Causes of loss of interest in String program

[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.

 

[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".)

 

[marcus]

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.

Dax is back! I was really glad to see your post, Lieutenant. I'd like to invite you to take a look at the program of next week's "Mixed Quantum Geometry/Gravity" conference
https://www.physicsforums.com/showthread.php?p=3348219#post3348219
and would very much like to know your thoughts on it.

It is the first major international conference I know of that mixes presentations of Noncommutative field theory and NC Geometry with Supergravity with explicitly Stringy with Loop QG, and even Renate Loll's Triangulations QG and Martin Reuter's asymptotic safety QG research. I think it is something of a triumph to get representative people from all these different approaches into one hall to listen to each other. I hope they share ideas and problems---I hope it is actually productive. Maybe some postdocs will be enabled to jump fences.

The titles of all 30-odd talks are posted. Should give some idea of the character of the conference. ETH Zurich. Nice venue, except Zurich hotels seem very expensive.

 

[marcus]

A half-dozen more titles have been posted of talks to be given at the annual string conference. The conference starts in about two weeks. There are now 20 titles listed.


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

Thomas Klose (Uppsala University) "Recent Results for Holographic Three-Point Functions"

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"

Juan Maldacena (IAS, Princeton) "Comments on de Sitter perturbation theory"

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

Yaron Oz (Tel Aviv University) "Holography and Hydrodynamics"

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"

Ashoke Sen (Harish-Chandra Research Institute, Allahabad) "What can black holes tell us about microstates?"

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

Dimitrios Tsimpis (Université de Lyon) "Uses of 3d toric varieties"

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

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

Fabio Zwirner (University of Padua) review talk "LHC results and prospects from a theorist's viewpoint"

======
Here is the link:
http://www-conference.slu.se/strings2011/programme_NEW.html

I have highlighted the Frank Wilczek talk because it stands out as the one talk apt to provide a challenging vision---alternative to the future lines of development assumed likely by the other speakers.

 

[marcus]

In the previous post I listed Strings 2011 invited talks and gave a link to the conference website. There does clearly seem to be a significant change in the climate of interest surrounding the string research program (however different people prefer to describe it) and this annual showcase conference provides an excellent window on what is happening.

I think it's an important development we should try to understand---and doing that is not in any way to "bash" string mathematics---a fascinating and ingenious analytical toolkit with potential applications in several areas.

What we should be trying to understand are the reasons for the striking changes going on around the string program. It has been suggested that comparatively few of the Uppsala talks explicitly involved string. The majority of them were basically about QFT. Verlinde's remarkable talk referred to string thought as "motivation" and "inspiration" for his attempt to find some "underlying" description.

Could it be that a significant number of string researchers are finding their way out of the field and back into QFT? Or, in Verlinde's case, into someplace entirely new? I sometimes hear work that does not directly involve string described as "string inspired" and "guided by insights from string theory".

Anyway the Uppsala conference is over and we can try to summarize what we've learned from the videos. I have some observations and hope others have some as well.

 

[marcus]

One of the most telling points came right at the start of this video of Chris Hull's talk
http://media.medfarm.uu.se/flvplayer/strings2011/video16

At lunch today one of the organizers was observing that my talk was unusual in being one of the few talks actually about string theory. It would be interesting to speculate on what that might mean about the state of the field, but it would be invidious to do so here.
​

Evidently this is a sensitive subject (potentially invidious to point out). String researchers have noticed that collectively their work involves less and less actual string theory proper, and some are worried enough by this so that it can be considered untactful to speculate about why that is happening.

As I said, it's obvious that one can generally draw some connection between whatever and something studied in the string program. So presumably one can usually say that this or that is "string inspired" or "guided by insights from string" if it makes people feel better. As for instance Verlinde tactfully did in the introduction to his talk. It's good for morale. But Chris Hull and the conference organizer he quoted were taking a harder look.

It's helpful, I think, to see that against these features of the background:

1. String jobs have fallen way off. First time faculty hires in Usa and Canada are essentially nil this year---not the case for particle theory as a whole.

2. Annual citations to recent string research have fallen--this reflects how useful/significant the researchers themselves find their own recent work.

