It would need an infinite amount of energy, though.
Does doing something in half the time take half the energy?
Depends on the something: flipping a bit faster and faster surely requires more and more energy (no system is a perfect solid, the speed the components need to develop doubles every time, etc.)
Probably you could get at least infinity energy density in the collapsing black hole,near its singularity
It would need an infinite amount of energy, though.
Does doing something in half the time take half the energy?
Depends on the something: flipping a bit faster and faster surely requires more and more energy (no system is a perfect solid, the speed the components need to develop doubles every time, etc.)
Probably you could get at least infinity energy density in the collapsing black hole,near its singularity