Dark Energy

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In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the universe does not expand at a constant rate; rather, the universe's expansion is accelerating.[1][2] Understanding the universe's evolution requires knowledge of its starting conditions and composition. Before these observations, scientists thought that all forms of matter and energy in the universe would only cause the expansion to slow down over time. Measurements of the cosmic microwave background (CMB) suggest the universe began in a hot Big Bang, from which general relativity explains its evolution and the subsequent large-scale motion. Without introducing a new form of energy, there was no way to explain an accelerating expansion of the universe. Since the 1990s, dark energy has been the most accepted premise to account for the accelerated expansion. As of 2021, there are active areas of cosmology research to understand the fundamental nature of dark energy.[3] Assuming that the lambda-CDM model of cosmology is correct,[4] as of 2013, the best current measurements indicate that dark energy contributes 68% of the total energy in the present-day observable universe. The mass–energy of dark matter and ordinary (baryonic) matter contributes 26% and 5%, respectively, and other components such as neutrinos and photons contribute a very small amount.[5][6][7][8] Dark energy's density is very low: 6×10−10 J/m3 (~7×10−30 g/cm3), much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the universe's mass–energy content because it is uniform across space.[9][10][11]

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Two proposed forms of dark energy are the cosmological constant[12][13] (representing a constant energy density filling space homogeneously) and scalar fields (dynamic quantities having energy densities that vary in time and space) such as quintessence or moduli. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant can be formulated to be equivalent to the zero-point radiation of space, i.e., the vacuum energy.[14] However, scalar fields that change in space can be difficult to distinguish from a cosmological constant because the change may be prolonged.

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Due to the toy model nature of concordance cosmology, some experts believe[15] that a more accurate general relativistic treatment of the structures on all scales[16] in the real universe may do away with the need to invoke dark energy. Inhomogeneous cosmologies, which attempt to account for the back-reaction of structure formation on the metric, generally do not acknowledge any dark energy contribution to the universe's energy density.

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Recent Research Papers

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• Probing Dark Energy and Modifications of Gravity with Ground-Based Millimeter-Wavelength Line Intensity Mapping.  Azadeh Moradinezhad Dizgah, Emilio Bellini, Garrett K. Keating (2023) 

• Using Dark Energy Explorers and Machine Learning to Enhance the Hobby-Eberly Telescope Dark Energy Experiment.  Lindsay R. House, Karl Gebhardt, Keely Finkelstein, Erin Mentuch Cooper, Dustin Davis, Robin Ciardullo, Daniel J Farrow, Steven L. Finkelstein, Caryl Gronwall, Donghui Jeong, L. Clifton Johnson, Chenxu Liu, Benjamin P. Thomas, Gregory Zeimann.  (2023)

• Big Bang initial conditions and self-interacting hidden dark matter.  Jinzheng Li, Pran Nath (2023)

• Superfluid Dark Matter around Black Holes.  Valerio De Luca, Justin Khoury.  (2023)

• The effects of dark energy on the propagation of gravitational waves.  Antonio Enea Romano (2023)

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References

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 [1]  Overbye, Dennis (20 February 2017). "Cosmos Controversy: The Universe Is Expanding, but How Fast?". The New York Times. Archived from the original on 4 April 2019. Retrieved 21 February 2017.

[2]  Peebles, P. J. E.; Ratra, Bharat (2003). "The cosmological constant and dark energy". Reviews of Modern Physics. 75 (2): 559–606. arXiv:astro-ph/0207347. Bibcode:2003RvMP...75..559P. doi:10.1103/RevModPhys.75.559. S2CID 118961123.

[3]  Overbye, Dennis (25 February 2019). "Have Dark Forces Been Messing With the Cosmos? – Axions? Phantom energy? Astrophysicists scramble to patch a hole in the universe, rewriting cosmic history in the process". The New York Times. Archived from the original on 30 April 2020. Retrieved 26 February 2019.

