How old is the universe?

The story behind the answer

The universe is about 13.8 billion years old, determined by measuring its expansion and the afterglow of the Big Bang, the cosmic microwave background. Satellites like WMAP and Planck mapped tiny temperature ripples in this radiation; when fitted with the standard cosmological model, they yield an age of roughly 13.8 billion years. Independent checks, such as the ages of the oldest star clusters and radioactive dating of ancient stars, agree.