Causes of loss of interest in String program

[marcus]

OK folks, here is the revised tabulation. No one has explained why there were so many papers for so long and then suddenly, in most cases, so few:

          1995-1998      1999-2002      2003-2006      2007-2010

Strominger     23             14             22              4
Maldacena      27             33             24              9 
Polchinski     21             17             11              4
Harvey,J       16             15              9              2
Duff,M         24             17              8              5
Gibbons,G      17             29             11              2
Dijkgraaf      18             11              9              7
Ooguri         31             18             13              8
Silverstein,E  16             15             16             10
Seiberg,N      19             16             22              1

Suggestions of other choices of DESY classifications? Anyone who wants can try running other search tallies. Or do a detailed examination of this one and look for excuses in the case of individual researchers? The overall picture is what impresses me.

BTW it does look to me, just glancing at their papers that Petr Horava and Erik Verinde are writing less string these days, also possibly other stars ike Giddings, Gubser, Marolf. Don't want to bother adding more names at this point. Overall picture is clear enough.

Attendance and activity at the annual Strings conference would be another indicator. Eg. the fraction of invited talks at Strings 20xx that were actually about strings/branes and extraD--aimed at unification of fundamental physics (not some offshoot application.)
Here's a recent list of locations: Toronto, Beijing, Madrid, Geneva, Rome, College Station, Uppsala.
The last one where I could sense real excitement (via web) was Toronto, although Rovelli's talk at Geneva (Strings 2008) was notable, as was the following Q/A discussion.

 

[smoit]

OK folks, here is the revised tabulation. No one has explained why there were so many papers for so long and then suddenly, in most cases, so few:

          1995-1998      1999-2002      2003-2006      2007-2010

Strominger     23             14             22              4
Maldacena      27             33             24              9 
Polchinski     21             17             11              4
Harvey,J       16             15              9              2
Duff,M         24             17              8              5
Gibbons,G      17             29             11              2
Dijkgraaf      18             11              9              7
Ooguri         31             18             13              8
Silverstein,E  16             15             16             10
Seiberg,N      19             16             22              1

Suggestions of other choices of DESY classifications?

As has been pointed out to you on several occasions, the most glaring problem with your estimate is that you are operating in terms of absolute numbers without taking into account the sample size. Also, your keyword search does not take into account the change of perspective of what is and what is not a string related paper. People have already given you many examples of papers, which your phony "core string" criterion failed to take into account, e.g. http://www-library.desy.de/cgi-bin/spiface/find/hep/wwwtopics?key=7529236"
List of keywords assigned to the paper: Chiral symmetry breaking and intersecting D-brane systems

symmetry breaking, chiral
D-brane
holography
Jona-Lasinio-Nambu model
Gross-Neveu model

 

[marcus]

So go ahead and run your own search tally for those ten people with what you think are better terms! All the defensiveness and denial is amusing---anyone who takes an unbiased look can see the program is in trouble (with top people devoting more of their effort to straying off in different directions).

The interesting thing, I think, is WHY. I suspect that a lot of it has to do wth the 2003 KKLT paper and Susskind's panicky reaction. KKLT failed to deal with positive cosmo constant in a satisfactory way and hung the 10^{too many} vacuums nightmare out in plain view. Since then, things have pretty much gone to College Station .

 

[fzero]

So go ahead and run your own search tally for those ten people with what you think are better terms! All the defensiveness and denial is amusing---anyone who takes an unbiased look can see the program is in trouble (with top people devoting more of their effort to straying off in different directions).

Can you explain to us what different directions are being strayed to, why they are so different from what is considered string theory proper, and how the topics are unusual given the past research interests of the physicists involved?

 

[marcus]

Can you explain to us what different directions are being strayed to, why they are so different from what is considered string theory proper, and how the topics are unusual given the past research interests of the physicists involved?

Sure. Bear in mind that I am primarily interested in the (no prior geometry) QG program with only moderate curiosity about string research. I started watching around 2003 and was impressed by the KKLT paper at that time and Susskind's "anthropic" fit that occurred a few months later. A lot of rumpus on Usenet at the time. This may tend to color my understanding---so I'd like to hear other explanations.

As a retired mathematician, I perhaps see the Langlands Program differently from you. In 2006 I attended 3 ninety-minute lectures by Witten on his main research interest at the time. He was hosted by the Math and Physics departments here. He did not mention String at all, and gave a one sentence reply at the end of the last lecture when it came up in a question from audience.

As a string researcher you may have a differerent perspective in which String is a big central prominence and everything relates to it in some way. So you may perhaps NOT see the part-time dispersion of interest that I see.

But anyway you wanted some examples of top people straying off from the main program (I haven't suggested this was full-time, just a significant part-time reallocation of research activity.)