3. Conference attendance is down. Registered participants at Strings 2011 numbered 257.

It may indeed be time for people to redefine their interests. Peter Woit had this comment:

One can make as much hype as one wants claiming that all good ideas in the hot topics of today (amplitudes, N=2 SUSY, various applications of gauge-gravity dualities, etc.) historically come from string theory, but the undeniable fact of the matter is that if you watch the talks at Strings 2011, virtually no one is talking about string theory itself or using string theory anymore to do anything. A student who wants to work on any of the hot topics has no reason to bother to learn string theory anymore.

What’s remarkable is that this seems to be true even in those areas where string theory has had some success, far away from the heavily promoted ones. Besides virtually no talks about string theory and unification, there’s also almost nothing about string theory as a theory of quantum gravity. The hot topic of recent years, the idea that string theory would explain heavy ion physics, seems to have completely disappeared.
​

http://www.math.columbia.edu/~woit/wordpress/?p=3811&cpage=1#comment-94426

 

[marcus]

Jeff Harvey, who had the important job of giving the summary talk at the end of the Strings 2011, compared string theory to the dead parrot in the Monty Python sketch, where the pet store clerk is trying to sell the customer a parrot is insisting that it isn't dead. He said string unification was not dead, it was "just sleeping" (quoting the M.P. pet store clerk.)
http://media.medfarm.uu.se/flvplayer/strings2011/video37
The specific reference to the Monty Python parrot, comes almost exactly 1/4 of the way along the timebar, where he starts talking about String as applied to Physics, as contrasted with mathematics.

Harvey acknowledged near the beginning (about 1/8 of the way along the timebar) that a lot of people at the conference had been asking "Where are the Strings?" He addressed that issue and put the best possible face on it, I thought. In fact, he said, many of the results presented at the conference could have been (or were) derived without any reference to strings, BUT many of those were inspired/motivated by IDEAS--or based on INSIGHTS--from string theory.
====================

I would urge people to also watch David Gross's opening talk (often the opening and summary talks give valuable perspective on the current state of the field in question). By comparison with Harvey, I thought Gross seemed more forlorn, apologetic, less upbeat. You might see what you think.
http://media.medfarm.uu.se/flvplayer/strings2011/video1

 

[atyy]

Did the parrot go to heaven or hell?

 

[marcus]

Atyy, you would have to go back and listen to Jeff Harvey's talk about the the current state of the field, and the conference papers. He reminded the audience of the salient details of the Monty Python skit.

As I recall John Cleese was the customer. It was clearly a stuffed parrot, and he was trying to make this clear to the salesman. "My good fellow, this...is...an ex-parrot!"

 

[JollyJoker]

The Monty Python sketch

http://www.youtube.com/watch?v=npjOSLCR2hE"

 

[atyy]

The Monty Python sketch

http://www.youtube.com/watch?v=npjOSLCR2hE"

Cool! String theory was right!

 

[marcus]

Cool! String theory was right!

Definitely! it is uncanny how it has proven to be so right all along
Post #274 on the previous page mentioned some reasons that could help to explain the change in the climate of interest surrounding the program.
https://www.physicsforums.com/showthread.php?p=3333598#post3333598 We should try to fill out the picture and put that together with the fact that at Strings 2011 the observation kept being made that the talks did not use string theory. This struck several people at the conference as odd. (Stringy thinking can well have contributed ideas, motivation, inspirations, insights but when it came right down to it the talk was about something else.) So it required comment.

Could this have something to do with the decline in string jobs? Drop in offers of first-time faculty positions, at least in Usa and Canada, possibly elsewhere? I will summarize some of the relevant numbers.

Annual first-time faculty hires (US and Canada) in HEP theory as a whole, and in string, averaged over 3 year periods

period                           1999-2001    2002-2004   2005-2007    2008-2010
annual HEP theory hires as a whole      18           24          23           13
annual string hires                      9            8           6            2

Registered participants in the annual conference (some years omitted for brevity)

Strings 2003 Kyoto     396
Strings 2005 Toronto   415
Strings 2007 Madrid    440
Strings 2009 Rome      450
Strings 2010 Texas A&M 193
Strings 2011 Uppsala   257

Number of recent string papers making the top fifty in the annual Spires HEP topcite list

year (some omitted for brev.)   2001    2003    2005    2007    2009    2010
recent work highly cited in year  12       6       2       1       1       0

Here a paper is counted as recent if it appeared in the previous five years. This gauges the quality/significance of current work by how other researchers in the field receive it.

