User:3df/Encyclopaedia Galactica

"Encyclopaedia Galactica" is the twelfth episode of the American documentary television series Cosmos: A Personal Voyage. It premiered on December 14, 1980 on PBS.

Episode summary
The episode begins with Sagan posing the question of whether extraterrestrial beings have visited Earth. He skeptically recounts the story of Barney and Betty Hill, who reported being abducted by aliens in 1961. Unconvinced, Sagan points out fallacies in the narrative and notes that such reports are never corroborated with alien artifacts that could be studied.

Sagan discusses the life and work of Jean-François Champollion, who deciphered Egyptian hieroglyphs in the early 19th century. Sagan explains that the decipherment was aided by two crticial artifacts – the Rosetta Stone and the Philae obelisk – where the names of Ptolemy and Cleopatra were found in both Egyptian and Greek scripts. He reconstructs an approach to decipherment by looking at symbols common to both names. He goes on to explain that once Champollion deciphered the hieroglyphs, a wealth of information about the once mysterious ancient Egyptian society had become available, like a message waiting to be received.

Just as a decipherment was needed to unlock the knowledge of ancient Egypt, Sagan says, so too will one be required to communicate with extraterrestrial beings. He proposes that the "cosmic Rosetta Stone" could be a shared understanding of spectral lines or prime numbers; messages could be exchanged with radio telescopes. At the Arecibo Observatory, Sagan attempts to estimate the number of extraterrestrial civilizations that could be reached in the Milky Way, with varying parameters of an equation by Frank Drake, and imagines how a civilization could spread out and colonize the galaxy.

As part of their searches for other civilizations, Sagan speculates that advanced extraterrestrial intelligences may assemble a "vast repository of the knowledge of countless worlds" – an encyclopedia "galactica". Using a computer terminal, he begins to browse an imaginary database of billions of worlds. Some inhabited worlds are seen with artificial rings or shells built around them. The most advanced worlds enclosed entire stars with shells for immense solar power. Finally, Sagan opens the encyclopedia's entry for Earth, wondering what alien civilizations would think about humanity.