Past, Future And Elsewhere In Quantum Mechanics

Paul Busch, PEKKA J. LAHTI

Sascha Vongehr

A century ago, "past" and "future", previously strictly apart, mixed up and merged. Temporal terminology improved. Today, not actualized quantum states, that is merely "possible" alternatives, objectively "exist" (are real) when they interfere. Again, two previously strictly immiscible realms mix. Now, modal terminology is insufficient. Both times, extreme reactions reach from rejection of the empirical science to mystic holism. This paper shows how progress started with the relativization of previously absolute terms, first through Einstein's relativity and now through Everett's relative state description, which is a modal realism. The historical parallels suggest mere relativization is insufficient. A deformation of domains occurs: The determined past and the dependent future were restricted to smaller regions of space-time. This light cone description is superior to hyperspace foliations and already entails the modal realism of quantum mechanics. Moreover, an entirely new region, namely the "absolute elsewhere" was identified. The historical precedent suggests that modal terminology may need a similar extension. Discussing the modal realistic connection underlying both relativities, Popper's proof of future indeterminism is turned to shatter the past already into many worlds/minds, thus Everett relativity is merely the Bell inequality violating correlation between possible empirical records.

Albert Einstein, Richard C. Tolman, Boris Podolsky

It is well known that the principles of quantum mechanics limit the possibilities of exact prediction as to the future path of a particle. It has sometimes been supposed, nevertheless, that the quantum mechanics would permit an exact description of the past path of a particle. \n \nThe purpose of the present note is to discuss a simple ideal experiment which shows that the possibility of describing the past pathof one particlewould lead to the predictions as to the future behaviour of a second particle of a kind not allowed in the quantum mechanics. It will hence be concluded that the principles of quantum mechanics actually involve an uncertainty in the description of past events which is analogous to the the uncertainty in the prediction of future events. And it will be shown for the case in hand, that this uncertainty in the description of the past arises from a limitation of the knowledge that can be obtained by measurement of momentum.

Michael Drieschner