  The biochemical attachment of photolyase to ultraviolet (uv) absorbed DNA
molecules provides a method for registering whether a source has emitted
photons. Here using laws of chemical kinetics and related experimental methods
we argue that the instant after which this information becomes discernible can
be empirically determined by retrodicting from relevant data when the
photolyase binding to uv-absorbed DNA molecules has started occuring. Thus an
empirically investigable twist is provided to the quantum measurement problem.
