(ORDO NEWS) — Black holes create natural time machines that allow travel to both the past and the future.
But don’t expect to return to the age of the dinosaurs anytime soon, as trying to travel back in time with a black hole may be the last thing you’ll ever do.
A black hole is an extremely massive object that typically forms when a dying star collapses.
Like planets and stars, black holes are surrounded by gravitational fields.
As a general rule, the more massive an object, the stronger its gravitational field. The gravitational field of a black hole is so strong that even light cannot escape from it.
Albert Einstein’s general theory of relativity tells us that matter and energy bend and stretch space. The more massive an object, the more space stretches and curves around it.
A massive object creates a kind of valley in space. As objects approach, they fall into the valley. When you get close enough to any massive object, including a black hole, you fall towards it.
The valley formed by the black hole gets steeper and steeper as you approach it from afar. The point at which it becomes so steep that light cannot escape is called the event horizon.
Event horizons are of interest not only to would-be time travelers but also to philosophers because they influence how we understand the nature of time.
As space expands, so does time. Clocks near a massive object will tick slower than those near a small object.
Clocks near a black hole will tick very slowly compared to clocks on Earth. Thus, black holes can be used to travel into the future.
If you want to jump into the future of the Earth, just fly close to the black hole and then return to Earth.
If you get close enough to the center of the black hole, your clock will tick slower, but you can still escape until you cross the event horizon.
What about the past? This is where things get really interesting. A black hole warps time so much that it can reverse itself.
Imagine that you take a sheet of paper and connect the two ends to form a loop. This is what a black hole seems to do over time.
This creates a natural time machine. If you could somehow get into the loop that physicists call a closed time curve, you would be on a path through space that starts in the future and ends in the past.
So you’ve found a black hole and 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. This means that if the black hole was created after the dinosaurs died out, then you can’t go back far enough.
Second, you would probably have to cross the event horizon to get into the loop.
This means that in order to exit the loop at a specific time in the past, you would need to exit the event horizon. This means faster-than-light travel, which we are pretty sure is impossible.
Third, you and your ship will be spaghettified. When you cross the event horizon, you will be stretched like noodles.
In fact, you would probably be stretched so thin that you would just be a string of atoms spiraling into the void.
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