The "arrow of time," a concept introduced by astrophysicist Arthur Eddington in 1927, refers to the one-way directionality or asymmetry of time's flow. A central paradox in physics is that while we experience a relentless progression from past to future, the fundamental microscopic laws of physics (such as Newtonian mechanics and the Schrödinger equation) are time-reversal symmetric, meaning they function equally well forwards and backwards.

To explain this asymmetry, physicists categorize time into several distinct "arrows":

Thermodynamic Arrow: The most prominent explanation for time's direction is dictated by the Second Law of Thermodynamics, which states that the entropy (disorder or dispersed energy) of an isolated system tends to continually increase. Ludwig Boltzmann mathematically modeled this via the H-theorem, demonstrating  ...