For most of us, the closest to time travel is watching an episode of "Doctor Who". A group of physicists from the Moscow Institute of Physics and Technology (MIPT), however, have come closer together: using a quantum computer, they successfully simulated the inversion of time.
Simulated, of course, is the key word: lead author from Gordey Lesovik of the MIPT told CNN that we are "not really" approaching the possibility of actually reversing time. But it could still have important practical and theoretical consequences.
A team of MIPT physicists, which also included scientists from Switzerland and the United States, examined "the possibility of violating the second law of thermodynamics," Lesovik said in a print
Billiard balls that return to a triangle
The law indicates that the entropy, or disorder, of a closed system will always increase over time. In an analogy offered by the researchers, a row of billiard balls struck by a cue ball will scatter on the table, but the rotating balls will not spontaneously return to the clean triangle from which they started.
The necessary increase in entropy establishes the "arrow of time" or the irreversible progression from the past to the future. The time arrow problem, Lesovik told CNN, is "one of the most ancient, fundamental and fascinating problems" in physics. "It is nothing but natural to try to solve it," he said.
According to Lesovik, the results of the study will eventually allow scientists to "solve all aspects" of the time arrow problem in practice. They also have a practical application: they will help improve future quantum computers, he said, as well as the operation of nuclear magnetic resonance (NMR) technology, which is used in medical magnetic resonance imaging.
How to make a video in reverse
And the non-physical between us, however – does the study bring us closer to "Doctor Who" – time travel, with or without a Tardis? Animesh Datta, associate professor of theoretical physics at Warwick University, gave a direct answer after giving a look at the study: "No".
Datta called the study "interesting", adding: "It is an example of the types of creative things that can be simulated on a quantum computer."
It offered an analogy to explain the results. "You can compare this with running a reverse video," he said. "It gives you the feeling that the world is going backwards, but it's just a feeling. The world doesn't really change."
The Moscow researchers began with a quantum computer comprising two qubits, the basic element of quantum information. They observed the computer through four phases: order – the starting point – degradation, temporal inversion and chaos.
During the degradation phase, the researchers explained in a press release that they launched an "evolution program" that caused morphing of the qubits in "an increasingly complex pattern of zeros and ones."
In the time reversal phase, they executed a program that modified the quantum computer to "evolve backwards", moving "from chaos to order".
In the final phase, the scientists relaunched the evolution program. Instead of degenerating into further chaos, the qubits have been restored to their original state – returning, in effect, to the past.
With two qubits, the quantum computer has returned to its original state in 85% of the time; when a third qubit was added, the success rate dropped to 50%.