Natural Order and Science

[Alex K]

Thanks Alex, that clarified quite a bit for me. Especially the inverse square law of gravity increasing in strength, I should have remembered that. One question though, if nothing can go faster than the speed of light and not even light can escape from a black hole, then how can they evaporate by radiating random noise called Hawking radiation? Why do physicists think that this happens?

p.s. with Einstein, it is only approximately an inverse square, because gravity itself begets gravity in Einstein theory, which is not a thing in Newton theory. This means that once gravity gets strong enough, it boosts itself until it becomes more severe more quickly than a simple inverse square would. Hence you get extreme phenomena such as black holes.

The derivation that is most illustrative is as follows: near the event horizon, quantum field theory makes it so that pairs of virtual particles appear. Usually, if nothing is nearby, they would simply disappear again and nothing happens. If they appear near the horizon, it can happen that one of them falls behind the horizon, whereas the other one can leave. What we see as hawking radiation is then the one that got lucky

One might now wonder why something falling in can let a black hole decrease. Now, virtual particles are not bound by E = m c^2, and if a pair appears ex nihilo, one of them will in fact carry negative energy to balance out the positive energy of the other. Only events where the negative-energy one falls in will actually happen. We did the calculation in my relativity lecture, but that was 11 years ago and I forgot how the details went