Johannes Fankhauser (St Edmund Hall): ‘How we ought (not) to understand weak measurements of Bohmian velocities’
Whilst Bohmian Mechanics' - a deterministic hidden variables quantum theory for quantum particles - empirical adequacy remains beyond dispute, a principal objection to the theory, voiced e.g. by Einstein, Pauli and Heisenberg targets the observationally elusive nature of its dynamics: Due to its construction, the individual particle trajectories are undetectable. This lore has recently been somewhat called into question in light of a novel, nonlinear type of measurements. Wiseman touted so-called weak measurements as providing a means to observe the Bohmian velocity field of the guiding equation. Weak velocity measurements denote setups in which a quantum state can be measured without significantly disturbing it. Successive weak position measurements within small time intervals can then be used to define a quantity intuitively construed as the operationalization of a velocity field. Advocates of Bohmian Mechanics naturally identify this velocity field as the field whose flow generates the Bohmian particles' trajectories. This talk will critically examine this claim. Weak velocity measurements constitute no new arguments, let alone empirical evidence, in favor of the theory. This is revealed by a careful reconstruction of the physical arguments on which the description of weak velocity measurements rests. Another error, we diagnose, is one of philosophical confusion over what it means to confirm a theory.