braneworld models.

 

[atyy]

The possible observation of a Z' boson at CERN, if it holds up, will lead to a lot of string phenomenology papers, because a Z' is a standard feature of braneworld models.

Are there any hopes for realistic braneworld scenarios in AdS/CFT at the moment?

 

[mitchell porter]

Are there any hopes for realistic braneworld scenarios in AdS/CFT at the moment?

There are dozens of phenomenology models using braneworlds and dozens using AdS/CFT. But I am still confused about the reality of the AdS space. In a braneworld model, you know that the bulk, the space outside the braneworld, is supposed to be taken literally: the gravitons travel there so the bulk radius sets the scale of gravity, high-energy interactions on the braneworld can exhibit missing energy or Kaluza-Klein modes, and so on. But in the application of AdS/CFT to particle phenomenology, you might expect AdS space to be more of a construct, as in AdS/CMT - just a way to make strongly coupled theories calculable (by placing them on the boundary and constructing a weakly coupled AdS supergravity dual). Braneworlds are mostly studied in flat space, or, if they are meant to be cosmologically realistic, in expanding space.

Before I ever started studying AdS/CFT (and certainly before I encountered the idea that AdS space might just be a representation of RG flow / energy scales), http://golem.ph.utexas.edu/~distler/blog/archives/001256.html#c034279" what the existence of an AdS dual implied about the actual geometry of the extra dimensions. He replied:

There’s a very particular class of field theories ... which have holographic duals ... you can use one of these holographic theories to describe the same long distance physics as a theory with radically different short-distance physics ...

All of the Type-II/M-theory compactifications ... which have chiral matter and nonabelian gauge fields have the feature that the latter are localized on (possibly singular) submanifolds of the compactification manifold, whereas gravity lives in the bulk.

In the presence of large warping, the local physics in the vicinity of those submanifolds looks very much like AdS/CFT. But ... the details are rather different. There’s no AdS dual for the 8-dimensional gauge theories that arise on 7-branes.

So from this you might conclude that AdS/CFT is not literally realized in nature. Even if we do live on a braneworld, the bulk won't be AdS, though it may be "warped" similarly, near the branes.

You might also conclude from this that there is a level of enlightenment, regarding the realization of the holographic principle in string theory, higher than the level that I have attained :-) ... my level being characterized only by a study of direct AdS/CFT dualities, and not these "AdS/CFT-like" scenarios.

Or, to pick another source and treat it as oracle, arxiv:0711.0387 says the following:

An ubiquitous theme in string (motivated) phenomenology is the translation of field theoretic data into geometry. Prominent examples are the engineering of Standard Model-like gauge theories via singular geometries and D-branes, and the dual representation of the gauge hierarchy in terms of warped extra dimensions. The holographic interplay between gauge and gravitational degrees of freedom underscores the crucial role D-branes play in establishing a string-theoretic link between gauge theory and gravity. Indeed, a large number of D-branes will melt into geometry. This process can in fact be done continuously. Starting from a configuration with a large number of D-branes which is captured by the geometry, at distances closer to the tip of the cone, the dual description in terms of a stack of branes will cause the initially large number of branes to sequentially decrease until only a finite number of branes are left at the ‘bottom’ of the geometry. In the dual gauge theory this corresponds to a duality cascade whereby a series of Seiberg dualities sequentially decreases the ranks of the gauge group as the RG flow proceeds from the UV to IR so that deep in the IR the resulting gauge groups have small finite rank.

That's an interesting, but difficult, paper, by the way: it describes https://www.physicsforums.com/showthread.php?t=503432".)