Locality and reality

Abstract

Einstein's principle that no signal travels faster than light suggests that observations in one spacetime region should not depend on whether or not a radioactive decay is detected in a spacelike-separated region. This locality property is incompatible with the predictions of quantum theory, and this incompatibility holds independently of the questions of realism, objective reality, and hidden variables. It holds both in the pragmatic quantum theory of Bohr and in realistic frameworks. It is shown here to hold in a completed realistic quantum theory that reconciles Einstein's demand for a description of reality itself with Bohr's contention that quantum theory is complete. This completed realistic quantum theory has no hidden variables, and no objective reality in which observable attributes can become definite independently of observers. The theory is described in some detail, with particular attention to those aspects related to the question of locality. This completed realistic quantum theory is in principle more comprehensive than Bohn's pragmatic quantum theory because it is not limited in principle by the requirement that the observed system be physically separated from the observing one. Applications are discussed.