Variable speed of light "c"/"c" where "c" is light speed in flat space. Peter Bergmann did not agree with Einstein, but left the dispute out of his earlier book in 1942 to get Einstein’s endorsement. After Einstein died Bergmann wrote a new book in 1968 claiming that vector light velocity could change direction but not speed. This has become a prevailing opinion in science, but not in agreement with Einstein’s unambiguous math. Bergman did acknowledge that the apparent speed of light would change in a gravity field and go to zero at an event horizon as viewed by a distant observer. Max Born agreed
Speed of Darkness fiction, named The Science of Discworld, written by Terry Pratchett, Ian Stewart and Jack Cohen. In a 2011 interview on BBC Radio 1, frontman Dave King explained that the title track and album title was taken from a quote of Dino Misetić, the artist who designed the album cover, which appeared in the book Sarajevo Marlboro. Dino, who grew up in the Balkans during the Balkan Wars, is quoted in the book, saying: "They taught us what the speed of light is, but nobody can teach you what the speed of darkness is." Flogging Molly: Additional musicians: Speed of Darkness