The Big Bang theory is the prevailing scientific explanation for the origin and early development of the universe. According to this theory, the universe began as an extremely hot and dense point called a singularity around 13.8 billion years ago. From this singularity, the universe rapidly expanded and cooled, leading to the formation of matter and the subsequent evolution of galaxies, stars, and other celestial structures.
Immediately after the Big Bang, the universe was in a state of extremely high energy and temperature, consisting primarily of subatomic particles such as quarks, leptons, and photons. As the universe expanded and cooled, the energy converted into matter, resulting in the formation of protons, neutrons, and electrons.
Within the first few minutes after the Big Bang, a process called nucleosynthesis occurred. During nucleosynthesis, the high temperatures and densities allowed for the formation of light atomic nuclei, such as hydrogen and helium. These are the two most abundant elements in the universe, with hydrogen constituting about 75% and helium about 25% of the elemental composition.
As the universe continued to expand and cool, matter began to clump together under the influence of gravity. Over billions of years, these gravitational interactions led to the formation of larger structures like galaxies, galaxy clusters, and superclusters. Within galaxies, stars were born through the gravitational collapse of gas and dust clouds, and within stars, nuclear fusion processes created heavier elements, such as carbon, oxygen, and iron.
In summary, the Big Bang marked the beginning of the universe and initiated the formation of matter and energy. Through a series of physical processes, including nucleosynthesis, gravity-driven structure formation, and stellar evolution, the universe evolved to its current state, comprising galaxies, stars, planets, and various other cosmic structures.