This is a question about black hole formation. To be clear, I’m not suggesting that black holes don’t form. It’s that I’m having trouble with the accepted explanation so there’s a flaw in my logic that, hopefully, someone can point out.
Imagine you are in flat space and you launch a probe toward a black hole. As your probe approaches the event horizon, you see it (eventually) moving slower and slower and the signals you receive from it begin to red shift. The probe approaches the event horizon asymptotically and you will never see the probe actually cross the event horizon.
By the same token, there is no experiment you can do from flat space that will give you any information about what is going on inside the event horizon. In other words, there is no measurement or observation you can make from flat space that will tell you that something is now “actually” inside the event horizon.
If both of those things are true, you can never observe the event horizon grow. All the matter that falls into the black hole will appear, from flat space, to be concentrated just outside the event horizon.
But if that is correct, how do black holes form in the first place? Event horizons (where escape velocity = c) initially form in the very center of a collapsing spherical body, regardless of the initial mass. If you are watching the collapse that forms a black hole from flat space, don’t you see all the matter collapsing towards the center but never actually crossing the event horizon just as you never saw your probe cross the event horizon? If this is correct then the event horizon – if you are observing from flat space – is where the singularity should be, a single point at the very center of mass.
To go farther out on a weirder limb, while it would appear to take an infinite amount of time for our probe to fall through the event horizon, black holes don’t persist for an infinite amount of time. Eventually, they evaporate via Hawking radiation. So what do we observe? Since we can continuously observe our arbitrarily tough and robust probe and we never see it pass the event horizon, does it still exist once the black hole evaporates? If not, why not?
In short, there seems to be a contradiction between what an observer in flat space experiences and what an observer falling into a black hole experiences. If black holes persisted indefinitely, that wouldn't be a problem. But they don't. Anything falling into the black hole that doesn't cross the event horizon eventually ends up in flat space again. So when it's all over, the flat space observer says, "I saw you get stuck at the event horizon but you never crossed it. You experienced severe time dilation. But now you're back." What does the falling observer say? It can't be, "Actually, I didn't experience any time dilation at all. I fell through the event horizon and was crushed by the singularity almost instantly."
If our probe does continue to exist, from our perspective, it has gone from being in flat space to being arbitrarily near the event horizon to being in flat space again. From the probe’s perspective, it flew towards the black hole which turned out to be a wormhole which deposited it in the far future in a blaze of Hawking radiation.
So how does this work? Why doesn’t the fact that black holes have a non-infinite life span – and, therefore, nothing can ever be observed to cross the event horizon – solve a lot of black hole paradoxes?
Again, I’m not suggesting that black holes don’t actually form. I’m just trying to figure out where I’m going wrong.
