Abstract

Several features of cosmology are of striking philosophical interest. Unlike other branches of physics which deal with kinds of occurrences and relations, cosmology investigates only one unique entity, the physical universe. Hence the science cannot avail itself of standard inductive procedures which depend on the assembling of samples. Cosmologists are therefore obliged to choose between two other procedures. Mr. Bondi calls them the "extrapolative" and the "axiomatic-deductive" lines of thought. The former starts from physical laws known to hold of terrestrial or near-terrestrial phenomena. It then tries to frame an answer to the question: "What is the largest set of phenomena to which these laws can be applied consistently and successfully?" The result of this approach has been the construction of a number of "models" of the universe at large, each patterned on verified laws of physics. The axiomatic-deductive approach starts from certain a priori assumptions which are held to underlie any physical science whatever and which are equivalent to certain suppositions about the structure of the universe. From these assumptions, together with special axioms adopted for the purpose, the laws of cosmology are deduced. Then the deductions are checked with the observational data. Here again, various models of the cosmos have resulted.