Is Time Travel Possible?

10 November 2022

How would it be to go back in time to change the direction of your life – or just to save the whole of humanity? Or to take off to the year 2323 to find out if robots will take over the planet: since the publication of H.G. Wells’ novel “The Time Machine” in 1895, human beings have dreamed of travelling back in time. But is time travel even possible?

This very question was addressed by no lesser a person than Albert Einstein. And the answer given by the father of relativity theory was this: time travel is possible. Theoretically, at least. And in one direction only. Here’s one method, as described by US physicist Brian Greene: you could travel to the edge of a black hole. There, time slows down until it comes to a complete stop. The reason for this is the massive gravitational pull exerted by black holes. If you were to spend one hour there and then return to Earth, you would find that years or decades had passed in your absence. But the catch is this: the next black hole that we know about is some 1,000 light years away. And if you were to get there, its unbelievable gravitational pull would mean that you would never get away again. In any case, you would never survive your visit, because your body would be stretched until it came apart. A phenomenon that is as fascinating as it is gruesome, for which Stephen Hawking coined the term “spaghettification”.

A question of speed

Wannabe time travellers who would rather avoid this experience could alternatively try travelling at very high speeds instead. According to Einstein’s Theory of Relativity, time passes more slowly for objects at rest than it does for those in motion. For space travellers, travelling in time goes with the territory, as it were. And the foremost of these is Gennady Padalka: this cosmonaut spent a total of 879 days hurtling around the Earth on board Mir and the ISS. During these two-and-a-half years, he aged less than the rest of us – by a grand total of 1/44 of a second. In other words, for a fraction of a second Gennady Padalka travelled into the future.

If we should ever be in the position to fly at something close to the speed of light, significantly longer journeys through time would become feasible. Astronauts on a round trip to the planet known as Kepler-186f, some 500 light years away, would only age about ten years, during which time a whole millennium would have passed on Earth.

To date, however, travel at close to the speed of light has been a privilege reserved for very small particles. Take protons, for instance, which are accelerated by massive electromagnets to near light speed in installations like the Large Hadron Collider close to Geneva. To accelerate an object of the size and mass of a spaceship to such speeds, however, would require completely new materials and propulsion systems and inconceivable amounts of energy.

No way back?

To sum up, huge technical challenges would need to be overcome, although these would still be easier to solve than those posed by any attempt to travel back into the past. Most physicists consider this to be simply impossible. Stephen Hawking decided to put this assertion to the test: in 2009 he sent out invitations to a party – but he only did so after the party had been held. However, the eagerly awaited time travellers from the future did not turn up. The physicist was left with a roomful of snacks and champagne: possible proof that travelling back into the past is not possible. But who knows? Perhaps the invited guests from the future had calibrated their time machines wrongly, experienced issues with their flux compensator or were simply otherwise engaged.