Modeling the Past Hypothesis: A Mechanical Cosmology
arXiv:2309.08662 · doi:10.1007/s10701-023-00745-3
Abstract
There is a paradox in the standard model of cosmology. How can matter in the early universe have been in thermal equilibrium, indicating maximum entropy, but the initial state also have been low entropy (the "past hypothesis"), so as to underpin the second law of thermodynamics? The problem has been highly contested, with the only consensus being that gravity plays a role in the story, but with the exact mechanism undecided. In this paper, we construct a well-defined mechanical model to study this paradox. We show how it reproduces the salient features of standard big-bang cosmology with surprising success, and we use it to produce novel results on the statistical mechanics of a gas in an expanding universe. We conclude with a discussion of potential uses of the model, including the explicit computation of the time-dependent coarse-grained entropies needed to investigate the past hypothesis.
arXiv comment13 pages, 11 figures
References in corpus (22)
- The Dynamics of General Relativity
- Thermodynamical Aspects of Gravity: New insights
- The Measure Problem in Cosmology
- Entanglement Theory and the Second Law of Thermodynamics
- Quantum cosmology: a review
- Measure and Probability in Cosmology
- Quantum coarse-grained entropy and thermodynamics
- Attractor Solutions in Scalar-Field Cosmology
- A brief introduction to observational entropy
- Inflationary Attractors and their Measures
- Revisiting Dark Matter Freeze-in and Freeze-out through Phase-Space Distribution
- Cosmological particle production and generalized thermodynamic equilibrium
- Gravity and Nonequilibrium Thermodynamics of Classical Matter
- Simple Cosmological Model with Relativistic Gas
- Thermodynamics and Kinetic Theory of Relativistic Gases in 2-D Cosmological Models
- Area scaling entropies for gravitating systems
- Where was past low-entropy?
- Scalar Fields and the FLRW Singularity
- Diffusion of relativistic gas mixtures in gravitational fields
- Observational entropy, coarse quantum states, and Petz recovery: information-theoretic properties and bounds
- Equilibration and freeze-out of an expanding gas in a transport approach in a Friedmann-Robertson-Walker metric
- Thermodynamics of diffusive DM/DE systems