A close pair of figures
How old is the universe?
The big-bang model, Britannica says, is a widely held theory of the evolution of the universe. Its essential feature is the emergence of the universe from a state of extremely high temperature and density — the so-called big bang that occurred 13.8 billion years ago. Britannica The discovery of the 2.7 K cosmic microwave background radiation in 1965 by Arno Penzias and Robert Wilson was convincing evidence that the universe originated 13.8 billion years ago from a very dense and hot state in the big bang. Britannica
WMAP, NASA says, determined the universe to be 13.77 billion years old to within a half percent. NASA A NASA illustration on the same page represents the evolution of the universe over 13.77 billion years. NASA
13.8, or 13.77?
Several of the pages we checked, including NASA’s Q&A with John Mather, a NASA Hubble page (“Some 13.8 billion years ago”), and Britannica, give the age of the universe as 13.8 billion years. A NASA WMAP overview says WMAP determined the universe to be 13.77 billion years old to within a half percent, and a NASA illustration on the Hubble page represents the evolution of the universe over 13.77 billion years. The figures are close. They are not the same wording, so both stay in view.
The universe's first stars were 30 to 300 times more massive than our Sun and millions of times brighter. NASA WMAP also showed, that article says, that the first stars in the universe formed half a billion years after the big bang. Britannica Mather says the tiny ripples of temperature they observed were the seeds that eventually grew into galaxies. We don't know exactly when the universe made the first stars and galaxies — or how. NASA
When did the first stars form?
A NASA overview says the universe’s first stars were 30 to 300 times more massive than our Sun and millions of times brighter. Britannica, citing WMAP, says the first stars formed half a billion years after the big bang. John Mather, in the NASA Q&A, says we don’t know exactly when the universe made the first stars and galaxies — or how — and that JWST was built to help answer that. We do not treat the date as settled.
New ideas and major discoveries made during the 20th century transformed cosmology, NASA says, although much remains unknown. NASA