# Is it possible to have infinite amount of dimension?

1. Dec 12, 2004

### scilover89

Quote:
"Because gravity also spreads outside spacetime, only a fraction of its strength is available inside spacetime, and this is given as the explanation of why gravitation is so much weaker than the other forces."

If this statement is true, is it still possible that there are infinite amount of dimension? If there are infinity of dimension, then the gravity force will certainly be zero, as gravity must spreads into every dimension.

2. Dec 12, 2004

### jujio77

I don't think the quote is correct. The idea behind that statment is that our visible universe is constrained on a brane, but spacetime itself is higher dimensional. This allows gravity to live on the brane in our visible universe and, also leak into the extra dimensions.

It could just be symantics, but I consider spacetime to consist of everything. Therefore, there is no such thing as being outside spacetime.

You are correct that gravity will get weaker, but it falls off outside the brane as 1/r^{d-3} (that could be off).

In theories of Quantum gravity like string theory, the number of dimensions is constrained. If these constraints aren't met, things fall apart.

If you want to just talk about gravity, you may be able to create a theory with an infinite number of dimensions, but I can't think of how, nor do I think I would want to. Seems pretty mesy to me.

3. Dec 13, 2004

### Haelfix

In string theory, critical dimensions are based on field theory anomolies cancelling. If you want to live in any other dimension, you break a crucial symmetry of the theory.

4. Dec 13, 2004

### Chronos

So, if gravity in our spacetime is leaking into other dimensions, why isn't gravity leaking from other dimensions into our spacetime? Does this just happen to be the only spacetime that contains matter? If so, just exactly what does gravity think it is accomplishing by wandering into other dimensions where it has nothing to act upon? Should we be looking for gravitational monopoles? I can't say I'm sold on the leaky universe idea.

5. Dec 13, 2004

### jujio77

What I am saying is that in one theory gravity can propogate in all the dimensions where as all other particles (us) live on a brane. This is one way to explain why gravity is weaker than the other forces.

As to whether you are sold on the idea or not, what's the point?

6. Dec 14, 2004

### Chronos

My point is it makes no sense. I see it as a backdoor way of suggesting 3+1 dimensional spacetime is somehow a preferred reference frame. Why would gravity, unlike any other force, have special priveleges in extra dimensions? Why would any natural force 'leak' into extra dimensions where there is nothing for it to act upon? And if there are no observable consequences in this universe, how is it relevant? Does that suggest a causality violation? It does to me.