> I think there are more. Like radiation from evaporating black holes.
Evaporating black holes?
Yes, if you are willing to wait a very, very long time, and have collectors over a large area.
However, if you want to get stuff done before your protons evaporate, you could instead throw matter into a black hole, thus increasing its mass. The radiation given off by the accretion disc is substantial, and can be collected... over a large area.
IIRC, the mass-to-energy efficiency is something like 40%, which is really good.
Evaporating black holes?
Yes, if you are willing to wait a very, very long time, and have collectors over a large area.
However, if you want to get stuff done before your protons evaporate, you could instead throw matter into a black hole, thus increasing its mass. The radiation given off by the accretion disc is substantial, and can be collected... over a large area.
IIRC, the mass-to-energy efficiency is something like 40%, which is really good.
They are a little difficult to set up however...