gravitational waves
Gravitational waves are distortions, or 'ripples', in the fabric of space-time – and scientists have now announced their detection iStock

Time travel is possible – at least in theory. Two physicists have come up with a mathematical model that describes a viable time machine.

The perspective of building a machine which could help us travel in the past and change the course of our lives is an appealing one. In 1885, HG Wells published his sci-fi book The Time Machine, and the idea of travelling through time has never ceased to fascinate people ever since. It is at the core of many modern works of fiction – from the Harry Potter books to the latest series of Games of Thrones.

In their study recently published in the journal Classical and Quantum Gravity, the scientists created a created a mathematical model of a time machine known as Traversable Acausal Retrograde Domain in Space-time (or TARDIS, just like the fictional time machine in Doctor Who).

"People think of time travel as something as fiction," says study author Ben Tippett, from the University of British Columbia. "And we tend to think it's not possible because we don't actually do it. But, mathematically, it is possible."

With his co-author David Tsang, he describes the TARDIS machine as a ''bubble'' of space-time geometry carrying those who step inside backward and forwards through space and time, as it speeds along a large circular path.

Because this bubble moves through space and time at speeds greater than the speed of light at times, it would allow people to move backward in time.

hodor game of thrones
The last series of Games of Thrones saw some of the characters travelling back in time HBO

Einstein's theory of general relativity, which states that gravitational fields are caused by waves – or distortions – in the fabric of space and time, is central to the scientists' mathematical model. Drawing from it, they explain that the curvature of space-time accounts for the curved orbits of the planets – and this property would also allow people to travel back in time.

"The time direction of the space-time surface also shows curvature. There is evidence showing the closer to a black hole we get, time moves slower," Tippett explains. "My model of a time machine uses the curved space-time – to bend time into a circle for the passengers, not in a straight line. That circle takes us back in time."

In the study, the scientists are able to describe the way this bending of time with mathematical equations.

But while the mathematical demonstration stands, it is unlikely that time travel will one day become reality. The scientists' model shows that it is theoretically possible to travel back in time – but building such a machine is so far technically unfeasible.

To build a TARDIS, the scientists point out they would need to use and understand the properties of exotic matter (matter that deviates ''normal'' matter) – a perspective that remains elusive.