Apocryphal quote from Stephen Hawking's A Brief History of Time:
A well-known scientist (some say it was Bertrand Russell) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said: "What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise." The scientist gave a superior smile before replying, "What is the tortoise standing on?" "You're very clever, young man, very clever," said the old lady. "But it's turtles all the way down!"But I like the reference from William James.
William James published a different version in his book The Will To Believe (1898), specifically in the essay "The Sentiment of Rationality" (p. 104 of The Will To Believe in the Dover reprint):This is about the regressive tendency of thought, and our inability to see to the foundations of our premises. A topic dear to my heart.
"Like the old woman in the story who described the world as resting on a rock, and then explained that rock to be supported by another rock, and finally when pushed with questions said it was rocks all the way down, -- he who believes this to be a radically moral universe must hold the moral order to rest either on an absolute and ultimate should, or on a series of shoulds all the way down."