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 turtle standing on’ ‘You’re very clever, young man, very clever,’ said the little old lady. ‘But it’s turtles all the way down.’

– Stephen William Hawking