For a long time physicists regarded the world as conforming very closely to what I will call ‘the classical picture’. The classical picture is most importantly based upon Newtonian mechanics, a beautiful and very powerful theory which is still used to make very accurate predictions about a wide variety of phenomena. But the classical picture is not restricted solely to Newtonian theories: by this term I mean a whole family of theories which were developed in the period before Einstein, and which were in broad agreement with Newton about fundamental matters. For example, what is known as classical electrodynamics is a theory that goes well beyond Newtonian mechanics in the sort of phenomena it describes, but it is still recognisably part of the classical picture.

In the following sections, I will present a heavily simplified version of the classical picture. Many of the ideas will be familiar to many readers, and it might seem unnecessary to rehearse them. It is often unappreciated, however, that these features interact to generate an overall conception of the world. To make the classical picture vivid, I will ask you to imagine a fictitious being, much like a deity, attempting to record in perfect detail exactly how the world is at a particular time.