A number of arguments have been given to show that the modal interpretation of ordinary nonrelativistic quantum mechanics cannot be consistently extended to the relativistic setting. We find these arguments inconclusive. However, there is a prima facie reason to think that a tension exists between the modal interpretation and relativistic invariance; namely, the best candidate for a modal interpretation adapted to relativistic quantum field theory, a prescription due to Rob Clifton, comes out trivial when applied to a number of systems (...) of physical interest. However, it is far from clear whether this difficulty for the modal interpretation is traceable to relativistic invariance per se or to the infinite number of degrees of freedom involved. In any case, the proponents of the modal interpretation have work to do. (shrink)

I show how an almost exclusive focus on the simplest case - the case of a single particle - along with the commonplace conception of the single-particle wave function as a scalar field on spacetime contributed to the perception, first brought to light by I. Bloch, that there existed a contradiction between quantum theory with instantaneous state collapses and special relativity. The incompatibility is merely apparent since treating wave-function values as hypersurface dependent avoids the contradiction. After clarifying confusions which fueled (...) the perception of a paradox, I elaborate on an analysis of the wave function due to Wayne Myrvold to show that nothing special, or ad hoc, is required in treating wave-function values, even in the single-particle case, as hypersurface-dependent; rather, the hypersurface dependence of these values is the natural development of nonlocal entanglement in the context of the relativity of simultaneity. Properly understood, what Bloch's paradox reveals is that the combination of nonlocal entanglement together with a hypersurface-dependent process of state collapse conflicts with the thesis of spatiotemporal separability and, in particular, with the idea that chances are local matters of fact. (shrink)

Earman and Ruetsche ([2005]) have cast their gaze upon existing no-go theorems for relativistic modal interpretations, and have found them inconclusive. They suggest that it would be more fruitful to investigate modal interpretations proposed for "really relativistic theories," that is, algebraic relativistic quantum field theories. They investigate the proposal of Clifton ([2000]), and extend Clifton's result that, for a host of states, his proposal yields no definite observables other than multiples of the identity. This leads Earman and Ruetsche to a (...) suspicion that troubles for modal interpretations of such relativistic theories "are due less to the Poincaré invariance of relativistic QFT vs. the Galilean invariance of ordinary nonrelativistic QM than to the infinite number of degrees of freedom of former vs. the finite number of degrees of freedom of the latter" (577-78). I am skeptical of this suggestion. Though there are troubles for modal interpretations of a relativistic quantum field theory that are due to its being a field theory—that is, due to infinitude of the degrees of freedom—they are not the only troubles faced by modal interpretations of quantum theories set in relativistic spacetime; there are also troubles traceable to relativistic causal structure. (shrink)