Consequence for Wavefunction Collapse Model of the Sudbury Neutrino Observatory Experiment

The “measurement problem” can be thought of as indicating a serious flaw in the foundations of quantum theory[1], and therefore a potential clue to new physics. When a measurement is described by Schrödinger’s equation, the statevector evolves to a superposition of apparatus states, each recording a different outcome. This conflicts with the interpretation of the statevector as describing “reality” since only one of these apparatus states exists in reality. One resolution of this problem is to modify Schrödinger’s equation, adding a term so that the “collapse” of the statevector to a macroscopically unique state occurs dynamically. The added term depends upon a randomly fluctuating quantity. The particular realization of that quantity determines the particular macroscopic collapse outcome, and the statistics of the quantity gives the outcomes with the Born probabilities[2, 3]. Arguably, the Continuous Spontaneous Localization (CSL) model[4, 5] is at present the most sucessful dynamical collapse model[6]. In CSL, the fluctuating quantity is a scalar field. In each added term it is coupled to the operator representing the number density of particles of a particular type (e.g., electrons, protons, neutrons...) by a coupling constant gα (e.g., ge, gp, gn...). The construction of CSL crucially depended upon the advent of a model of Ghirardi, Rimini and Weber (GRW)[7]. In the GRW model, the overall rate of collapse for any isolated particle in a superposition of “widely separated” states is chosen to be λ = 10 sec. “Widely separated” refers to greater than the