Links to sources here
https://www.physicsforums.com/showthread.php?p=3373453#post3373453

=============================
Atyy, when Jeff Harvey referred to the dead parrot in the Monty Python sketch, he was specifically talking about STRING UNIFICATION, not about other areas of string research FWIW.
"This parrot is not dead, it's only resting."

It's quite possible that the program of string unification is "only resting"!
He suggested that it was only resting and that we might see a major advance, such as a solution to the Landscape Problem or something comparable to that, in the next few years.

 

[atyy]

Atyy, when Jeff Harvey referred to the dead parrot in the Monty Python sketch, he was specifically talking about STRING UNIFICATION, not about other areas of string research FWIW.
"This parrot is not dead, it's only resting."

It's quite possible that the program of string unification is "only resting"!
He suggested that it was only resting and that we might see a major advance, such as a solution to the Landscape Problem or something comparable to that, in the next few years.

Jeff Harvey is like the shop keeper.

I remember Moshe Rozali saying strings, as the focus of research, had died many years ago, and how he wished the general public knew about it.

 

[marcus]

Jeff Harvey is like the shop keeper.
...

I think when Jeff Harvey said "string unification" was just "resting" he did not mean string in any narrow sense. He meant all the stuff we usually associate with the term: superstring/M, dualities of different stringy theories in different numbers of dimensions, gravity/gauge duality.
It was pointed out that there was surprisingly little of any of that at Strings 2011.
A substantial number of the people, perhaps a majority, were back to doing Quantum Field Theory.

So this was commented on by people at the conference.

We are not talking about some perception of the general public, and how the experts know better, I'm sure you realize. We are talking about something that surprised the experts this year and so they were talking about it, asking "Where's the Strings?" Harvey, in his summary talk, had to respond somehow to that question because it was on a lot of the participants' minds. And he did, early on in his talk.

As I recall it was about 1/8 of the way thru---maybe earliest 10%, or 12%, of the timebar.

 

[atyy]

I think when Jeff Harvey said "string unification" was just "resting" he did not mean string in any narrow sense. He meant all the stuff we usually associate with the term: superstring/M, dualities of different stringy theories in different numbers of dimensions, gravity/gauge duality.
It was pointed out that there was surprisingly little of any of that at Strings 2011.
A substantial number of the people, perhaps a majority, were back to doing Quantum Field Theory.

So this was commented on by people at the conference.

We are not talking about some perception of the general public, and how the experts know better, I'm sure you realize. We are talking about something that surprised the experts this year and so they were talking about it, asking "Where's the Strings?" Harvey, in his summary talk, had to respond somehow to that question because it was on a lot of the participants' minds. And he did, early on in his talk.

As I recall it was about 1/8 of the way thru---maybe earliest 10%, or 12%, of the timebar.

But how can one's *literary sense* allow a resting parrot?

 

[marcus]

But how can one's *literary sense* allow a resting parrot?

That reminds me, the most adept talk in a *literary sense* (among all the Uppsala talks I've watched so far) was the one by Frank Wilczek.

He opened by saying he had been asked to talk about the state of physics and its possible future---and that he took that to mean particle physics and cosmology. Then looked around a bit diffidently and said that of course he may have been wrong to assume that.

Then he launched into discussion of standard model QUANTITATIVE UNIFICATION saying that what with LHC and the new cosmology observations expected in the next few years it was a good time to talk about these things. So he pointed to all the signs that there probably was some aesthetic improvement, say some SO(10) unification, out there to be had. By then, the talk was about 1/8 along the timebar, and he commented:

If you find yourself wondering "what does this all have to do with string theory"...well, you're asking a very good question.​

It was elegantly honest, double-edged and scalpel-sharp.

Wilczek bears watching. Depth. Literary finesse. Gentle disarming manner.

David Gross apologetic opening talk could be watched to provide a sense of contrast.

=======================
But more to the point of your question. Do parrots never sleep? And if a literary parrot is desired, shall we not sing a lullaby to one?

Rockabye Polly in the tree top.
Where the beams meet, the femtobarns rock.
Symmetry breaks and the Higgsy will fall,
And down will come...[etc etc]

[for reasons of meter, I considered "per femtobarn" as a synonym for "inverse femtobarn", which has too many syllables, as does "Higgs boson", to fit the line. Finally settled on simply "fb".]