Erik Verlinde is one case.
Petr Horava is another.

And you wanted me to describe the directions. Well in Verlinde and Horava case it is about gravity in 4D There are no string/branes in the picture, and no compactified extraD.
There is no drive for unification. The emphasis is on actually understanding gravity.

That same general direction characterized Witten's talk at Strings 2007. No strings/branes/extraD but rather a focus on understanding gravity. Then he declined to give a talk at Strings 2008, and again in 2009 only gave a public lecture which was not about string. As I recall his Strings 2010 talk was in a direction similar to 2007---low dimension gravity---but I would have to check. I think now, out of simple loyalty, he HAS to say nice things in public and give a more stringy paper at Uppsala. We'll see when the program comes out. Senior people have to give some moral support to the community, in the present situation.

A lot of the talks at Strings 2010 were spinoff to condensed matter or QCD. Finding uses for the math. But one misses the old TOE-spirit. The zeal and enthusiasm of 10 years ago.

 

[fzero]

As a retired mathematician, I perhaps see the Langland Program differently from you. In 2006 I attended 3 ninety-minute lectures by Witten on his main research interest at the time. He was hosted by the Math and Physics departments here. He did not mention String at all, and gave a one sentence reply at the end of the last lecture when it came up in a question from audience.

As a string researcher you may have a differerent perspective in which String is a big central prominence and everything relates to it in some way. So you may perhaps NOT see the part-time dispersion of interest that I see.

I explained in post #24 that the only Langlands papers that were assigned as string papers were the ones where the abstract made clear that results from mirror symmetry were being used. I don't recall how many this was, perhaps 2 or 3, but the majority were assigned to pure QFT in the absence of a detailed reading.

But anyway you wanted some examples of top people straying off from the main program (I haven't suggested this was full-time, just a significant part-time reallocation of research activity.)

Erik Verlinde is one case.
Petr Horava is another.

And you wanted me to describe the directions. Well in Verlinde and Horava case it is about gravity in 4D There are no string/branes in the picture, and no compactified extraD.
There is no drive for unification. The emphasis is on actually understanding gravity.

These authors are not in your table that you keep posting. What about those authors?

That same general direction characterized Witten's talk at Strings 2007. No strings/branes/extraD but rather a focus on understanding gravity. Then he declined to give a talk at Strings 2008, and again in 2009 only gave a public lecture which was not about string. As I recall his Strings 2010 talk was in a direction similar to 2007---low dimension gravity---but I would have to check. I think now, out of simple loyalty, he HAS to say nice things in public and give a more stringy paper at Uppsala. We'll see when the program comes out. Senior people have to give some moral support to the community, in the present situation.

A lot of the talks at Strings 2010 were spinoff to condensed matter or QCD. Finding uses for the math. But one misses the old TOE-spirit. The zeal and enthusiasm of 10 years ago.

Witten has consistently published and publicized non-string work in QFT and mathematical applications. The central result of my analysis was that the ratio of string to nonstring physics hasn't changed significantly over the last six years. Witten's most recent paper is undeniably a string paper, even if it is not a phenomenological one.

As I said before, most string theory papers dating back as far as 1995 and even beyond are not about direct ToE topics. I also said that this was not unusual in physics, one often studies less realistic models to develop techniques and uncover clues about universal behavior. I cited lattice gauge theory as another example where you would find a bulk of papers that were less about the real world and more about methods and drawing lessons.

 

[marcus]

Verlinde and Horava are useful examples to illustrate where I think the program is drifting.
If you find it for some reason inconsistent that they are not on the table, I will add them.

It is hard to see a direction in the current program. One possible perspective is that M-theory has failed to emerge as a definite formulated theory. M stands for Missing, I guess. And so far the understanding of gravity appears dependent on prior geometry or some dubious excessively elaborate structure. This is not to criticize the program but to try to get an idea of directions in current research.

I see Strominger, for example, studying black holes in ordinary 3D or 4D. Talking about this at Strings 2010.
Weinberg used to do string and thought highly of it at one time, he gave an invited talk at Strings 2010 which was on a non-string approach to QG that does not involve extraD. The asymptotic safety approach.

Since I am not an insider I can only speculate as to how it looks from within the community but one suspicion I have is that people like Strominger Horava Verlinde Weinberg see a deficiency that they are trying in various ways to remedy--just getting ordinary 4D quantum gravity right.

Maybe you would like to analyze the research output of some of these people. That would be very helpful!

