That's not a stupid question! It is the exact inverse of the speed of light through the medium in question. It's like asking how light passes through a vacuum when there is nothing in it for it to pass through (imagine a thick plastic case, completely see through - make the insides a vacuum, then shine a torch onto one side - what happens).PK2k9 said:"What's the speed of dark?" -.-
Stupid question award for me goes to this little gem:
"Wow it's windy. Hey, why does the rain not fall straight down like I would if I jumped?".
From a 23 year old uni student. Faith in humanity. Zero.