# String theory

1. Jun 20, 2009

### keepitmoving

would string theory work if some of the extra dimensions were "larger" dimensions than our dimensions? In other words our visible dimensions would be the "Calabi Yau" dimensions of the larger dimensions universe.

2. Jun 21, 2009

### Chalnoth

So far as we know, our dimensions are infinite. So it's not really possible for other dimensions to be "larger".

3. Jun 21, 2009

### keepitmoving

maybe i used the word "larger" in a wrong way. I was referring to our visible dimensions being larger than the Calabi Yau dimensions and supposing that our visible dimensions might be embedded in "larger" dimensions.

4. Jun 21, 2009

### Chalnoth

I don't quite see how this overcomes my objection.

5. Jun 21, 2009

### keepitmoving

just to be clear, im trying to understand, not overcome your objection. Im here to learn.
Im using the word larger to describe a series of larger and larger Calabi Yau spaces (dimensions).

6. Jun 21, 2009

### Chalnoth

Yes, but if our three spatial dimensions are infinite, how would any others be larger?

7. Jun 21, 2009

### keepitmoving

i hope i dont sound argumentative here!
I guess im using the word "larger" in the same sense that our visible dimensions are larger than the Calabi Yau spaces (by the way, are the calabi Yau spaces infinite?). In that sense could our visible dimensions be someone elses Calabi Yau dimensions?

8. Jun 21, 2009

### Chalnoth

I don't mind being a bit argumentative. I just don't understand what you're saying. What do you mean by larger?

9. Jun 21, 2009

### keepitmoving

i guess im using the word "larger" wrong.
Could our visible dimensions be inaccessible to creatures in a world of dimensions other than the Calabi Yau dimensions? Could whats going on in our dimensions be analogous to the strings doing things in the Calabi Yau spaces?

10. Jun 21, 2009

### keepitmoving

i guess im using the word "larger" wrong.
Could our visible dimensions be inaccessible to creatures in a world of dimensions other than the Calabi Yau dimensions? Could whats going on in our dimensions be analogous to the strings doing things in the Calabi Yau spaces?

11. Jun 21, 2009

### Chalnoth

There are two ways in which we currently are aware that these extra dimensions might potentially exist, but still be consistent with the fact that we don't observe them.

The first is that they may be very, very small. In this situation they'd still be directions we can move, it's just that we move so little in those directions that we never notice. Typically this sort of extra dimension would be smaller than the size of a proton. For them to be this small, these dimensions must wrap back on themselves, and there are a wide variety of ways in which they can do that. Those different ways of wrapping back on themselves are described by Calabi-Yau manifolds.

The second way in which these extra dimensions might exist but be hidden from us is if normal matter is confined to a 3+1 dimensional brane. In this situation, the other dimensions are out there, and may be quite large, but we can't move in those directions because we're stuck on this 3+1 dimensional surface. This works for most everything except gravity: gravity is always able to escape the brane in these situations, and so detailed tests of gravity may eventually confirm that something like this is the case.