Time-Reversal Phenomenon: In the Quantum Realm, Not Even Time Flows As You Might Expect

 

Recent study shows the border between time moving forward and backward may blur in quantum mechanics.

 

A group of physicists at the Universities of Bristol, Vienna, and the Institute for Quantum Optics and Quantum Information (IQOQI-Vienna) has revealed how quantum systems can simultaneously progress along two opposite time arrows — both forward and backward in time.

 

The study, published in the Communications Physics, demands a rethink of how the flow of time is understood and described in contexts where quantum laws play a vital role.

 

For a long period of time, researchers have been pondering the reality of time. Yet, in the real world, our experience seems to extinguish any disbelief that time exists and goes on. Certainly, in nature, things tend to evolve instantly from states with less disorder to states with more disorder, and this propensity can be used to recognize an arrow of time. In physics, this is termed ‘entropy’, which is the physical quantity describing the amount of disorder in a system.

 

 

Artistic illustration of a gondolier trapped in a quantum superposition of time flows. Credit:

© Aloop Visual & Science, University of Vienna, Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences

 

Dr. Giulia Rubino from the University of Bristol’s Quantum Engineering Technology Labs (QET labs) and lead-author of the publication, stated that:

 

“If a phenomenon generates a large amount of entropy, observing its time-reversal is so doubtful as to become basically impossible. Though, when the generated entropy is small enough, there is a non-negligible probability of observing the time-reversal of a phenomenon happen naturally.

 

“We can take the series of things we do in our daily routine as an example. If we were shown our toothpaste moving from the toothbrush back into its tube, we would be in no uncertainty it was a rewinded recording of our day. Yet, if we squeezed the tube softly so only a small part of the toothpaste came out, it would not be so unlikely to see it re-entering the tube, sucked in by the tube’s decompression.”

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