Ten or twenty billion years ago, something happened—the Big Bang, the event that began our universe. Why it happened is the greatest mystery... That it happened is reasonably clear. All the matter in the universe was concentrated at extremely high density—a kind of cosmic egg, reminiscent of the creation myths of many cultures—perhaps into a mathematical point with no dimensions at all.

Carl Edward Sagan (9 November 1934 – 20 December 1996) was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator. His best known scientific contribution is research on extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation. Sagan assembled the first physical messages sent into space, the Pioneer plaque and the Voyager Golden Record, universal messages that could potentially be understood by any extraterrestrial intelligence that might find them. Sagan argued the hypothesis, accepted since, that the high surface temperatures of Venus can be attributed to, and calculated using, the greenhouse effect. He testified to the US Congress in 1985 that the greenhouse effect will change the earth's climate system.