Four ways in which time travel could be possible

Time travel 'may be possible', says new research

23 June

Physicists studying the behaviour of single particles of light say they can now discount one of the main theoretical objections to time travel.

During research published in Nature Communications, scientists at the University of Queensland designed an experiment that simulated the effect of a photon – a particle of light – travelling back in time and interacting with its older self.

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"Time travel was simulated by using a second photon to play the part of the past incarnation of the time-travelling photon," said University of Queensland physics professor Tim Ralph.

The lead author of the paper, PhD student Martin Ringbauer, said the experiment aimed to examine the intersection of quantum mechanics and Einstein's theory of relativity.

"The question of time travel features at the interface between two of our most successful yet incompatible physical theories," Ringbauer said. "Einstein's general relativity and quantum mechanics."

Einstein's theory of relativity suggests that it may be feasible to travel backwards in time by following a "space-time path" that doubles back and returns to its own starting point in space, but at an earlier time, NDTV news reports. Physicists refer to such paths as closed time-like curves (CTCs).

Researchers ran two versions of the experiment. In the first version, they looked at what might happen when a photon "travels through a wormhole into the past, then interacts with its older version". In the second case, they wanted to investigate what might happen when a photon "travels through normal space-time, but interacts with another photon that is trapped inside a CTC forever".

"The results revealed that time travel on a quantum level seems to be possible," the Daily Mail reports.

Physicists and philosophers have long struggled with the grandparent paradox. As Science Alert explains, a time traveller could in theory prevent his or her grandparents from meeting, "thus preventing the time traveller’s birth". This would make it impossible for the time traveller to have set out in the first place and kept the grandparents apart.

The new research suggests that such paradoxes may not render time travel impossible, the Mail notes, "albeit only on a quantum level for now".