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Arun Gupta's post reconstructed

  1. Sep 1, 2004 #1

    marcus

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    Arun Gupta wrote the following in SPS Quasinormal Mode thread. As his post appears there, it is interjected with moderator comment, sometimes breaking into mid sentence or mid thought, and becomes difficult to follow. To get a clearer sense of what he said, I have reconstructed Arun Gupta's post here. Numbers in brackets show where to place the moderator comments, which are listed afterwards.

    -----Arun Gupta wrote---
    Is physics reverting to religion?
    [1]
    Lubos Motl <motl@feynman.harvard.edu> wrote

    > LQG is not string theory, and therefore it can't describe gravity.

    Newton and Einstein have done fairly good jobs so far, describing
    gravity without string theory. Yes, I know you mean a quantum theory.
    [2]
    But then demonstrate that there are no other routes to a quantum
    theory of gravity, not mistaking mathematical difficulty for impossibility.
    [3]
    Or, following the usual route of physics, demonstrate experimental
    results so distinct and compelling that possible competing theories are
    of little interest.

    Since neither of the above are available,
    [4]
    I can only interpret the attacks on people who seek gravity outside of
    string theory as quasi-religious fervor.

    It seems obvious that if you don't look, you can't find.
    [6]
    And ultimately, if the search fails, it will be a compelling argument in
    favor of string theory, so why fear it?
    [7]
    If the search succeeds, it won't be a disaster for physics, as someone has
    claimed.
    [8]

    -Arun
    -------end quote from Arun, start quote from Lubos--------
    1.[Moderator's note: This is the only off-topic message in this thread that
    will be tolerated. Please find a newsgroup about religion if you
    want to continue with this sort of non-string-theoretical discussion. LM]

    2.[Moderator's note: Yes and no. I meant what I wrote. I wrote that LQG
    can't describe gravity. LQG may be a quantum theory, but it is not a theory
    of gravity. Yes, of course the constraint is that string theory is
    the unique *quantum* theory of gravity. LM]

    3.[Moderator's note: It may be mathematically *difficult* to prove that
    string theory is the unique solution, but it does not mean that it is not
    unique. This uniqueness may be hard to see for someone who knows very
    little about string theory, but the more you will know about theoretical
    physics and the possible inconsistencies in various candidate theories -
    and the miraculous ways how string theory avoids these inconsistencies -
    the more you will realize how true and deep my statement is and how
    false and shallow is yours. LM]

    4.[Moderator's note: The strategy that you propose is unscientific. It is
    not necessary to disprove all conceivable alternatives to string theory
    if we want to rule out LQG. It was enough to rule out LQG which was a
    much easier task. LM]

    5.[Moderator's note: if you learned some technical stuff instead of your
    current philosophical/religious words, you might become able to do
    better and find a better interpretation. LM]

    6.[Moderator's note: I assure you that I look. Conversely, if you don't
    look, you can't see the problems with *any* inconsistent theory. LM]

    7.[Moderator's note: I don't fear anything. I just stated a rather
    well-known insight about uniqueness of string theory among the known
    quantum theories of gravity. It seems to me that it is *you* who fears
    it. LM]

    8.[Moderator's note: Anyone is allowed to search for anything, which does
    not mean that all searches are equally justified and reasonable. LM]

    ----end quote----
     
  2. jcsd
  3. Sep 1, 2004 #2

    marcus

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    I want to try to understand the exchange.

    Lubos gave the following argument.
    As he acknowledges in his comment [2], the major premise (or "constraint") is that string theory is the only possible *quantum* theory of gravity.
    "Yes of course, the constraint is that string theory is the unique *quantum* theory of gravity." So it is a simple syllogism:

    A. String theory is the unique *quantum* theory of gravity.

    B. LQG is not string theory,

    C. therefore it cannot describe gravity.

    Notice that Lubos does not make a specific criticism of LQG here (though he does elsewhere) but rather bases his conclusion on the uniqueness doctrine that Whatever theory must be wrong if it is Not String. LQG is not string so it is ipso facto wrong. This is a curious argument and appears to have elicited Arun Gupta's response.
    ----quote, central point bolded for emphasis----

    Is physics reverting to religion?

