Is time travel possible? Astrophysicist explains the science behind science fiction

Have you ever dreamed of time travel like characters in science fiction movies do? For centuries, the concept of time travel has captured people's imaginations.  You may have seen in the movies characters using special machines, magic devices, or even jumping in a futuristic car to travel backwards or forwards through time.

But is this just a fun idea for movies, or can it actually happen?

The question of whether time is reversible remains one of the biggest unsolved questions in science. If the universe follows the laws of thermodynamics, this may not be possible. The second law of thermodynamics states that things in the universe either remain the same or become more disturbed over time.

It's a bit like saying you can't break eggs apart after they've been cooked. According to this law, the universe cannot completely return to what it was before. Time can only move forward, like a one-way street.

Time is relative

However, the special theory of relativity of physicist Albert Einstein suggests that time passes at different rates for different people. A person traveling at speed on a spacecraft moving at a speed close to the speed of light - 671 million miles per hour! - He will live a slower time than anyone on Earth.

People haven't yet built spaceships that can move at speeds close to the speed of light, but astronauts visiting the ISS orbit Earth at speeds approaching 17,500 miles per hour. Astronaut Scott Kelly spent 520 days on the International Space Station, and as a result he grew older a little slower than his twin brother — and fellow astronaut — Mark Kelly. Scott was six minutes younger than his twin brother. Now, because Scott has been traveling much faster than Mark for several days, he is 6 minutes and 5 milliseconds younger than him.

Some scientists are exploring other ideas that might theoretically allow time travel. One concept involves wormholes, or virtual tunnels in space, that can create shortcuts to journeys across the universe. If someone can build a wormhole and then figure out a way to move one end of it at a speed close to the speed of light – such as the virtual spaceship mentioned above – the moving limb will age more slowly than the fixed end. The person who entered the moving limb and exited the wormhole through the fixed limb will come out in their past.

However, wormholes remain a theory: scientists have not yet been able to detect them. It also seems that it would be very difficult to send humans through a wormhole space tunnel.

Paradoxes and failed dinner parties

There are also paradoxes associated with time travel. The famous "grandfather paradox" is a hypothetical problem that can arise if someone travels through time and accidentally prevents their grandparents from meeting. This would create a paradox as you were never born, raising the question: How could you have traveled time in the first place? It is a mind-boggling mystery added to the time travel puzzle.

It is known that physicist Stephen Hawking tested the possibility of time travel by holding a dinner party that invitations indicating the date, time and coordinates were sent only after it happened. He hoped that his call would be read by someone who lives in the future and has the ability to travel through time. But no one showed up.

"The best evidence we have that time travel is not possible, and will not be, is that we have not been invaded by hordes of tourists from the future," he noted.

Telescopes are time travel machines

Interestingly, astrophysicists armed with powerful telescopes possess a unique form of time travel. When they look at the vast expanse of the universe, they gaze at the universe's past. Light from all galaxies and stars takes time to travel, and these rays carry information from the distant past. When astrophysicists observe a star or galaxy through a telescope, they don't see it as it is at present, but rather as it existed when light began its journey to Earth millions to billions of years ago.

NASA's newest space telescope, the James Webb Space Telescope, looks at galaxies that formed at the beginning of the Big Bang, about 13.7 billion years ago.

Although it's unlikely that we will have time machines like those in movies anytime soon, scientists are constantly researching and exploring new ideas. But for now, we'll have to enjoy the idea of time travel in our favorite books, movies and dreams.