A Breathing Universe is Consistent

Abstract

We consider a toy FRW universe with the exotic topology $S^1\times S^3$. We show that for a specific choice of quantum field content, the semi-classical Friedman equations are consistent with temporal periodicity as required by the $S^1$ timelike factor. A straightforward consequence is that entropy reversals occur during each cycle, consistent with Hawking's proposed connection between the thermodynamic and cosmological arrows of time.

7 pages, 1 figure, updated to reflect journal version 2026 Class. Quantum Grav

References in corpus (17)

• In the Realm of the Hubble tension $-$ a Review of Solutions
• Early Dark Energy Can Resolve The Hubble Tension
• Quantum Gravity in Everyday Life: General Relativity as an Effective Field Theory
• The trouble with $H_0$
• Dark Energy Survey Year 1 Results: Cosmological Constraints from Cosmic Shear
• Entanglement entropy in free quantum field theory
• Can interacting dark energy solve the $H_0$ tension?
• $\nu \Lambda$CDM: Neutrinos help reconcile Planck with the Local Universe
• Turnaround in Cyclic Cosmology
• Bouncing Universes with Varying Constants
• Floquet States in Open Quantum Systems
• Universality and Ambiguities of the Conformal Anomaly
• Is there a Floquet Lindbladian?
• Exploring eternal stability with the simple harmonic universe
• Entropy bounds for massive scalar field in positive curvature space
• Life on a closed timelike curve
• On heat coefficients, multiplicative anomaly and 4D Casimir energy for GJMS operators