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> imagine the limit case where the earth were a hollow sphere

If it were a hollow sphere with the same total mass as our actual Earth, as measured from the outside, then clocks everywhere inside the hollow sphere would run slow relative to clocks just on the outer surface of the sphere, by roughly the same amount as clocks at the center of the actual Earth. The "clock rate" in the interior of the sphere's material would decrease a lot faster, per unit distance down from the outer surface, than it does in our actual Earth, because the material of the hollow sphere would have to be a lot denser than the material of our actual Earth, in order to have the same total mass.




What is the force of gravity at any point in such a sphere? So what does GR have to say?


The force of gravity is 0. But the potential of gravity is higher than on the outside, so clocks run slower.


> the potential of gravity is higher than on the outside, so clocks run slower

Correction: the potential of gravity is lower inside the sphere than outside, so clocks run slower.




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