I was trying to find an answer as to why light does not escape black holes and I stumbled upon this Phys.SE question. In the answer it said that:
"Since all future lies within the event horizon, photons are trapped inside the black hole."
But what does that mean? It sounds to me that if light were to escape a black hole it has to travel back in time. And this leads to another question, why does the future lie within the event horizon? This could make sense to me if there was another reason as to why light can't escape a black hole once it has passed through the event horizon, and as a result of that, the future lies within the event horizon. But that just makes the answer to the linked question a circular proof, it is the same as saying that light can not escape a black hole because of X reason and that is the reason why the future lies within the event horizon. And the future lies within the event horizon because of X reason. So is there an "X" reason, if so, what is it?