GETTY Time travel is possible and has already happened

One way to achieve time travel into the future would be travelling at the speed of light in space, as first theorised by Albert Einstein. Indeed Cosmonaut Sergei Krikalev technically lives in the future due to his extended period on the International Space Station. After spending almost 804 days in space arrived back in Earth 0.02 seconds in the future thanks to a process known as time dilation. Under accepted theories of time travel engineers would have to build a space ship which could travel at the speed of light (186,000 miles-per-SECOND), and head out into space. Theoretical physicist and string theorist Brian Greene, of Columbia University, said: “You can build a spaceship, go out into space [and travel] near the speed of light, turn around and come back.

“Imagine you go out for six months and you turn around and you come back for six months.” While you are travelling at the speed of light, time stays slow relative to the people who are standing still back on Earth. As a result, you would be going fast while your clock would still be going slow. Prof Greene: “When you step out of your ship, you’re one year older but Earth has gone through many, many years. “It can have gone through 10,000, 100,000 or a million years depending on how close to the speed of light you traveled.” However, the only problem is that a machine travelling at such speed would require an “unimaginable” amount of energy, while the stress from the centrifugal force on the body would likely prove fatal.

GETTY One way to travel in time is to hang out near the edge of a black hole

But there is another feasible way to travel though time, and once again it involves going into outer space. Einstein also theorised that if you were to situate yourself on the edge of a black hole, time would pass more slowly. Prof Greene explains in his Big Think video: “You hang out [next to a black hole] for a while, you come back, get out of your ship and it will be any number of years into the future, whatever you want all depending on how close you got to the edge of the black hole and how long you hung out there. “That is time travel to the future.” But time travel has already happened.

GETTY Cosmonaut Sergei Krikalev has already travelled through time

Serial ISS resident Sergei Krikalev holds the record for the longest amount of time spent in space with 803 days, 9 hours, 39 minutes under his belt. The ISS travels at around 7.66 km/s when orbiting around Earth, and due to the high speed and length of time which he spent in space, the cosmonaut actually arrived back in Earth 0.02 seconds in the future thanks to a process known as time dilation.

GETTY The ISS

The time would run a fraction of a millisecond faster when on board the ISS at that speed away from Earth. Physicist Colin Stuart said in a Ted Talk that time dilation due to gravity “is quite small because Earth’s gravity is quite weak and so the time dilation due to their speed wins out and astronauts really do travel a tiny amount into their futures.” But for those wishing to travel back in time, you may be out of luck.

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