Experience in quantum physics: toward a theory of everything

A theory of everything should not only tell us the laws for matter, gravity, and possibly boundary condition for the universe. In addition, it should specify the relation between theory and experience. Here I argue for a minimal prescription in extracting empirical predictions from path integrals by showing that alternative prescriptions are unjustifiable. In this minimal prescription, the relative probability for one experience is obtained by summing over all configurations compatible with that experience, without any further restriction associated with other experiences of the same or other experiential beings. An application to Wigner's friend settings shows that quantum theory admits objective predictions for subjective experiences. Still, quantum theory differs from classical theory in offering individualized as opposed to collective accounts of experiences. This consideration of experience in fundamental theories issues several challenges to popular quantum interpretations, and points to the outstanding need for a theory of experience in understanding physical theories of everything.