String Fellows

Today’s Guardian has an article by a writer who recently visited the Institute in Princeton to talk to Witten and others there about string theory. The author of the piece makes the obvious analogy between Witten and Einstein, and asks the string theorists about Einstein’s 20-year misguided and failed attempt to unify gravity and electromagnetism during his years at the IAS. String theory and Einstein’s failed program get further identified by the author’s claim that if Einstein were alive today he would be working on string theory, and by a quote from Seiberg that “Being in the place where Einstein was is clearly an inspiring idea.”

Seiberg also has something very true to say:

“Most string theorists are very arrogant,” says Seiberg with a smile. “If there is something [beyond string theory], we will call it string theory.”

Witten’s attitude towards string theory seems to remain unchanged, he’s quoted as saying:

“Critics of string theory say that it might be too big a step. Most physicists in other fields are simply agnostic and properly so,” says Witten. “It isn’t an established theory. My personal opinion is that there are circumstantial reasons to suspect that it’s on the right track. ”

His recent work on twistor string theory is mentioned, including the fact that there was a workshop at Oxford last week on the subject. About this, the writer reports

“Witten is not convinced yet. ‘I think twistor string theory is something that only partly works,’ he says.”

I wonder exactly what he meant by that. What’s the part of twistor string theory that he thinks doesn’t work?

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16 Responses to String Fellows

  1. Instead of twistors, I believe in hyper-octonionic spinors! “Hyper” means multiplying imaginary units with commuting sqrt(-1) so that sub-space of complexified octonions with Minkowski signature of number theoretic norm results.

    The generalization of the notion of calibration

    [see the homepage of Jose Figueroa-O’Farrill at
    http://www.maths.ed.ac.uk/~jmf/Research/susy_7.html%5D

    leads to the notion of Kaehler calibration. When combined with the number theoretic spontaneous compactification of hyper-quaternionic M^8 to M^4xCP_2, this leads to the conjecture that the basic theorems about connection between calibrations, minimal surfaces, and spinors generalize.

    Absolute minima of Kaehler action would correspond to the solutions of massless equation for octonionic 2-spinor satisfying Weyl condition representables as hyper-octonion real analytic maps and satisfying d’Alember equation as a consequence of generalized Cauchy-Riemann conditions.

    Incredible it sounds but classical TGD would reduce to free Dirac equation for hyper- octonionic spinors equivalent with hyper octonions!

    For an enthusiastic blurb see

    http://www.physics.helsinki.fi/~matpitka/newtgd.html#calib.

    A detailed representation can be found at

    http://www.physics.helsinki.fi/~matpitka/tgd.html#visionb

    With Best Regards,

    Matti Pitkanen

  2. Jian says:

    “…Most physicists in other fields are simply agnostic and properly so,”

    “An agnostic thinks it impossible to know the truth in matters such as God and the future life with which Christianity and other religions are concerned. Or, if not impossible, at least impossible at the present time.”

    Bertrand Russell, “What is an Agnostic?”

  3. D R Lunsford says:

    If Einstein were alive today, he’d probably be a patent clerk.

    -drl

  4. R says:

    “If Einstein were alive today, he would probably be a string theorist…”

    This made me laugh for a while….
    good job 🙂

  5. Thomas Larsson says:

    as for the fate of N=1 SUSY in the LHC we just have to wait and see, don’t we?

    I have no doubt that people will look for SUSY at the LHC, and I am awaiting the results as eagerly as anybody. If it is found, then I will have learnt something. No big deal.

    However, experimental particle physics did not start with the LHC. My post referred to several large and expensive experiments, and I think that it is wrong to simply ignore them. I have recently, and more than once, seen the situation summarized in the phrase “SUSY requires fine-tuning at the percent level”. This is of course not conclusive, but it gives a hint what we may expect at the LHC.

    Besides, LHC will not affect the outcome of a 2-loop calculation of the running coupling constants. If it has been done, I would like to see a reference. If not, it is about time that somebody does it.

