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The Big Bang

The Big Bang is a physical theory that describes how the universe expanded from an early state of high density and temperature. Our universe began about 13.787±0.02 billion years ago and has been expanding and cooling ever since. During the earliest moments, the universe underwent cosmic inflation—an extraordinarily brief period of accelerated expansion—followed by a "hot Big Bang" where matter and antimatter particles constantly formed and destroyed each other. As the universe cooled, atoms formed and eventually coalesced under gravity to create stars and galaxies. The Big Bang matters because it explains key observations like the cosmic microwave background radiation, why galaxies move away from each other, and the abundance of elements we observe today.

Sources

• en.wikipedia.org: “The Big Bang is a physical theory that describes how the universe expanded from an early state of high density and temperature.”
• en.wikipedia.org: “Detailed measurements of the expansion rate of the universe place the cosmic inflation at an estimated 13.787±0.02 billion years ago, which is considered the age of the universe.”
• en.wikipedia.org: “Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, the redshift of galaxies and the large-scale structure of the universe.”