So lets say you pass beyond the event horizon in a black hole. It is my understanding that to people outside the black hole you will appear to be virtually immobile due to time slowing dramatically. I don’t know how much time slows down, but I’ve heard it slows to a near crawl and an infinity can pass in the rest of the universe.
So it is physically possible that if someone fell past the event horizon, hundreds of years could pass in the rest of the universe and in that time period humanity discovers how to pass into and out of black holes safely, so the person who falls in nearly instantly finds themselves rescued by a human from the 26th century before their body is torn apart?
Time passes more slowly inside a gravity well. So if you’re near a large enough mass 500 years could pass outside in “flat” space while only a second passes for you. You don’t need to cross the event horizon for that. If you do cross the event horizon, then as far as we know you can’t get back out.
ETA of course the gravity required to make time “slow down” that much might also crush you or more likely rip you apart by tidal forces.
The most literal-minded answer to your question is no: As we understand physics currently, it’s not physically possible for anything (human or non-human, now or in the future) to pass safely into & out of a black hole.
Now, maybe we’ll discover loopholes in the laws of physics at some point in the future. Any method by which one could escape from a black hole would probably (again, given our current understanding) allow for some kind of time travel as well; so on that level, you shouldn’t be surprised to see people from the distant future rescuing you from inside a black hole. But I wouldn’t go jumping into one with the expectation that you’ll wake up in the year 2525.
The event horizon is the point of no return by definition, so you can’t rescue someone from beyond an event horizon full-stop. Of course it may be that physical black holes don’t form true event horizons.
From the point of view of an outside observer, a clock falling into a black hole will slow such that it asymptotically stops at the event horizon. I.e. from the pov of the outside observer the clock doesn’t cross the event horizon as time appears to reach a standstill at that point. Therefore it is always possible to mount a rescue on a rocket ship falling towards the event horizon. For the observer rescued near the event horizon, no matter how long the rescue, took an arbitrarily short period of time may’ve passed, so they could indeed wake up in the far future.
The larger the black hole, the less the tidal forces at the event horizon, so there is no need in principle for a rocket ship to be ripped apart at the event horizon. However the quicker the rescue takes (from the point of view of a faraway observer) and the nearer the event horizon the rescued rocket ship, the greater the forces you will need to exert on the rocket ship to rescue it. Meaning you could rip it apart during the rescue.
If you have faster than light travel, then yes, you can escape from the event horizon of a black hole. Faster than light travel is also time travel, so the rescuers could be time travelers from before you fell into the black hole just as easily as after. Or anything, really. Once we allow faster than light travel there’s no telling what is allowable.
Even more worryingly if you follow the paths of FTL observer going straight through a black hole they could in theory travel through the antihorizon to a parallel Universe.
One caveat, here: We’re assuming a static, classical black hole. In reality, once you get too close to the apparent horizon (like, as close as you’d get after 500 years passed for the outside observer), it’d be all too possible for the horizon to enlarge and engulf you, either from the hole eating other matter, or (possibly) from quantum fluctuations. Real horizons (as opposed to apparent ones) aren’t detectable by any finite means.
What would allow the rescuer to grab onto you and pull you out? Wouldn’t he, in turn, be trapped as well? Or is that the part that we haven’t figured out yet?
Anything, absolutely anything (including light) that passes the event horizon of a black hole can never, ever get out. It is physically impossible. Period. Full stop. Abandon all hope ye who enter.
It is true that to an outside observer they will see the person falling in to the black hole seem to go slower and slower. Indeed they will never see them pass the event horizon. They will seem to slow down and red shift out of existence but never pass the event horizon.
HOWEVER!
The person falling in will have no such issues and they will “see” themselves pass the event horizon in normal time by their watch (for the sake of argument let’s assume they survive the transit which is actually possible with a supermassive black hole).
I just realized that I’ve made a stupid error here, from looking at a spacetime diagram based on Schwarzschild coordinates, rather than the more useful Penrose diagram.
An observer on the outside the event horizon they can never know for sure if the rocket will cross the event horizon (imagine the dead rocket suddenly springs back to life and is able to rescue itself) because they can never observe it crossing the horizon. This is because the event horizon does not lie in the past light-cone of any observer outside the horizon.
However the question of whether they can mount a rescue themselves is different. It specifically depends on whether the event of the rocket crossing the horizon is in their future light-cone . So for a rocket drifting over the event horizon there will be a finite time for a given observer, after which that observer will no longer be able to assist the rocket ship. The nearer to the black hole and the further in the past the observer is the more likely they will be able to assist.
In other words observers in the far future are not able to render assistance to a rocket ships falling towards a black hole.
This was the premise for the syndicated series Andromeda. Minor spoilers as this is all revealed in the pilot-
The starship Andromeda Ascendant is attacked from without and betrayed from within. Captain Dylan Hunt ends up going down with his ship- into the gravity well of a black hole. For him and the ship, time stops. Three centuries later, a ragtag gang of smugglers take the ship out of the black hole. Hunt discovers that the Commonwealth Of Worlds has collapsed. He vows to bring the cosmos back to order.
The show was mostly very good. But, even I knew the rescue from the black hole was impossible. I chose to ignore that bit. People called off distances in space in light years, light minutes and light seconds. The acting was mostly very good. The writing was mostly very good until the show jumped the shark.
I realize I made yet another stupid mistake! I haven’t taken into account the possibility of a rotating black hole and/or that the rocket ship may have orbital angular momentum. Obviously, from arguments made in the last thread about bodies orbiting black holes the rocket ship could be rescued by an observer in the far future after experiencing only a short amount of time themselves.
However if we do only consider rocket ships that are falling directly into a non-rotating black hole the time we have to rescue the rocket ship is very short. For example if two rocket ships are hovering together over a 100 million solar mass black hole at a distance of 10 times the event horizon (7 billion miles or a bit over 1000th of a light year) and one of the rocket ships suddenly loses all power, then the rocket ship with power has only a maximum of 11 hours to rescue the stricken rocket ship before it is lost forever (unless the stricken rocket ship can recover its engines before it crosses the horizon).
Except if you have starships that can travel faster than light, you can skip in and out of the event horizon with no problem. If you can only travel at the speed of light or slower, then yes crossing the event horizon is a one way trip. But with FTL, just ignore that shit. If this doesn’t seem realistic, it’s because as far as we know in our universe there’s no way to travel faster than light. But in a universe where you could, then the event horizon is more of a suggestion than a rule.