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A LARGER ESTIMATE OF THE ENTROPY OF THE UNIVERSE
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Using recent measurements of the supermassive black hole (SMBH) mass function, we find that SMBHs are the largest contributor to the entropy of the observable universe, contributing at least an order of magnitude more entropy than previously estimated. The total entropy of the observable universe is correspondingly higher, and is S obs = 3.1 +3.0 −1.7 × 10 104 k . We calculate the entropy of the current cosmic event horizon to be S CEH = 2.6 ± 0.3 × 10 122 k , dwarfing the entropy of its interior, S CEH int = 1.2 +1.1 −0.7 × 10 103 k . We make the first tentative estimate of the entropy of weakly interacting massive particle dark matter within the observable universe, S dm = 10 88 ± 1 k . We highlight several caveats pertaining to these estimates and make recommendations for future work.
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“Stotobs≃Sγ+Sν+SIGM+SBH≈(5.9+4.1+2.0+3.1×1014)×1088”
From Counting Cosmic Cycles: Past Big Crunches, Future Recurrence Limits, and the Age of the Quantum Memory Matrix Universe (2025) · cites this paper as [40]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“Equation (9) agrees with the benchmark compilation Stotobs=(3.1±0.3)×10104 by Egan and Lineweaver [40].”
From Counting Cosmic Cycles: Past Big Crunches, Future Recurrence Limits, and the Age of the Quantum Memory Matrix Universe (2025) · cites this paper as [40]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
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“(Their higher value includes dark matter phase-space entropy, which we exclude because in QMM it is represented separately as imprint entropy.)”
From Counting Cosmic Cycles: Past Big Crunches, Future Recurrence Limits, and the Age of the Quantum Memory Matrix Universe (2025) · cites this paper as [40]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
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“Taking into account the present uncertainties in the cosmological data, Egan and Lineweaver (2010) found from this the following numerical value:”
From On a quantum Weyl curvature hypothesis (2022) · cites this paper as Egan and Lineweaver (2010)
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“the biggest contribution to non-gravitational entropy comes from the CMB photons, with the value”
From On a quantum Weyl curvature hypothesis (2022) · cites this paper as Egan and Lineweaver (2010)
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“The best estimates of the current entropy give numbers of order 10 103 [12].”
From In What Sense Is the Early Universe Fine-Tuned? (2014) · cites this paper as [12]
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“Now, as a matter of fact, the amount of entropy presently associated with supermassive black holes outweighs that of ordinary matter by a factor 10 15 (see e.g.[43]).”
From Conformal Cyclic Cosmology, gravitational entropy and quantum information (2023) · cites this paper as [43]
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“We see that the non-gravitational entropy is completely negligible.”
From On a quantum Weyl curvature hypothesis (2022) · cites this paper as Egan and Lineweaver (2010)
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“The dominating contributions from the gravitational side are supermassive black holes (SMBHs), followed by stellar black holes.”
From On a quantum Weyl curvature hypothesis (2022) · cites this paper as Egan and Lineweaver (2010)
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Citations
Cites
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Metadata
- Authors
- Egan, C. A., & Lineweaver, C. H.
- Affiliations
- Australian National University (AU)
- Corresponding author
- Egan, Chas A.
- Venue
- The Astrophysical Journal
- Publisher
- American Astronomical Society
- Published
- 2010-02-03
- Volume
- 710
- Issue
- 2
- Pages
- 1825-1834
- ISSN
- 0004-637X (ISSN-L)
- 1538-4357
- OpenAlex
- W2100463561
- Cited by
- 232
- References
- 48
- Citations by year
- 2026: 15 · 2025: 43 · 2024: 6 · 2023: 24 · 2022: 17 · 2021: 15 · 2020: 9 · 2019: 12 · 2018: 4 · 2017: 14 · 2016: 15 · 2015: 8 · 2014: 9 · 2013: 15 · 2012: 10
- FWCI
- 6.97
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- The Astrophysical Journal (publishedVersion)
- arXiv (Cornell University) (submittedVersion)
- ANU Open Research (Australian National University) (submittedVersion)
- arXiv (Cornell University)
- Topics
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Cosmology and Gravitation Theories
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Galaxies: Formation, Evolution, Phenomena
- Physical Sciences › Physics and Astronomy › Nuclear and High Energy Physics › Dark Matter and Cosmic Phenomena
- Keywords
- supermassive black holes, cosmic event horizon, WIMPs, black hole entropy
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