Islands in the Fluid: Islands are Common in Cosmology

Abstract

We discuss the possibility of entanglement islands in cosmological spacetimes with a general perfect fluid with an equation of state $w$. We find that flat universes with time-symmetric slices where the Hubble parameter vanishes always have islands on that slice. We then move away from such slices, considering still universes with a general perfect fluid. Under the local thermal equilibrium assumption, the comoving entropy density $s_c$ is constant. As a result, the conditions for an island become an inequality between the energy density (or Hubble parameter) and the temperature at some time of normalization. The consequences are that islands can exist for practically all fluids that are not radiation, i.e. $w\ne 1/3$. We also discuss the ramifications of our results for universes with spatial curvature. Finally, we show that islands occur in the Simple Harmonic Universe model which has no classical singularity at the background level, in contrast to all previous examples where islands occurred only in space-times with singularities.

arXiv comment26 pages, 5 figures

References in corpus (18)

• Holographic Derivation of Entanglement Entropy from AdS/CFT
• Aspects of Holographic Entanglement Entropy
• A Covariant Holographic Entanglement Entropy Proposal
• Entanglement entropy and conformal field theory
• Quantum Extremal Surfaces: Holographic Entanglement Entropy beyond the Classical Regime
• Quantum corrections to holographic entanglement entropy
• The entropy of bulk quantum fields and the entanglement wedge of an evaporating black hole
• Eternal inflation and its implications
• Inconsistency of Islands in Theories with Long-Range Gravity
• Islands in cosmology
• Inflationary schism after Planck2013
• Islands in Flat-Space Cosmology
• Islands in Closed and Open Universes
• Gravitational Waves in Bouncing Cosmologies from Gauge Field Production
• Sourced fluctuations in generic slow contraction
• Sourced Scalar Fluctuations in Bouncing Cosmology
• Banks-Zaks Cosmology, Inflation, and the Big Bang Singularity
• The Grand Canonical Multiverse and the Small Cosmological Constant

Cited by in corpus (4)

• Closed FRW holography: A time-dependent ER=EPR realization
• New insights on mutual information in the island approach to the Page curve
• Cosmological Implications of Thermodynamic Split Conjecture
• Holography for de Sitter bubble geometries