Within the first second, the universe cooled from incomprehensible heat to allow subatomic particles to form. Quarks combined into protons and neutrons, and fundamental forces began differentiating. Tiny irregularities in density formed the blueprint for galaxies. Particle interactions at this stage set the stage for all future matter. This ultra-brief period shaped everything from atoms to galaxy clusters.
It matters because the first second determined the universe’s basic structure and matter content.
It also provides insights into particle physics beyond Earthly laboratories.
The universe’s destiny was set in just one second after its birth.
NASA [nasa.gov]