A New Census of the Universe's Entropy

Abstract

The question of what is the total entropy of the universe, how it compares to the maximal entropy of de Sitter space, and how it is distributed across the universe's components, bears considerable importance for a number of reasons. Here, we first update the computation of the entropy associated with various sectors of the observed universe, including in the diffuse cosmic and late-time gamma-ray and neutrino backgrounds, in baryonic matter both in diffuse components, in stars and stellar remnants, and in cosmic rays; we then update, crucially, the estimate of entropy in stellar-mass and super-massive black holes, whose abundance and mass function has come into increasingly sharp definition with recent observations and with the rapidly growing statistics of black-hole-black-hole mergers observed with gravity wave detectors. We also provide a new, corrected estimate of the potential entropy associated with a stochastic gravitational wave background, with dark sector radiations, and with several dark matter models. Finally, we utilize the similarly recently updated constraints on the abundance of hypothetical primordial black holes - black holes, that is, of non-stellar origin - to assess the maximal amount entropy they could store. We find that if supermassive primordial black holes exist, they can dominate the entropy budget of the universe consistently with current constraints on their abundance and mass function, to a level potentially not distant from the posited entropy associated with the cosmic event horizon of de Sitter spacetime. The same conclusion holds for certain dark sector models featuring a large number of dark degrees of freedom.

47 pages, 6 figures, version published on JCAP

References in corpus (53)

• Primordial Black Holes as a dark matter candidate
• Neutrino decoupling including flavour oscillations and primordial nucleosynthesis
• Fallback and Black Hole Production in Massive Stars
• On Effective Degrees of Freedom in the Early Universe
• A Measure of de Sitter Entropy and Eternal Inflation
• Predicting the Cosmological Constant from the Causal Entropic Principle
• Stochastic gravitational-wave background from metastable cosmic strings
• Primordial Neutrinos
• The Enrichment History of Baryons in the Universe
• Towards a precision calculation of the effective number of neutrinos $N_{\mathrm{eff}}$ in the Standard Model I: The QED equation of state
• Coevolution of metallicity and star formation in galaxies to z=3.7: I. A fundamental plane
• Missing Baryons and the Warm-Hot Intergalactic Medium
• First detection of stacked X-ray emission from cosmic web filaments
• An EAGLE view of the missing baryons
• Combined analysis of AMS-02 (Li,Be,B)/C, N/O, 3He, and 4He data
• Statistical theory of thermal evolution of neutron stars
• NANOGrav spectral index $\gamma =3$ from melting domain walls
• Detection of the Missing Baryons toward the Sightline of H1821+643
• Low energy cosmic rays
• A brief introduction to observational entropy
• What is the entropy of the universe?
• Resurrection of large lepton number asymmetries from neutrino flavor oscillations
• Gravitational shine of dark domain walls
• Formation of Primordial Black Holes from Warm Inflation
• Solving the Hubble tension without spoiling Big Bang Nucleosynthesis
• Limits on the cosmic neutrino background
• Probing the properties of relic neutrinos using the cosmic microwave background, the Hubble Space Telescope and galaxy clusters
• Adventures in de Sitter space
• The generalized second law of thermodynamics and the nature of the Entropy Function
• Variance of the Galactic nuclei cosmic ray flux
• Galactic diffuse gamma-ray emission from GeV to PeV energies in light of up-to-date cosmic ray measurements
• Gravitational wave hints black hole remnants as dark matter
• Lepton asymmetry, neutrino spectral distortions, and big bang nucleosynthesis
• The Black Hole Mass Function Across Cosmic Times I. Stellar Black Holes and Light Seed Distribution
• High-Statistics Measurement of the Cosmic-Ray Electron Spectrum with H.E.S.S
• The large-scale environment from cosmological simulations II: The redshift evolution and distributions of baryons
• Solutions to the Cosmic Initial Entropy Problem without Equilibrium Initial Conditions
• The Black Hole Mass Function Across Cosmic Times II. Heavy Seeds and (Super)Massive Black Holes
• Measurement of low-energy cosmic-ray electron and positron spectra at 1 AU with the AESOP-Lite spectrometer
• Effects of an Intermediate Mass Sterile Neutrino Population on the Early Universe
• Neutrino at different epochs of the Friedmann Universe
• Dark Radiation and the Hagedorn Phase
• Constraints on the maximal number of dark degrees of freedom from black hole evaporation, cosmic rays, colliders, and supernovae
• Thermodynamics of a Schwarzschild black hole surrounded by quintessence in the generalized uncertainty principle framework
• Big Bang Nucleosynthesis and Neutrino Cosmology
• Cosmic Neutrino Decoupling and its Observable Imprints: Insights from Entropic-Dual Transport
• Planck stars, White Holes, Remnants and Planck-mass quasi-particles. The quantum gravity phase in black holes' evolution and its manifestations
• Constraints on Primordial Black Holes from $N$-body simulations of the Eridanus II Stellar Cluster
• The Cosmic Neutrino Background
• Entropies of the various components of the universe
• Evolution of Entropy with Cosmic Time
• From entropy to gravitational entropy
• Relic neutrinos and cosmic background radiation: a new way of comparison

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