          1995-1998      1999-2002      2003-2006      2007-2010

Strominger     23             14             22              4
Maldacena      27             33             24              9 
Polchinski     21             17             11              4
Harvey,J       16             15              9              2
Duff,M         24             17              8              5
Gibbons,G      17             29             11              2
Dijkgraaf      18             11              9              7
Ooguri         31             18             13              8
Silverstein,E  16             15             16             10
Seiberg,N      19             16             22              1
Horava          6              5              4              6
Verlinde,E     10              7              7              2

http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+A+Verlinde%2C+E+AND+%28DK+STRING+MODEL+OR+DK+MEMBRANE+MODEL%29+AND+DATE+%3E+1994+AND+DATE+%3C+1999&FORMAT=www&SEQUENCE=

http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+A+Verlinde%2C+E+AND+%28DK+STRING+MODEL+OR+DK+MEMBRANE+MODEL%29+AND+DATE+%3E+1998+AND+DATE+%3C+2003&FORMAT=www&SEQUENCE=

http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+A+Verlinde%2C+E+AND+%28DK+STRING+MODEL+OR+DK+MEMBRANE+MODEL%29+AND+DATE+%3E+2002+AND+DATE+%3C+2007&FORMAT=www&SEQUENCE=

http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+A+Verlinde%2C+E+AND+%28DK+STRING+MODEL+OR+DK+MEMBRANE+MODEL%29+AND+DATE+%3E+2006+AND+DATE+%3C+2011&FORMAT=www&SEQUENCE=

Suggestions of other choices of DESY classifications? Anyone who wants can try running other search tallies. Or do a detailed examination of this one and look for excuses in the case of individual researchers? The overall picture is what impresses me.

 

[suprised]

Do you really believe what you write or is this just provoction, marcus?

 

[atyy]

It is true that Stominger's work is arguably not "pure string", as he himself repeatedly says. However, the non "pure string" part goes all the way back to 1997. http://arxiv.org/abs/hep-th/9712251

Furthermore, this result was first illuminated by Strominger and Vafa by strings. So if you want to define there to be a decrease in string research, it is because strings has become accepted physics, on which current quantum gravity research is built.

 

[marcus]

Do you really believe what you write or is this just provoction, marcus?

Of course I believe. I also credit what you have written (except when it is an attack or misrepresentation of me). I find some of your posts enlightening---they seem exceptionally well thought-out and have the ring of true insight. Really. This is not flattery.

Much of what we write is honest suspicion or conjecture. Perhaps your word "believe" is too strong. We cannot know for sure, or make unqualified statements. We are exploring what may be possible causes. I try to get to the truth and when I cannot be certain I qualify and say "may" or "could".

You have sometimes said that I misinterpret or misquote from your posts. I don't think so.

One thing you have suggested is that it is wrong to think of string in terms of compactified extra spatial dimensions.

You have indicated that you think the program may potentially have been damaged by taking wrong turns.

THIS RINGS TRUE TO ME. I also respect your insight as an insider of 25 years experience in string research. In fact much of my thinking in this thread is influenced directly by what you have said.

You have said that many in the program have gotten away from thinking in terms of extra spatial dimensions.

Again this rings true. It agrees with what I, as an occasional outside observer, have noticed hints of. And it makes sense, if those people realized it was wrong to think in those naive terms they would naturally want to change to a different perspective.
Moreover this is only part of the more complete message you've conveyed.

I think many of the top-level people have probably gotten away from thinking of reality as being composed of branes and strings, or having a requirement of supersymmetry.

So I am interested in what direction the program will take. Your ideas, as they come through, may be very helpful and informative about this.

 

[element4]

I have just read all 115 posts on this thread, and let me declare myself as a completely unbiased person in this topic, with no particular interest or agenda wrt. LQG vs string theory.

What strikes me the most, is Marcus' failure in understanding the critic of other people! His "analysis" regarding "decline of interest in string theory", is clearly oversimplified and gives a unreliable picture of the situation, as fzero showed by performing a more correct and detailed analysis. Furthermore in post #46, fzero demonstrated how flawed Marcus' analysis is by using the key word "quark model". In #47 Marcus replies

Yes perhaps this indicator is dreadfully flawed . We can still see what we make of it nonetheless.

which to me indicates that Marcus is more interested in pushing his own agenda, rather than performing a serious analysis. Furthermore others have been given many very good reasons why this simple analysis may give wrong results, but Marcus keep ignoring them and keep copy/pasting the same stuff in all his posts.

I really believe that a person like Marcus can be very dangerous for young students trying to get an Idea about what the current situation of QG research is. There is an incredible amount of LQG biased posts in this forum, almost entirely due to Marcus.

I am really glad I am not in the field of QG. It seems that lack of experimental input can make science into some sort of religion for some people, its mainly in these field people like Lobus Motl and Marcus can exist.

