Explain the big bang theory as it relates to the atom and its evolution?

I will summarize a very long explanation by saying that energy was all that existed at the time of the big bang, and this is where Einstein's theory of special relativity comes into play.

Therefore, the universe underwent an extremely rapid expansion very soon after the big bang, estimated to have doubled in size to half in a matter of seconds, if not less.

We don't know when things like quarks, mesons, bosons, and other subatomic particles came into existence, but at that point, all the hot energy in the universe started to slowly cool down and eventually gathered into atoms.

Consider it this way: everything was moving at the speed of light and, therefore, very hot on the first day following the big bang. However, because everything was so close together, heat energy was constant.

Imagine boiling water: if you take it outside in below-freezing temperatures, it will gradually cool down until it reaches its solid point. This is similar to how the universe began to slow down and cool down when it suddenly expanded, giving all this energy more space to move around.

The Big Bang theory explains how the universe came to be from a hot, dense state. It has nothing to do with how individual atoms evolved, but in the early universe, high temperatures made it possible for simple atomic nuclei to form. As the universe expanded and cooled, atoms formed by nuclear fusion. Eventually, these atoms came together to form stars and galaxies, which had an impact on the evolution of matter in the universe.

The Big Bang theory is a scientific explanation for the origin and evolution of the universe. According to this theory, the universe began as a singularity—a point of infinite density and temperature—and has been expanding and cooling ever since. As the universe expanded and cooled, subatomic particles like protons, neutrons, and electrons formed. These particles eventually combined to form atoms, the building blocks of matter.

In the early universe, conditions were extremely hot and dense, preventing atoms from forming. Instead, the universe consisted of a hot, ionized plasma of protons, electrons, and other particles. As the universe continued to expand and cool, it eventually reached a point where atoms could form. This process, known as recombination, occurred about 380,000 years after the Big Bang.

The first atoms to form were hydrogen and helium, the simplest and most abundant elements in the universe. Over time, these atoms clumped together under the influence of gravity to form clouds of gas. Within these clouds, the first stars and galaxies began to form through a process known as gravitational collapse.

Inside stars, nuclear fusion reactions converted hydrogen and helium into heavier elements like carbon, oxygen, and iron. When these stars reached the end of their life cycles, they expelled these heavier elements into space in massive explosions called supernovae. These ejected materials eventually mixed with other gas clouds, forming new stars, planets, and eventually, life.

In summary, the Big Bang theory explains how the universe began as a hot, dense singularity and has since expanded and cooled, leading to the formation of atoms, stars, galaxies, and ultimately, the diverse universe we observe today.