Why do we remember the past and not the future? The 'time oriented coarse graining' hypothesis

TL;DR

This paper proposes that the arrow of time and the low entropy of the past are due to the coarse-graining and macroscopic variables chosen by observers, rather than an improbable initial universe microstate.

Contribution

It introduces the 'time oriented coarse graining' hypothesis, linking the arrow of time to observer-dependent coarse-graining rather than initial conditions.

Findings

Any generic motion satisfies the second law with appropriate macroscopic variables.

The low entropy past may result from how we couple to the universe, not from initial microstates.

The hypothesis offers a new perspective on the thermodynamic arrow of time.

Abstract

Phenomenological arrows of time can be traced to a past low-entropy state. Does this imply the universe was in an improbable state in the past? I suggest a different possibility: past low-entropy depends on the coarse-graining implicit in our definition of entropy. This, in turn depends on our physical coupling to the rest of the world. I conjecture that $any$ generic motion of a sufficiently rich system satisfies the second law of thermodynamics, in either direction of time, for $some$ choice of macroscopic observables. The low entropy of the past could then be due to the way we couple to the universe (a way needed for us doing what we do), hence to our natural macroscopic variables, rather than to a strange past microstate of the world at large.