it’s not the expert at arithmetic who can tell you how likely someone is to interfere with the pennies in my drawer; a detective would be more use. It isn’t the physicist who can tell you how likely I am to catch up a cue and spoil his experiment with the billiard ball; you’d better ask a psychologist. And it isn’t the scientist who can tell you how likely Nature is to be interfered with from outside. You must go to the metaphysician.’