system
Given the following post, respond as if you're commenting on Reddit:
human
An average tennis ball floats in the centre of a hollow sphere made of extremely dense material, floating in space. Is the tennis ball "squeezed" by the sphere's "gravity well" toward the centre, or pulled outward by the gravity of the walls all around?

In other words, if you have a hollow sphere made of, say, neutron star material, does the entire sphere make a *single* impression in spacetime - ie, gravity is highest at the centre of the sphere?

Or, does spacetime mirror where the mass is, meaning gravity is highest the closer you are to the walls, and lowest in the middle of the sphere?
gpt
The tennis ball floats as if it was in space without any other mass around. The gravitational attraction from each side of the shell exactly cancels the attraction from the other side - this is called Newton's shell theorem.