Why I am REALLY disappointed about string theory

[mitchell porter]

Lubos Motl has made some comments lately, on neglected approaches to the fundamentals of string theory, which are worth recording here.

First, http://blog.vixra.org/2011/06/16/2000-papers-at-vixra-org/#comment-8456" with Robert Dijkgraaf.)

Second, http://motls.blogspot.com/2011/06/miss-usa-should-math-be-taught-in.html" in equations 1.3 and 1.8.

There was a paper last week http://arxiv.org/abs/1106.4036" . One of the investigators of generalized M-theory (which I think is just M-theory, approached via "generalized geometry") is David Berman, mentioned earlier in this thread for his work on M-branes.

I'm not on top of these topics at all, but they deserve a mention here.

 

[atyy]

Is double field theory related to http://arxiv.org/abs/hep-th/0406102" , or something completely different?

 

[tom.stoer]

@mitchell porter: I have a problem how to continue with this thread; would you be interested in writing a reply to my post #1 summarizing "lessons learned" and where I was right or wrong?

 

[mitchell porter]

Is double field theory related to http://arxiv.org/abs/hep-th/0406102" , or something completely different?

It's the same thing.

@mitchell porter: I have a problem how to continue with this thread; would you be interested in writing a reply to my post #1 summarizing "lessons learned" and where I was right or wrong?

It's too much, to answer all those detailed questions. But so far as I am concerned, the natural course in trying to explain the world is still, use field theory for particle phenomenology, and then realize your field theory within string theory.

It used to bother me that string phenomenology wasn't trying to calculate the observed particle masses, but I have a better appreciation of gradualism now. Just getting the mass hierarchies right is an important step itself and one that needs a lot of work.

I also used to think (even before Randall-Sundrum) that the emphasis on small extra dimensions was just prejudice, "cosmic agoraphobia" as Celia Green puts it. But having seen that they arise naturally in AdS/CFT, I'm also more comfortable with that aspect of string model-building orthodoxy.

I do think that M-theory isn't the final word, that bosonic string theory or "bosonic M theory" could be the full theory. And there is still a great deal of work to be done, in sorting through all the candidates for a deeper description of string theory (E11, pure spinors, matrix models...), in search of the most fundamental viewpoint. There has to be one; even if there are, say, three equally primordial ways of looking at string theory, then the fundamental viewpoint would be one which treats those three perspectives as equal.

 

[tom.stoer]

It's too much, to answer all those detailed questions.

Not very detailed; just a summary that addresses my original concerns.

I (partially) had to change my mind and I tried to indicate this during this discussion, but I think it's fair that somebody from the string community should present a brief response with an expert opinion.

 

[marcus]

I also would be interested to see a summing up by Mitchell.

Mitchell I remember you saying quite recently in one of the threads that you thought the way forward in fundamental physics was to construct a unified QFT and then translate that into stringy language.
If I understood you, the idea was to achieve threeway unification at a field theory level and then implement that in string. Perhaps then finessing gravity.

I found that vision of progress appealing, in part because "incrementalist" and evolutionary.
I characteristically mistrust enthusiastic flying leaps, inspired fervor based on coincidences (which in other contexts is called superstition). I picture scientific progress as slogging ahead gradually and testably improving what you've got---which in this case is the Standard Model.

That is why I like the program of "quantitative unification" which Wilczek presented in the first 40% of his talk. The Stuttered Muddle is astonishingly successful but ugly/unsatisfactory in certain ways he listed, and begging to be fused into a more elegant unity (even without worrying about gravity).

You already commented on Wilczek's talk. I'll post the link in case anyone reading this wants to watch it.
http://media.medfarm.uu.se/flvplayer/strings2011/video24

So maybe you and Wilczek would agree on where the main effort (in fundamental theory) now should be directed---namely use the LHC and new cosmology observations to achieve a greater perfection/coherence at the field theory level---which you would then say to translate into string.

 

[Haelfix]

String theory seems hokey until you actually sit down and start calculating things with it. It's really difficult to describe in words what goes on mathematically, which is why it often seems like hype when it really is anything but.

Even simple unrealistic toy models like toroidal compactifications, are quite miraculous. What seems like extra baggage (extra dimensions, tons of extra degrees of freedom) actually comes and rescues you from potentially fatal complications in next steps.

