How the universe began, its first seconds and minutes, and the evidence astronomers use — curriculum-shaped, with our own drawings and a public fact-check log. Where good sources disagree, we keep both in view.
The big-bang model, Britannica says, is a widely held theory of the evolution of the universe. Its essential feature is the emergence of the universe from a state of extremely high temperature and density — the so-called big bang that occurred 13.8 billion years ago. Britannica The Big Bang, Nobel laureate John Mather says in a NASA Q&A, is a really misleading name for the expanding universe that we see. NASA The universe doesn't have a center. The Big Bang happened everywhere at once and was a process happening in time, not a point in time. NASA
Some 13.8 billion years ago, that page says, the universe was a dense, tremendously hot (too hot for the existence of atoms), extremely tiny point that rapidly surged outward in all directions. NASA We can see the heat that was there at about 380,000 years after the expansion of the universe began 13.8 billion years ago (which, in that Q&A, is what is referred to as the Big Bang). NASA
The cosmic microwave background, a NASA Physics of the Cosmos page says, originated just 380,000 years after the Big Bang, when the Universe was dense, hot, and opaque. NASA The discovery of the 2.7 K cosmic microwave background radiation in 1965 by Arno Penzias and Robert Wilson was convincing evidence that the universe originated 13.8 billion years ago from a very dense and hot state in the big bang. Britannica
A simplified timeline of the early universe. The early steps are vastly closer together in real time than this line can show.Drawing: our own, simplified and not to scale