 

[atyy]

So he pointed to all the signs that there probably was some aesthetic improvement, say some SO(10) unification, out there to be had. By then, the talk was about 1/8 along the timebar, and he commented:

If you find yourself wondering "what does this all have to do with string theory"...well, you're asking a very good question.​

I think it's moot whether string theory is dead. In the search for quantum gravity, it has achieved at least as much as Nordstrom gravity for relativistic gravity.

I think F-theory predicts not SO(10)? http://arxiv.org/abs/0904.3932 says "Nevertheless, it has been explicitly demonstrated that charged exotics cannot be completely removed by internal fluxes in SO(10) models and this likely extends to higher rank groups as well. While one can try to engineer models that utilize additional mechanisms to remove exotics, these difficulties seem to single out SU(5) models, where exotic-free spectra can be obtained"

 

[marcus]

I think it's moot whether string theory is dead. In the search for quantum gravity, it has achieved at least as much as Nordstrom gravity for relativistic gravity...

I agree, it is rather a moot point. And oh my yes! The program has achieved a vast lot in the 43 years during which string research has been conducted.

Wilczek was brought in by the Strings 2011 organizers specifically to talk about the future of physics beyond the standard model. More specifically particle physics and cosmology, or at least that is how he took his assignment.

 

[marcus]

Went back and listened carefully to make sure I got any possible quotes right.
http://media.medfarm.uu.se/flvplayer/strings2011/video24
==my attempt at transcribing Wilczek's talk==
I was asked to speak on my view of the current state--and future--of fundamental physics--I took that to mean high energy physics and cosmology...maybe that was an error here, but that's what I took...

I will start with a word of warning--that my perspective is very much a zero-brane perspective (that's b-r-a-n-e)--and, without further ado: three ways that I see we should be going beyond the standard model.

I will discuss quantitative unification, axions, and portals. [Actually he only covered the first two, had to skip over most of the third because of the time limit.]

The standard model is astoundingly successful, but it has major esthetic flaws:
Several moving parts, tenuously connected.

Many continuously adjustable parameters.

Some of these shortcomings may reflect pure "environmental accidents", others may reflect selection bias ("anthropic principle").​

In those conditions it might be diffcult to maintain the traditional high standards of theoretical physics. We might be reduced to accommodating facts as opposed to constructively explaining them. In particular in the case of attempting to determine those continuous parameters that appear in the standard model.

We can identify a few outstanding empirical facts, however, that seem unlikely to be explained away along those lines:

The gauge group and multiplet structure of the Standard Model, that practically beg us to construct a unified theory.

And then if we go ahead and do it, that it works quantitatively remarkably well.

(reference to the approximate unification of gauge couplings at high energy.)

There are small but nonzero masses of the neutrinos. Very small compared to the masses of the other particles. (That's a qualitative fact. None of these facts appear at any reasonable level to have anything to do with the existence of an intelligent observer. So these are things which, even in a Landscape picture, we would still be required to understand.)

And the last one is the smallness of the QCD theta parameter.​

There may be others, but these are the ones that will appear in this talk.

These facts have inspired truth-worthy theoretical proposals--with wide-ranging implications.

With the coming of the LHC, and expected advances in observational cosmology, the trial date for those ideas is approaching--which is what makes it appropriate to talk about it.
==that may be all of the talk I have time to transcribe right now==

 

[marcus]

Mitchell and Lieutenant Dax have both suggested reasons for the decline in interest. I don't see any others. If you see some please point them out!

Earlier, atyy seemed to be pushing for me to define what measures of interest to use in this thread. So I did specify some. Attendance at the annual Strings conference, for one. Annual citations to recent string research, for another. (Essentially how string theorists show their interest in their own colleagues recent work---I use a 5-year cutoff for recent.)
We could also include as measure the annual rate that (US+Canada) physics departments hire stringers as new faculty---the first-time faculty hires that the theoretical particle physics grapevine tracks. What I'm looking for are objective real-world measures.

They all point the same way. The question is WHY? What's the cause of the trend?

Dax had some constructive things to point out---cause-type things, explanations. And now I find that what she said is consistent with what several other people said at the recent Strings 2011 conference at Uppsala. So I'll quote Dax and we can read it thoughtfully.

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.

Strings 2011 as a conference was very much about theorists "slowly transforming what they study" as Dax said to something more timely and closer to the real world of LHC and observation cosmology.

