Why do strings have to exist in 10 dimensions?

In summary, string theory proposes that instead of zero-dimensional point particles, the building blocks of the universe are one-dimensional strings, which resolves the incompatibility between relativity and quantum mechanics. These strings need extra dimensions in order to vibrate and manifest the properties of matter. The specific number of dimensions (10 or 11) is necessary for the theory to fit with predictions and maintain certain symmetries.
  • #1
11thDimension
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so i came across string theory and i don't understand (if your going to go along with it) why it is tiny strings that make up the universe and why exactly do they have to exist in more then 4 dimensions?
 
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  • #2
11thDimension said:
so i came across string theory and i don't understand (if your going to go along with it) why it is tiny strings that make up the universe...

In a very simplified nutshell:

The theory of relativity and quantum mechanics - two of the most carefully tested and confirmed models ever developed in scientific history - turn out to be incompatible.

If you try to resolve relativity over the subatomic distances where quantum theory applies, you get infinities. To oversimplify further, QM says that the smaller you look, the larger the uncertainty. Relativity, on the other hand requires zero-dimensional, infinitely small point particles. Put those two together and you get particle interactions (i.e. energy transfers) that are arbitrarily large and occur over zero time, i.e. infinite energy transfer. This makes no sense.

String theory proposes that particles are not zero-dimensional, but instead are one-dimensional (strings). This neatly resolves the whole issue, since it spreads any and all interactions over a non-zero distance and non-zero time.

As for the extra dimensions, well, the properties of matter (such as mass, spin, etc) are manifestations of the vibrations of the strings. These vibrations need these extra dimensions in order to vibrate (read about Kaluza -Klein theory).
 
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  • #3
so why do these strings also have to be able to exist in 11 dimensions
 
  • #4
11thDimension said:
so why do these strings also have to be able to exist in 11 dimensions

I'm not an expert, but it's my understanding that there is no a priori reason that the strings must exist in 11 dimensions, it's a requirement for the theory to fit with predictions. I could be mistaken of course.
 
  • #5
11thDimension said:
so why do these strings also have to be able to exist in 11 dimensions
They don't. They exist in 10 dimensions. 11 is the number of dimensions in M-theory, which is believed to be more fundamental than string theory.

Of course, now you will ask why 10? Well, classical string theory is well defined in any number of dimensions. However, some symmetries (like Lorentz invariance) may achieve anomalies when a classical theory is quantized. Anomalies destroy the symmetries, so you don't want them. It turns out that anomalies cancel in 10 dimensions only. That's why you need 10.
 

What is string theory?

String theory is a theoretical framework in physics that attempts to reconcile quantum mechanics and general relativity by describing the fundamental building blocks of the universe as tiny, vibrating strings instead of point-like particles.

Why is it called "string" theory?

String theory is named after the tiny, one-dimensional strings that make up the fabric of the universe according to this theory. These strings vibrate at different frequencies, giving rise to the different particles and forces in the universe.

What is the purpose of string theory?

The main purpose of string theory is to provide a unified understanding of all the forces and particles in the universe, including gravity. It also aims to reconcile the two major theories in physics - quantum mechanics and general relativity.

How is string theory different from other theories in physics?

String theory differs from other theories in physics in that it describes particles as tiny, vibrating strings instead of point-like particles. It also incorporates additional dimensions beyond the four we experience in our daily lives.

Is string theory proven?

No, string theory is currently not proven. It is still a theoretical framework and many aspects of it are still being researched and debated. However, it has shown promise in resolving some long-standing issues in physics and continues to be a topic of study and research for scientists.

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