 

[marcus]

I must say that I feel rebuked and abashed to be compared with Lubos Motl. I don't seriously think that indicator is "dreadfully flawed" or that anyone rough informal indicator matters all that much. Fzero only analysed one person out of a dozen or so, and he did not contradict my finding that the number of that person's string papers had declined (even with his broader definition.)

I think the String program is in deep trouble going back maybe to around 2003 or so. I'd like to know other people's views on this. What reasons for it they can think of. One should be able to talk openly about this.

So what would you propose that I do? I don't want to have to argue all the time with people who simply deny that there is a problem.

I do want to explore the underlying reasons the program is in trouble.

On the other hand I don't want to seem like a Motl to people like you (who seem to be of good faith and not to have an ax to grind).

 

[marcus]

BTW if anyone is interested here is a link to Strings 2011.
http://www-conference.slu.se/strings2011/programme_NEW.html

This gives a list of the confirmed invited speakers (scroll down to it).
As the conference takes shape, and titles of talks are listed, this will afford a window on the current state of the string program. So it should be interesting to watch.

Here are links to the websites of previous string conferences:
http://www-conference.slu.se/strings2011/links.html
As an example of the kind of information, in this case from Strings 2004:
http://strings04.lpthe.jussieu.fr/speakers_list.php
http://strings04.lpthe.jussieu.fr/participants.php (477)
It's a way to look back into the past.
And something more recent:
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/workshops/strings2008/?site=content/talks.html
http://indico.cern.ch/confRegistrantsDisplay.py/list?confId=21917

 

[negru]

Marcus, all the info and "data" you use to evaluate the level of interest in string theory could just as well be interpreted as evidence of some degenerative brain disease affecting all string theorists.

If you want to probe the interest in string theory, go around and ask string theorists if they are still interested in string theory. That's the only way to do it.

 

[marcus]

Marcus, all the info and "data" you use to evaluate the level of interest in string theory could just as well be interpreted as evidence of some degenerative brain disease affecting all string theorists.

If you want to probe the interest in string theory, go around and ask string theorists if they are still interested in string theory. That's the only way to do it.

Heh heh, that's funny! Actually what I'm looking for are the signs of coherent activity/vitality/direction in the field. The kind of thing that gives excitement and interest like what those of us who were around remember from 10 years ago. I don't know what interest means unless it shows in people's behavior.

Maybe I should have called it something else like "energy" or "focus", but I used the word interest.

So when I measure interest I look at the numbers of papers top people are producing AND how much they are cited by the rest of the community----not only activity but also an idea of the value of that activity.

There are a dozen signs that this is down--you really don't even need numbers. E.g. just listen to David Gross who for several years seemed to be repeating every chance he had "We don't know what string theory is!" and "We need a fundamentally new idea."

But if you like numbers you can look at the annual conference participants, for example:
Strings 2004 had 477 participants, Strings 2008 had 400,...want to fill in the blanks?

Strings 2004 477
Strings 2008 400
Strings 2010 193

I remember at Strings 2008 David Gross referred to the annual Strings conference as "the canary in the mine" and was urging people to come up with good ideas for future conferences. I like him, he is honest at times and is sincerely concerned with the health and direction of the field---he doesn't walk around with his eyes shut or wearing rosy glasses. He has often given the summary talk at the end of Strings, but this year he will give the opener.

 

[negru]

Ok, then for example how do you make the difference between people losing interest and problems getting harder via your method?

 

[marcus]

Ok, then for example how do you make the difference between people losing interest and problems getting harder via your method?

I'm hoping to hear other people's ideas about causes--hopefully underlying physics reasons--for a decline in activity or a loss of focus/direction. I suppose "problems getting harder" could be one possible explanation of what we see.

I hope you understand I have no particular "method"---I just start from a recognition of the obvious: the program is in trouble. This is widely realized and there are probably a dozen signs of it. (citations drop, conference attendance, what central figures say when not doing PR for the public, publication stats by top people, focus and direction, topics at conference, faculty hiring at univ. phys. dept., defensiveness, taboos against talking about the situation, oversensitivity, and so on...).

This is not "method", it is just acknowledging the elephant. To solve a problem you first have to recognize it. You mentioned "problems getting harder". Someone else brought that up earlier. He suggested people aren't working on what they need to be working on because those problems are hard and institutionally you need to write papers.
So you doodle around. That might be a factor, but it is not something that appeals to me as an explanation. I'm looking for something more specific.

In my view the most interesting reasons were indicated by a senior expert who doesn't enjoy being quoted. He got emotional and angry when I mentioned leadership, which I think indicates that deficient leadership may be contributing to the trouble. Leadership helps people focus on the hardest roadblocks and break them in a directed way bit by bit. Leadership can also recruit and build active participation even while the problems are getting harder. He also seemed to be saying not to depend on SUSY so much and not to think in terms of compactified XD.

