I think if we could figure out a way to remove quantum fluctuations from a vacuum, the contents of the cavity would not be subject to gravity/spacetime. If a baseball was inside, it would start to float.Has anyone ever put a vacuum in a Faraday cage?
I think this is wrong.
The vacuum does not exist without quantum fluctuations of virtual particles. Dark Energy drives the expansion of the universe and this is again likely caused by virtual particles.
In some theories the absorption of virtual particles ie the reduction of the density of virtual particles around matter causes gravity, and the apparent curvature of space time.
The density of virtual particles inside a black hole is likely less than outside the blackhole.
Black holes destroy matter falling into them, likely converting matter into radiation. A baseball inside the black hole would be torn apart.