Irreversibility in physics stemming from unpredictable symbol-handling agents

TL;DR

This paper argues that unpredictable symbol-handling agents introduce a fundamental source of irreversibility in physics, challenging the notion that time-reversal invariance of equations implies reversible physical processes.

Contribution

It demonstrates that including unpredictable agents and symbols in physical descriptions provides a new explanation for time-irreversibility beyond traditional thermodynamic and equation-based arguments.

Findings

Unpredictable agents cause irreversibility in physics.

Symbols exchanged by agents contribute to time asymmetry.

Expanding physics to include agents links theory with experimental evidence.

Abstract

The basic equations of physics involve a time variable t and are invariant under the transformation $t goes to -t$. This invariance at first sight appears to impose time reversibility as a principle of physics, in conflict with thermodynamics. But equations written on the blackboard are not the whole story in physics. In prior work we sharpened a distinction obscured in today's theoretical physics, the distinction between obtaining evidence from experiments on the laboratory bench and explaining that evidence in mathematical symbols on the blackboard. The sharp distinction rests on a proof within the mathematics of quantum theory that no amount of evidence, represented in quantum theory in terms of probabilities, can uniquely determine its explanation in terms of wave functions and linear operators. Building on the proof we show here a role in physics for unpredictable symbol-handling agents acting both at the blackboard and at the workbench, communicating back and forth by means of transmitted symbols. Because of their unpredictability, symbol-handling agents introduce a heretofore overlooked source of irreversibility into physics, even when the equations they write on the blackboard are invariant under t goes to -t$. Widening the scope of descriptions admissible to physics to include the agents and the symbols that link theory to experiments opens up a new source of time-irreversibility in physics.