A mathematical model has found that time travel is hypothetically possible.

The model, which was detailed in a paper recently published in the journal *Classical and Quantum Gravity*, challenges the conventional view time travel is physically impossible, although suggests that a machine based on the maths would require materials that have still to be discovered.

“People think of time travel as something fictional,” explained study lead author Ben Tippett, from the Faculty of Mathematics at 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.”

The model is based on Einstein’s theory of general relativity, which proposes that gravitational fields are the result of distortions in the fabric of space and time.

Building on this, Tippett says that such distortions result in the curved orbits of planets, and that because space and time are inextricably linked, this means that time also curves.

“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,” said Tippett. “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.”

The model, named Traversable Acausal Retrograde Domain in Space-time (TARDIS) in a clear reference to time-travelling cult TV show Doctor Who, characterises this time machine as a bubble of space-time geometry that moves its contents forwards and backwards through both space and time as it follows a massive circular route. By moving through space-time at speeds that can top the speed of light, this bubble is able to move its contents in time.

However, whether we can ever build such a time machine remains deeply in question. What is clear is that we do not currently know of a material that would allow such a machine to be constructed.

“HG Wells popularized the term ‘time machine’ and he left people with the thought that an explorer would need a ‘machine or special box’ to actually accomplish time travel,” explained Tippett.

“While is it mathematically feasible, it is not yet possible to build a space-time machine because we need materials—which we call exotic matter—to bend space-time in these impossible ways, but they have yet to be discovered.”