The black holes They are extremely dense cosmic objects, where gravity is so powerful that nothing can escape, not even light. They originate mainly from the death of large stars, but many of their characteristics remain a mystery as what they keep inside.
However, black holes generate an amazing phenomenon that is well known to experts in the field of physics and that in this case works as a ‘shortcut’ to the future.
How does something that seems out of science fiction become possible? The answer lies in gravity and its effects in space and time.
In fact, these two aspects of reality are intertwined as one: the space time which is “the stage” in which the entire universe unfolds, explains Carlos Argüelles, professor of Physics at Harvard University, to La República.
According to Einstein’s theory of general relativity, this scenario is not static, but distorts or sinks in the presence of an object with a lot of mass, such as a planet, a star or a black hole. That distortion is gravity and it affects other nearby objects.
The greater the mass, the stronger the gravity. This is why artificial satellites and the Moon orbit the Earth, which in turn orbits the Sun.
That is the effect in space. And if it affects space, it also affects time, which moves slower for the observer who is closer to the object that generates gravity.
This phenomenon is called gravitational time dilation and it has been verified several times on Earth, as we explained in a previous article.
The time dilation caused by our planet is imperceptible (fractions of a second each day with respect to an observer from space). But, near a black hole, things get much more extreme.
Black holes can have the weight of many stars put together and be of different sizes, but all of their mass is compressed into a single point (singularity). This creates an ‘abyss’ in space-time; that is, an absorbing gravity that does not let anything that falls inside escape.
In theory, time stands still inside a black hole, but time dilation is still noticeable outside it.
“A black hole generates a very strong gravitational well. It is a very brutal space-time distortion and that makes a close observer perceive time in a quite different way compared to an outside observer ”, explains Argüelles.
Could there be any way for humans to experience this effect without being swallowed up by the black hole? In theory, a spacecraft could orbit this massive object at a safe distance.
How much the perception of time will change for the crew of the spacecraft “will depend on the mass of the black hole and how close it is,” he adds.
For a practical example, the Peruvian physicist explains the hypothetical case of a group of 20-year-old explorers heading in their spacecraft towards the supermassive black hole at the center of the Milky Way.
At 4.3 million times the mass of the Sun, this cosmic monster has an estimated diameter of 26 million kilometers. That is the size of your event horizon, “the limit that, when you cross it, you can no longer return,” says Argüelles.
According to their calculations, if the rover ship orbits the black hole a million kilometers from the event horizon, time for them will pass 3.28 times slower than for people on Earth.
Assuming the spacecraft stays in that orbit for 10 years on Earth or their home planet – in this case one close to the galactic center – it will have been more than 32 years. Upon returning, the travelers would be 22 years younger than their age when they left the planet.
The same phenomenon, although much more extreme, was captured in the movie Interstellar (Nolan, 2014), where a group of astronauts spent three hours on a planet orbiting a black hole. When they returned to the main ship – away from the gravitational field – they found the crew member who remained 23 years older.
In any case, the gravitational dilation of time around a black hole is not a magic door that immediately transports you to another era. It’s more like taking a shortcut into the distant future.