The Big Bang theory is the leading explanation for the origin of the universe. It suggests that the universe began as an extremely hot and dense point approximately 13.8 billion years ago and has been expanding ever since. This expansion is evidenced by the redshift of distant galaxies, indicating that they are moving away from us. As the universe expanded, it cooled, allowing for the formation of subatomic particles and later simple atoms. Over time, these atoms coalesced to form stars and galaxies, leading to the complex structure we observe today. The Big Bang remains a fundamental concept in understanding the cosmos.