How do astronomers know the age of the universe?
Quick Answer
They estimate it from the expansion rate of the universe and the physics seen in the cosmic microwave background. The best current value is about 13.8 billion years.
The Full Story
The age of the universe is inferred mainly from measurements of the cosmic microwave background, the afterglow of the Big Bang, combined with the universe’s expansion rate. Space missions such as WMAP and Planck mapped tiny temperature variations in that radiation, allowing cosmologists to fit a detailed model. The Planck mission’s 2018 results gave an age of about 13.8 billion years. That number is not guessed from a single observation; it comes from multiple lines of evidence that agree remarkably well.
Key Facts
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