# Eleven dimensions?

1. Dec 27, 2003

### drme19811

what are the hidden dimensions? what are their names?
how did scientests discover them?

2. Dec 31, 2003

### Stryker

Read "The Universe in a Nutshell" by Stephan Hawking. This will help explain multiple universes. But honestly, I still really don't get it. And always remember, it's all hypothetical.

3. Dec 31, 2003

Staff Emeritus
I think by hidden dimensions he means the compacted dimensions of string theory, not multiple universes.

String theory requires more than three space dimensions to be consistent. Superstring theory requires 10 dimensions (1 time, 3 "normal space", and 4 "hidden space" dimensions). They have to be hidden because we don't see them, and they can't be eliminated without abandoning string theory. So the theorists took an idea from Kalusza and Klein of the old days and imagined the 4 extra dimensions are "compacted" into tiny shapes that are too small to detect. At every point around us, according to this theory, is such a compacted set of higher dimensions; they go around the tiny shape like little circles.

When you go from superstring theory to M-theory you add another space dimension for a total of 11.

Randall-Sundrum theory (a particular theory within superstring theory) has a different idea. They say our 3-D world is a "brane", a kind of boundary of the higher dimensional world, which they call the bulk. All the forces except one spread out only in our brane. But gravity can spread out into the bulk as well. They use this to explain why gravity is so much weaker than the other forces; it's because its strength is spread out among 4 or 5 extra dimensions.

4. Dec 31, 2003

### KLscilevothma

How about 26 dimensions? IIRC, mathematics in those theories show that only either 11 dimensions or 26 dimensions exists.
Is there any qualitative explanation of what the 26 dimensions are, besides dimensions of time and space ?

5. Dec 31, 2003

### Mentat

Don't you mean 6 "hidden" space dimensions?

I've wondered about this; does the Randall-Sundrum theory fit in with M-Theory...I mean, M-Theory was the way to unify the 5 previous superstring theories, but the Randall-Sundrum approach seems like a different idea altogether.

6. Dec 31, 2003

### Stryker

That's what I ment, Sorry dude.

7. Jan 1, 2004

### drme19811

26 dimensions??

what is that theory that shows that there is 26 dimensions??
is it a really or a fiction??
what r these dimensions?

8. Jan 1, 2004

### drme19811

do u mean by (hypothetical) that it is just a theory , a fiction or doesn't have practical uses??

9. Jan 1, 2004

### drme19811

i was meaning (the compacted dimensions of string theory), but is there a difference between this & multiple universes??

is there difference between
(multiple universes) & (paralel universes)??

10. Jan 1, 2004

Staff Emeritus
Stronger than a made up fiction, because it's part of a strong theory. But the theory has no experimental support yet. So we respect the theory, but don't yet grant it the status of relativity or quantum mechanics, which have tons and tons of expeimental verification.

11. Jan 1, 2004

Staff Emeritus
Re: 26 dimensions??

The oringinal "bosonic" string theory required 26 dimensions. It was an exciting theory in its day because it didn't require renormalization and predicted a graviton, which had been a holy grail for physicsts for generations. But it only did bosons, not fermions (the photon is a boson, the electron is a fermion. A physics with only photons and no electrons would be pretty feeble).

So supersymmetry was aded to string theory to make superstring theory, and this one could do both fermions and bosons. Also the supersymmetry "ate up" some of the original degrees of freedom and reduced the required dimensions from 26 to 10.

12. Jan 1, 2004