Cosmic coincidence problem
In cosmology, the cosmic coincidence problem is the observation that at the present epoch of the universe's evolution, the energy densities associated with dark matter and dark energy are of the same order of magnitude, leading to their comparable effects on the dynamics of the cosmos.[1][2] The problem was proposed by Paul Steinhardt during the proceedings of a conference celebrating the 250th anniversary of Princeton University in 1997.[3][2]
This coincidence is puzzling because these energies have vastly different effects on the universe's expansion—dark matter tends to slow down expansion through gravitational attraction, while dark energy seems to accelerate it. The observed similarity in the magnitudes of these two components' energy densities at this particular epoch in the history of the universe raises questions about whether there might be some underlying physical connection or shared origin between dark matter and dark energy. Indeed, some theories attempt to explain this coincidence by proposing that they are different manifestations of the same fundamental force or field.[4][5][6]
Values
According to 2018 Planck analysis of the Lambda-CDM model, the standard model of cosmology, the ratio of the dark energy density to the critical density is about ΩΛ = 0.685, while the ratio of energy density of matter (including ordinary baryonic matter and dark matter) divided by the critical density is about Ωm = 0.315.[2][7] As cosmological constant remains constant and matter density decreases with the expansion of the universe, the fact that these two values are fo the same order of magnitude means that the ratio ΩΛ/Ωm must be set to a specific infinitesimal value (of the order of 10−120) in the very early universe in order to have the current values today.[8]
Possible solutions
It has been proposed that dark energy and dark matter are related in some way. In quintessence models, an additional quintessence field provides a link between the energy contributions from matter and dark energy.[1]
See also
Reference
- ^ a b O’Raifeartaigh, Cormac; O’Keeffe, Michael; Nahm, Werner; Mitton, Simon (2018-04-01). "One hundred years of the cosmological constant: from "superfluous stunt" to dark energy". The European Physical Journal H. 43 (1): 73–117. arXiv:1711.06890. Bibcode:2018EPJH...43...73O. doi:10.1140/epjh/e2017-80061-7. ISSN 2102-6467.
- ^ a b c Velten, H. E. S.; vom Marttens, R. F.; Zimdahl, W. (2014-11-22). "Aspects of the cosmological "coincidence problem"". The European Physical Journal C. 74 (11): 3160. arXiv:1410.2509. Bibcode:2014EPJC...74.3160V. doi:10.1140/epjc/s10052-014-3160-4. ISSN 1434-6052.
- ^ Steinhardt, P. J. (1997). Critical Problems in Physics. Princeton, NJ: Princeton University Press.
- ^ Barreiro, T.; Copeland, E. J.; Nunes, N. J. (2000). "Quintessence arising from exponential potentials". Physical Review D. 61 (12) 127301. arXiv:astro-ph/9910214. Bibcode:2000PhRvD..61l7301B. doi:10.1103/PhysRevD.61.127301.
- ^ Deur, Alexandre (2009). "Implications of Graviton-Graviton Interaction to Dark Matter". Physics Letters B. 676 (1–3): 21–24. arXiv:0901.4005. Bibcode:2009PhLB..676...21D. doi:10.1016/j.physletb.2009.04.060.
- ^ De Felice, Antonio; Tsujikawa, Shinji (2010). "f(R) theories". Living Reviews in Relativity. 13 (1): 3. arXiv:1002.4928. Bibcode:2010LRR....13....3D. doi:10.12942/lrr-2010-3. PMC 5255939. PMID 28179828.
- ^ Planck Collaboration; Aghanim, N.; Akrami, Y.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Ballardini, M.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Basak, S.; Battye, R.; Benabed, K.; Bernard, J.-P.; Bersanelli, M. (2020). "Planck 2018 results: VI. Cosmological parameters". Astronomy & Astrophysics. 641: A6. arXiv:1807.06209. Bibcode:2020A&A...641A...6P. doi:10.1051/0004-6361/201833910. ISSN 0004-6361.
- ^ Zlatev, Ivaylo; Steinhardt, Paul J. (1999-07-29). "A tracker solution to the cold dark matter cosmic coincidence problem". Physics Letters B. 459 (4): 570–574. arXiv:astro-ph/9906481. Bibcode:1999PhLB..459..570Z. doi:10.1016/S0370-2693(99)00707-8. ISSN 0370-2693.