I assure you, when you see chiral fermions, realistic GUT groups, particle generations and explanations for various symmetry breaking patterns more or less fall onto your lap ought of quantum geometries, be sure that it makes an impression. As a phenomenologist it seems like nature is doing the job for you rather then endlessly guessing and twiddling nobs in order to get things to work, like is the situation with the standard model and regular field theory.

In some sense it's like the theory knows about physics that we currently don't, which is why it doesn't seem weird to me that it's being applied to so many seemingly different physical problems

 

[mitchell porter]

Tom, I am not an expert from the string community. I am a self-taught outsider and there are big gaps in my knowledge. Perhaps you can think of my level of knowledge as like a PhD student during the literature review stage of their thesis.

Marcus, despite how I phrased it, GUT phenomenology can't be restricted to field theory only. Field theory by itself is still a big source of ideas, but working within a class of string phenomenological models also offers guidance.

The standard way to go beyond the standard model is GUT, supersymmetry, string theory, and the world may in fact work exactly like that. My opinions lie in dynamic tension between this much-explored orthodox framework, and a few heterodox ideas (Alejandro Rivero on supersymmetry, Marni Sheppeard on M theory). A lot of the fuel for my own studies comes from the desire to be able to resolve that tension, and to actually know who's right.

 

[tom.stoer]

Perhaps we can find somebody else?

 

[Haelfix]

Tom, the answer to many of your questions is 'No one knows'. Perhaps it would be best if you focused on one question, formulated into a sufficiently precise statement (by doing a few minutes of self research to get the basics) and asked them one at a time.

For instance, how one gets particle generations out of string theory is somewhat involved, but often quite beautiful. There can be a very precise answers, but as usual depend on which type of vacua you live in. As an example, in heterotic string theory, the number of particle generations (minus the number of anti generations) is a topological invariant.

So suppose you are given the exact metric, and look for smooth continuous changes of the geometry (induced by say quantum effects). The massless spectrum might change as the generations and anti generations pair up to become massive or vice versa, however the actual total number is always fixed, implying that the net number of generations in some corner of the configuration space is stable.

You might get a different mechanism elsewhere. But what is weird is that the *structure* and many if not most qualitative features of the physical world seems to fall out of the mathematics, even in unrealistic models. I mean why should a theory of strings, know anything about particle generations?

 

[smoit]

Just to add to the above, family replication is just one manifestation of a topological complexity which leaves its imprint in the particle physics spectrum. This is part of a very generic trend, namely the multiplicity of particles with similar or identical properties in a given string compactification. The other examples are: multiple geometric moduli, multiple axions, multiple non-Abelian hidden sectors, multiple U(1)s. This multiplicity looks rather mysterious within a strictly 4-dimensional theory but occurs generically in string theory. Particularly interesting and potentially testable is the idea of multiple species of string-theoretic axions, so-called "String Axiverse", where the QCD axion is just of of the many http://arxiv.org/abs/1004.3558" .

 

[atyy]

http://arxiv.org/abs/1004.3558"

Bosenova

 

[tom.stoer]

Tom, the answer to many of your questions is 'No one knows'. Perhaps it would be best if you focused on one question, formulated into a sufficiently precise statement (by doing a few minutes of self research to get the basics) and asked them one at a time.

In-depth clarification of individual details was not my intention for this thread. I know some of these results, either from papers or from discussions here in this forum, sometimes with active string theorists. And if I want to understand more regarding one specific problem I will ask this question in an own thread.

My intention was different: I started this thread with a rather broad and generic criticism regarding the string theory research program as a whole. A reply should be equally broad and generic leaving out many interesting details, but it should address my generic criticism and of course summarize gain knowledge achieved during this discussion. Just as an example: it is not relevant that heterotic string theory has topological invariants which can be identified with fermion generations; that's interesting mathematically but irrelevant physically as long as we do not know "why heterotic string theory instead of something else" and as long as we have no good reason why the results should be three. But the find that "string theory" is not like QCD but more like "gauge theory", i.e. a framework instead of one individual theory, combined with the idea that string theory harmonizes different theories (like gauge theories, SUSY-GUTs and SUGRAs) into one single theory with different vacua is a very deep result and profound knowledge.

So my idea was to let one expert answer the generic questions I started with and to summarize the main achievements, both of the theory and of course of our common understanding developed together as part of this discusson. This seems to be fair.

If the answer to some question is "we don't know yet", then this answer should be part of the reply, why not?