Is time travel even possible? An astrophysicist explains the science behind science fiction
By Addie Ford, University of Maryland, Baltimore County (This article first appeared on The Conversation and is republished with permission)
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Would it be possible for time travel to happen? – Alana C., 12, Queens, New York
Have you ever dreamed of traveling through time like characters do in science fiction movies? For centuries, the concept of time travel has captured people’s imaginations. Time travel is the concept of moving between different points in time, just as you move between different places. In movies, you may have seen characters using special machines, magical devices, or even jumping into a futuristic car to travel backwards or forwards in time.
But is this just a fun idea for movies, or could it actually happen?
The question of whether time is reversible remains one of the biggest unsolved questions in science. If the universe followed the laws of thermodynamics, this might not be possible. The second law of thermodynamics states that things in the universe either stay the same or become more disordered over time.
It’s a bit like saying you can’t crack eggs after they’re 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, physicist Albert Einstein’s theory of special relativity suggests that time passes at different rates for different people. A person is riding fast on a spaceship moving at close to the speed of light – 671 million miles per hour! -He will live slower than anyone on Earth.
People have not yet built spaceships that can move at speeds close to the speed of light, but astronauts visiting the International Space Station 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 has aged slightly more slowly than his twin brother – and fellow astronaut – Mark Kelly. Scott was six minutes younger than his twin brother. Now, since Scott has been traveling much faster than Mark for several days, he is 6 minutes and 5 milliseconds younger than him.
Time is not the same everywhere.
Some scientists are exploring other ideas that could theoretically allow time travel. One concept involves wormholes, or virtual tunnels in space that could create shortcuts for journeys across the universe. If someone could build a wormhole and then figure out a way to move one end of it at close to the speed of light — like the hypothetical spaceship mentioned above — the moving end would age more slowly than the fixed end. The person who entered the moving end and exited the wormhole through the fixed end would exit in his past.
However, wormholes remain a theory: scientists have not yet been able to discover them. It also seems like 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 “grandparent paradox” is a hypothetical problem that could arise if someone traveled through time and accidentally prevented their grandparents from meeting. This would create a paradox since you were never born, which raises the question: How could you have time traveled in the first place? It’s a mind-boggling mystery that adds to the mystery of time travel.
Famously, physicist Stephen Hawking tested the possibility of time travel by throwing a dinner party where invitations indicating the date, time and coordinates were not sent out until after the fact. He hoped that his invitation would be read by someone living in the future, who had the ability to travel through time. But no one showed up.
He also noted: “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”
Telescopes are time 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 are staring at the past universe. Light from all galaxies and stars takes time to travel, and these rays of light carry information from the distant past. When astrophysicists observe a star or galaxy through a telescope, they do not see it as it exists today, but rather as it existed when light began its journey to Earth millions to billions of years ago.
Telescopes are a kind of time machine, they allow you to look into the past.
NASA’s newest space telescope, the James Webb Space Telescope, is looking at galaxies that formed at the beginning of the Big Bang, about 13.7 billion years ago.
While it’s unlikely that we’ll have time machines like the ones in movies anytime soon, scientists are actively researching and exploring new ideas. But for now, we just have to enjoy the idea of time travel in our favorite books, movies, and dreams.
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Addie Ford, assistant professor of astronomy and astrophysics, University of Maryland, Baltimore County
This article is republished from The Conversation under a Creative Commons license. Read the original article.