One of the big themes at the conference was "Where's the strings?" Jeff Harvey made that the legend on one of his first slides in his summary talk at the conclusion of the conference. The prominent people invited to present talks at Uppsala are using actual string and brane and M-thinking less and less.

Dax pointed out something very simple: the incremental style of progress. And one of the most important talks at String 2011 echoed that. Wilczek's talk about "3 ways beyond the SM" was about how to make progress and the main ideas were incremental and timely. Wilczek proposed the criteria of plausible and accessible.
He presented two research thrusts: quantitative unification (threeway) and axion cosmology. And he said that now was a good time to talk about these things because they are now accessible---the ideas are now going to be put on trial.

The gentle message that Wilczek was presenting throughout his talk was that theorists should talk about what is timely---what is accessible.

By coincidence you can also see this idea in Dax second paragraph. And you can see it in prominent string theorist's behavior. They are percolating out of string/brane-centered research, and noticing that, and even, at the conference, asking about it.

Mitchell had something earlier to say about how this shift or percolation should be viewed.
I am still trying to integrate what he and Dax said, and what was said at the conference.

Here's the kind of thing we're trying to explain---find physics-based causes for---in this thread:

Annual first-time faculty hires (US and Canada) in HEP theory as a whole, and in string, averaged over 3 year periods, with prelim. estim. for 2011

period                   1999-2001    2002-2004   2005-2007    2008-2010    2011
annual HEP theory hires    18           24          23           13          11 
annual string hires         9            8           6            2           0

http://particle.physics.ucdavis.edu/rumor/doku.php

Several comments so far have been relevant to understanding this and related trends.

 

[mitchell porter]

Marcus, I guess you're referring to my remarks quoted in comment #261 (page 17 of this thread), about strings and branes perhaps being interpreted as abstract entities living in the "RG space" of a quantum field theory. I gave some problems for this perspective in comment #271. But just to recapitulate: this is essentially a question of how to interpret the appearance of a string theory in the holographic AdS bulk of a conformal field theory in flat space. You could take the attitude that the CFT, the boundary theory, is the real theory, and the string theory is a sort of auxiliary construct, an unphysical representation of composite states in the boundary theory, in a "space" (anti de Sitter) which is actually just a parametrization of energy scale and a few other properties of the boundary states. And certainly, in many of the applications of AdS/CFT, the AdS space is treated as just a helpful construct.

If you tried to take this perspective seriously, you might conclude that M-theory is the universal theory of a very large class of CFTs, when represented in this way. That in itself is a mysterious and interesting fact - why should M2-branes and M5-branes and the rest of the apparatus show up so naturally, in the expanded holographic interpretation of CFTs satisfying a few simple properties like http://arxiv.org/abs/0907.0151" ? The fact that CFTs also define a "skeleton" of the space of all possible QFTs (from the perspective of RG flow) only serves to underline the obscure intuition that M-theory here has a fundamental relationship to QFT in general.

But if we try to limit the significance of M-theory to being a master theory of RG flow for QFTs in flat space, we run up against the problem that string theory has been defined on backgrounds other than anti-de-Sitter! For most of the subject's history, string theory was studied on flat space backgrounds, and cosmological realism has led to the study of string theory in expanding space-times such as de Sitter space. The de Sitter example is interesting, because one version of "dS/CFT" would say that time is the extra holographic dimension here (as opposed to the extra radial dimension of space in AdS/CFT) - the CFT is a timeless Euclidean CFT which exists at past infinity, and the RG flow of that theory is the phenomenological time in which we perceive events as happening! That would also mean that time exists in the holographic bulk, where the strings and branes also live; with the further implication that if we regard our everyday space and time as physical, then we will have to regard the strings and branes as physical too, and the CFT as the peculiar asymptotic construct which lives at past infinity. Though I'm sure some people would convince themselves that they had found a way to tune into the timeless pre-holographic pre-big-bang reality... :-) Of course, this is all severe speculation, about the future of physics and about how it will be received, way beyond the present state of the art.

