Introduction:
The concept of time and space as we understand it today may not apply before the start of the universe. It is important to note that our understanding of the universe's origins is based on scientific theories and observations, which are constantly evolving. With that in mind, let's explore the prevailing theory of the Big Bang and how the universe may have come into existence.

The Big Bang Theory:
The Big Bang theory is the prevailing explanation for the origin of the universe. According to this theory, the universe began as an extremely hot and dense point, often referred to as a singularity. However, it is still unclear what caused this singularity to exist.

The Expansion of the Universe:
After the singularity, the universe rapidly expanded and continues to expand to this day. This expansion is supported by various observations, such as the redshift of distant galaxies, which indicates that they are moving away from us.

Inflationary Period:
Shortly after the initial expansion, scientists believe there was a period of rapid expansion called cosmic inflation. During this time, the universe expanded exponentially, stretching out space itself. This rapid expansion could explain the uniformity of the cosmic microwave background radiation observed throughout the universe.

Formation of Atoms:
As the universe expanded and cooled, the energy density decreased, allowing particles to form. Initially, the universe was filled with a hot plasma of particles, mainly consisting of protons and electrons.

Nucleosynthesis:
During a process called nucleosynthesis, the protons and neutrons combined to form the nuclei of atoms such as hydrogen and helium. However, it took some time for the universe to cool down enough for electrons to combine with these nuclei to form stable atoms.

Recombination:
Approximately 380,000 years after the Big Bang, the universe had cooled enough for electrons to combine with nuclei, a process known as recombination. This allowed photons to travel freely through space, resulting in the cosmic microwave background radiation we observe today.

Conclusion:
While the exact mechanisms behind the origin and expansion of the universe are still being studied, the Big Bang theory provides a framework for understanding the early moments of the universe. The concept of time and space as we know it may not apply before the Big Bang, making it difficult to comprehend the precise nature of the singularity. However, through scientific observations and theories, we continue to gain a deeper understanding of the universe's origins and evolution.