Could time travel soon become a reality?

If a time traveller went back in time and stopped their own grandparents from meeting, would they prevent their own birth?

That’s the crux of an infamous theory known as the 'grandfather paradox', which is often said to mean time travel is impossible - but some researchers think otherwise.

A group of scientists have simulated how time-travelling photons might behave, suggesting that, at the quantum level, the grandfather paradox could be resolved

The research was carried out by a team of researchers at the University of Queensland in Australia and their results are published in the journal Nature Communications.

The study used photons - single particles of light - to simulate quantum particles travelling back through time.

By studying their behaviour, the scientists revealed possible bizarre aspects of modern physics

In the simulation, the researchers examined two possible outcomes for a time-travelling photon.

In the simulation, the researchers examined the behaviour of a photon traveling through time and interacting with its older self.

In their experiment they made use of the closely related, fictitious, case where the photon travels through normal space-time and interacts with another photon that is stuck in a time-travelling loop through a wormhole, known as a closed timelike curve (CTC). 

Simulating the behaviour of this second photon, they were able to study the behaviour of the first - and the results show that consistent evolutions can be achieved when preparing the second photon in just the right way.

By definition ‘quantum’ refers to the smallest possible particles that can independently exist - such as photons.

However, for macroscopic systems time-travel still faces problematic paradoxes.

In 1991 it was first predicted that time travel would be possible in the ‘quantum world’ because quantum particles behave almost outside the realms of physics.

'The properties of quantum particles are "fuzzy" or uncertain to start with, so this gives them enough wiggle room to avoid inconsistent time travel situations,' said professor Timothy Ralph, one of the researchers on the latest study.

The results also give a better understand to how two theories in physics, on the biggest and smallest scales, are able to relate to one another.

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

'Einstein's theory describes the world at the very large scale of stars and galaxies, while quantum mechanics is an excellent description of the world at the very small scale of atoms and molecules.'

Einstein's theory suggests the possibility of travelling backwards in time by following a space-time path that returns to the starting point in space but at an earlier time - a closed timelike curve (CTC).

This possibility has puzzled physicists and philosophers alike since it was discovered by Austrian-American scientist Kurt Gödel in 1949, as it seems to cause paradoxes in the classical world.

These include the 'grandparents paradox', where a time traveller could stop their 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.

But this new research suggests that such interactions might indeed be possible - albeit only on a quantum level.