"When Knowledge Conquered Fear" is the third episode of the American documentary television series Cosmos: A Spacetime Odyssey. It premiered on March 23, 2014 on Fox, and premiered on March 24, 2014 on National Geographic Channel.The episode received positive reviews, with critics remarking on the homage the series paid to theories that evolved due to contributions from Isaac Newton, Nicolaus Copernicus, Edmond Halley, and Robert Hooke.