An argument against string theory; geometry is dynamic

In summary, the conversation discusses the dynamic nature of geometry in string theory and how the properties of elementary particles are affected by the topology of higher-dimensional manifolds. The idea of fundamental strings as basic objects and their stability over time is also questioned, with comparisons made to cosmic strings and topological defects in condensed matter physics. The discussion also touches on the use of Feynman diagrams and the polyakov path integral in string theory calculations. Overall, there are concerns about the applicability and validity of string theory as a description of the real world and the need for a non-perturbative formulation or alternative approach such as loop quantum gravity.
  • #1
bananan
176
0
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.
 
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  • #2
bananan said:
String theory is the wrong approach to quantum gravity. What is needed is something like loop quantum gravity where spacetime is dynamic.
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:
 
  • #3
Demystifier said:
I'm playing angel's advocate. :wink:

Lucifer was an angel too.
 
  • #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 which an incoming string separates in two outgoing ones. By a lorentz transformation that vertex is shown to be equivalente to ones in which 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 which 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 which 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 which make me felle somewhat uncofortable with them. If I see them flawed for the very beginning 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.
 

Related to An argument against string theory; geometry is dynamic

1. What is string theory and how does it relate to geometry?

String theory is a theoretical framework in physics that attempts to explain the fundamental nature of particles and forces. It proposes that particles are not point-like objects, but rather tiny strings vibrating at different frequencies. In this theory, the geometry of space-time is also described by these strings.

2. What is the main argument against string theory?

The main argument against string theory is that it has not yet been experimentally proven. Despite decades of research, there is currently no way to test or verify the predictions of string theory. This lack of empirical evidence has led some scientists to question its validity as a complete theory of the universe.

3. How does the dynamic nature of geometry challenge string theory?

The dynamic nature of geometry, as opposed to the fixed geometry proposed by string theory, challenges the idea that space-time is described by strings. In a dynamic geometry, the shape of space-time is constantly changing, making it difficult for strings to exist in a consistent and stable manner.

4. Are there any alternative theories to string theory?

Yes, there are several alternative theories to string theory, such as loop quantum gravity, causal dynamical triangulation, and emergent gravity. These theories also attempt to explain the fundamental nature of particles and forces, but they do not rely on strings as the building blocks of the universe.

5. What impact would a disproof of string theory have on the scientific community?

If string theory were to be disproven, it would have a significant impact on the scientific community. It would mean that decades of research and theories based on string theory would need to be reevaluated and potentially discarded. It could also lead to new avenues of research and theories to explain the fundamental nature of the universe.

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