What evidence supports the Big Bang theory?

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

One of the most compelling pieces of evidence for the Big Bang theory is the cosmic microwave background radiation (CMB). This is a faint glow of radiation that permeates the entire universe and is thought to be the leftover heat from the Big Bang. The CMB was first discovered in 1964 by Arno Penzias and Robert Wilson, and its properties match what would be expected from a hot, dense early universe.

Another piece of evidence comes from the abundance of light elements in the universe. The Big Bang theory predicts that the early universe was hot and dense enough for nuclear fusion to occur, producing helium, deuterium, and lithium. Observations of the relative abundances of these elements match what would be expected from the Big Bang, providing further support for the theory.

Finally, the observed expansion of the universe is consistent with the Big Bang theory. In the 1920s, Edwin Hubble discovered that distant galaxies are moving away from us, and the farther away they are, the faster they are moving. This suggests that the universe is expanding, and if we run the clock backwards, we can infer that the universe must have started from a hot, dense state - the Big Bang.

Overall, the Big Bang theory is supported by a wealth of observational evidence, making it the most widely accepted model for the origin and evolution of the universe.