Scientists learn how to reverse time — in theory

For most of us, the closest we’ll get to time travel is watching an episode of “Doctor Who.” A team of physicists from the Moscow Institute of Physics and Technology (MIPT), however, have come closer than most: using a quantum computer, they successfully simulated the reversal of time.

Simulated, of course, is the key word: lead author of the study Gordey Lesovik of MIPT told CNN that we’re “not really” approaching the ability to actually reverse time. But it still could have important practical and theoretical ramifications.

A team of physicists from MIPT, which also included scientists from Switzerland and the US, looked into “the possibility of violating the second law of thermodynamics,” Lesovik said in a press release.

Pool balls returning 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 rack of pool balls struck by a cue ball will scatter across the table, but rolling balls will not spontaneously return to the neat triangle where they started.

That necessary increase in entropy establishes the “arrow of time,” or the irreversible progression from the past into the future. The problem of the arrow of time, Lesovik told CNN, is “one of the most old, fundamental and fascinating” problems in physics. “It is nothing but natural to try to resolve it,” he said.

According to Lesovik, the findings of the study will ultimately allow scientists to resolve “basically all the aspects” of the arrow of time problem. They also have a practical application: they’ll help improve future quantum computers, he said, as well as the operation of nuclear magnetic resonance spectroscopy (NMR) technology, which is used in medical magnetic resonance imaging.

Like running a video in reverse

What about the non-physicists among us, though — does the study bring us any closer to “Doctor Who”-esque time travel, with or without a Tardis? Animesh Datta, associate professor in theoretical physics at the University of Warwick, gave a direct answer after taking a look at the study: “No.”

Datta called the study “interesting,” adding: “It is an example of the types of creative things one can simulate on a quantum computer.”

He offered an analogy to explain the findings. “You can compare this to running a video in reverse,” he said. “It gives you the feeling of the world going backwards, but it’s only a feeling. The world doesn’t actually change.”

The Moscow researchers began with a quantum computer comprising two qubits, the basic element of quantum information. They observed the computer through four stages: order — the starting point — degradation, time reversal and chaos.

During the degradation phase, the researchers explained in a press release, they launched an “evolution program” that resulted in the qubits morphing into “an ever more complex changing pattern of zeros and ones.”

In the time reversal phase, they ran 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 were restored to their original state — returning, in effect, to the past.

With two qubits, the quantum computer reverted to its original state 85% of the time; when a third qubit was added, the success rate dropped to 50%.


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