But it's worth recalling Wittgenstein's remark on the subject: "" Tell me, "" he asked a friend, "" why do people always say it was natural for man to assume that the Sun went 'round the Earth, rather than that the Earth was rotating? "" And his friend replied, "" Well, obviously, because it just looks as though the Sun is going round the Earth. "" Wittgenstein replied, "" Well, what would it have looked like if it had looked as though the Earth was rotating? "" (Laughter) Science has taught us, against all intuition, that apparently solid things, like crystals and rocks, are really almost entirely composed of empty space.