Physicist, what do you think? Zero gravity inside a massive hollow sphere?
Zero gravity from the sphere itself, yes. Put a black hole (or a planet, or a star, or a crouton, or...) somewhere, inside or outside of the sphere, and you'll feel the gravitational field from that, but the field from the sphere itself will be zero inside.
Consider any arbitrary chunk of the sphere. It subtends some patch of solid angle with respect to you. The gravitational pull from that chunk is opposed by the pull of a similarly-shaped chunk on the opposite side of you. Get this: the size (and therefore the mass) of each chunk will grow as the square of its distance from you. Its gravitational pull will fall off as the square of its distance from you. Those two factors cancel, thus the pull from each piece is equal and opposite. That zero-pull argument works for any arbitrary piece in any arbitrary direction. Integrate that zero over the entire sphere, and you get zero.