by Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.
Will it ever be possible for time travel to happen? – Alana C., age 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 like 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 back or forward in time.
But is this a fun idea for movies, or could it actually happen?
The question of whether time is reversible remains one of the greatest unsolved questions in science. If the universe follows the laws of thermodynamics, it may not be possible. The second law of thermodynamics states that things in the universe can stay the same or become more disordered over time.
It’s a bit like saying you can’t peel eggs once they’re cooked. According to this law, the Universe cannot go back exactly as it was before. Time can only go 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 man swinging on a spaceship moving at close to the speed of light – 671 million miles per hour! – time experience will be slower than a person on earth.
Humans have yet to build spacecraft that can move at speeds anywhere near the speed of light, but astronauts visiting the International Space Station orbit Earth at speeds approaching 17,500 mph. Astronaut Scott Kelly has spent 520 days on the International Space Station, and as a result he has aged a little slower than his twin brother – and fellow astronaut – Mark Kelly. Scott used to be 6 minutes younger than his twin brother. Now, because Scott was traveling much faster than Mark and for so many days, he is 6 minutes and 5 milliseconds younger.
Some scientists are exploring other ideas that could theoretically allow time travel. One concept involves wormholes, or hypothetical tunnels in space that could create shortcuts for journeys across the universe. If one could build a wormhole and find a way to move one end close to the speed of light – like the hypothetical spaceship mentioned above – the age of the moving end would be slower than the stationary end. Someone who entered the moving end and exited the wormhole through the fixed end would come out in the past.
However, wormholes are still theoretical: Scientists have yet to see one. It also seems like putting people through a wormhole space tunnel would be extremely challenging.
Paradoxes and failed dinner parties
There are also paradoxes related to time travel. The famous “grandfather paradox” is a hypothetical problem that could arise if a person traveled back in time and accidentally prevented their grandparents from meeting. This would create the paradox that you were never born, which begs the question: How could you have traveled back in time in the first place? It’s a mind boggling puzzle that adds to the mystery of time travel.
Physicist Stephen Hawking famously tested the possibility of time travel by throwing a dinner party where invitations noting the date, time and coordinates were not sent out until after the event. His hope was that his invitation would be read by someone who lived in the future, who had the ability to travel back in time. But no one showed up.
As he said: “The best evidence we have is that we cannot, and never will, be invaded by hordes of tourists from the future.”
Telescopes are time machines
Interestingly, astrophysicists with powerful telescopes experience a unique form of time travel. As they look into the vast expanse of the cosmos, they see the past. Light from all galaxies and stars takes time to travel, and these beams of light carry information from the distant past. When astrophysicists look at a star or galaxy through a telescope, they don’t see it as it is now, but as it was when light began its journey to Earth millions to billions of years ago.
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.
Although we are unlikely to have time machines like the ones in movies anytime soon, scientists are actively 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.
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This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. Like this article? Subscribe to our weekly newsletter.
It was written by: Adi Foord, University of Maryland, Baltimore County.
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Adi Foord does not work for, consult with, share in, or be funded by any company or organization that would benefit from this article, nor has he disclosed any relevant affiliations beyond their academic appointment.