He also said not to consider the Landscape a disaster, which I think is an appeal for calm and a reference to the damage caused by Susskind's panicky rush into Multiverse in 2003.
Now this is my interpretation: I think that some developments in 2003 did considerable harm to the program and that has not been completely repaired yet.

These are not "positions" I necessarily want to defend. Arguing is often a waste of time. These are some sample ideas I am laying out to show you the kind of thing I am looking for. I want to understand better the loss of focus or whatever you want to call it, and hear discussion causes and ways out of the doldrums.

 

[suprised]

One thing you have suggested is that it is wrong to think of string in terms of compactified extra spatial dimensions.

...
You have said that many in the program have gotten away from thinking in terms of extra spatial dimensions.

This is not what I said. I said that the concept of extra dimensions is highly ambiguous (for example completely different classical geometries can describe the same physics), so one should not attribute an unambiguous physical reality to them. Focusing too much on a particular geometry may lead to a misleading intuition.

For example someone may strictly believe that a "brane world" describes our world, whereas this may be just one of many dual formulations of the theory, and other formulations do not have branes at all. So in this sense there is no unambiguous physical reality to these branes.

Similarly, AdC/CFT duality furnishes a higher dimensional interpretation of simple (N=4 susy) gauge theory. When viewed in the appropriate limit of the parameter space, indeed the theory looks as if it would come from a type II string compactified one some AdS_5 x S_5 space. But in the more familiar limit of small number of colors, no trace of those extra dimensions is seen. So are these higher dimensions real or not?

My point was to emphasize that whereas the higher dimensional viewpoint plays a very important role, it is in general an ambiguous concept and one should be careful not to be too biased towards this picture; it applies literally only to a fraction of the string parameter space.

marcus, you give these statements a spin and now claim that "program have gotten away from thinking in terms of extra spatial dimensions" . This is totally wrong and misleading.

Similar your claims that the string program lost interest... just have a look in the daily hep-th listing and you see that there is no decline of string papers at all. The few selected names you cite do not "prove" that the field is in decline, you miss certain important points. One is that also these people get older, and older people write less papers, for various different reasons. Why not focus on other people who have their productivity peak today? Moreover, the situation today is different than during the "duality revolution" 10-15 years ago, when it was easier to write many papers. Currently it is hard to write short important papers, rather papers are typically longer and more technical (and thus take considerably more time to produce).

So with your statements you do neither justice to many hard working people nor any favor to science.

 

[marcus]

I'm delighted that you have given us additional explanation, suprised. Thanks!

 

[negru]

Even if your numbers do work out (i'm not convinced), one other reason might be that these days string theory needs less justification than it did back in the day. With string theory so firmly established in various contexts, people can afford to take it easier, since they don't have to prove anything anymore.

When I was visiting grad schools talking to various people, there was no special distinction being made by anyone between string theory, lattice qcd, observational astronomy, or what have you. Perhaps the only thing I found surprising was how many CMT people were getting interested in ads/cft stuff.

Your attempts to have discussions on the current state of the ST program are completely decent, and I think that most people here cooperated fully giving their honest impressions and assessments. However, most if not all of your posts are completely biased towards portraying string theory in some kind of deep and terrible crisis. Your motivation is clearly not to understand the cause of this stringy apocalypse, but simply to repeat the words "crisis", "loss of interest", etc. If you want non-defensive, honest and objective discussions, you should stop making threads like:

Causes of Imminent and Indisputable Doom of String Theory
Number of papers Witten wrote:
1990: 100
2000: 10
2010 (estimate): -80

Why is string theory dying. Discuss

 

[suprised]

PS: I can't really understant why people who are not working in the field, believe that they have enough judgement to go out in the open and teach the public about their "insights". Especially if they are not even working scientists, but rather blog or book authors, etc.

 

[Haelfix]

PS: I can't really understant why people who are not working in the field, believe that they have enough judgement to go out in the open and teach the public about their "insights". Especially if they are not even working scientists, but rather blog or book authors, etc.

You would think that if someone asks a sociology question, and then 4 or 5 professionals working in the field show up and answer the sociology question, that it would give some amount of pause before disputing them.

Quite honestly it is rather surreal reading pages upon pages about the motivations of people that are friends, colleagues, advisors, mentors, coauthors and so forth.

Not like any of this matters one way or the other!

