Uncovering the origin of the arrow of time remains a fundamental scientific challenge. Within the framework of statistical physics, this problem was inextricably associated with the Second Law of Thermodynamics, which declares that entropy growth proceeds from the system’s entanglement with the environment. It remains to be seen, however, whether the irreversibility of time is a fundamental law of nature or whether, on the contrary, it might be circumvented.

The study’s lead author Gordey Lesovik said, "This is one in a series of papers on the possibility of violating the second law of thermodynamics. That law is closely related to the notion of the arrow of time that posits the one-way direction of time from the past to the future."

"We began by describing a so-called local perpetual motion machine of the second kind. Then, in December, we published a paper that discusses the violation of the second law via a device called Maxwell’s demon. The most recent paper approaches the same problem from a third angle: We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time."

Scientists were keen to know if time could spontaneously reverse itself at least for an individual particle and for a tiny fraction of a second. Thus, they decided to check and examine a solitary electron in empty interstellar space.

Study co-author Andrey Lebedev from MIPT and ETH Zurich said, "Suppose the electron is localized when we begin observing it. This means that we’re pretty sure about its position in space. The laws of quantum mechanics prevent us from knowing it with absolute precision, but we can outline a small region where the electron is localized."

"The advancement of the electron state is represented by Schrodinger’s equation. In spite of the fact that it sees no difference amongst the future and the past, the region of space containing the electron will spread out all around rapidly."

"That is, the system will in general turn out to be more chaotic. The vulnerability of the electron’s position is growing. This is practically equivalent to the increasing disorder in a large scale system, for example, a billiard table—because of the second law of thermodynamics."

Valerii Vinokur, a co-author of the paper, from the Argonne National Laboratory, U.S. said, "However, Schrodinger’s equation is reversible. Mathematically, it means that under a certain transformation called complex conjugation, the equation will describe a ‘smeared’ electron localizing back into a small region of space over the same time period. Although this phenomenon is not observed in nature, it could theoretically happen due to a random fluctuation in the cosmic microwave background permeating the universe."

Scientists then set out to ascertain the likelihood to observe an electron "smeared out" over a small amount of a second immediately localizing into its recent past. It worked out that across over the entire lifetime of the universe—13.7 billion years—observing 10 billion freshly localized electrons consistently, the reverse evolution of the particle’s state would just happen once. Also, and, after its all said and done, the electron would travel close to a mere one ten-billionth of a second into the past.

Large-scale phenomena involving billiard balls and volcanoes obviously unfold on much greater timescales and feature an astounding number of electrons and other particles. This explains why we do not observe old people growing younger or an ink blot separating from the paper.

The researchers then attempted to reverse time in a four-stage experiment. Instead of an electron, they observed the state of a quantum computer made of two and later three basic elements called superconducting qubits.

Schrodinger's equation describes the evolution of a particle's electron state. The region of space containing the electron quickly expands. Chaos increases as systems scale.

"However, Schrodinger's equation is reversible," said Valerii Vinokur, a researcher at the Argonne National Laboratory in the United States. "Mathematically, it means that under a certain transformation called complex conjugation, the equation will describe a 'smeared' electron localizing back into a small region of space over the same time period."

Researchers crunched the numbers and found that if 10 billion freshly localized electrons were observed every second for the entirety of the universe's lifetime, 13.7 billion years, only one particle would be observed reversing time -- spontaneously localizing against the arrow of time.

Next, scientists attempted to manufacture a violation of the second law of thermodynamics. They built a quantum computer with two and three superconducting qubits. Physicists used the quantum computer to conduct a four-stage experiment.

Stage one features an ordered state, with each qubit grounded at zero, like a single electron confined to a small localized region. During the second stage, order is lost. Scientists used an evolution program on the quantum computer to trigger the degradation of order, causing the qubits to begin assuming an increasingly complex pattern of zeros and ones, like an electron getting smeared out across a larger and larger region of space.

For stage three, scientists used another program to reverse time, causing the qubits to evolve from chaos to order -- to reground themselves at zero. For stage four, the evolution program is relaunched from the second stage, causing the qubits to reverse time and revert to their earlier state.

When scientists used a two-qubit computer to conduct the four stage experiment, they observed qubits moving from chaos to order every time. When they introduced a third qubit, the computer produced more errors, and the qubits were able to reverse time only half of the time.

Researchers suggest their findings -- published this week in the journal Scientific Reports -- could be used to improve the precision of quantum devices.

"Our algorithmic rule may be updated and wont to take a look at programs written for quantum computers and eliminate noise and errors," Lebedev mentioned.