Why people age slower on an airplane: astrophysicist explains time paradoxes on Earth and in space

Dmytro IvancheskulNews
Time can change its course under the influence of speed or gravity. Source: OBOZ.UA/Salvador Dali The Persistence of Memory

Time seems to us to be something eternal, constant, and unshakable. Scientists know that we cannot make it move backwards or jump into the future. But is time really sinless?

Albert Einstein once predicted that it was not. He was convinced that time would slow down if you reached a certain speed, for example, in an airplane. And the higher the speed, the more time would slow down. But to really see and feel the change over time, you need not only speed but also extremely powerful gravity.

In an article for the BBC, Chris Lintott, a professor of astrophysics at Oxford University, writer and broadcaster, talked about interesting paradoxes in time, such as why your head ages faster than your legs and why a black hole could turn into a natural time machine.

In 1971, physicists Joseph Hafele and Richard Keating proved Einstein's theory in an experiment. To do this, they took extremely accurate atomic clocks on an airplane and flew one to the west and the other to the east. When they returned to their laboratory, where the third clock was kept, it turned out that these extremely accurate clocks showed slightly different times.

The effect of this phenomenon is actually very small and can only be noticed with an atomic clock. As Lintott explains, a flight from London to New York will cause the clock to be ten-millionths of a second behind the one on the ground. But it's not just about the clock. A person on an airplane will also age ten-millionths of a second less than someone who is on the ground at the same time.

In addition to speed, gravity also affects the passage of time. Thus, the lower the gravitational force, the faster time will move. This is true even if we are talking about a person standing on the surface of the planet. The time at their feet will move slower than the time at their head. Thus, the head will always age faster. The effect of this time distortion is incredibly small, but the farther away from the Earth you are, the stronger it becomes. Humanity is aware of this, and that is why the GPS, which provides navigation for the entire world thanks to satellites 20,000 km above the planet, must take this into account to work properly.

At the same time, as the astrophysicist notes, on the scale of the universe, the Earth is, after all, a small planet. So if we really want to see time warping, we need to get under the gravity of much larger objects, such as black holes, which have a super-powerful gravitational pull that even light cannot fight against.

As the scientist explains, it is practically impossible to approach a black hole and stay alive because everything that falls under the gravity of a black hole undergoes a "spaghettification" effect, when the object is stretched into a thin thread.

Theoretically speaking, a person falling into a black hole would not feel any changes in the course of time. However, they would see that the entire universe around them has accelerated.

If we could see the Earth while falling into a black hole, we would see the evolution of the planet. In what would seem to us like minutes, entire epochs would have passed on Earth, until the moment when the Sun would have turned into a red giant and swallowed the Earth.

Instead, someone watching the astronaut fall into a black hole from a safe distance would see the opposite effect. If the astronaut were to wave goodbye before disappearing into the black hole, his colleague would see this movement getting slower and slower.

This effect was clearly shown in Christopher Nolan's movie Interstellar. There, astronauts exploring a planet near a black hole returned to the mothership and saw that the hours that had passed for them on the planet had become years for the astronauts on the ship.

At the same time, as Lintott notes, "It makes no sense to ask whether the time that passes near a black hole is 'right' or far from it; relativity tells us that there is no such thing."

He suggests that when the doomed traveler crosses the point of no return, the black hole's event horizon, he will be forced to move towards the center of the black hole.

"This means that his perception of time could change dramatically and he might even be able to move back and forth in time," the astrophysicist said.

Lintott explains that in ordinary life, people move in the three dimensions of space as they please, but they do that through time in one way only, which is forward. Instead, after crossing the event horizon, according to some scientists, the very movement in space - to the center of the black hole - will mean movement in time.

"In this sense, a black hole can act as a time machine, allowing anyone brave enough to enter it to return to times long before they crossed the event horizon, up to the creation of the black hole itself," the scientist explained.

The only problem with such a trip is that, as far as we can tell, there is no way out of a black hole, so no time traveler from the future will be able to use this trick to visit us.

Earlier, OBOZ.UA explained what will happen when the Milky Way crashes into Andromeda.

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