Age of the universe

In physical cosmology, the age of the universe is the time elapsed since the Big Bang. Astronomers have derived two different measurements of the age of the universe:^[1] a measurement based on direct observations of an early state of the universe, which indicate an age of 13.787±0.020 billion years as interpreted with the Lambda-CDM concordance model as of 2021;^[2] and a measurement based on the observations of the local, modern universe, which suggest a younger age.^[3]^[4]^[5] The uncertainty of the first kind of measurement has been narrowed down to 20 million years, based on a number of studies that all show similar figures for the age. These studies include researches of the microwave background radiation by the Planck spacecraft, the Wilkinson Microwave Anisotropy Probe and other space probes. Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang,^[6] and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time. The range of the estimate is also within the range of the estimate for the oldest observed star in the universe.

^ "From an almost perfect Universe to the best of both worlds". Planck mission. sci.esa.int. European Space Agency. 17 July 2018. last paragraphs. Archived from the original on 13 April 2020.
^ 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.
^ Riess, Adam G.; Casertano, Stefano; Yuan, Wenlong; Macri, Lucas; Bucciarelli, Beatrice; Lattanzi, Mario G.; et al. (12 July 2018). "Milky Way cepheid standards for measuring cosmic distances and application to Gaia DR2: Implications for the Hubble constant". The Astrophysical Journal. 861 (2): 126. arXiv:1804.10655. Bibcode:2018ApJ...861..126R. doi:10.3847/1538-4357/aac82e. ISSN 1538-4357. S2CID 55643027.
^ ESA/Planck Collaboration (17 July 2018). "Measurements of the Hubble constant". sci.esa.int. European Space Agency. Archived from the original on 6 October 2020.
^ Freedman, Wendy L.; Madore, Barry F.; Hatt, Dylan; Hoyt, Taylor J.; Jang, In-Sung; Beaton, Rachael L.; et al. (29 August 2019). "The Carnegie-Chicago Hubble Program. VIII. An independent determination of the Hubble constant based on the tip of the red giant branch". The Astrophysical Journal. 882 (1): 34. arXiv:1907.05922. Bibcode:2019ApJ...882...34F. doi:10.3847/1538-4357/ab2f73. ISSN 1538-4357. S2CID 196623652.
^ Bennett, C.L.; et al. (2013). "Nine-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: Final maps and results". The Astrophysical Journal Supplement Series. 208 (2): 20. arXiv:1212.5225. Bibcode:2013ApJS..208...20B. doi:10.1088/0067-0049/208/2/20. S2CID 119271232.

[1] "From an almost perfect Universe to the best of both worlds". Planck mission. sci.esa.int. European Space Agency. 17 July 2018. last paragraphs. Archived from the original on 13 April 2020.

[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.

[3] Riess, Adam G.; Casertano, Stefano; Yuan, Wenlong; Macri, Lucas; Bucciarelli, Beatrice; Lattanzi, Mario G.; et al. (12 July 2018). "Milky Way cepheid standards for measuring cosmic distances and application to Gaia DR2: Implications for the Hubble constant". The Astrophysical Journal. 861 (2): 126. arXiv:1804.10655. Bibcode:2018ApJ...861..126R. doi:10.3847/1538-4357/aac82e. ISSN 1538-4357. S2CID 55643027.

[4] ESA/Planck Collaboration (17 July 2018). "Measurements of the Hubble constant". sci.esa.int. European Space Agency. Archived from the original on 6 October 2020.

[5] Freedman, Wendy L.; Madore, Barry F.; Hatt, Dylan; Hoyt, Taylor J.; Jang, In-Sung; Beaton, Rachael L.; et al. (29 August 2019). "The Carnegie-Chicago Hubble Program. VIII. An independent determination of the Hubble constant based on the tip of the red giant branch". The Astrophysical Journal. 882 (1): 34. arXiv:1907.05922. Bibcode:2019ApJ...882...34F. doi:10.3847/1538-4357/ab2f73. ISSN 1538-4357. S2CID 196623652.

[arxiv-20121220-6] Bennett, C.L.; et al. (2013). "Nine-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: Final maps and results". The Astrophysical Journal Supplement Series. 208 (2): 20. arXiv:1212.5225. Bibcode:2013ApJS..208...20B. doi:10.1088/0067-0049/208/2/20. S2CID 119271232.

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