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An argument against string theory; geometry is dynamic

  1. Nov 29, 2006 #1
    I'm playing devil's advocate here I want to explore ramifications.

    According to GR, geometry is dynamic. In string theory, 6-7 dimensions are compactified as a Yau-Calibi manifold. The properties of elementary particles depend on the topology of these manifolds. Presumably any gravitational curvature would change the topology of these manifolds so as to change the prorperties of the string worldsheet diagrams, making these higher-dimensional moduli unstable. Any change in these moduli, or even changes in the 4D large spacetime would change the string worldsheet diagram, which is in contradiction to observation. The strings themselves have a back-reaction on the configuration of the higher dimensional moduli, which would change the strings own properties as experienced as elementary particles.

    I am well aware that KKLT's proposal is to stablize and "freeze" these higher dimensions through magnetic fluxes and anti-branes. There's still a problem.

    If string theory were to describe the real world, the 11D spacetime would have be frozen and nondynamic, including the higher dimensions, b/c any changes in them would change the properties of strings and d-branes, which would change the properties of elementary particles, which is in contradiction to evidence provided to us by GR and the SM.

    String theory is the wrong approach to quantum gravity. What is needed is something like loop quantum gravity where spacetime is dynamic.
    Last edited: Nov 29, 2006
  2. jcsd
  3. Nov 30, 2006 #2


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    Not necessarily. What we need is a non-perturbative formulation of string theory, while the current well-understood form of string theory is a perturbative one. Even string theorists agree that the current perturbative form of string theory is not completely satisfying.

    I'm playing angel's advocate. :wink:
  4. Nov 30, 2006 #3


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    Lucifer was an angel too.
  5. Nov 30, 2006 #4


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    Is it a religion forum, or a physics forum? :confused:
  6. Nov 30, 2006 #5
    I was waiting to end reading the "d-branes" book and reviewing some aspects before asking questions against string theory here, but I think that I will use these thread to ask them.

    I do copy & paste from other place:

    I particularly have a problem with string theory far before all these questions even appear in the theoretical development. For me the problems begin at the very idea of an string as a basic object.

    I mean, in the macroscopic world you can have an string. We know that we can describe it in terms of component (atoms) which keep joined themselves by means of their electronic interactions.

    But, what about "fundamental" strings? What keeps them joined? I mean, we can think that we have some one-dimensional region of space witch shares some common features which differ from the ones of their environment and that is what we can call an string. The question is , why does it remains joined under time evolution?

    I find that it would be natural to expect that their component point evolve in a manner that makes them to separate and we end up without an string any more.

    Of course you can simply postulate that the string keeps joined. But for me it is an unsatisfactory situation. How could we circumvent it?

    Well, let’s look at what we know. Where else do we have strings?

    Well, there are another kind of strings apart from the one made of atoms. The cosmic strings. They appear as topological defects when a phase transition occurred. Similar topological defects happen in condensed matter physic. Could we think of a preliminary sate of the universe which went under some phase transition leaving as a result topological defects such as strings and branes?


    of course you always can accept that strings (or branes) keep joined as a postulate, as seemingly everybody does without even worrying about how bizarre these notion could be and keep doing formalism. If you adopt these viewpoint the goodness of string theory relays in their good mathematical properties and ultimately in experimental confirmation.

    ...I watched for the previous introduction of one-dimensional objects inphysics. That was the knot theory of Thompson and Tait. But they had solved the problem of stability. A previous result of Helmholtz stated that once formed a vortex in a perfec fluid it remains stable. In thtat time the eter theory was aceepted and the eter could be watched as a perfecto fluid. So for their theory there was a reason. I don´t see a similar for string theory from these viewpoint.


    Well, apart of these ontological questions we always could listen to Feyman and go with the "don´t think, calculate" premise. But, can we?

    The fundamental calculational tool in string theory is the polyakov path integral. If you read the correponding chpaters in the string books they aregue that one virtue of string theory if that you don´t need so many feyman diagrams and taht you basically need one kind of vertex, the one in wich an incoming string separates in two outgoing ones. By a lorentz transformation that vertex is shown to be equivalente to ones in wich you have two incoming strings who join in a single one.

    In QFT (sdecond quantized theory) you get a prescritpion on how the Vertex are form teh form of the lagrangian. In perturbative string theory they are put "by hand".

    My question, of course is, why no other diagrams?. For example you could have a diagram with tow incoming and two outgoing strings, or an string breaking in more than two pieces. In fact you could, as far as i see, have an string breaking itself in an arbitray n of strings, and i don´t see that you could reduce these case to the simple one.

    But i recognice that these could easily be a missunderstanding on the polyakov integral, may be someone could explain me if it is so.


    An adendum to these would be if we take acount of the previous theory of knots. Thempson and all viewed thatit was the knoting of that vortex wich could explain the properties of matter. So they beguined to study knott theory, fine. The questionis, in the polyakov integral as far as I understand it is not allowed configurations in wich closed string would become knotted. And I don´t see a good reason why those configurations woud be forbiden. Mostly because in string theory knotting is allowed in, for example, the knotting of a string about a compactified string.

    Well, that are a kind of doubts I allways have had with strngs wich make me felle somewhat uncofortable with them. If I see them flawed for the very begining I just can watch the later developments but never trust them too much. As nobody else seem to worry about the problems I state here I supose that they are stupid somwhere. Well, tell me what I am missing.

    P.S. About the other conventinally problems of string theory I don´t feel so worried.
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