[4]  Idicherian Lonappan, Anto; Kumar, Sumit; R, Ruchika; Ananda Sen, Anjan (21 February 2018). "Bayesian evidences for dark energy models in light of current observational data". Physical Review D. 97 (4): [5]  Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.; et al. (Planck Collaboration) (22 March 2013). "Planck 2013 results. I. Overview of products and scientific results – Table 9". Astronomy and Astrophysics. 571: A1. arXiv:1303.5062. Bibcode:2014A&A...571A...1P. doi:10.1051/0004-6361/201321529. S2CID 218716838.

[5]  Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.; et al. (Planck Collaboration) (31 March 2013). "Planck 2013 Results Papers". Astronomy and Astrophysics. 571: A1. arXiv:1303.5062. Bibcode:2014A&A...571A...1P. doi:10.1051/0004-6361/201321529. S2CID 218716838. Archived from the original on 23 March 2013.

[6]  Jump up to:a b 

[7]  "First Planck results: the Universe is still weird and interesting". 21 March 2013. Archived from the original on 2 May 2019. Retrieved 14 June 2017.

[8]  Sean Carroll, Ph.D., Caltech, 2007, The Teaching Company, Dark Matter, Dark Energy: The Dark Side of the Universe, Guidebook Part 2 page 46. Retrieved 7 October 2013, "...dark energy: A smooth, persistent component of invisible energy, thought to make up about 70 percent of the current energy density of the universe. Dark energy is known to be smooth because it doesn't accumulate preferentially in galaxies and clusters..."

[9]  Paul J. Steinhardt; Neil Turok (2006). "Why the cosmological constant is small and positive". Science. 312 (5777): 1180–1183. arXiv:astro-ph/0605173. Bibcode:2006Sci...312.1180S. doi:10.1126/science.1126231. PMID 16675662. S2CID 14178620.

[10]  "Dark Energy". Hyperphysics. Archived from the original on 27 May 2013. Retrieved 4 January 2014.

[11]  Ferris, Timothy (January 2015). "Dark Matter(Dark Energy)". Archived from the original on 10 June 2015. Retrieved 10 June 2015.

[12]  "Moon findings muddy the water". Archived from the original on 22 November 2016. Retrieved 21 November 2016.

]13]  Jump up to:a b Carroll, Sean (2001). "The cosmological constant". Living Reviews in Relativity. 4 (1): 1. arXiv:astro-ph/0004075. Bibcode:2001LRR.....4....1C. doi:10.12942/lrr-2001-1. PMC 5256042. PMID 28179856. Archived from the original on 13 October 2006. Retrieved 28 September 2006.

[13]  Kragh, H (2012). "Preludes to dark energy: zero-point energy and vacuum speculations". Archive for History of Exact Sciences. 66 (3): 199–240. arXiv:1111.4623. doi:10.1007/s00407-011-0092-3. S2CID 118593162.

[15]  Buchert, T; Carfora, M; Ellis, G F R; Kolb, E W; MacCallum, M A H; Ostrowski, J J; Räsänen, S; Roukema, B F; Andersson, L; Coley, A A; Wiltshire, D L (5 November 2015). "Is there proof that backreaction of inhomogeneities is irrelevant in cosmology?". Classical and Quantum Gravity. 32 (21): 215021. arXiv:1505.07800. Bibcode:2015CQGra..32u5021B. doi:10.1088/0264-9381/32/21/215021. ISSN 0264-9381. S2CID 51693570.

[16]  Clarkson, Chris; Ellis, George; Larena, Julien; Umeh, Obinna (1 November 2011). "Does the growth of structure affect our dynamical models of the Universe? The averaging, backreaction, and fitting problems in cosmology". Reports on Progress in Physics. 74 (11): 112901. arXiv:1109.2314. doi:10.1088/0034-4885/74/11/112901. ISSN 0034-4885. S2CID 55761442.