# How does GR explain twist at the poles

1. Nov 7, 2015

### CRT

[Moderator's note: spun off from previous thread on a different topic.]

how general relativity explains the variation in value of g at equator and poles?
why the twist in spacetime is more at poles than equator and not viceversa

Last edited by a moderator: Nov 7, 2015
2. Nov 7, 2015

### rootone

The difference in gravity is not attributable to GR, it has more to do with the shape of the Earth not being perfectly spherical.

3. Nov 7, 2015

### Staff: Mentor

Careful. GR can certainly explain it; it's just that GR is overkill for explaining it, since the Newtonian approximation can do so just as well.

4. Nov 7, 2015

### Staff: Mentor

By the fact that the Earth is rotating and is not perfectly spherical, so the gradient of the gravitational potential (which is what "g" is) is different at the poles than it is at the equator. As I noted in my response to rootone just now, however, you don't need GR to derive this result; simple Newtonian mechanics is sufficient.

What do you mean by "the twist in spacetime"? What sort of observations do you think show this?

5. Nov 9, 2015

### CRT

sir i read somewhere that massive earth distorts spacetime as we all know
but distortion is more at poles due to sperical shape of earth.This last line was the main root of confusion.

6. Nov 9, 2015

### CRT

I agree with Sir Donis that Newtonian mechanics is sufficient over GR.Thanks sir

7. Nov 9, 2015

### Staff: Mentor

Yes, the Earth's mass causes spacetime curvature.

Are you just referring to the fact that $g$ is different at the poles? $g$ is not the same thing as spacetime curvature.

Also, the reason $g$ is different at the poles, in Newtonian terms, is that the Earth is not spherical; it's an oblate spheroid which is rotating.