Based on this question, and paying attending to shell theorem, what would happen to gravity if there were multiple hollow shells within each other?

Would the effective mass and gravity of each shell combine into one gravity field at the surface of the outer sphere with complete zero g throughout the entire inside the largest sphere regardless of mass or masses inside... or would each sphere have its own separate gravity field on the exterior of each shell with a zero g section in between and in the center of the smallest sphere? Something else?

I understand that in a hollow sphere, all the internal points experience no gravity and only the surface outward from said sphere has gravity... but where I get confused conceptually is what if there is one or more objects massive enough to have its' own gravity inside said sphere.

I ask this question because I was randomly wondering one day if somehow a Dyson sphere suddenly appeared out of nowhere enclosing the Earth and the Sun... would everything inside suddenly go to zero g, and what would that mean for the structural forms and atmospheres and lifeforms of the planets and sun inside? Anyway, I am trying to make this a simpler question, so this paragraph is simply explaining why I'm asking and is not intended to be a question itself.

For the purposes of this theoretical question, assume three shells of 0.7AU, 1AU, 1.3 AU starting off perfectly aligned, each shell contains enough mass that if place independently of each other they would have 1g at the exterior surface, with nothing in the center, and without other influences. How this was constructed is irrelevant to the best answer. If my numbers make no sense, feel free to adjust them to something more realistic.

You are welcome to show your math if you choose, but please also provide a layman's explanation.


1 Answer 1


The shell theorem states that a uniform massive shell does not exert any net gravitational force at any point inside the shell. If there is a shell outside your current position, it has no gravitational effect on you. That doesn't mean it "zeros out" all the gravitational effects of things that aren't the shell, however, just that the shell itself has no gravitational effect at points inside the shell. You'd still feel the gravitational pull of a point mass placed anywhere inside or outside the shell, or of another shell that you weren't inside.

If a massive uniform shell suddenly appeared outside the earth, there would be no change in net gravitational forces anywhere inside the shell. If second shell appeared outside the solar system, you'd feel no effect from either shell when inside both shells; you'd feel the gravity from the first shell alone between the first and second shells; and you'd feel the gravity from both shells when outside both shells. There would still be a gravitatational effect when between the shells, the larger shell doesn't have any net force contribution when inside of it, but it doesn't eliminate the net force contribution from the smaller shell, which you are outside of.

If a large shell appeared outside the earth, we would not notice anything from a gravitational perspective. It would impart zero net force to us, and would not affect the gravitational force that the earth already exerts on us.

  • $\begingroup$ Thank you, that seems to resolve my confusion! I will wait for a time to give others a chance to post answers before selecting the best one. $\endgroup$
    – nijineko
    May 1 at 18:14

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