The Long Cosmic Night After the Big Bang, the universe began in fire. For hundreds of thousands of years, it was a sea of hot plasma, glowing but opaque, like a star stretched across infinity. Then came a moment called recombination, about 380,000 years after the beginning. Protons and electrons cooled enough to join together into atoms of hydrogen and helium. For the first time, light was free to travel. This light still exists today—the cosmic microwave background—a faint glow left over from that ancient moment. But though the universe was now transparent, it was dark. No stars