An Extension of " Popper's Experiment " Can Test Interpretations of Quantum Mechanics

Karl Popper proposed a way to test whether a proposed relation of a quantum-mechanical state to perceived reality in the Copenhagen interpretation (CI) of quantum mechanics-namely that the state of a particle is merely an expression of " what is known " about the system-is in agreement with all experimental facts. A conceptual flaw in Popper's proposal is identified and an improved version of his experiment (called " Extension step 1 ")-which fully serves its original purpose-is suggested. The main purpose of this paper is to suggest to perform this experiment. The results of this experiment predicted under the alternative assumptions that the CI-together with the above connection of the state function with reality-or the " many-worlds " interpretation (MWI) is correct are shown to be identical. Only after a further modification (called " Extension step 2 ")-the use of an ion isolated from the macroscopic environment as particle detector-the predictions using the respective interpretations become qualitatively different. This is because " what is known " by a human observer H can fail as a basis for the prediction of the statistical distribution of measurement results within the MWI in special cases: The temporal evolution of a system un-entangled with H-like the isolated ion-can depend on another system's state components that are entangled with states ortogonal to H. Thus-within the CI-for H they are " known not to exist ". Yet H can infer their existence by studying the evolution of the ion.