 

[MTd2]

Strings 2004 477
Strings 2008 400
Strings 2010 193

Strings 2003 396
Strings 2005 415
Strings 2006 186
Strings 2007 (site broken)
Strings 2009 450

 

[marcus]

Strings 2003 396
Strings 2005 415
Strings 2006 186
Strings 2007 (site broken)
Strings 2009 450

http://www-conference.slu.se/strings2011/links.html

Thanks MTd2. I recall Strings 2006 was in Beijing. Where did you get the number 186?
==quote http://www.math.columbia.edu/~woit/wordpress/?p=415 ==
Update: There’s an article in Tuesday’s New York Times about Hawking and the Beijing conference by Dennis Overbye. According to Overbye there are 800 physicists there and 6000 people turned out to hear Hawking. Anyone know if this is right?

Update: There’s a detailed report on the first day of the conference from Jonathan Shock.

Update: Victor Rivelles reports on day 2 of the conference. He describes Yau as taking credit for proving the Poincare Conjecture, which, if true, would be seriously misleading. ChinaDaily describes the number of physicists at the conference as 600. I’m guessing that 400 is the number of participants from outside China, 6-800 the total number. If so, this would be the largest string theory conference ever held.
==endquote==

Let me know if there is any reason we should not take the lower figure of 600? With this correction I'll merge our two lists:

Strings 2003 396
Strings 2004 477
Strings 2005 415
Strings 2006 ~600
Strings 2007 (site broken)
Strings 2008 400
Strings 2009 450
Strings 2010 193

If I had to summarize what has surfaced so far about "causes of loss of interest in String program" I would have to say that the most meaningful listing so far was given in Tom's thread. At this point I will simply quote without trying to interpret, as I did earlier. I'd like to get some other ideas to add to this. And of course someone could also start a thread about "causes of gain of interest in String program"---the program could be simultaneously gaining energy from some direction (CMT?) and losing it in another and there might be interesting reasons for both

I think this exchange is fairly profound, and deserves careful study:

Last but not least my feeling is that at a rather early stage there was a wrong turn (I cannot tell exactly which one) which prevents us from asking the right questions. This is our blind spot.

Think about condensed matter physics and classical electrodynamics. You can do a lot based on continuous approximations like electrodynamics in media using polarizability, susceptibility, ...; you can use effective theories like navier-stokes equations; you can study London equations, Ginzburg–Landau theory, ... I would say that collecting those effective theories one can study a huge amount of condensed matter physics. Perhaps one can even use a kind of construction principle, I would say this could be Maxwell plus Schroedinger equations.

Unfortunately based on this construction principle one is not able to ask questions based on photons. They simply do not exist in this framework. So the framework allows us to construct a nearly exhaustive description of low-energy phenomena is therefore certainly "right". But at the same time it's incomplete as it is unable to ask the right questions about photons. Now in this case you have experiments at hand which force you to think about potons (photo-electric effect), but in string theory these experiments are missing. Therefore we must find the correct theory (theories) simply by matehmatics, logics and intuition. No experimental guideline! Even worse we are not even able to say which experiments are missing. We are not ableto ask these questions in the string theory framework.

String theory (as any other theory) limits our ability to ask questions. w/o further experimental input we are stuck. In the standad model we can ask questions regarding the Higgs boson. We can even ask questions regarding alternative mechanisms and we are not stuck once the LHC shows that there is no Higgs boson.

Now the problem is that I can only say that at a very early stage in string theory we may have chosen the wrong direction. From that point onwards we lost the ability to ask questions which would enable us to overcome the blind spot of string theory.

Now let's talk about other theories, like LQG. I don't want to promote LQG as the alternative theory to string theory in sthe sense that it has the ability to achieve unification of forces. I don't think so. I am simply saying that LQG is able to ask different questions. LQG is able to ask questions regarding an algebraic spacetime structure. This question is (afaik) not pronounceable in the language of string theory (maybe I am wrong; I am not an expert on matrix models).

So an alternative theory X may have some value because it enables us to ask different questions. If these questions seem to be "wrong" in the context of string theory this is not a problem of theory X, but a step forward for string theory - provided one accepts that this question could make sense in general and that one should try to find out what prevents string theory from asking this question.

Perhaps there are string theorists here able to tell us what could have been this wrong turn in the very beginning.

I guess there were many potentially wrong turns - at least in the sense of bias towards certain ways of thinking about string theory. Here a partial list of traditional ideas/beliefs/claims that have their merits but that potentially did great damage by providing misleading intuition:

- That geometric compactification of a higher dimensional theory is a good way to think about the string parameter space
- That perturbative quantum and supergravity approximations are a good way to understand string theory
- That strings predict susy, or have an intrinsic relation to it (in space-time)
- That strings need to compactify first on a CY space and then susy is further broken. That's basically a toy model but tends to be confused with the real thing
- That there should be a selection principle somehow favoring "our" vacuum
- That a landscape of vacua would be a disaster
- That there exists a unique underlying theory
- That things like electron mass should be computable from first principles

Most of these had been challenged/revised in the recent years, and many people think quite differently about them than say 15-20 years ago.

