Bang dating space
The universe continued to decrease in density and fall in temperature, hence the typical energy of each particle was decreasing.
Symmetry breaking phase transitions put the fundamental forces of physics and the parameters of elementary particles into their present form.
More recently, measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating, an observation attributed to dark energy's existence.
In 1964 the cosmic microwave background radiation was discovered, which was crucial evidence in favor of the Big Bang model, since that theory predicted the existence of background radiation throughout the universe before it was discovered.
Based on measurements of the expansion using Type Ia supernovae and measurements of temperature fluctuations in the cosmic microwave background, the time that has passed since that event, otherwise known as the "age of the universe" is 13.799 ± 0.021 billion years.
The earliest phases of the Big Bang are subject to much speculation.
Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed.
The majority of atoms produced by the Big Bang were hydrogen, along with helium and traces of lithium.