Macroscopic arrow of time from multiscale perspectives

TL;DR

This paper reviews how macroscopic irreversibility and the arrow of time emerge from fundamental symmetric physical laws through multiscale energy transfer, thermodynamics, and open system interactions.

Contribution

It provides a comprehensive overview of frameworks explaining time symmetry breaking in macroscopic systems, emphasizing multiscale energy flux and open system dynamics.

Findings

Multiscale energy transfer influences the macroscopic arrow of time.

Open systems exhibit irreversibility due to exchanges with environment.

Causality contributes to breaking time reversal symmetry.

Abstract

Fundamental laws of physics are symmetric under time reversal ($T$) symmetry, but the $T$ symmetry is strongly broken in the macroscopic world. In this Perspective, I review $T$ symmetry breaking frameworks: \textit{second law of thermodynamics, multiscale energy transfer}, and \textit{open systems}. In driven dissipative nonequilibrium systems, including turbulence, the multiscale energy flux from large scales to small scales helps determine the arrow of time. In addition, open systems are often irreversible due to particle and energy exchanges between the system and the environment. Causality is another important factor that breaks the $T$ symmetry.