Keeping a shell positioned would be easy; just put an electric charge on both it and the black hole.
This won’t work for spherical shells and uniformly distributed charge for the same reason that a spherical shell has no net gravitational force on anything inside it. You’ll need active counterbalancing.
This won’t work for spherical shells and uniformly distributed charge for the same reason that a spherical shell has no net gravitational force on anything inside it. You’ll need active counterbalancing.
Ah, true, I didn’t think of that, or rather didn’t think to generalize the gravitational case.
Amusingly, that makes a nice demonstration of the topic of the post, thus bringing us full circle.