Can general relativity explain the difference in tides between land and sea?

[dodo]

Hello,
general relativity describes gravity not as a force (as opposed to the classical view), but as the effect of bodies following an inertial path on a distorted spacetime.

How does that explain the sea tides on Earth? The moon pulls the water without pulling the surrounding land by the same amount. I understand that the moon does pull the land (which is a nuisance for satellite ground measurements), but certainly we perceive a relative difference in heights between land and sea. How is that explained in terms of objects following a spacetime geodesic, when land and sea are, near their areas of contact (the shores), at such proximity?

Thanks!

 

[JesseM]

particles only move along geodesic paths through curved spacetime if there are no non-gravitational forces acting on them, i.e. if they are in freefall. There are inter-atomic forces between the particles in both land and water, so these particles don't follow geodesics, and the fact that we see tides has to do with the fact that these inter-atomic forces are stronger in land than in water, so the solid land doesn't get deformed as much from a spherical shape as the oceans do. This page has a simple diagram:

 

[dodo]

Ah, alright. So I gather that the question is similar to imagining a system of masses connected by springs (some looser, some stronger), and asking how would it work on a non-euclidean space.

Thanks for the link!

 

[JesseM]

Ah, alright. So I gather that the question is similar to imagining a system of masses connected by springs (some looser, some stronger), and asking how would it work on a non-euclidean space.

Yes, that's an excellent way of thinking about it.