What is the scientific method used to determine the age of the universe?

The age of the universe is primarily determined through a combination of observational evidence and theoretical models, particularly using the cosmic microwave background (CMB) radiation and the expansion rate of the universe. The CMB provides a snapshot of the early universe, while measurements of the Hubble constant, which describes the rate of expansion, help estimate the time elapsed since the Big Bang. By analyzing these data alongside models of cosmic evolution, scientists estimate the universe to be approximately 13.8 billion years old.