Question: I have read that scientists till don't know where does the stuff entering a black hole go. Is there any progress in this topic? Is there a chance that the stuff is going to another parallel universe?
The most common explanation is that stuff that enters the black hole simply “enters” the black hole, i.e. they are pulled further and further in, beyond the event horizon.
Due to the way the black hole’s gravity distorts time around it, an outside observer would never see you fall in though. He/she would see you slow down, getting slower and slower as you approach the event horizon, until you come to a stop at this point. This is why we say your information would be “smeared” across the event horizon of a black hole. From your perspective though, you would be able to fall in.
It is possible that if there are other Universes, in separate “regions” of space time, or other dimensions, that the black hole could push right the way through space-time into another Universe. The other Universe would then see this as a “white hole”- a region of space time which cannot be entered from the outside, but from which matter and light keep escaping- a sort of reverse black hole.
The white-hole theory isn’t in fashion anymore, largely because we just don’t observe any in our own Universe, but we can detect a lot of likely blackholes. We’d expect a roughly equal number of both.
That being said, it is possible that the Universe *began* in this fashion, as a white hole, caused by a black hole in another Universe, or possibly a “big crunch” again, in which an entire Universe became a black hole.
If space-time in our own Universe curves back on itself in the right way, it’s also possible that wormholes could form, connecting two different regions of spacetime together, like this:
I think it’s fair enough to say that part of the main problem with this sort of question is that it’s very hard to come up with an experiment that will tell you what the inside of a black hole is like — after all, you’d never be able to transmit information out again, and anything you built would be very, very destroyed on its way down. I personally think that these sorts of questions are fundamentally experimental, and there’s no way of knowing without doing something based on experiment, and thinking long and hard about its implications. Maybe one day we’ll know!