Quantum Pasts and the Utility of History

TL;DR

This paper explores how quantum mechanics allows for predicting and retrodicting histories of events, examining the differences between classical and quantum retrodiction, the nature of the past, and the usefulness of reconstructing historical information.

Contribution

It discusses the distinction between prediction and retrodiction in quantum cosmology and introduces information-theoretic measures for the utility of reconstructing histories.

Findings

Quantum mechanics assigns probabilities to histories in decoherent sets.

Retrodiction differs fundamentally from prediction in quantum contexts.

Reconstructing the past has informational and philosophical implications.

Abstract

From data in the present we can predict the future and retrodict the past. These predictions and retrodictions are for histories -- most simply time sequences of events. Quantum mechanics gives probabilities for individual histories in a decoherent set of alternative histories. This paper discusses several issues connected with the distinction between prediction and retrodiction in quantum cosmology: the difference between classical and quantum retrodiction, the permanence of the past, why we predict the future but remember the past, the nature and utility of reconstructing the past(s), and information theoretic measures of the utility of history. (Talk presented at the Nobel Symposium: Modern Studies of Basic Quantum Concepts and Phenomena, Gimo, Sweden, June 13-17, 1997)