ABSTRACT
During the first 300,000 years after the big bang, the universe was small and cramped, like the first twoholed torus near the top of Figure 19.2. The galaxies hadn’t yet formed, and hydrogen and helium gas filled the whole universe. This was no ordinary gas, though. Because all the energy of the universe was packed into such a small volume, the temperature was extremely high, in excess of 3000 K. At such high temperatures, electrons get knocked loose from their atoms, and the gas takes the form of a so-called plasma, consisting of ions, electrons, and radiation. In other words, the
whole universe was filled with a hot glowing sub stance much like the outer layers of the modern sun. If you could somehow take a (heat resistant!) time ma chine back to that era, you’d find yourself in a blazing hot fog.
