Cosmology

The term ’cosmology’ has three main uses. At its most general, it designates a worldview, for example, the Mayan cosmology. In the early eighteenth century, shortly after the term made its first appearance, Christian Wolff used it to draw a distinction between physics, the empirical study of the material world, and cosmology, the branch of metaphysics dealing with material nature in its most general aspects. This usage remained popular into the twentieth century, especially among Kantian and neo-scholastic philosophers. But recent developments in science that allow the construction of plausible universe models have, effectively, pre-empted the use of the term in order to designate the science that deals with the origins and structure of the physical universe as a whole. Cosmology may be said to have gone through three major phases, each associated with a single major figure – Aristotle, Newton and Einstein. The ancient Greeks were the first to attempt to give a reasoned account of the cosmos. Aristotle constructed a complex interlocking set of spheres centred on an immovable central earth to account for the motions of the heavenly bodies. Newton formulated a theory of gravitational force that required space and time to be both absolute and infinite. Though the laws of nature could, in principle, be specified, nothing could be said about the origins or overall structure of the cosmos. In 1915, Einstein proposed a general theory of relativity whose field-equations could be satisfied by numerous universe-models. Hubble’s discovery of the galactic red shift in 1929 led Lemaître in 1931 to choose from among these alternatives an expanding-universe model, which, though challenged in the 1950s by a rival steady-state theory, became the ‘standard’ view after the cosmic microwave background radiation it had predicted was observed in 1964. The ‘Big Bang’ theory has since been modified in one important respect by the addition of an inflationary episode in the first fraction of a second of cosmic expansion. As a ‘cosmic’ theory, it continues to raise issues of special interest to philosophers.