The Big Bang Theory: Origins of the Universe Explained

The Big Bang theory says the universe began about 13.8 billion years ago from an extremely hot, dense state.
It wasn’t an explosion in space, but an expansion of space itself.
In the first moments, matter, energy, space, and time all came into being.
Tiny fluctuations in the early universe seeded the formation of galaxies.
The cosmic microwave background is leftover radiation from about 380,000 years after the Big Bang.
The universe has been expanding ever since, with galaxies moving farther apart.
Abundances of hydrogen and helium today match predictions from Big Bang nucleosynthesis.
Edwin Hubble’s discovery of galaxy redshifts in the 1920s first confirmed cosmic expansion.
The theory is supported by multiple lines of evidence, making it the leading model of cosmic origins.
While it explains how the universe evolved, what triggered the Big Bang remains a mystery.