The Big Bang theory is bolstered by several lines of compelling evidence, including cosmic microwave background radiation, the abundance of light elements, and the observed expansion of the universe.

One of the most persuasive pieces of evidence for the Big Bang theory is the cosmic microwave background radiation (CMB). This faint glow of radiation fills the universe and is believed to be the residual heat from the Big Bang. The CMB was first detected in 1964 by Arno Penzias and Robert Wilson, and its characteristics align precisely with the predictions for a hot, dense early universe.

Another significant line of evidence pertains to the abundance of light elements found in the universe. The Big Bang theory posits that the early universe was sufficiently hot and dense to allow nuclear fusion to occur, resulting in the formation of helium, deuterium, and lithium. Observations of the relative abundances of these elements closely match the predicted outcomes from the Big Bang, offering additional support for the theory.

Lastly, the observed expansion of the universe lends further credence to the Big Bang model. In the 1920s, Edwin Hubble discovered that distant galaxies are receding from us, and the rate of their movement increases with distance. This observation implies that the universe is expanding; if we extrapolate this expansion backward in time, it suggests that the universe originated from a hot, dense state—often referred to as the Big Bang.

In summary, the Big Bang theory is underpinned by a robust body of observational evidence, rendering it the most widely accepted explanation for the origin and evolution of the universe.