The boundary between time moving forward and backward blurs in quantum mechanics

Physicists at the Universities of Bristol, Vienna, the Balearic Islands and the Institute for Quantum Optics and Quantum Information (IQOQI-Vienna) have demonstrated how quantum systems simultaneously evolve along two opposite time arrows, both forward and backward in time. Published in the latest issue of Communications Physics, the results of the study urge a rethink of how the flow of time is understood and represented in contexts where quantum laws play a role.

Dr Giulia Rubino from the University of Bristol said: “If a phenomenon produces a large amount of entropy, observing its time-reversal is so improbable as to become essentially impossible. However, when the entropy produced is small enough, there is a non-negligible probability of seeing the time-reversal of a phenomenon occur naturally.

The authors of the study applied the idea of entropy to the quantum realm, where quantum superposition says if two states of a quantum system are both possible, then that system can also be in both states at the same time.

The study quantified the entropy produced by a system evolving in quantum superposition of processes with opposite time arrows. When small amounts of entropy are involved one can physically observe the consequences of the system having evolved along the forward and backward temporal directions simultaneously.

The paper “Quantum superposition of thermodynamic evolutions with opposing time’s arrows” can be found in Communications Physics. DOI: 10.1038/s42005-021-00759-1

Original Release: Eureka Alert