Mechanics, classical

Understood at its most general, ‘classical mechanics’ covers the approach to physical phenomena that dominated science from roughly the time of Galileo until the early decades of the twentieth century. The approach is usually characterized by the assumption that bodies carry an inherent mass and well-defined positions and velocities. Bodies subsist within a three-dimensional absolute space and influence one another through reciprocal forces. These objects obey the three laws of motion articulated by Isaac Newton in 1686 in a deterministic manner: once a mechanical system is assembled, its future behaviour is rigidly fixed. Such ‘classical’ assumptions were eventually rejected by Einstein’s theory of relativity, where the assumption of a three-dimensional Euclidean space is abandoned, and by quantum mechanics, where determinism and well-defined positions and velocity are eschewed. Classical mechanics is frequently characterized as ‘billiard ball mechanics’ or ‘the theory of mechanism’ on the grounds that the science treats its materials in the manner of colliding particles, or clockwork. Such stereotypes should be approached with caution because the basic framework of classical mechanics has long been subject to divergent interpretations that unpack the content of Newton’s ‘three laws’ in remarkably different ways. These differing interpretations provide incompatible catalogues of the basic objects that are supposed to comprise the ‘classical world’ – are they point masses, rigid bodies or flexible substances? Or, as many writers have suggested, should mechanics not be regarded as ‘about’ the world at all, but merely as a source of useful but fictitious idealizations of reality? These foundational disagreements explain why classical mechanics has often found itself entangled in metaphysics. Much of modern philosophy of science is characterized by attitudes that were originally articulated during the nineteenth century’s attempts to clarify the grounds of classical mechanics.