Coming down to earth, there's the more factual question of string theory's relationship to experiment, and how that will evolve in future. Well, string theory research clearly has a broad span that stretches from high theory and the mathematical study of strings in spaces quite unlike reality, to the numerous models that are produced by string phenomenologists. Dax's implication that string theorists are becoming "ever more detached" from experimental physics just isn't true, or else we wouldn't have new papers every month trying to realize the standard model, and extensions of it, in string theory. The new data from the LHC (i.e. the complete absence of anything beyond the standard model below 1 TeV, and the probable absence of the Higgs) is first of all going to roil the waters in ordinary field theory - there will be an attempt to establish which model should become the next standard model. This will certainly affect string phenomenology, in that people will now be trying to construct the "next standard model", and it won't just be one-way traffic either, since ideas about how to break supersymmetry are greatly informed by the available options in string theory.

Just as there is a spectrum of opinions in fundamental physics about what comes next, there's a spectrum of skepticisms - some are just skeptical about string theory, some are skeptical about supersymmetry, some about the Higgs and grand unification... some about relativity :-) ... etc. In certain respects, I think the interesting question for the immediate future will be attitudes towards supersymmetry, not string theory. If the LHC shows nothing new, the skeptics who reject, not just string theory, but also SUSY and perhaps GUT, will become more vocal. We might get a few more surprising "apostates" among the "elders" of physics. A failure of the Higgs to show will in any case be bringing new theories into prominence, and a lot of people will be clamoring for attention.

I can't say anything reliable about how that will play out, but I pay attention to a few rather heterodox ideas myself, so I can at least describe my own thinking. First, I should say that the more I've learned, the more I've appreciated the logic of various "orthodox" positions. The Higgs performs a function, supersymmetry performs several functions, string theory provides a further unification and a UV completion. This hegemonic view of what's next was not arrived at arbitrarily. In any case, when I study something that's really from left field, like Marni Sheppeard's motivic twistorial octonionic extension of Bilson-Thompson's braids, I don't do it just because it's a radical alternative to the stringy status quo. Inevitably there is also some possibility of hybridization or reinterpretation of string at stake, too. If you look at the ingredients of Sheppeard's synthesis, twistors are already mainstream, motives are definitely coming up, only the octonions are a little fringy. (As for the braids, the idea that particles are "octopi in the spin foam" is definitely fringe, but you can have knotted Wilson loops in perfectly orthodox gauge theories, so there's a good chance that some of the mathematics will cross over.) It is entirely possible that completely mainstream string phenomenological models have a mathematical re-expression in terms of motivic, twistorial, octonion-valued loop observables! The conceptual revolutions internal to string theory are definitely not over; the http://arxiv.org/abs/hep-th/0111068" , in particular, remains thoroughly unexplained.

So I think one can reliably predict that the future of string theory includes further conceptual change ("M is for motive"), and changes in the focus of phenomenological work, as new experimental data arrives. The big practical question is, I believe, string cosmology, and this will decide whether the eternal inflationary landscape that, say, Susskind favors is the right way to approach vacuum selection, or whether some other approach (a set of disjoint AdS superselection sectors, corresponding to different boundary CFTs?) ends up dominating. The centrality of CFTs to QFT, and of strings to AdS/CFT duality, also guarantees that strings will remain part of physics so long as QFT remains part of physics.

 

[marcus]

Mitchell, thanks for so much thoughtful and hopeful comment. Each paragraph deserves a detailed answer and I hope we get some from other interested people.
Much of what you say links the continued individual subjective fascination of the subject to the diffusion and dissipation of its thrust---and the present tendency to blend in with other fields, fields not specifically stringy braney eMmy or even extraDeeful.
So, paradoxically, you are giving compelling reasons for our seeing a realworld loss of interest while morally and at a speculative level one's interest can be as strong as ever.
We can see the prospects for SUSY dwindle, and first-time faculty string hires drop off, and yet we know that string will always be with us, because of its intrinsic fascination and the fact that it is (as you explain) inextricably interwoven with ordinary 4D quantum field theory!

I find what you say here particularly compelling:

The centrality of CFTs to QFT, and of strings to AdS/CFT duality, also guarantees that strings will remain part of physics so long as QFT remains part of physics.​

Of course there are degrees of "remaining a part of", and degrees of "centrality." But for many people, even as they percolate out into more ordinary d=4 quantum field theory research, the string inspiration will remain alive in their hearts.

I hope everyone reads the comments at Woit's blog to his 25 July post:
"String theorists throw SUSY under the bus."
http://www.math.columbia.edu/~woit/wordpress/?p=3864
John Baez and Bee Hossenfelder both commented.