The age of the universe is estimated to be approximately 13.8 billion years. This value is based on scientific observations and measurements, primarily from the study of cosmic microwave background radiation, the rate of the universe's expansion, and the ages of the oldest known objects in the universe.
One of the key pieces of evidence supporting the age of the universe is the measurement of the cosmic microwave background (CMB) radiation. The CMB is the faint radiation left over from the early stages of the universe, which can be detected as a faint glow throughout the entire sky. Precise measurements of the CMB by satellite missions such as the Wilkinson Microwave Anisotropy Probe (WMAP) and the Planck spacecraft have provided valuable data about the composition, geometry, and age of the universe.
Additionally, the concept of an expanding universe plays a crucial role in determining its age. The observations of galaxies moving away from each other, as well as the measurement of the rate of expansion called the Hubble constant, indicate that the universe has been expanding since its early stages. By extrapolating backward in time, scientists have estimated the age of the universe to be around 13.8 billion years.
Other lines of evidence, such as the ages of the oldest star clusters and white dwarf stars, provide further support for the estimated age. These objects are thought to have formed shortly after the Big Bang, and their ages can be determined through various methods, including the measurement of radioactive isotopes.
It's important to note that our understanding of the universe's age is based on the current scientific knowledge and observations. As our understanding improves and new data becomes available, our estimates and theories may be refined. However, the age of 13.8 billion years is widely accepted within the scientific community and is supported by a substantial body of evidence.