How is the universe different from today?

The universe today is vastly different from its early stages, specifically shortly after the Big Bang. Initially, it was a hot, dense plasma composed of fundamental particles, expanding rapidly. Over billions of years, it cooled, allowing atoms to form, leading to the creation of stars and galaxies. Today, the universe is structured with vast cosmic webs of galaxies, dark matter, and dark energy, and has evolved to exhibit complex phenomena like black holes and cosmic microwave background radiation.