The Big Bang theory provides an explanation for the origin and evolution of the universe. According to this theory, the universe began as an extremely hot and dense state, often referred to as a singularity. As the universe expanded and cooled, various processes occurred that eventually led to the formation of atoms and particles.
In the early stages of the universe, during a phase called the "inflationary epoch," the rapid expansion caused the universe to cool down significantly. This cooling allowed energy to convert into matter and antimatter particles. However, due to an imbalance between matter and antimatter, a small excess of matter particles remained. This excess matter formed the building blocks for the atoms we observe today.
After this initial phase, the universe continued to expand and cool further. As it expanded, the density and temperature decreased, enabling the formation of more complex structures. Atoms, which consist of a nucleus composed of protons and neutrons, surrounded by electrons, eventually formed. These atoms started to combine through gravitational attraction, leading to the formation of stars, galaxies, and larger cosmic structures.
While the early universe experienced significant changes and breakdown of its earliest characteristics, the fundamental laws of physics, such as conservation of energy and conservation of matter, allowed for the preservation and transformation of matter and energy over time. The processes of fusion and nuclear reactions within stars, for example, continue to generate new elements and maintain the existence of atoms.
It's important to note that the evolution of the universe is a complex and ongoing process. Over billions of years, various astrophysical phenomena and interactions have shaped the distribution and behavior of matter and particles. While the universe has changed and undergone transformations since the initial moments of the Big Bang, the conservation laws and physical principles still govern the existence and persistence of atoms and particles in the universe as we observe them today.