Stephen Hawking's A Brief History of Time tells the story of a cosmologist whose speech is interrupted by a little old lady who informs him that the universe rests on the back of a turtle. Ah, yes, madame, the scientist replies, but what does the turtle rest on? The old lady shoots back: You can't trick me, young man. It's nothing but turtles, turtles, turtles, all the way down.
