The prevailing theory for the origin and evolution of the universe is the Big Bang theory. According to this theory, the universe began as a singularity—a state of infinite density and temperature—approximately 13.8 billion years ago. The Big Bang marked the beginning of both space and time.
In the early moments after the Big Bang, the universe underwent a rapid expansion known as cosmic inflation. This expansion caused the universe to grow exponentially and smoothed out irregularities in the distribution of matter and energy.
As the universe expanded and cooled, matter and energy began to form. Quarks combined to form protons and neutrons, and eventually, the first atomic nuclei formed. Over time, matter continued to condense and clump together under the influence of gravity, giving rise to the formation of stars and galaxies.
Around 380,000 years after the Big Bang, the universe had cooled enough for electrons to combine with atomic nuclei, forming neutral atoms. This event, known as recombination, allowed light to travel freely through space, resulting in the cosmic microwave background radiation—the afterglow of the early universe—which can still be observed today.
Over billions of years, galaxies, clusters of galaxies, and other cosmic structures continued to form through gravitational interactions. The universe also underwent a process of expansion, driven by a mysterious force called dark energy. This accelerated expansion is supported by observational evidence, such as the redshift of light from distant galaxies.
While the Big Bang theory provides a comprehensive framework for understanding the origin and evolution of the universe, there are still many open questions in cosmology. Scientists continue to investigate phenomena such as dark matter, dark energy, and the nature of the singularity itself in order to deepen our understanding of the universe's history.