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Laymans question: 2 Why is string theory

  1. Sep 6, 2007 #1

    GUS

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    Laymans question: 2 Why is string theory......

    ....a theory if thereis no empirical evidence for it ? The only way I can understand there is a difference between String theory and say "inteligent" design is that string theory works out mathematically. ie That we can become aware of things mathematically before our technology becomes sufficiently advanced to detect evidence on very small levels or whatever in the real world. Is this correct ?
    Is this correct, if not is there any evidence for string theory , have any tests to validate it shown it could be correct and if not why not ?
    Are there any plans for experiments in the future that may be able to test for experimental evidence for string theory ? Is the CERN accelerator going to make an difference to string theory ?
     
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  3. Sep 6, 2007 #2
    The questions that you are asking are somewhat unprobable. Nobody could answer those questions at this point of time. But I will hope that LHC at CERN would provide some proofs for string theory.
     
  4. Sep 6, 2007 #3

    marcus

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    properly speaking "string theory" does not exist.
    Gerard 't Hooft made that point in a forceful and memorable way.
    It is a mistake in our language to use the term and it immediately leads to confusion and misunderstanding.

    Better term would be "string framework", or "approach."
    A framework within which several different theories might eventually be constructed.
    A framework within which one can find various kinds of work in progress.
    An approach to unification.

    I've noticed a trend recently, in serious writing for the scientific community, not in popular journalism, to use better language----use words like "proto-theory", "approach", "framework".

    To the extent that there is anything deserving the name "string theory" it is more a vague hope than a reality. David Gross, a leader in the stringy community, often says "We still don't know what string theory is." there still are no fundamental principles, axioms, no main equation. And no definite prediction which, if not observed, would invalidate the approach---i.e. cause it to be thrown out.

    =================

    I suppose the language used in the string community could eventually get more in line with the way non-string QG people talk. They never refer to the Loop approach to QG as "Loop theory" or "Loop Quantum Gravity theory".
    It is a type of research. One of several non-string QG approaches.
    there are other approaches: Reuter's QEG (quantum Einstein gravity) Ambjorn's CDT (causal dynamical triangulations), Spinfoam models, Causal Sets.....

    some of these are now becoming rather definite, crystalized so to speak. They do not yet, but may soon provide testable predictions according to which they will survive or be invalidated. But they are still being called "approaches" by the non-string QG community, not "theories". It is a restrained and unpretentious style of talking which I think helps avoid public misunderstanding.

    there is a new survey-type book in the works called "Approaches to Quantum Gravity: towards a new understanding of space time and matter". Dan Oriti is editing it for Cambridge University Press. The title is significant---Oriti does not say "theories" of quantum gravity.

    the key criterion is making definite falsifiable predictions. the "bar mitzvah" day when a proto-theory or approach can stand up and say "today I am a theory" is when it commits to a definite prediction that is not already a consequence of prior established theory---lays it on the line, bets its life on an outcome derived from its principles

    as long as it is so mushy that it can accommodate any future outcome that is not already ruled out by prior established theory then it is as yet unpredictive and amorphous----sign of immaturity, or of work-in-progress

    I think largely what I am doing is paraphrasing what you suggested in your question, so in a way simply agreeing with the reasoning behind the question

    Anyway I agree with your question, let's try to say approach and framework more, as we do in the case of nonstring QG
     
    Last edited: Sep 6, 2007
  5. Sep 6, 2007 #4

    marcus

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    Unfortunately the string community has not signed off on any definite prediction for LHC. Beyond what is already expected according to prior established physics, one can say that no matter what is seen it is OK with them and does not invalidate their research line.
    So there is no test.

    If evidence of supersymmetry is seen, it is OK. If evidence of supersymmetry is not seen, it is OK. And so on. David Gross, for instance, has said flatly that there is no prediction. he should know, right? :smile:
     
  6. Sep 7, 2007 #5

    Demystifier

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    How about "paradigm"?
     
  7. Sep 7, 2007 #6

    marcus

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    If it sounds right to you, let's try it out in some posts to see how it works.
    I have no basis for preferring, except that I've seen people use the term "string framework" recently.

    they say things like "So far, string is not a theory, but rather a framework within which to construct theories."

    The term "string approach" is one I don't remember ever hearing anyone use. The appeal of that term is that approach comes up rather consistently in discussions of quantum gravity. One does not say "LQG theory" one says "the LQG approach".
     
  8. Sep 7, 2007 #7

    Fra

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    Scientific methods: theory vs strategy

    I personally think the more important question is what kind of scientific method, or strategy we use. I often smell differences in the way people tend to think in various debates and writings.

