It is a truism of science that the more fundamental the subject, the more universally applicable it is. Neverthelens, it is important to strike a level of "fundamentalness" appropriate to the task in hand. For example, an in-depth study of the mechanics of motor cars would tell one nothing about the dynamics of traffic. Traffic exists on a different "level" - it is dependent upon the existence of motor vehicles but the physics and mathematics of traffic can be adequately addressed by considering motor vehicles as mobile "blobs," with no consideration of how they become mobile. To start a...