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Center for Nonlinear Studies |
Conventional textbook quantum mechanics introduces randomness of measurement outcomes, along with the Born rule, as a postulate of the theory. Nonetheless, after various attempts the Born rule was recently derived from the other postulates. A common assumption of these derivations is that different "branches" of the wavefunction represent alternative situations. Without this assumption there is no compelling reason for a probabilistic interpretation: alternatives are possible. Here, by using envariance and a modified Bell inequality that employs no Born rule, we show that randomness of outcomes is inevitable if one wants the theory to be local, and hence causal. In other words, we prove inevitability of randomness using locality to justify Everett's identification of random "events" with "branches", and thus show that one can obtain the Born rule replacing the wavefunction-branches assumption with a physically-motivated locality one.
Host: Wojciech Zurek