The Big Bang theory is the prevailing cosmological model that explains the origin and evolution of the universe. According to this theory, the universe began as a singularity—a point of infinite density and temperature. As the universe rapidly expanded from this initial state, it underwent a series of transformations that eventually led to the formation of particles and atoms.
In the very early stages of the universe, the conditions were incredibly hot and dense. The energy in the form of high-energy photons (particles of light) dominated the universe. As the universe expanded and cooled down, these photons started to lose energy. At a certain point, the temperature dropped enough for the energy to convert into matter.
During this process, particle-antiparticle pairs were spontaneously created and annihilated due to the high-energy environment. This phenomenon is known as particle-antiparticle pair production. Occasionally, when a particle and its corresponding antiparticle collided, they would annihilate each other, releasing energy in the form of photons. However, as the universe continued to cool, there was insufficient energy available to recreate these annihilated particles. This resulted in a slight excess of matter particles over antimatter particles.
As the universe continued to expand and cool further, the temperature dropped to a point where the energy was no longer sufficient to create particle-antiparticle pairs. At this stage, the universe consisted primarily of photons and a small number of matter particles, such as protons and neutrons.
The next significant event in the formation of atoms was the process known as recombination. Roughly 380,000 years after the Big Bang, the universe had cooled to a temperature of about 3,000 Kelvin (around 2,726 degrees Celsius or 4,940 degrees Fahrenheit). At this point, the electrons and protons in the universe combined to form neutral hydrogen atoms. This process allowed photons to travel freely without being constantly scattered by charged particles. As a result, the universe became transparent to light, and the cosmic microwave background radiation, which is the remnant of the early hot and dense universe, was released.
In summary, the Big Bang theory suggests that the initial high-energy conditions of the universe allowed for the creation of particle-antiparticle pairs. As the universe expanded and cooled, these pairs annihilated each other, leaving behind a slight excess of matter particles. Eventually, as the universe cooled further, protons and neutrons combined to form atoms, primarily hydrogen. These processes marked the early stages of particle and atom formation in the universe as we know it today.