The Big Bang theory posits that the universe began as a singularity, a point of infinite density and temperature, around 13.8 billion years ago. This singularity rapidly expanded, leading to the formation of basic particles like protons, neutrons, and electrons. As the universe cooled, these particles combined to form the first atoms, primarily hydrogen and helium. Over time, gravitational forces caused these atoms to clump together, forming clouds of gas that eventually gave rise to the first stars and galaxies.
These early stars, through nuclear fusion, synthesized heavier elements, enriching the universe's elemental composition. Subsequent generations of stars, planets, and galaxies formed from these elements, culminating in the vast and diverse universe we observe today. The Big Bang theory provides a comprehensive framework for understanding the universe's origin, evolution, and the formation of the fundamental structures we see in the cosmos.