# Thread: Brane universe and curled up dimensions

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Jul 2003
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## Brane universe and curled up dimensions

So basically all I want to know if I get this right:

The extra spatial dimensions in string theory and are required to be curled up and very tiny to explain a) only three perceivable spatial dimensions and b) the relative extraordinary weakness of gravity.

Now with M theory where the three spatial dimensions could be a 3-brane and to which open strings stick to and closed loop strings (gravitons) don't, this isn't required anymore. Three spatial dimensions come from the 3-brane to which all particle strings are limited (no curled up extra dimensions). Gravity is actually massively stronger but appears weak because most gravitons radiate away from our universe (no need for tininess/curvature of extra dimensions).

So we can possibly have 11 flat dimensions. Sounds about right?

2. Could be. What would those other 11 dimensions be, though? We currently perceive 3 space and 1 time. Is it possible those other dimensions are something else entirely? For that matter, what is the definition of a dimension?

3. 10 spatial dimensions and time. Since open strings are tied to the 3D brane which is our universe, we are unable to detect the other seven spatial dimensions. Therefore, though originally the idea of curled up dimensions came from Kaluza-Klein, I do not think that they need necessarily be curled up and small. We just can't detect them, no matter what size.

4. Think of a circuit-breaker panel with 10 positions, but only 4 circuits used. Spare circuits are included, so you can easily upgrade later. The extra dimensions are there in case god ever decides to upgrade our universe from 4 to 11 dimensions.

Ok, that wasn't a mainstream position. Just a guess.

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