Does time move in only one direction?
What about the arrows of time at the macro and micro level? Maybe they are not the same.
This paper seems to be highly theoretical!
"... "However, there are processes, such as the motion of a pendulum, that look just as believable in reverse. The puzzle is that, at the most fundamental level, the laws of physics resemble the pendulum; they do not account for irreversible processes. ...
To simplify the problem, the team made two key assumptions.
First, they treated the vast environment surrounding the system in such a way that they could focus only on the quantum system itself.
Second, they assumed that the environment—like the entire universe—is so large that energy and information dissipate into it, never returning.
This approach enabled them to examine how time emerges as a one-way phenomenon, even though, at the microscopic level, time could theoretically move in both directions.
Even after applying these assumptions, the system behaved the same way whether time moved forward or backwards. This discovery provided a mathematical foundation for the idea that time-reversal symmetry still holds in open quantum systems—suggesting that time's arrow may not be as fixed as we experience it. ..."
From the abstract:
"Deriving an arrow of time from time-reversal symmetric microscopic dynamics is a fundamental open problem in many areas of physics, ranging from cosmology, to particle physics, to thermodynamics and statistical mechanics.
Here we focus on the derivation of the arrow of time in open quantum systems and study precisely how time-reversal symmetry is broken.
This derivation involves the Markov approximation applied to a system interacting with an infinite heat bath. We find that the Markov approximation does not imply a violation of time-reversal symmetry.
Our results show instead that the time-reversal symmetry is maintained in the derived equations of motion. This imposes a time-symmetric formulation of quantum Brownian motion, Lindblad and Pauli master equations, which hence describe thermalisation that may occur into two opposing time directions.
As a consequence, we argue that these dynamics are better described by a time-symmetric definition of Markovianity. Our results may reflect on the formulations of the arrow of time in thermodynamics, cosmology, and quantum mechanics."
Physicists uncover evidence of two arrows of time emerging from the quantum realm (original news release) "What if time is not as fixed as we thought? Imagine that instead of flowing in one direction – from past to future – time could flow forward or backward due to processes taking place at the quantum level. This is the thought-provoking discovery made by researchers at the University of Surrey, as a new study reveals that opposing arrows of time can theoretically emerge from certain quantum systems."
Fig. 1 Schematic showing the concept behind the time-reversal transformation. The system and environment move backward in time. In quantum mechanics this is implemented using the time-reversal operator, which reverses the momenta, followed by the transformation
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