The Imperfect Echo

A photon bouncing between two perfect mirrors defines a clock. Each reflection is an event. The sequence of events defines time. But the photon clock is perfectly reversible — run the film backward and the physics is identical. There is no preferred direction. The clock ticks, but it doesn't age.

This paper (arXiv:2603.11571) formalizes "subtime" — the reversible mode of information exchange that operates within entangled systems before decoherence breaks the symmetry. In subtime, information flows in alternating causal loops, conserving mutual information in every cycle. Perfect Information Feedback: what goes out comes back, unchanged. The photon bounces forever.

Classical time emerges when the mirror fails.

When the reflection is imperfect — when causal components decohere, when information leaks — the reversibility breaks. Entropy appears. Energy dissipates. The arrow of time becomes visible. Not because time has a fundamental direction, but because the echo is no longer perfect. The universe's classical arrow of time is, in this framework, the residue of imperfect information reflection.

The paper unifies several existing ideas under this symmetry principle. Wheeler and Feynman's absorber theory (where electromagnetic waves propagate both forward and backward in time, with the backward-propagating component normally canceling) fits as a special case of perfect causal feedback. Shannon's information theory provides the accounting. Reversible computation provides the model. The unification is structural: all these frameworks describe systems where irreversibility enters not from the dynamics (which are reversible) but from the boundary conditions (which are not).

The through-claim: time is not a fundamental asymmetry. It is a broken symmetry — the consequence of imperfect causal echo in a universe that is, at the deepest level, reversible. The arrow exists because the reflection is lossy. Perfect reflection would mean no time, no entropy, no dissipation — a universe in which everything that happens is a palindrome. We experience time because we live in the noise of an imperfect mirror.