Black holes form natural time machines that allow travel to both the past and the future, but this doesn't mean we can go back to the Jurassic Period.
Currently, humans have not been able to build any spacecraft capable of taking us close to a Black Hole. If we ignore this detail, time travel is completely possible using a Black Hole.
What is a black hole?
A black hole is an extremely massive object that is usually formed when a star is dying or collapsing in on itself. Like planets and stars, black holes have a gravitational field around them. The gravitational field is what keeps us standing on the ground of Earth and keeps the Earth orbiting the Sun.
According to the laws of nature, the heavier an object is, the stronger its gravitational field is.
The Earth's gravitational field makes space travel extremely difficult. That's why we build rockets that have to travel very fast to escape the Earth's gravity.
Black holes form natural time machines that allow travel to both the past and the future. (Photo: Getty Images)
The gravitational field of a black hole is so strong that not even light can escape it. That's impressive, since light is the fastest thing known to science.
That's also why Black Holes appear black. We can't reflect light from a Black Hole the way we can reflect a flashlight beam off a tree in the dark.
Space-time dilation
The general theory of relativity by the brilliant physicist Albert Einstein tells us that matter and energy have strange effects on the universe. Matter and energy bend and stretch space. The more massive an object is, the more space is stretched and bent around it.
A massive object creates a kind of 'valley' or hole in space. As objects get closer, they fall into the 'valley'.
That's why when you get close enough to any massive object, including a Black Hole, you fall toward it. That's also why light can't escape from a Black Hole, or in other words, the edges of the hole are so steep that light can't escape fast enough.
The valley created by a Black Hole gets 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' are not only interesting to people who want to be time travelers, they are also interesting to philosophers, because they have implications for how we understand the nature of time.
If you want to go to Earth's future, just fly near a black hole and then return to Earth. (Photo: Getty Images)
As space stretches, so does time. A clock near an object with a large mass will run slower than a clock near an object with a much smaller mass.
Clocks near a black hole would run slower than clocks on Earth. A year near a black hole could be equivalent to 80 years on Earth, as you may have seen illustrated in the movie Interstellar (2014).
In this way, Black Holes can be used to travel to the future. If you want to go to Earth's future, just fly near a Black Hole and then return to Earth.
If you get close enough to the center of the black hole, your clock will run slower, but you can still escape as long as you don't cross the 'event horizon'.
Time Loop
What about the past? This is where things get really interesting. A Black Hole warps time in some pretty crazy ways. Imagine taking a piece of paper and connecting the two ends to make a loop. That's what a Black Hole can do to time.
This creates a natural time machine. If you could somehow enter the loop, which scientists call a closed time-like curve, you would find yourself traveling on a trajectory through space that begins in the future and ends in the past.
Inside the loop, you'll also find that cause and effect are difficult to untangle. What happened in the past creates the future, and this in turn causes what happened in the past.
The gravity of a black hole is so great that it bends space and time near the event horizon. (Photo: ESO)
You found a black hole and you want to use a trusty spaceship to go back to visit the dinosaurs?
First, you can only travel into the past of the Black Hole. That means if the Black Hole was created after the dinosaurs became extinct, then you wouldn't be able to travel back to a time so far in the past.
Second , you may have to cross an 'event horizon' to enter the loop. This means that to exit the loop at a specific point in the past, you would need to cross the 'event horizon'. You would have to travel faster than light, which is currently impossible.
Third , and perhaps worst, you and your ship will undergo a process called 'spaghettification' . As you pass the 'event horizon' , you will be stretched out, like a noodle. In fact, you may be stretched so thin that you are just a string of atoms spiraling into space.
So while it's exciting to think about the time-bending properties of black holes, a visit to the dinosaurs or a trip to the future remains a pipe dream for the foreseeable future.
