Philosophy of Cosmology

Cosmology has made enormous progress in the last several decades. It is no longer a neglected subfield of physics, as it was as recently as 1960; it is instead an active area of fundamental research that can boast of a Standard Model well-supported by observations. Prior to 1965 research in cosmology had a strikingly philosophical tone, with debates focusing explicitly on scientific method and the aims and scope of cosmology (see, e.g. Munitz 1962; North 1965; Kragh 1996). One might suspect that with the maturation of the field these questions have been settled, leaving little room for philosophers to contribute. Although the nature of the field has changed dramatically with an increase of observational knowledge and theoretical sophistication, there are still ongoing foundational debates regarding cosmology’s proper aims and methods. Cosmology confronts a number of questions dear to the hearts of philosophers of science: the limits of scientific explanation, the nature of physical laws, and different types of underdetermination, for example. There is an opportunity for philosophers to make fruitful contributions to debates in cosmology and to consider the ramifications of new ideas in cosmology for other areas of philosophy and foundations of physics. Due to the uniqueness of the universe and its inaccessibility, cosmology has often been characterized as “un-scientific” or inherently more speculative than other parts of physics. How can one formulate a scientific theory of the “universe as a whole”? Even those who reject skepticism regarding cosmology often assert instead that cosmology can only make progress by employing a distinctive methodology. These discussions, in my view, have by and large failed to identify the source and the extent of the evidential challenges faced by cosmologists. There are no convincing, general no-go arguments showing the impossibility of secure knowledge in cosmology; there are instead specific problems that arise in attempting to gain observational and theoretical access to the universe. In some cases, cosmologists have achieved knowledge as secure as that in other areas of physics — arguably, for example, in the account of big bang nucleosynthesis. Cosmologists do, however, face a number of distinctive challenges. The finitude of the speed of light, a basic feature of relativistic cosmology, insures that global properties of the universe cannot be established directly by observations (§5). This is a straightforward limit on observational access to the universe, but there are other obstacles of a different kind. Cosmology relies on extrapolating local physical laws to hold universally. These extrapolations make it possible to infer, from observations of standard candles such as Type Ia supernovae,1 the startling conclusion