    The classic view is that there is some hypothesis generator, and then the science consists of testing the hypothesis against empirical evidence and experiment. If the hypothesis fails to predict and explain experiments, it is discarded. In this view the essential requirement is that whatever hypothesis we come up with, must be in principle testable in the sense that it must make predictions that allow experiment to decide if it's right or wrong.

    Note that at this point, NO emphasis is made on the effiency or fitness of the hypothesis generator itself, which is obviously of huge importance. So this view of the scientific method is IMO too simple.

    The next level I imagine is if you conside a theory of theories in the context of evolving theories, then there is a feedback between the experiment/theory correlation and not only theory corrections but also corrections to the strategy of the hypothesis generator.

    So in effect we get theories also for the more "clever" or "fit" hypothesis generator, which I would call the strategy. Successful strategies live and evolve, the other ones "die".

    My personal opinion is that of equal importance to making definite, falsifiable predictions, my desired scientific strategy should also suggest a correction in direct response to a deviation. A strategy that makes a false prediction, and then as a direct response predicts the proper correction can still be highly fit.

    The simplest possible strategy is the; discard and press pick a new random hypothesis. This may certainly be at play at times, but that would be when the feedback doesn't induce any discriminations.

    So, to falsify a "simple" theory, is one thing, but to falsify a strategy? In reality the concept of strategy must certainly be the more relevant one.

    I'd like to know, regardless of right or wrong, what is the scientific *strategy* behind the string think? Is there one?

    When ideas and information are scarce, even the remote crapshot may be digestable, but for anyting more than a crapshot, I'd expect some kind of survival strategy?

    I personally get extremely frustrated when sometimes all you see is a patchwork or more or less plausible arguments, handwaving and arguments, but no real strategy implemented in the framework itself. Or is the "strategy" to simply assume that those theorists (ie humans) that generate unsuccessful theories will die / get out of business, and those that generate successful theories live / stay in business? That is certainly the way it is, and that's going to stay liek that, but still... that is not good enough is it? or is it? I don't feel satisfied by that... I think we can do better.

    I often think that the revolution in physics we all wait for, will also tangent a change of the level of sophistication of the scientific methods we use?

    /Fredrik
     
  9. Sep 8, 2007 #8

    Haelfix

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    Stringy people emphasize this a lot, but it is a bonafide theory in the sense that it is *unique*, at least perturbatively in some approximation (non perturbatively in others). The problem is that it apparently has an infinite number of classical solutions to our low energy classical world.

    Its really the reverse of field theory (the standard model) and General Relativity (Einstein's framework). There we talk about *theories* that are most assuredly not unique, even though there is exactly one solution to each. Fortunately in those cases we have experiment and a few other criteria that can single out which theory and its corresponding unique solution applies to the real world. Not so for String theory or any quantum theory of gravity, we have no way of measuring that energy scale directly.

    In many ways, the reason a lot of proffessionals really buy into it, is b/c it is amongst the simplest objects we can currently think off that can successfully quantize gravity. By 'simplest' I mean the least amount of crucial physical assumptions that must be dropped.

    For instance String theory does not drop the requirement of Lorentz Invariance, Unitarity, Quantum Mechanics or the framework effective field theory. It does not drop the requirement for the analyticity of the SMatrix, etc etc. Keeping all these properties (that we know and love) is extremely difficult mathematically, and there are various no go theorems that preclude going off on wild tangents. You really are extremely constrained when doing quantum gravity, theres not much *else* it can be.
     
  10. Sep 8, 2007 #9

    Chronos

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    Well done. Your explanation is deep, brief, and well stated. ST cannot be wrong, merely misunderstood. I object to its inspecificity. It needs new entrails.
     
    Last edited: Sep 8, 2007
  11. Sep 8, 2007 #10

    GUS

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    Right on , cheers guys/gals, Haelfix you kind of showed me wht ST gets more kudos than Tarot cards amongst the scientific community ! Cheers all.
    However I would appreciate it if any of you could put in one clear sentance, intelligable to a non physisist, why string theory has attracted the atteention of serious scientists and universities whereas intelligent design hasnt ?
     
    Last edited: Sep 8, 2007
  12. Sep 8, 2007 #11

    dx

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    Because the string framework is a proposal for extending/unifying already tested and well understood theories (which work very well, and are the basis of all the technology we have today) whereas intelligent design is just an arbitrary hypothesis (although it certainly could be true) which was invented mainly to give a "scientific feel" to another arbitrary hypothesis (guess which).
     
  13. Sep 8, 2007 #12

    GUS

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    Halleluluyah ! thankyou !
    BTW I seriously doubt "intellignet design could be true" but thats just me.
     
    Last edited: Sep 9, 2007
  14. Sep 10, 2007 #13

    Demystifier

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    This is exactly what many physicists think to be the DRAWBACK of string theory. ("Not even wrong".) If you want to convince others that string theory is good, don't ever say that again!
     
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