The universe is approximately 13.8 billion years old.
en.wikipedia.org
The most precise estimate, based on the Planck satellite's 2018 data (which analyzed the cosmic microwave background, or CMB), is 13.787 ± 0.020 billion years.
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This aligns with other observations, such as those from the Atacama Cosmology Telescope (ACT), which also support around 13.8 billion years.
aau.edu
How We Know ThisScientists determine the universe's age primarily through the ΛCDM model (Lambda Cold Dark Matter), the standard model of cosmology. Key methods include:Cosmic Microwave Background (CMB): This is leftover radiation from ~380,000 years after the Big Bang. Satellites like Planck and WMAP map tiny temperature fluctuations in the CMB to infer the universe's expansion history, composition (ordinary matter, dark matter, dark energy), and age.
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Hubble Constant (H₀) and Expansion Rate: By measuring how galaxies recede (via redshift) and using the cosmic distance ladder (e.g., Cepheid variables, supernovae), we back-calculate to the Big Bang. Uncertainties in H₀ measurements create minor "tensions," but they generally point to ~13.8 billion years.
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Oldest Stars and Other Checks: The ages of the oldest stars (e.g., in globular clusters) and white dwarfs provide lower limits consistent with this figure. Nucleosynthesis (element formation in the early universe) also matches.
magiscenter.com
Notes on Alternatives and UncertaintiesA few fringe or alternative models (e.g., one proposing ~26.7 billion years) have been suggested, often by tweaking assumptions about expansion or tired light, but these are not widely accepted and conflict with overwhelming evidence from CMB, supernovae, and large-scale structure.
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The value has high confidence (~1% uncertainty) but isn't exact due to factors like dark energy and potential new physics. Future missions (e.g., JWST, Euclid) continue refining it.
magiscenter.com
In short, 13.8 billion years (often rounded) is the robust scientific consensus. This timeline places the Big Bang at the start, followed by the formation of the first stars, galaxies, and eventually our solar system ~4.6 billion years ago.