Imagine yourself in the coffee houses of 18th century Edinburgh, in the elegance of the New Town when it really was new, the civilization of those paved streets, and the intellectual excitement of the Scottish Enlightenment. It was there that the philosopher David Hume fi rst cast doubt on scientifi c method, peering at ideas about what causes what and
fi nding there was nothing there. All you can do, he said, is say that events tend to happen together. Yet, if we can see nothing causing things under the philosophical microscope, that hands the scientists a big logical problem. It doesn’t matter how many times they do an experiment, or watch the sun rising bang on time, it doesn’t mean these events are any more likely to happen tomorrow.