Physics, metaphysics

How is it that scientific inquiry - 20th-century physics in particular - has made such astounding progress in the production of knowledge? Traditional empiricism maintains that non-empirical considerations do not enter into the assessment or content of scientific knowledge. This view, claims Nicholas Maxwell, is unable to explain various key elements of science, including the notion and possibility of progress.

In its place, he offers a revamped empiricism, asserting that metaphysical theses feature centrally in the improvement of scientific methodologies and in the content of knowledge. The most crucial metaphysical thesis is that nature is comprehensible. Maxwell argues that despite remaining implicit within scientific practice, a particular notion of comprehensibility has been responsible for the great march forward in physics. His aim is to make this thesis explicit, thereby better facilitating the advancement of knowledge. Comprehensibility is defined in terms of an invariant, omni-spatiotemporally present "something", the dispositional properties of which give rise to the diversity of natural phenomena. The greater the extent to which a physical theory unifies seemingly distinct components of the natural world (different kinds of particles, fields, and forces, for example), the greater the theory's comprehensibility.

Unity, then, is first and foremost among the non-empirical virtues. Progress is, in fact, progress towards a "theory of everything", in which seemingly disparate phenomena are unified and explained as aspects of one fundamental thing composing all there is. Comprehensibility is an attribute of the world and of successful theories, and a heuristic principle all rolled into one.

Maxwell does not downplay the ambition of his project. His arguments are intended to do no less than "change the nature of science" by explicitly integrating metaphysics into scientific practice. The ensuing reflections, though, are restricted to certain physical theories and their immediate applicability to biological, chemical and other sciences is an open question.

Given this, Maxwell performs a heroic feat in making the physics accessible to the non-physicist, including appendices that provide an introduction to the required mathematical and physical concepts. Understanding and evaluating are different matters, of course, and anyone who is here learning for the first time about the physical theories involved will not be in a position to evaluate critically the claim that progress in terms of physical comprehensibility has typified the recent history of science.

Philosophically, there is much here to stimulate and provoke. In particular, there are rewarding comparisons to be made between the functional roles assigned to Maxwell's metaphysical "blueprints" and Thomas Kuhn's paradigms, as well as between Maxwell's description of theoretical development and Imre Lakatos's methodology of scientific research programmes.

Critics may decry the examples of progressive theoretical unification given as rationalisation post hoc - elements of earlier theories unified in later ones are often preserved by restricting their range of application to limiting cases that are physically impossible.

But those who share Maxwell's intuitions about progress, even those uncommitted to "theories of everything", will find encouragement here for thinking about how one does justice to such a possibility.

Anjan Chakravartty is researching a PhD in the philosophy of science at King's College, Cambridge.