The Big Bang Theory is the leading explanation of how the universe began. It states that the universe started from an extremely hot and dense singularity approximately 13.8 billion years ago. This singularity then expanded rapidly, in what is called the Big Bang.At first, the universe was a hot, dense soup of particles like protons, neutrons, and electrons. As it expanded, it cooled down, allowing particles to form atoms. Over time, these atoms grouped together to form stars, galaxies, and all the structures we see in the universe today.Key evidence supporting the Big Bang includes:Cosmic Microwave Background Radiation: A faint glow left over from the early universe, detectable as background radiation.Redshift of Galaxies: Galaxies appear to be moving away from us, which suggests the universe is still expanding.Abundance of Light Elements: The proportions of hydrogen, helium, and lithium in the universe match predictions of the Big Bang model.The theory doesn't explain what caused the singularity or what happened before it, but it provides a solid framework for understanding the evolution of the universe from its earliest moments to its current state.