    Interest in SYM is not mainly due to hopes that it is a realistic theory, but that it is a more tractable version of SYM than those without SUSY.

    Fine. But if some conclusion relies critically on SUSY (AdS/CFT perhaps), and SUSY is not part of nature, we haven’t really learnt anything about physics, have we?

  6. raj says:

    “Most string theorists are very arrogant,” says Seiberg with a smile. “If there is something [beyond string theory], we will call it string theory.”

    One wonders. Does arrogance among string “theorists” substitute for evidence among scientists? Quite frankly, I’d prefer evidence.

  7. Urs says:

    Interest in SYM is not mainly due to hopes that it is a realistic theory, but that it is a more tractable version of SYM than those without SUSY.

    The goal is to understand field theory as such. YM is hard. So let’s move in field theory space to a more symmetric version and try to understand that first. That’s still hard enough. When done, we can try to move back to the asymmetrical point.

    SYM in four dimensions is about the most symmetrical gauge theory that you can get. Therefore its importance. Therefore the interest in it.

    See the introduction to the Clay millenium mass gap problem for a detailed discussion why field theorists want to understand SYM.

  8. Anonymous says:

    The idea is to calculate QCD amplitudes by expressing them as combination of SUSY amplitudes (which can be now simplified using twistor methods), and one non-SUSY amplitude, that one can choose to be as simple as possible. In fact, one does not use SUSY directly in the calculations, just what is called “cut-constructibility” which works for some non-SUSY calculations as well. As nobody really knows the full ramifications of the idea before exploring them (and it does look good right now), it is not useful to make apriori judgements.

    The twistor string itself was proposed only for N=4 anyhow; as for the fate of N=1 SUSY in the LHC we just have to wait and see, don’t we?

    M.

  9. Thomas Larsson says:

    I forgot: no deviation in muon g-2.

  10. Thomas Larsson says:

    Whether SYM amplitudes can be calculated with twistor methods may or may not be true. The big question is why physicists should care about SYM amplitudes in the first place, given the mounting evidence against supersymmetry (no sparticles, no proton decay, no light Higgs, no WIMPs, no permanent electric dipole moment, and perhaps the 2-loop result that coupling constants don’t meet exactly at one point).

  11. serenus zeitblom says:

    “It sparked a whole slew of papers from his fellow theorists and interest is still growing.”

    103 cites after more than a year? By EW’s standards, that is far from a “slew”. Nor do I see any evidence that interest is growing in this rather dull, technical subspace of the string world.

  12. Lubos Motl says:

    Hi Moshe, I know that you can derive it (the connected expression) from the B-model, but you can also derive it from e.g. Berkovits’ models. It’s just too simple so that the details of the string theory are not too important. How’s life? LM

  13. Anonymous says:

    Lubos,

    1. The “connected instanton” formula of Roiban et. al. is a new expression for helicity amplitudes which was not available before, and is “derived” (not very rigorously) from the toplogical B-model. That expression is correct, though not as efficient as others.

    2. The versions of topological strings currently on the market do not work on the loop level, but maybe there is some hope still, “whatever you do” covers a lot of ground…

    Moshe

  14. Lubos Motl says:

    The picture of string theory – namely topological string theory – has not been too useful in any of the recent developments that shed light on the new formulae to calculate the Yang-Mills scattering amplitudes.

    The picture of the topological B-model on CP3|4 is problematic also because it contains the extra conformal supergravity states, and it’s expected that whatever you do, you will get a disagreement at the loop level.

  15. Anonymous says:

    Representation of SYM amplitudes in twistor space makes some of their simplicity manifest, and is very useful as a calculational tool. The idea of cooking up a topological string theory to reproduce these amplitudes works only at tree level, for loop level there are unwanted contributions (from conformal gravity) that one needs to decouple somehow.

  16. D R Lunsford says:

    What part of TST doens’t work?

    Probably the usual issues of conformal ideas when sources are present (of whatever kind).

    -drl

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