Cosmology
Cosmology treats the entire universe as a single physical system and asks where it came from, what it's made of, and where it's going. The headline result is that space has been expanding for billions of years from a hot, dense beginning — a picture built from light that has traveled to us across that whole history, and described by Einstein's general relativity. A natural first question: exactly how old is it?
Drill down
Age of the Universe
The time since the Big Bang, about 13.8 billion years, pinned down by combining the expansion rate, the CMB, and the ages of the oldest stars.
Redshift
The stretching of light to longer, redder wavelengths as the universe expands; more distant objects are more redshifted.
Cosmic Timeline
The universe's history in epochs, from the first fraction of a second through inflation, the CMB, the first stars, and on to today.
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