How old is the universe?
The universe is about 13.8 billion years old. Scientists calculate this from measurements of the cosmic microwave background, the faint afterglow of the Big Bang.
The most precise estimate comes from the Planck space telescope, which mapped the cosmic microwave background between 2009 and 2013. By comparing the patterns in this ancient light with models of how the universe evolved, scientists worked out an age of about 13.8 billion years, with an uncertainty of only tens of millions of years.
Other methods give similar answers. Astronomers measure how fast galaxies are moving away from us and calculate how long they have been spreading out. They also study the oldest stars, found in tight groups called globular clusters, which appear to be around 12 to 13 billion years old, which fits with a universe slightly older than them.
A puzzle in the numbers
Different ways of measuring the expansion rate of the universe, called the Hubble constant, give slightly different results. This mismatch, known as the Hubble tension, is one of the biggest open questions in cosmology. It does not change the age much, but it may point to new physics.
Did You Know?
Earth is about 4.5 billion years old, so the universe had already existed for roughly 9 billion years before our planet formed.