Is time travel possible?

If you could travel to any point in time, where would you go? Would you go back and witness the time of the dinosaurs, attend an Edwardian ball to find your Mr. Darcy, or see if you could hop on board a space flight to another planet in the future? Time travel captures our imaginations because it contains endless possibilities for adventure and holds the answers to many of our questions. But is it possible?

Travelling back to the future...

Technically we are all travelling through time at a rate of one second per second, but to go further in either direction is tricky. Let’s start with travelling to the future. To travel forwards in time, you simply need to move fast. Special relativity states that the speed of light is a cosmic speed limit, nothing can go faster than light. But as we get closer to this speed, strange things start to happen: time itself slows down.  A person in a spaceship travelling away from Earth at close to the speed of light, will experience less time passing than the people back on Earth. This means that if we send a twin up in this spaceship, when they come back they will be much younger than the twin who stayed at home! Or maybe, they will return to find only the ruins of their civilisation, as what was only a few years for them, was thousands of years back on Earth. The problem with this method of time travel is it only works one way, there’s no going back.

Wormholes and the dinosaurs...

Travelling back in time is a bit harder. One possible option is to use a wormhole, which is a theoretical object in space that acts like a tunnel between two places. In theory, these two places could be at different times to each other, so you could go through the entrance in the present and come out of the exit in the past! One disappointing feature of this kind of time travel is you can only go as far back as the creation of the worm hole, so no visiting the dinosaurs with this one.

Stephen Hawking suggested that an obvious argument for the impossibility of travelling back in time is the lack of tourists from the future. Surely if time travel has been invented in the future, we would have met some curious historians who have come to see our time for themselves. Hawking went one further and constructed an experiment to prove that visiting the past is impossible: he threw a party for time travellers and didn’t send out the invitations until after the party was over! No one came to the party, which means either Stephen Hawking is really unpopular in the future, or travelling back in time is impossible.

So, our question was “is time travel possible?”, and my answer is yes. Thanks to the laws of special relativity, whenever you travel in a train, plane or automobile you are experiencing time slower than those walking around you! It may be only a tiny fraction of second that you are skipping by, but it is time travel nonetheless. It may seem insignificant, but this time adds up and becomes very important in GPS satellites, whose clocks run “too slow” because of this effect.

Though visiting the distant past or future may be contained to the pages of science fiction for now, scientists are expanding our understanding of the Universe and making new discoveries all the time. Who knows when we will come up with our own blue police phone box and go exploring. Until then, my Mr Darcy will just have to wait.

For more physics from Beth, check out our video How to make a lightsaber!