Carl Edward Sagan (November 9, 1934 – December 20, 1996) was an American astronomer who pioneered exobiology and promoted the Search for Extraterrestrial Intelligence (SETI) and science in general. He is less well known for his skepticism.
Born in Brooklyn, New York, Sagan attended the University of Chicago, where he received a bachelor’s degree (1955) and a master’s degree (1956) in physics, before earning his doctorate (1960) in astronomy and astrophysics. He taught at Harvard University until 1968, when he moved to Cornell University.
Sagan became a full professor at Cornell in 1971 and directed a lab there. He contributed to most of the unmanned space missions that explored our solar system. He conceived the idea of adding an unalterable and universal message on spacecraft destined to leave the solar system, that could be understood by any extraterrestrial intelligence that might find it.
The first message that was actually sent out into space was a gold-anodized plaque on board of the space probe Pioneer 10. He continued to refine his designs and the most elaborate such message he helped to develop was the Voyager Golden Record that was sent out with the Voyager space probes.
He was well known as a coauthor of the paper that warned of the dangers of nuclear winter. He also perceived global warming as a growing, man-made danger and likened it to the natural development of Venus into a hot life-hostile planet through greenhouse gases.
His interest in these topics was in large part motivated by his interpretation of the Drake equation and the Fermi paradox. He believed that the Drake Equation suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations suggests that technological civilizations tend to destroy themselves rather quickly.
This stimulated his interest in identifying ways that humanity could destroy itself, with the hope of avoiding such destruction and eventually becoming a space-faring species.
He wrote (with Ann Druyan, whom he later married) and narrated the highly popular thirteen part PBS television series Cosmos; he also wrote books to popularize science (The Dragons of Eden (which won a Pulitzer Prize), Broca’s Brain, etc.) and a novel, Contact, that was a best-seller and had a film adaption starring Jodie Foster in 1997. The film won the 1998 Hugo award.
From Cosmos Sagan became associated with the catchphrase “billions and billions” which he never actually used in the television series. (He simply often used the word “billions.”) Late in his life, Sagan’s books developed his skeptical/atheist view of the world, including The Demon-Haunted World: Science as a Candle in the Dark and Billions and Billions: Thoughts on Life and Death at the End of the Millennium, which includes Ann Druyan’s account of Sagan’s death as a non-believer.
Sagan caused mixed reactions among other professional scientists. On the one hand, there was general support for his popularization of science, his efforts to increase scientific understanding among the general public, and his positions in favor of skepticism and against pseudoscience.
On the other hand, there was some unease that the public would misunderstand some of the personal positions and interests that Sagan took as being part of the scientific consensus rather than his own personal views, and there was some unease, which some believe to have been motivated in part by professional jealousy, that scientific views contrary to those that Sagan took (such as on the severity of nuclear winter) were not being sufficiently presented to the public.
After a long and difficult fight with myelodysplasia, Sagan passed away at the age of 62, on December 20, 1996.
The landing site of the unmanned Mars Pathfinder spacecraft was renamed the Carl Sagan Memorial Station in honor of Dr. Sagan on July 5, 1997.