[ad_1]
Black holes create natural time machines that allow us to travel to the past and the future. But don’t expect to be returning to visit the dinosaurs anytime soon.
We currently have no spacecraft that can get us anywhere near a black hole. But, that little detail aside, trying to travel back in time using a black hole might be the last thing you do.
What are black holes?
A black hole is a supermassive object, typically formed when a dying star collapses in on itself.
Like planets and stars, black holes have gravitational fields around them. It is the gravitational field that keeps us stuck to the Earth, and keeps the Earth moving around the Sun.
As a general rule, the more massive an object, the stronger its gravitational field.
Earth’s gravitational field makes it extremely difficult to reach space. This is why we build rockets: we need to travel fast to escape Earth’s gravity.
Read more: How Gravitational Waves Can ‘See Inside’ Black Holes
A black hole’s gravitational field is so strong that even light cannot escape it. That’s amazing because light is the fastest thing known to science!
Incidentally, this is why black holes are black: we can’t bounce light off a black hole like we can bounce a flashlight off a tree in the dark.
Spread the space
Albert Einstein’s general theory of relativity tells us that matter and energy have a curious effect on the universe. Matter and energy bending and stretching space. If something is more massive, more space is stretched and folded around it.
A giant object creates a kind of valley in space. When items are delivered, they fall into the valley.
This is why when you get close to any massive object, including a black hole, you fall into it. This is why light cannot escape from a black hole: the sides of the valley are so steep that light cannot travel fast enough to escape.
The valley formed by the black hole gets steeper and steeper as you get closer. The area where 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 have implications for how we understand the nature of time.
Stretching time
As space unfolds, so does time. A clock near a giant object beats slower than a clock near a much smaller object.
A clock near a black hole ticks very slowly compared to a clock on Earth. A year near a black hole can mean 80 years on Earth, as you may have seen in the movie Interstellar.
In this way, black holes can be used to travel in the future. If you want to jump to Earth in the future, simply fly near a black hole and then return to Earth.
If you get closer to the center of the black hole, your clock will slow down, but you should still be able to escape as long as you don’t cross the event horizon.
Rings in time
What about the past? This is where things really get interesting. A black hole can bend time and fold back on itself.
Imagine taking a piece of paper and joining the two ends together to form a loop. This is what a black hole looks like over time.
This creates a natural time machine. If you somehow get into a loop that physicists call a closed-time curve, you’ll find yourself on a spacewalk that starts in the future and goes back in time.
In a loop, you will find it difficult to connect cause and effect. The past causes things to happen in the future, which in turn causes the past to happen!
The catch
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 back in time to a black hole. That means that if the black hole formed after the dinosaurs died, then they can’t go back far enough.
Second, you may have to cross the event horizon to enter the loop. This means that you need to exit the event horizon to exit the loop at some point in the past. This means traveling faster than light, which is definitely impossible.
Third, and perhaps worst of all, you and your ship would be “spaghettified.” Sounds delicious, right?
Unfortunately, no. As you pass the event horizon, you flatten out like a noodle. In reality, you’ll be a string of atoms spiraling into nothingness.
So, while it’s fun to think about the time-consuming properties of black holes, future visits to dinosaurs must remain a fantasy.
This article was reprinted from The conversation (Opens in a new tab) Under a Creative Commons license. Read Original text (Opens in a new tab).
[ad_2]
Source link
