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SYDNEY, Jan. 4 (talk) Black holes form natural time machines that can travel to the past and future. But don’t expect to go back and visit dinosaurs anytime soon.
Currently, we don’t have a spacecraft that can bring us close to a black hole. But even setting aside this small detail, trying to travel back in time using a black hole is probably the last thing you do.
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What is a black hole?
A black hole is an extremely massive object that usually forms when a dying star collapses on itself.
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Like planets and stars, black holes have gravitational fields around them. The gravitational field keeps us glued to the earth and keeps the earth orbiting the sun.
As a rule of thumb, the more massive an object is, the stronger its gravitational field will be.
Earth’s gravitational field makes going into space extremely difficult. That’s why we make rockets: we have to fly really fast to escape Earth’s gravity.
The gravitational field of a black hole is so strong that not even light can escape. That’s impressive, 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 the way we can bounce a flashlight off a tree in the dark.
Stretch space
Albert Einstein’s general theory of relativity tells us that matter and energy have strange effects on the universe. Matter and energy bend and stretch space. The larger an object is, the more the space around it is stretched and curved.
A massive object has created a kind of valley in space. When objects get close, they fall into the valley.
That’s why when you get close enough to any massive object, including a black hole, you plummet toward it. This is also why light cannot escape a black hole: the sides of the valley are so steep that light cannot travel fast enough to climb out of the black hole.
The valley formed by the black hole gets steeper and steeper as you approach it from a distance. The point at which it becomes so steep that light cannot escape is called the event horizon.
Event horizons aren’t just interesting for potential time travelers: they’re interesting for philosophers, too, because they have implications for how we understand the nature of time.
Stretch time
When space is stretched, time is also stretched. A clock near a massive object will run slower than one near a much less massive object.
Clocks near black holes tick very slowly compared to clocks on Earth. A year near a black hole could mean 80 years on Earth, like you see in the movie Interstellar.
In this way, the black hole can be used to travel into the future. If you want to jump into Earth’s future, just fly near a black hole and return to Earth.
If you get close enough to the center of the black hole, your clock will run slower, but as long as you don’t cross the event horizon, you should still be able to escape.
time loop
What about the past? This is where things get really interesting. A black hole bends time so far that it can wrap around itself.
Imagine taking a piece of paper and joining the ends to form a ring. This is what black holes seem to do with time.
This creates a natural time machine. If you could somehow enter loops, which physicists call closed timelike curves, you would find yourself on a trajectory in space that starts in the future and ends in the past.
Inside loops, you’ll also find cause and effect difficult to untangle. Past events cause future events, and future events cause past events!
catch
So, you’ve discovered 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 back into the black hole’s past. This means that if the black hole was created after the extinction of the dinosaurs, you wouldn’t be able to travel far enough back.
Second, you may have to cross the event horizon to enter the loop. This means that to break out of the loop at a specific time in the past, you need to exit the event horizon. That means going faster than the speed of light, which we’re pretty sure is impossible.
Third, and possibly worst, you and your ship will experience “spaghettiification”. Sounds delicious, right?
Sadly, this is not the case. When you cross the event horizon, you’re flattened like spaghetti. In fact, you could be stretched so thin that you’re just a string of atoms spiraling into the void.
So while it’s fun to contemplate the time-warping properties of black holes, visiting dinosaurs will have to stay in the realm of fantasy for the foreseeable future. (dialogue)
(This is an unedited and auto-generated story from a Syndicated News feed, the content body may not have been modified or edited by LatestLY staff)
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