Boltzmann babies in the proper time measure

TL;DR

This paper examines the cosmological measure problem, focusing on the proper time cutoff, and finds it predicts unobserved phenomena like Boltzmann babies, highlighting its incompatibility with observations.

Contribution

It advocates a phenomenological approach to the measure problem and critically analyzes the proper time cutoff, demonstrating its failure to align with empirical data.

Findings

Proper time cutoff predicts Boltzmann babies as typical observers.

The youngness problem is intensified by considering universe expansion and geometry.

Modifications to the proper time measure do not resolve observational inconsistencies.

Abstract

After commenting briefly on the role of the typicality assumption in science, we advocate a phenomenological approach to the cosmological measure problem. Like any other theory, a measure should be simple, general, well-defined, and consistent with observation. This allows us to proceed by elimination. As an example, we consider the proper time cutoff on a geodesic congruence. It predicts that typical observers are quantum fluctuations in the early universe, or Boltzmann babies. We sharpen this well-known youngness problem by taking into account the expansion and open spatial geometry of pocket universes. Moreover, we relate the youngness problem directly to the probability distribution for observables, such as the temperature of the cosmic background radiation. We consider a number of modifications of the proper time measure, but find none that would make it compatible with observation.