 

[suprised]

marcus, you should pay attention to the last sentence you cited. These issues are mostly ones of the past!

 

[marcus]

The last sentence:

Most of these had been challenged/revised in the recent years, and many people think quite differently about them than say 15-20 years ago.
​

marcus, you should pay attention to the last sentence you cited. These issues are mostly ones of the past!

Yes! I have been thinking about that last sentence a lot! And I tried to bring the "many people" idea forward a few posts back. But I thought you then contradicted me. I'm glad to see you bringing that point back up.

Subject of course to your correction, I would venture to apply that last sentence to this:

That geometric compactification of a higher dimensional theory is NO LONGER a good way to think about the string parameter space.
​

And I would tentatively venture to conclude that many people (I would guess more advanced people) have already gotten away from thinking in terms of compactified extra spatial dimensions.

If this is true (I hear some American string theorists objecting that it is not) then I see this as positive and hopeful for the program.

The blue statement is, of course, my own understanding of what you said, so please correct if mistaken.

 

[marcus]

Anyone who is at all interested in this discussion should read post #123
https://www.physicsforums.com/showthread.php?p=3265766#post3265766
which has a clarification by Suprised spelling out in detail how he wants us to understand this point.

You should read the whole post, but here's an excerpt that give a taste of what he's saying:

the concept of extra dimensions is highly ambiguous (for example completely different classical geometries can describe the same physics), so one should not attribute an unambiguous physical reality to them. Focusing too much on a particular geometry may lead to a misleading intuition.

For example someone may strictly believe that a "brane world" describes our world, whereas this may be just one of many dual formulations of the theory, and other formulations do not have branes at all. So in this sense there is no unambiguous physical reality to these branes.

Similarly, AdC/CFT duality furnishes a higher dimensional interpretation of simple (N=4 susy) gauge theory. When viewed in the appropriate limit of the parameter space, indeed the theory looks as if it would come from a type II string compactified one some AdS_5 x S_5 space. But in the more familiar limit of small number of colors, no trace of those extra dimensions is seen. So are these higher dimensions real or not?

My point was to emphasize that whereas the higher dimensional viewpoint plays a very important role, it is in general an ambiguous concept and one should be careful not to be too biased towards this picture; it applies literally only to a fraction of the string parameter space.
​

 

[atyy]

Fundamentally, there is no loss of interest in the string programme. The subtle points about geometric/non-geometric interpretation of paramters in string theory should not be taken to support the untrue premise of the thread's title.

 

[marcus]

Fundamentally, there is no loss of interest in the string programme. The subtle points about geometric/non-geometric interpretation of paramters in string theory should not be taken to support the untrue premise of the thread's title.

I'm tired of arguing about that one, Atyy. "Subtle" or not, I'm very interested in the points that Suprised has made here. I'd like to understand better how the program is going to evolve---what direction it will take going forward. Maybe it's just me (I suspect not) but right now I don't see a clear direction/paradigm and in fact I think that is at the heart of the earlier discussion Tom and Suprised were having, which I quoted. Take another look at Tom's post.

Call it loss of focus or direction if you like. People mean too many different things by interest---it gets defined by how you decide to measure it.

 

[negru]

But I'm pretty sure most people already knew about these ambiguities. I distinctly remember talking about extra dimensions in a different thread. I'm not sure why you are still focusing on this point.

Just take a simple example. Suppose our real 4d world(whatever that is) is equivalent to some other 5d theory. How many dimensions are there then, and what is the 5th one? It's simply a bad question to pose. The way we interpret these things makes no difference. I could very well think of extra dimensions as real dimensions, or as some extra degrees of freedom. It's the same thing.

 

[atyy]

Fundamentally, there is no loss of interest in the string programme. The subtle points about geometric/non-geometric interpretation of paramters in string theory should not be taken to support the untrue premise of the thread's title.

I'm tired of arguing about that one, Atyy. I'm interested in the points that Suprised has made here.

Good. Let's make it clear that you do not take a discussion of suprised's points to indicate any loss of interest in string theory.

 

[marcus]

Good. Let's make it clear that you do not take a discussion of suprised's points to indicate any loss of interest in string theory.

As I say, "interest" is a tricky word. Discussion of Suprised's points does in fact represent my interest in the string program. I am quite interested in it, via discussion of these points.

How those points came out in the first place is past history. They came up in the "really disappointed" thread. Try to think about the situation realistically. There is an urgency about these points. All is not hotsy-totsy and hunky-dory in the program. But that's past history. Let's discuss Suprised's actual points, not the circumstances in which they arose.

