The Big Bang Theory is a scientific idea explaining how the universe began and developed. Around 13.8 billion years ago, the entire universe was incredibly hot and packed into a tiny space, called a singularity.
Then, suddenly, it started expanding and cooling down. This expansion created the basic building blocks of matter, like hydrogen and helium. As things cooled even more, these building blocks formed stars and galaxies.
The proof for this theory comes from things like the cosmic microwave background radiation, a faint glow spread throughout the universe. Scientists have studied this theory a lot, and while it explains a lot about the universe, there are still things we’re trying to figure out, like dark matter and dark energy.