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Big Bang scientific theory

The Big Bang theory is the prevailing cosmological model that describes the early development of the Universe. According to the theory, the Big Bang occurred approximately 13.75 billion years ago, after which time the Universe was in an extremely hot and dense state and began expanding rapidly. After the initial expansion, the Universe cooled sufficiently to allow energy to be converted into various subatomic particles, including protons, neutrons, and electrons. Though simple atomic nuclei could have formed quickly, thousands of years would have been needed before the appearance of the first electrically neutral atoms. The first element produced would have been hydrogen, along with traces of helium and lithium.