# Weak field limit

1. Oct 9, 2009

### keepitmoving

what is the weak field limit?

2. Oct 10, 2009

### Chalnoth

Generally, it's when the field in question is small. With gravity, for instance, the gravitational field is small when you're far away from any massive objects.

3. Oct 10, 2009

### keepitmoving

Chalnoth,
like i said, im just an amateur but couldnt the extra dimensions actually be visible as the expansion of space and that they are staring us right in the face. Also, the actual physical world isn`t limited to what science can test for. thank you for your answer on the afield limit.

4. Oct 10, 2009

### Chalnoth

Well, it is always possible to visualize curvature by considering a surface embedded in a larger-dimensional space. For instance, the surface of a sphere is a purely two-dimensional surface. We visualize the curvature of this surface, however, by looking at the surface in three dimensions.

One of the main insights of differential geometry (the mathematics behind General Relativity), however, is that you don't actually need to have extra dimensions to have curvature. The curvature in General Relativity (which is how the expansion is described: it's curvature in space-time) is fully depicted with no reference to any extra dimensions.

Er, but it is only stuff that we can test for, whether directly or indirectly, that we can be confident exists. The real world may well not be limited by our experimental abilities. And that's fine. But we had better limit ourselves to our experimental abilities lest we mislead ourselves.

5. Oct 10, 2009

### keepitmoving

thanks chalnoth but keep pushing that envelope out!

6. Oct 10, 2009

Naturally :)