# Space dilation in GR

1. Aug 6, 2008

### Zman

I have read in various places that according to General Relativity space contracts around large bodies. And moving further out of the gravitational field, space dilates.

What is the logical basis for this?
Is it in fact even true and can it be measured?
Does anybody know of any sources on the web that cover this topic?

2. Aug 6, 2008

### Varnick

It can and has been measured in various experiments, that show light to "Bend" (it is of course not light, but space that is bending) around massive objects such as the sun. Someone with more experience of experiments related to Relativity may be able to enlighten you further.

V

3. Aug 6, 2008

### Zman

I see what you are saying but does distorted space near a body need to be more contracted than further away from the body for light to curve?

4. Aug 6, 2008

### Varnick

Light does not bend, relative to space, light travels in straight lines (known as Geodesics). Instead, when space bends, light APPEARS to bend, even though it's really going straight, relative to space. "Contracted" is a bad word to use in this context, generally physicists talk about the curvature of space-time. Yes, space nearer a massive body will be more curved, and therefore the gravitational force will be stronger.

V

5. Aug 6, 2008

### Zman

From what you are saying, physicists in GR don't refer explicitly to contraction of space but instead to curvature of space. Whereas in SR contraction of space is considered a valid description of space-time.
I presume that curvature of space in GR has no implications as to volume?

6. Aug 6, 2008

### Varnick

In SR, space doesn't contract, things contract in space (such as hypothetical spaceships going at relativistic speeds). Curvature does not affect volume, no, it merely changes the geodesic paths on the space-time manifold.

V

7. Aug 6, 2008

Thanks V

8. Aug 6, 2008

### Ich

No, in SR space alone (not spacetime) is seen contracted by anybody who does not define space as orthogonal to his worldline, but skewed. Things would never contract, they aren't allowed to by the relativity principle. They simply look different (in the sense of "are measured differently").
Curvature may well affect volume, whatever this means (Trace(Rij) <>0 in this case). But only if energy or pressure are inside the volume. Outside of masses, volumes get distorted, but not changed in size.

9. Aug 6, 2008

### MeJennifer

You might want to lookup the difference between Weyl and Ricci curvature. Ricci curvature certainly can have volume reducing effects.

10. Aug 7, 2008

### Varnick

Thanks MeJennifer, I'll look into that.

V