The Big Bang theory is the prevailing cosmological model describing the early rapid expansion of the universe from an extremely hot, dense state. According to this framework, the cosmos began approximately 13.8 billion years ago and has been expanding and cooling ever since. In the initial moments, the universe was a superheated plasma dominated by fundamental particles. As time elapsed, energy underwent transformations, leading to the formation of subatomic particles, followed by atomic nuclei, primarily hydrogen and helium. The subsequent cooling allowed these nuclei to bind with electrons to form the first stable atoms. Over vast stretches of time, gravity caused these primordial clouds of gas to collapse into the first stars and galaxies, initiating the large-scale structure observed throughout the universe today, which continues to expand and cool.