Using photons, Australian scientists managed to create a model in which quantum particles can move back in time. As it turned out, the laws of standard quantum mechanics may be violated at the same time.

Physicists from the University of Queensland in Australia set out to simulate a computer experiment, which could prove the possibility of time travel at the quantum level, predicted in 1991.

They managed to simulate the behavior of a single photon passing through a wormhole in space-time in the past and engaging with itself. Such a trajectory of a particle is called a closed timelike curve, i.e. a photon returns to the original space-time point and its worldline closes.

The researchers studied two scenarios. In the first, the particle passes through a wormhole, returning to the past, and interacts with itself. In the second scenario, the photon, forever enclosed in a closed timelike curve interacts with another, ordinary particle.

According to the scientists, their work will make an important contribution to the unification of the two great theories in physics, which till this moment had little in common: the Einstein’s general theory of relativity and quantum mechanics.

“Einstein’s theory describes the world of stars and galaxies, while quantum mechanics studies mainly the properties of elementary particles, atoms and molecules,” said Martin Ringbauer of University of Queensland.

Einstein’s General Relativity allows the possibility of traveling back in time to the object, which gets stuck in a closed timelike curve. However, this possibility can cause a number of paradoxes: a time traveler could, for example, prevent his parents from meeting each other, and thus make his own birth impossible.

In 1991, it was suggested for the first time that time travel in the quantum world can prevent such paradoxes, since the properties of quantum particles are not precisely defined, according to Heisenberg’s uncertainty principle.

Computer simulations of the Australian scientists allowed to study for the first time the behavior of quantum particles in such a scenario. At the same time, new interesting effects were revealed, the occurrence of which is considered impossible according to the standard quantum mechanics.

For example, it turned out that it is possible to accurately identify the various states of a quantum system, which is quite possible if we remain within the framework of the quantum theory.