Why Constructive Relativity Fails

Abstract

Are time and space independently existing entities? Or is their existence secondary in that they are merely properties of other, more fundamental physical systems? The parameters of this enduring debate have shifted according to the physical theory in which it are set. In the 17th century, Newton\'s notions of Absolute Time and Space strongly favored the idea of independently existing times and spaces. Yet Leibniz famously plagued Newton by pointing to changes that Newton must suppose real even though they issued in no observable differences. Most recently, with the advent of general relativity and quantum theories of gravity that seek to incorporate it, the balance has shifted once again. Is the independence of space and time now finally revealed by the metric field of space and time absorbing the matter of the gravitational fields? Or has time and space has lost its independence from matter in so far as space and time have been absorbed into the matter of the gravitational field? The focus of my talk will be an intermediate episode of this debate that plays out in the context of special relativity. Lorentz noted that moving electrodynamical systems slow in time and shrink in space. The realist tradition explains this slowing and shrinking through the adaptation of matter fields to a real, independently existing Minkowski spacetime. A dissident constructive tradition has long felt that the reverse is the case. These spatio-temporal effects are best explained by the properties of matter theories, most notably, their Lorentz covariance. Harvey Brown has advocated a form of this latter constructivism in his Physical Relativity: Space- time Structure from a Dynamical Perspective. This debate between these two views has proven hard to resolve. That is largely because the notion of explanation is not sufficiently understood for us to adjudicate cleanly between competing claims of what explains what better. In my talk, I will review a new approach to the debate. Constructivists have tacitly assumed a technical result, that it is indeed possible to construct a Minkowski spacetime from Lorentz covariant matter theories. I will show that this is incorrect. This construction project can succeed only in so far as constructivists presume antecedently the basic tenets of the realist view of spacetime. Hence constructivism fails as an alternative to realism about spacetime.