HOW OLD IS THE UNIVERSE, REALLY?
ANA CASTRO, VIA EMAIL
The age of the Universe can be derived by measuring its current rate of expansion and then extrapolating backwards. In practice, however, we also have to know how that expansion rate may have changed through time, and this is dictated by the matter composition and energy density of the Universe. Fortunately, this information is embedded in the tiny temperature fluctuations found in the cosmic microwave background, the faint glow of light that fills the Universe with residual heat left over from the Big Bang. The latest estimate, in 2021, sets the age of the Universe at 13.797 billion years, using the so-called Lambda-CDM concordance model of cosmology.