You might think about the point "Do not consider the Landscape a disaster." Do you have some idea of what that implies?

 

[suprised]

Good. Let's make it clear that you do not take a discussion of suprised's points to indicate any loss of interest in string theory.

Actually the opposite is true. These subtleties made the whole business more interesting and fascinating to study. That's actually part of the reasons that keep us continuing this kind of research. marcus, you got it all patently wrong, again.

 

[fzero]

ck up.

Subject of course to your correction, I would venture to apply that last sentence to this:

That geometric compactification of a higher dimensional theory is NO LONGER a good way to think about the string parameter space.
​

And I would tentatively venture to conclude that many people (I would guess more advanced people) have already gotten away from thinking in terms of compactified extra spatial dimensions.

If this is true (I hear some American string theorists objecting that it is not) then I see this as positive and hopeful for the program.

The blue statement is, of course, my own understanding of what you said, so please correct if mistaken.

Marcus, what surprised and many others have tried to explain to you is that the "good" description of physics in a quantum theory often depends on where we are in the parameter space of couplings. This is the lesson have learned over the past 2 decades in QFT and string theory. If we are studying a point in coupling constant space where the string coupling is small and certain other volume parameters are big, then the picture of perturbative strings on a CY background will be an excellent description of the physics. In other regions of coupling constant space this description will be a bad one. In those other regions we need nonperturbative, nongeometric degrees of freedom to describe the physics. In most cases, we do not know what the correct degrees of freedom and equations of motion are.

The "wrong turn" (which is probably too strong a language) can be explained as the statement that from around 1984-1994, most efforts focused on studying perturbative string theory and there was an expectation that good models of nature might come out of studying perturbative, geometric compactifications. So the lamp-post problem was that people had a reasonable grasp of perturbative string theory and explored that regime much more than any other. Of course, not everyone did this, and a gradual picture began to emerge from 1990-1995 about topology-changing transitions and nonperturbative degrees of freedom. By 2000, many models of strong coupling points in string backgrounds were discovered. During the same time, the role of nonperturbative physics in low-energy phenomena was also explored, suggesting that good models of nature would require a deeper understanding of nonperturbative physics in general.

So you are failing to understand many things when you try to grasp onto a few statements that surprised has made. The first is your apparent belief that string theorists have somehow only recently understood that some ideas that arose circa 1984 were probably naive. In fact, these subtleties have been known for the past 15 years and progress has continually been made toward understanding the pertinent issues. Would string theorists be happier if far more progress had been made in the interim? Of course, but these are known to be hard problems. Lattice QCD has been known for far longer and there are still many fundamental obstacles that have not been overcome. I don't think anyone expects the full theory of QG to be any simpler.

Second, you are still having problems grasping the concept of a duality in QFT or string theory. The different descriptions in different regions of coupling constant space are all describing the same theory, but each has its own appropriate regime where it is a useful description. When we use the word nongeometric, we might mean two different things. The first would be simply a usual CY model in some small volume limit. In this case the CFT corresponding to the CY degrees of freedom is not a good (perturbative) description. In many examples, dualities connect these points to some other dual model that is a good description. This could be another CY model or it could be one the other types of nongeometric models, namely a Gepner or free-fermion/boson model. These are the critical models we form from putting together arbitrary CFTs on the worldsheet. Whenever we have dualities like this, we do not say the geometric description is not good. Rather, we understand that there is a region in coupling constant space where the geometric description is good, and there are other regions where it is bad. If nature exists as some nongeometric phase of a string theory, the chance is almost 100% that dualities connect that point to a geometric phase. That much we do understand about string theory.

Now, it may be unnecessary to attach real significance to the geometric interpretation. But there is almost no way in which you can argue that using geometric insights to study appropriate corners of moduli space is a wrong turn. You can only say that you should not restrict your attention entirely to perturbative, geometric points. There is virtually no string theorist that has not been aware of this for the last 15 years.

 

[marcus]

... marcus, you got it all patently wrong, again.

Read my post #134, Suprised. You got it wrong that I got it wrong. What Atyy called "subtleties" are what gets my attention and enlivens my interest. And, as you say, they also do that for you.

Of course "interest" has many different meanings depending on how one decides to measure. I guess for the purposes of this thread if I was pressed to choose a simple definition/measure I would say that at the bulk or community level the best indicators are citations to current work and attendance at the main annual conference.

Those are fairly common ways used, in academic circles, to gauge the vitality of a field. They come up over and over again in many contexts (not just theoretical physics). So for the purposes of this thread, that is what "interest" will mean. Until you hear from me otherwise