    Lubos Motl <motl@feynman.harvard.edu> wrote

    > LQG is not string theory, and therefore it can't describe gravity.

    Newton and Einstein have done fairly good jobs so far, describing
    gravity without string theory. Yes, I know you mean a quantum theory.
    But then demonstrate that there are no other routes to a quantum
    theory of gravity, not mistaking mathematical difficulty for impossibility.
    Or, following the usual route of physics, demonstrate experimental
    results so distinct and compelling that possible competing theories are
    of little interest.

    Since neither of the above are available, I can only interpret the attacks on people who seek gravity outside of string theory as quasi-religious fervor.

    It seems obvious that if you don't look, you can't find. And ultimately, if the search fails, it will be a compelling argument in favor of string theory, so why fear it? If the search succeeds, it won't be a disaster for physics, as someone has claimed.


    -Arun


    ---end quote---
     
    Last edited: Sep 1, 2004
  4. Sep 1, 2004 #3

    marcus

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    Clarification is needed here:
    "... I can only interpret the attacks on people who seek gravity outside of string theory as quasi-religious fervor.
    It seems obvious that if you don't look, you can't find
    ...."

    Gupta uses the colloquial "you" when he means "If one doesn't look..."
    or "If people don't look, they won't find..."

    However Lubos replied as if he understood this to refer to him Lubos personally. "If you Lubos don't look, then you can't find" and the
    moderator comment was words to the effect: "I DO look. It is you Gupta who are not looking!"

    Gupta's point here deserves a more sympathetic reception and essentially is this.

    People who explore alternative quantum gravity theories should not be attacked because they are doing the physics community a beneficial service and no one any harm:

    If they succeed and find something that works better than string, so much the better. If they fail then this should be grounds for satisfaction (e.g. on Lubos part) because it would tend to confirm the string approach. The search is beneficial however it turns out.

    Gupta's main point is that a doctrinaire attack on those exploring non-string QG does seem to smack of a religious-like fervor. I would go further and say almost a kind of dogmatism---especially if it happens repeatedly in a predictable way.

    I think this point is a valid one to make in the SPS context because of
    something similar that happened to Arivero (see "Alejandro and the graviton" thread) and to Sergei Alexandrov.

    However Lubos has apparently ruled out that anyone will be able to criticize him about this resemblance to religious-fervor. He says that no more talk like that in Gupta's post "will be tolerated". See mod comment [1].
    He (disingenously?) misinterprets Gupta as wanting to talk about religion
    rather than what he really wants to do which is remonstrate with LM for
    religious-like dogmatism. So he (distingenuously?) says

    ---quote from Lubos---
    Please find a newsgroup about religion if you
    want to continue with this sort of non-string-theoretical discussion. LM

    ---end quote---
     
    Last edited: Sep 1, 2004
  5. Sep 1, 2004 #4

    arivero

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    There is a subtle point: that, I suppose, from the point of view of strings+M_theoretists, any theory that can be reached as a limit of strings is part of string theory.
     
  6. Sep 1, 2004 #5

    marcus

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    "Greater String Theory" :smile:
    be careful or it will engulf Darwin's theory of Evolution and
    the bible-thumpers will take issue.

    I was wondering who is Arun? There was an Arun Gupta
    who did Electrical Engineering at IIT-Madras and then
    Theoretical Physics at Caltech. dont know if it's the same person.
     
  7. Sep 1, 2004 #6

    Chronos

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    A. String theory is the unique *quantum* theory of gravity.

    B. LQG is not string theory,

    C. therefore it cannot describe gravity.

    Impeccible logic. Spoken like a true demagogue. Burn the heretics.
     
