20 questions linked to/from Why are extra dimensions necessary?
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### Why does M-theory need 11 dimensions? [duplicate]

I have looked on the internet and no one can tell me why M-theory needs eleven dimensions?
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### How do we know there are dimensions above the third? [duplicate]

Excluding the interpretation of time being the forth dimension, what mathematical evidence is there that suggests it exists? When talking about string theory they say how there is 12 dimensions and I ...
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### Why was there a need of defining spatial dimensions more than 3? [duplicate]

3 dimensional universe looks like the limit for me. I can't even imagine a fourth dimension, and there are physicists talking of 11 dimensional spacetime. There are even mathematical generalisations ...
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### What experiment would disprove string theory?

I know that there's big controversy between two groups of physicists: those who support string theory (most of them, I think) and those who oppose it. One of the arguments of the second group is ...
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### Experimental evidence of a fourth spatial dimension?

As human beings, we observe the world in which we live in three dimensions. However, it is certainly theoretically possible that more dimensions exist. Is there any direct or indirect evidence ...
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### Why does string theory require 9 dimensions of space and one dimension of time?

String theorists say that there are many more dimensions out there, but they are too small to be detected. However, I do not understand why there are ten dimensions and not just any other number? ...
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### Have we proven that higher dimensions exist? [duplicate]

Have we proven higher dimensions exist?
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### Measuring extra-dimensions

I have read and heard in a number of places that extra dimension might be as big as $x$ mm. What I'm wondering is the following: How is length assigned to these extra dimensions? I mean you can ...
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### Can we actually prove with 100% certainty that there are more than 3 dimensions plus time $(t,x,y,z)$? [duplicate]

Can we actually prove with 100% accuracy that there are more than 3 dimensions plus time? In the news there are always articles like "there are probably 7, 11 or more dimensions", "time is actually ...
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### 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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### Pedagogical explanations of critical dimensions of string theories

Once you understand the formalism, I think it's clearest to say the critical dimension of the space-time arises because we need to cancel the central charge of the (super)conformal ghosts on the ...
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### Total Number of Dimensions in the Universe? [duplicate]

I have often heard that there are more than 4 (3 space and 1 time) dimensions of spacetime. What are the theories that say so, and how many does each predict? Has any experimental evidence been ...
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### Mathematically rather than physically speaking, is there something “special” about 10 (or 11) dimensions?

As I understand it, string theory (incorporating bosons and fermions) "works" in $9+1=10$ spacetime dimensions. In the context of dual resonance theory, I've read descriptions of why that is "...
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 ...