Meeting a friend in the corridor, Ludwig Wittgenstein (1889-1951) said: "Tell me, why do people always say that it was natural for men to assume that the sun went around the earth rather than the earth was rotating?"

His friend said: "Well, obviously, because it just looks as if the sun is going around the earth."

To which the philosopher replied: "Well, what would it look like if it had looked as if the earth were rotating?"