  8. Sep 1, 2004 #7
    Although I appreciate the method of discernng the original post, it sometimes amazes me the different context in which language may culturally divide our perceptions and symbologies, all the while using those same words.

    So in this sense, I defend Lubos, not that he needs it :smile:

    What Lubos said about strings being a model for quantum Gravity is exactly what Sean Carroll's selected staement was refering too. Something profound. Although Sean did not refer distinctly to what that profound model was. It is generally accepted that a method is needed to describe How GR and QM can be joined so that cosmo-logically and in the world of the small, a discription might become relevant?

    As you say Marcus, which ever method can, and we'd all be of benefit, regardless which model succeeded. One you might know, or Arivero, or even Sergei. Or even, little ole me :biggrin: Okay, maybe not me. :smile:
     
  9. Sep 2, 2004 #8

    arivero

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    Well, not so. I guess that their quest for a theory to be reached as a limit of strings is only in the scope of particle physics :-) Actually, particle content seems a more important selling point that gravity.

    Let me to explain. The empirical input up to date is that we have found 12 fermions and 12 bosons. We also are looking for a gravity mechanism and for a symmetry breaking mechanism, but no definite evidence has come from experiments.

    The bosonic string is a 2 dimensional object living in a 26 dimensional world. Thus locally one can expect 24 (bosonic) degrees of freedom for the string to move. The supersymetric heterotic string does a bit better: Its background has 10 susy degrees of freedom and 16 bosonised degrees. It comes short of fermions, and long on bosons. But almost. A couple more of fermionic dimensions should be wellcome. So all the buzz on 11 and 12 dimensions. Besides, we have input from other theoretical areas telling us that the symmetry breaking degrees have a strong similitude to coordinates; two complex higgs doublets should add 8 coordinates to the 4 of space-time, and they could be allocated to the partners of the susy degrees. But this is not so in string theory, it should be in a very nearby theory, that we could call, er, the M-issing theory. It seems that there was, time ago, a hope of reaching this theory by understanding the duality mechanism of the supersymmetric strings. Regretly, they keep some insistence on susy and strings, IMHO the two properties that the M-theory will not have.

    I'd add that some extra hints about the organisation of the particle content come from the facts of having a pattern in four basic fermionic spaces (related to space time?) and of having three very peculiar uncharged fermions (related to the difference from 10 to 12 dimensions? Or to the signature of 3+1 space time? or both?).
     
  10. Sep 2, 2004 #9

    arivero

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    Hmm perhaps I should add that the 12 bosons, or force carriers, are the generators of the groups U(1)xSU(2)xSU(3) (1+3+8, respectively). They can not be interpreted as SUSY partners of the 12 fermions because they have different charge structure.
     
  11. Sep 2, 2004 #10
    So if we talk about a tree which "epoch" would you be referring too? Only in grand unification, or before this?

    I should clarify tree. "Organizationing property" that is evident through all phases of the epoch's to today's gravitational weak field cosideration.
     
    Last edited: Sep 2, 2004
  12. Sep 2, 2004 #11

    arivero

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    Current particle spectrum. I am no universe-maker :-) We have found 12 different mass eigenstates in the fermionic spectra. And we have found 12 gauge group generators in the boson spectra. I know, I am using different criteria; lets say that I am trying not to use labels based in charges.
     
  13. Sep 2, 2004 #12
    If we do not use spectrum then how shall I observe the particle discriptions?

    There had to be a consistant basis to this formulation, and it has to be evident through all phases. There was a "result" in such observations, in microscopically discerning the nature of those same particles?
     
  14. Sep 2, 2004 #13

    arivero

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    Well, the basic problem is the following: QM states are subspaces of Hilbert space, labeled ("the spectrum") by the application of an operator. The operator that provides the labels of charge do not commute with the operator that provides the labels of mass. So from an strict mathematical point of view, a particle does not have mass and charge at the same time. If I use mass labels, I get 12 subspaces for the known fermions. If I use charge labels, I get 4 subspaces.
     
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