Bell Inequality and Many-Worlds Interpretation

Bell’s work [1] led to a revolution in our understanding of Nature. I remember attending my first physics conference on “Microphysical Reality and Quantum Formalism,” in Urbino, 1985. Most of the talks were about Aspect’s experiment [2] confirming the nonlocality of quantum mechanics based on the experimental violations of Bell’s inequalities. Although I did not share the skepticism of many speakers regarding the results of Aspect, I was not ready to accept that a local action in one place can instantaneously change anything at another place. So, while for the majority the lesson from Bell was that quantum mechanics requires some “spooky action at a distance”, I was led by Bell’s result to an alternative revolutionary change in our view of Nature. I saw no other way, but accepting the many-worlds interpretation (MWI) of quantum mechanics [3, 4]. I shall start by presenting the Einstein-Podolsky-Rosen (EPR) [5] argument. Then, Bell’s idea will be presented using the Greenberger-HorneZeilinger setup [6] in the form proposed by Mermin [7, 8]. The discussion of nonlocality will suggest that Bell’s inequalities are the only manifestation of action at a distance in Nature. The demonstration of the necessity of action at a distance will be done through a detailed analysis of the GHZ experiment. Then, I shall show how multiple worlds resolve the problem of action at a distance. After discussing the issue of nonlocality in the MWI I shall conclude by citing Bell’s view on the MWI.