Age of the universe

In Big Bang models of physical cosmology, the age of the universe is the cosmological time back to the point when the scale factor of the universe extrapolates to zero.^[1] Modern models calculate the age now as 13.79 billion years.^[2] Astronomers have two different approaches to determine the age of the universe. One is based on a particle physics model of the early universe called Lambda-CDM, matched to measurements of the distant, and thus old features, like the cosmic microwave background. The other is based on the distance and relative velocity of a series or "ladder" of different kinds of stars, making it depend on local measurements late in the history of the universe.^[3] These two methods give slightly different values for the Hubble constant, which is then used in a formula to calculate the age. The range of the estimate is also within the range of the estimate for the oldest observed star in the universe.^[4]

^ Kolb, Edward; Turner, Michael S. (2018). The Early Universe. Boulder: Chapman and Hall/CRC. ISBN 978-0-201-62674-2.
^ Planck Collaboration (2020). "Planck 2018 results. VI. Cosmological parameters". Astronomy & Astrophysics. 641. page A6 (see PDF page 15, Table 2: "Age/Gyr", last column). arXiv:1807.06209. Bibcode:2020A&A...641A...6P. doi:10.1051/0004-6361/201833910. S2CID 119335614.
^ Verde, Licia; Schöneberg, Nils; Gil-Marín, Héctor (13 September 2024). "A Tale of Many H0". Annual Review of Astronomy and Astrophysics. 62: 287–331. doi:10.1146/annurev-astro-052622-033813. ISSN 0066-4146.
^ Vagnozzi, Sunny; Pacucci, Fabio; Loeb, Abraham (1 November 2022). "Implications for the Hubble tension from the ages of the oldest astrophysical objects". Journal of High Energy Astrophysics. 36: 27–35. arXiv:2105.10421. Bibcode:2022JHEAp..36...27V. doi:10.1016/j.jheap.2022.07.004. ISSN 2214-4048.

[KolbTurner-1] Kolb, Edward; Turner, Michael S. (2018). The Early Universe. Boulder: Chapman and Hall/CRC. ISBN 978-0-201-62674-2.

[Planck_2018-2] Planck Collaboration (2020). "Planck 2018 results. VI. Cosmological parameters". Astronomy & Astrophysics. 641. page A6 (see PDF page 15, Table 2: "Age/Gyr", last column). arXiv:1807.06209. Bibcode:2020A&A...641A...6P. doi:10.1051/0004-6361/201833910. S2CID 119335614.

[VerdeReview2024-3] Verde, Licia; Schöneberg, Nils; Gil-Marín, Héctor (13 September 2024). "A Tale of Many H0". Annual Review of Astronomy and Astrophysics. 62: 287–331. doi:10.1146/annurev-astro-052622-033813. ISSN 0066-4146.

[4] Vagnozzi, Sunny; Pacucci, Fabio; Loeb, Abraham (1 November 2022). "Implications for the Hubble tension from the ages of the oldest astrophysical objects". Journal of High Energy Astrophysics. 36: 27–35. arXiv:2105.10421. Bibcode:2022JHEAp..36...27V. doi:10.1016/j.jheap.2022.07.004. ISSN 2214-4048.

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