Linked Questions

2 votes
1 answer
5k views

Why are there specifically 10, 11, or 26 dimensions in string theory? [duplicate]

I know that current string theories state that there are 10, 11, or 26 spacetime dimensions in superstring theory, M-theory, and bosonic string theory, respectively. But when I looked up why those ...
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0 votes
0 answers
89 views

Compactification of additional dimensions [duplicate]

The extra dimensions in string theory are supposed to close in on themselves to form circles. Are there other possibilities for compactification? For example a compactification in segment.
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0 votes
0 answers
28 views

Number of dimensions of the universe according to the string theory [duplicate]

I am not a physicist, but what is the current idea of the number of dimensions of the universe according to the string theory?
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  • 1
33 votes
9 answers
11k views

Why are extra dimensions necessary?

Some theories have more than 4 dimensions of spacetime. But we only observe 4 spacetime dimensions in the real world, cf. e.g. this Phys.SE post. Why are the theories (e.g. string theory) that ...
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  • 731
79 votes
1 answer
6k views

Why exactly do sometimes universal covers, and sometimes central extensions feature in the application of a symmetry group to quantum physics?

There seem to be two different things one must consider when representing a symmetry group in quantum mechanics: The universal cover: For instance, when representing the rotation group $\mathrm{SO}(3)...
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  • 105k
89 votes
1 answer
9k views

Classical and quantum anomalies

I have read about anomalies in different contexts and ways. I would like to read an explanation that unified all these statements or points of view: Anomalies are due to the fact that quantum field ...
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  • 6,350
12 votes
2 answers
964 views

What uniquely defines a CFT?

So, I am quite new to CFT (and a as descriptive answer as possible would be appreciated). I want to know what uniquely defines a CFT in 2D and otherwise. Firstly in 2D, What defines a CFT? So I know ...
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4 votes
2 answers
1k views

How exactly do superstrings reduce the number of dimensions in bosonic string theory from 26 to 10 and remove the tachyons?

In bosonic string theory, to obtain the photon as the first excited state, the ground state must have a negative mass (tachyon). By applying $1 + 2 + 3 + \cdots = -1/12$, it can be shown (in a ...
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  • 9,187
4 votes
2 answers
843 views

Conformal theory with zero central charge

Suppose there is a conformal field theory which has the global conformal symmetry namely $SL(2,R).$ and after central extension it is enhanced to Virasoro algebra with central charge, $c=0$ (also ...
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1 vote
3 answers
1k views

The size of extra dimensions

Supposing we have a model, like the String one, which predicts (or requires) $N$ spacetimes dimensions, for the precision let's talk only about space dimensions. What is the process, the rule or the ...
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  • 3,458
3 votes
0 answers
661 views

Clarification on the 11 dimension in the M-theory [closed]

In the book the Grand Design by Stephen Hawking, he wrote about the M-theory, and how in that theory it has 11 dimensions. I do not quite get that, so can someone explain it to me a little bit. I ...
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3 votes
2 answers
158 views

Are there versions of String Theory formulated in $D$ spacetime dimensions or even in infinitely many dimensions?

There are a lot of different versions of string theory, and almost all of them differ in the number of dimensions. The most famous ones are formulated in 10, 11 or 26 dimensions. But are there any ...
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  • 505
2 votes
1 answer
296 views

Fundamental string theory questions

Can anyone answer some basic string theory questions for me? The Veneziano Amplitude is celebrated for predicting the scattering amplitude of mesons and for practically giving birth to string theory....
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  • 51
1 vote
2 answers
355 views

Is any one compact dimension for one particle the same as for another particle?

In the 3+1 dimensions of everyday life and GR particles can share the same extended dimensions. Probably all particles share the same 3+1 dimensions. In string theory compact dimensions seem to be ...
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1 vote
0 answers
240 views

Instability of higher dimensional universes

According to superstring theory, there are at least 10 dimensions in the universe (M-theory actually suggests that there are 11 dimensions to spacetime; bosonic string theories suggest 26 dimensions). ...
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