Black Holes


I don’t understand black holes. I don’t understand how things get inside a black hole from the perspective of an outside observer. I would have thought an outside observer would just see the object approach the event horizon, and by general relativistic effects the object would become time dilated, and slow down as it approaches the event horizon. The object’s appearance would become more and more red shifted, but never quite making it inside the black hole.

A friend tells me the above is true for infinitesimal test masses, but actual particles have actual mass, and through some crazy gravity interaction can actually get inside a black hole.

I also don’t understand Hawking radiation. I vaguely understand the idea of the spontaneous creation of particle and virtual particle pairs, and I can understand that the virtual particles could fall into the black hole and the real particle escaping. This would allow a black hole to radiate energy. What I don’t understand is why smaller black holes radiate more energy. With less surface area, you would think the process as described would lead to fewer particles radiated, and presumably less energy.

Most importantly I don’t understand this idea that the surface area of a black hole represents it’s entropy. In fact I’m told that that every four units of planck area is one bit of entropy. It seems to me that the size of a black hole would depend on the gravitational strength, and hence would depend on the mass. Why would it be the case that if I throw a hot cup of tea into a black hole, the surface area would increase more than by throwing a cold cup of tea into it?


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Russell O’Connor: contact me