Back to the Future: Is Time Travel Possible?

Would you like to take a trip to the year 3000? It might not be as impossible as it seems; in fact, time travel is going on every day on a tiny scale, and one astronaut currently holds the record for time travel (yes, you read that right).

Don’t get too excited though. When Gennady Padalka returned to Earth after spending 879 days in space, he found the Earth to be 1/44^th of a second in the future of what he had expected. Hardly a fitting plot for a sci-fi film. And yet it demonstrates in real-life terms Einstein’s theory of general relativity, which states that time is not fixed but rather depends on speed. He also suggested that gravity slows time, meaning that being far out in space would make time run faster.

Astrophysicists such as Richard Gott of Princeton University think they know how to create a time machine that could take you much further forward than Padalka’s measly record, by travelling much faster than his 17,000 miles per hour. On a subatomic level this has been achieved—the Large Hadron Collider does send protons into the future by accelerating them to 99.999999% of the speed of light. Conceptually, it is possible to do something similar with humans. To visit the Earth in the year 3000, it is necessary only to hop in a spaceship that can travel at 99.995% of the speed of light. For example if you were to pick a planet that’s a bit less than 500 light years away, travelling at 99.995% of the speed of light it would take you about 500 years to get there from our perspective, and another 500 to get back, so you would arrive home in 3018. But since you are travelling so fast, your internal clock would be going at only 1/100^th of the speed of the clocks on earth; hence, you would only experience the journey as ten years and would age accordingly.

For now, engineering limitations prevent us from realising this possibility. The fastest spacecraft ever made will soon be the Parker Solar Probe, which can travel only 0.00067% of the speed of light. It would also take an enormous amount of energy to propel a spaceship at almost the speed of light, energy which is not provided by any fuel that we currently use. Other obstacles would also compromise the safety of the astronaut and their ability to travel as far as possible into the future. Theoretically, however, these can be overcome.

What if you want to go back in time to have dinner with Julius Caesar? As the limerick goes, “There was a young lady named Bright/ Whose speed was far faster than light;/She set out one day/ In a relative way/ And returned on the previous night”. Unfortunately, however, Einstein’s theory posits the speed of light as the ultimate speed limit beyond which it is not possible for anything to travel— so you’ll have to cancel your dinner plans.

Applicants for Physics or Natural Sciences should be familiar with Einstein’s theory of general relativity and should think about its implications for the future of technology and space travel. What practical obstacles would there be to human time travel, and how could these be overcome?