Black holes provide organic time travel devices that enable access to both the past and the future. So don’t plan on returning to see the dinosaurs anytime soon.
There is currently no spacecraft available that could take us even remotely close to a black hole. Even putting that minor point aside, attempting to use a black hole to travel back in time might be the last thing you ever do.
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Why do black holes exist?
An incredibly enormous object known as a black hole normally develops when a dying star collapses in on itself. Black holes have gravitational fields surrounding them, just like planets and stars do. We are anchored to Earth by a gravitational field, which also causes Earth to revolve around the sun.
Generally speaking, an object’s gravitational field is stronger the more massive it is. Reaching space is incredibly challenging due to the gravitational pull of the Earth. Hence, we manufacture rockets: To escape the gravity of Earth, we must go incredibly quickly. Even light cannot escape from a black hole’s gravitational field due to its extreme strength. Given that light is the quickest substance known to science, that is remarkable!
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By the way, this is why black holes are black because we cannot reflect light off them the way we might in the dark from a flashlight off a tree.
Extending space
According to the general theory of relativity developed by Albert Einstein, the cosmos is affected in an odd way by matter and energy. Space is bent and stretched by matter and energy. An object’s ability to stretch and bend the space around it increases with its mass.
A large object bends space into a sort of valley. Things fall into the valley when they are close by. That is why you fall toward any large object, including a black hole, when you are close enough to it. The fact that the valley’s sides are so steep prevents light from moving quickly enough to climb out is another reason why light cannot escape a black hole.
As you draw closer to a black hole from a distance, the valley it has created gets steeper and steeper. The event horizon is the point where it becomes so steep that light cannot escape. Since they have consequences for how we understand the nature of time, event horizons are fascinating to philosophers as well as potential time travelers.
Black holes distort time.
Time is stretched along with space. A clock will run more slowly when it is close to a large item than when it is next to a smaller, much less substantial object. As comparison to a clock on Earth, one located close to a black hole will tick incredibly slowly. As you may have seen depicted in the film Interstellar, one year close to a black hole may be equivalent to 80 years on Earth.
You may employ black holes in this manner to go into the future. Simply fly close to a black hole, jump into the future, and then come back to Earth. If you get close enough to the center of the black hole, your clock will tick slower, but you should still be able to escape so long as you don’t cross the event horizon.
Loops in time
What about the past? This is where things get truly interesting. A black hole bends time so much that it can wrap back on itself.
Imagine taking a sheet of paper and joining the two ends to form a loop. That’s what a black hole seems to do to time. This creates a natural time machine. If you could somehow get onto the loop, which physicists call a closed timelike curve, you would find yourself on a trajectory through space that starts in the future and ends in the past.
Inside the loop, you would also find that cause and effect get hard to untangle. Things that are in the past cause things to happen in the future, which in turn cause things to happen in the past!
The catch
So, you’ve found a black hole and you want to use your trusty spaceship to go back and visit the dinosaurs. Good luck.
There are three problems. First, you can only travel into the black hole’s past. That means that if the black hole was created after the dinosaurs died out, then you won’t be able to go back far enough.
Second, you’d probably have to cross the event horizon to get into the loop. This means that to get out of the loop at a particular time in the past, you’d need to exit the event horizon. That means traveling faster than light, which we’re pretty sure is impossible.
Third, and probably worst of all, you and your ship would undergo spaghettification. Sounds delicious, right? Sadly, it’s not. As you crossed the event horizon you would be stretched flat, like a noodle. In fact, you’d probably be stretched so thin that you’d just be a string of atoms spiraling into the void.
So, while it’s fun to think about the time-warping properties of black holes, for the foreseeable future that visit to the dinosaurs will have to stay in the realm of fantasy
Sam Baron, an associate professor at the Australian Catholic University of Philosophy of Science A Creative Commons license has been used to republish this article from The Conversation. Check out the original article.
The bottom line is that black holes are time machines that can go into the past and the future. Yet, it’s not quite that easy.
