It is - quite literally - the stuff of science fiction.
But now the possibility of time travel may well be a (very) small step closer.
Scientists have built what could loosely be described as a time machine which, while not quite on the , has defied the second law of thermodynamics, which governs the direction of “time’s arrow” from past to future.
Working in the weird realm of quantum mechanics, they achieved the equivalent of causing a broken rack of pool balls to re-order itself.
To an outside observer, it looks as if time is running backwards.
Lead researcher Dr Gordey Lesovik, who heads the Laboratory of the Physics of Quantum Information at the Moscow Institute of Physics & Technology (MIPT), said: “We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time.”
It was as if the balls scattered randomly around a pool table went into reverse and packed themselves back into their original pyramid formation.
The “time machine” described in the journal Scientific Reports is based on a quantum computer that carries out calculations using basic elements known as superconducting “qubits”.
A qubit is a unit of information described by a “one”, a “zero”, or a mixed “superposition” of both states.
In the experiment, an “evolution programme” was launched on a computer which caused the qubits to become an increasingly complex changing pattern of zeros and ones.
During this process, order was lost – just as it is when the pool balls are struck and scattered at a break-off.
Another programme then modified the state of the quantum computer in such a way that it evolved “backwards”, from chaos to order.
The state of the qubits was rewound back to its original starting point.
An analogy would be giving the pool table such a perfectly calculated kick that the balls roll back into an orderly pyramid.
The scientists found that, working with just two qubits, “time reversal” was achieved with a success rate of 85%.
When three qubits were involved more errors occurred, resulting in a 50% success rate.