Causes of loss of interest in String program

[Sardano]

Marcus, it is usually very clear to an expert what the origins of an idea are. It is not too much trouble to read though the literature on, say, SUSY gauge theories and decide what techniques are being used. No matter how upsetting it may be to you, the fact remains that there are results that either can only be derived using string theory techniques or are much simpler to derive from string methods as opposed to brute force field theory computations.

You also seem to have various misunderstanding about the existence of supergravity theories on their own. It is extremely unlikely that supergravities are UV complete, though maximal supergravities seem to be much less divergent than we would have thought. Therefore all SUGRAs should be thought of as effective field theories related to some superstring theory.

Finally, you have a vast misunderstanding of how basic research is done. There is no focus and direction provided by any central figure. Researchers are generally free to choose topics on their own, without interference from anyone. There are small exceptions, such as grad students and postdocs who might be expected to work closely with their advisor/supervisor. Even these are rare, as in larger groups, postdocs are very independent and the main thing stopping grad students from being so is maturity in the discipline.

Even funding and job security are not huge impediments to freedom of choice in research topics. Grant and hiring committees tend to do a good job of evaluating research on it's academic value. If you do excellent work you will get jobs and funding, whether you are working on AdS/CFT or CY compactifications. There is no one that will "officially" or otherwise tell someone publishing important papers on AdS/CFT that they should be studying cosmology.

Also, as I have mentioned previously, only a small amount of research that is begun actually gets published. It is impossible to determine what areas people have worked on if they decided not to publish for whatever reason.

I completely agree with you. In fact, when I started mi PhD one year ago I worked in the ideas proposed by my tutor, and after the first paper, I have been give completely freedom to do research. I stick into ST because it is what I like to do and because my tutor is a ST physicist. Besides, You cannot get the idea of which are the actual lines of research of ST, or which were in the past and how they have changed by just using the arxiv or inspire sitting at home, if you are not an actual researcher. You will miss so many things that you would get the wrong idea.

 

[Micha]

To get an idea what string theorists are up to nowadays have a look here:

http://arxiv.org/abs/1104.5502"

Pretty impressive stuff.

 

[fzero]

Speaking of dualities (as you were) you might be interested in this:

http://arxiv.org/pdf/1010.2481
Einstein gravity as a 3D conformally invariant theory
Henrique Gomes, Sean Gryb, Tim Koslowski
27 pages. Published in Class.Quant.Grav.28:045005,2011

Each of the three authors is giving a talk at Loops 2011 this month in Madrid.

I saw the other thread about this. I'm quite sure what to make of it. There are very old results on how very different classical systems can be related by introducing new gauge degrees of freedom. Perhaps the most striking is Bars' two-time physics, where he even related the free particle, harmonic oscillator and H-atom http://arxiv.org/abs/hep-th/9804028. The quantum theories are obviously not related at finite coupling, so it's not clear what significance one should place on the "duality."

In any case, these relations should be further studied. In the late 90s, Steve Shenker was promoting the possibility there could be a new formulation of string theory where dual theories would correspond to different gauge choices. I don't believe any of these ideas were published anywhere, which is another example of how looking at the literature is sometimes insufficient to determine what people have been thinking about.

 

[PAllen]

Just to make it clear. For most of the time, the QG keyword is meaningless. For one, almost no string theorists put their papers under QG on the arxiv. The reason is that the QG is over flooded with garbage LQG papers. In fact I don't know a single physicist who even opens up the QG section to check recent papers. Even worse, if they are suggested to even look at the QG for a particular paper, they would ask: what is it doing under QG, if it's any good?
I have no idea how desy people do it, but I'm pretty sure it works about the same way.

Can you clarify something for me? When I go to arxiv, I don't see a QG section, I see GR-QC, in which LQG papers are a small minority. And I see Strominger's paper cross listed here (as well as hep-th). I assume (hope?) you don't consider all GR research worthless.

 

[negru]

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.

 

[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.