Although black holes create natural time machines that provide travel to both the past and the future, don’t expect to visit dinosaurs thanks to them. Currently, there is no spacecraft that can take us near a black hole. But even putting that little detail aside, attempting to travel back in time using a black hole may be the last thing you do.
A black hole is an extremely massive object typically formed when a dying star collapses into itself. Like planets and stars, black holes have gravitational fields around them. The gravitational field is the force that keeps us on the Earth and makes the Earth revolve around the Sun. In general, the greater the mass of an object, the stronger the gravitational field.
Earth’s gravitational field makes it extremely difficult to go into space. We continue to develop rockets as we have to move very quickly to escape Earth’s gravity.
But the gravitational field of a black hole is so strong that even light cannot escape it. Considering that light is the fastest thing known, you can imagine how impressive this is.
Albert Einstein’s general theory of relativity tells us that matter and energy have an interesting effect on the universe. Matter and energy bend and stretch space. The more massive an object is, the more the space around it will stretch and bend. A massive object creates a kind of valley in space. Objects fall into this valley when approaching.
Therefore, when you get close enough to any massive object, including a black hole, you will fall towards it. It is the same reason why light cannot escape from a black hole. The sides of the valley formed by the black hole are so steep that the light does not travel fast enough to get out. The valley created by a black hole becomes steeper as you approach it from afar. The point where the light becomes so steep that it cannot escape is called the event horizon.
Event horizon zones are interesting not only to time travelers, but also to philosophers. The event at these borders raises some questions about how we understand the nature of time.
When space stretches, time does too. A clock near a large object will run slower than a clock near a much less massive object. Near a black hole, this can be taken to even more extremes.
In this way, black holes can be used to travel into the future. If you want to jump into the future of Earth, simply return to Earth after a short flight near a black hole. If you get close enough to the center of the black hole, your time will slow down, but you may still be able to escape as long as you don’t cross the event horizon.
When it comes to travel to the past, things get really interesting. A black hole bends time enough to wrap itself around itself. This creates a natural time machine. If you could somehow enter the loop that physicists call a closed time-like curve, you would be able to find yourself on an orbit in space that begins in the future and ends in the past.
However, there are three problems with this. For one, you can only travel back into the black hole’s past. So, if the black hole appeared after the dinosaurs died, you wouldn’t be able to go back far enough to see the dinosaurs.
Second, you’ll probably have to cross the event horizon to get into the loop. This means that to get out of the loop at a certain time in the past, you have to get out of the event horizon. So to get out of this loop, you have to move faster than light in a way that we’re pretty sure is impossible.
Third, and possibly worst, you and your ship will experience an event described as “spaghetti”. Unfortunately, this event is not as good as its name suggests. You’ll be stretched out like a stick of spaghetti as you cross the event horizon. In fact, you’re probably stretched so thin that you’re a string of atoms spiraling through space.
So while it’s fun to think about the time-bending properties of black holes, visiting dinosaurs in the near future will have to remain in the fantasy world.
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