History of Science and Technology Colloquium

The physicist I. Bloch in his 1967 paper "Some Relativistic Oddities in the Quantum Theory of Observation" came to the conclusion that the instantaneous collapse of the quantum state, as it has traditionally been conceived, presented a problem for compatibility with relativity. This problem has been called "Bloch’s Paradox". Rather offhandedly, Bloch suggested that the problem might be avoided by taking the state transition due to a measurement to occur along a Lorentz invariant surface in Minkowski spacetime (i.e., the spacetime of special relativity). In particular, Bloch focused attention on the past light cone of the measurement event. The idea of positing the past (or future) light cone of a measurement event as the collapse transition surface in spacetime has a natural attractiveness to it because of the privileged status of the light cone structure in relativity theory. In this talk, I review the historically significant interactions with this proposal in the literature and critically examine objections to it. (The essence of the proposal and most of the objections to it can be understood pictorially with the help of spacetime diagrams.) Ultimately, the proposal fails to perform the explanatory work we seek from the process of state collapse in EPR situations. Reflection upon this failure provides insights which motivate embracing a hypersurface-dependent account of quantum state collapse of the sort first advocated by Aharonov and Albert in 1984.