Cosmology, initial conditions, and the measurement problem

TL;DR

This paper presents a unified, objective interpretation of probability, entropy, and information in cosmology, linking initial conditions to later states through deterministic laws and spatial symmetries.

Contribution

It offers a novel, unified account of probability and statistical properties in cosmology based on spatial symmetries and the universe's infinite extent.

Findings

Probabilities have an exact, objective physical interpretation.

Statistical entropy and information are objective properties of the universe.

Probabilistic descriptions are linked to spatial volume fractions in an infinite universe.

Abstract

The assumption that a complete description of an early state of the universe does not privilege any position or direction in space leads to a unified account of probability in cosmology, macroscopic physics, and quantum mechanics. Such a description has a statistical character. Deterministic laws link it to statistical descriptions of the cosmic medium at later times, and because these laws do not privilege any position or direction in space, the same must be true of these descriptions. If the universe is infinite, we can identify the probability that the energy density at a particular instant and a particular point in space (relative to a system of spacetime coordinates in which the postulated spatial symmetries are manifest) lies in a given range with the fractional volume occupied by points where the energy density lies in this range; and similarly with all other probabilities that figure in the statistical description. The probabilities that figure in a complete description of the cosmic medium at any given moment thus have an exact and objective physical interpretation. The statistical entropy and the information associated with each cosmological probability distribution are likewise objective properties of the universe, defined in terms of relative frequencies or spatial averages.