Black holes are interesting, in every possible way, including the way that gets us to time travel.
They are “born” when stars “die”, stars which are at least 3 times more massive than our Sun. Now, every object in the Universe which is made of matter, from the smallest grain of dust, to the most ginormous galaxy, has got mass. You can imagine “mass” as the property of matter to modify, stretch if you want, the space around it.
Visualise balls, some of them smaller, some bigger, that you can put on a very elastic surface, and watch them sinking on this surface. The more massive they are, the more they will deform that surface. Gravity is a direct consequence of that curving of the surface.
But that surface isn’t just space, it's space-time. The more an object is capable of deforming that mesh, the more it will deform time. Ordinary stars can be pretty massive, and have enough of an effect on space-time that if you could get close to them with a spaceship and then go back home to your family, you’ll find that the watch that you’re wearing and the one hanging on the wall in the kitchen are not synchronised anymore, by seconds or minutes, depending on the star and how close to it you dared to go. And for how long of course.
If you have an extremely precise watch, you can measure this effect even just going to the moon and back. You’ll be measuring tiny fractions of a second in difference, but that’s all you need to do to travel through time. Go somewhere where the gravity is stronger and you’ll effectively travel to the future. Or go away from Earth’s gravity well and you’ll see your friends on Earth age very slightly slower than you. That’s exactly what happens to the astronauts in orbit in the ISS.
Now let’s go extreme and back to black holes. Black holes are not more massive than the stars they originate from, actually a bit less (because the stars explode violently and lose the outer shell when they “die”). But, and this makes all the difference in the Universe, they are immensely more dense than the original star. Basically infinitely dense. Most of the original mass has been compressed into an infinitesimally small point. How can we visualise black holes using the same image of the balls on the elastic mesh? Imagine that instead of putting a ball as big as a soccer ball of the weight of 1 kg on an elastic sheet, we exert the same force of 1 kg using a long needle, or, like in the next picture, a tiny metallic ball made of an ultra dense metal.
The force is the same but it acts much more strongly on the area immediately around the point where the ball is touching the mesh.
What happens if you take your spaceship and go where the mesh is deformed violently? You’ll experience a much more extreme time-dilation. For every second you spend there, many seconds or minutes might pass on Earth, and the extent of the time dilation can increase or decrease a lot just with small movements towards the bottom of the pit or away from it. You might zap there with your super fast ship, orbit for maybe 30 minutes, just the time to prepare a cup of tea and sip it calmly, zap back home and realise that just in the time you were having tea, your little brothers have done a whole semester at school (this, only if you can avoid going beyond the point of no return, called event horizon. After you pass that, there’s nothing in the Universe that can make you see your family again).
In all of these cases you’ll be travelling to the future. There is no known mechanism in the Universe which isn't wildly speculative that could make you go back to the past. No way to recover the time you have been away from your family.
As you can see I haven't mentioned wormholes yet. Because they are rather unnecessary at this point, since black holes are all you need to travel to the future. And for other reasons: wormholes are only theoretical, again wildly speculative. They are sort of a stretch of the laws of physics that we know, but nobody really believes that they can exist, and if they exist nobody thinks that they could be actually useful. And, they wouldn't even occur naturally, hanging around black holes. We would have to produce them ourselves, using preposterous amounts of energy.
I say wormholes are only useful as movie tropes. I’d be happy to be wrong.
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