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Yakir Aharonov
Tel Aviv University, IL, and Chapham University, Orange, USA

Finally making sense of the double-slit experiment

Feynman stated that the double-slit experiment “. . . has in it the heart of quantum mechanics. In reality, it contains the only mystery” and that “nobody can give you a deeper explanation of this phenomenon than I have given; that is, [just] a description of it.” We rise to the challenge with an alternative to the wave function-centered interpretations: instead of a quantum wave passing through both slits, we have a localized particle with nonlocal interactions with the other slit [Aharonov, Cohen, Colombo, Landsberger, Sabadini, Struppa & Tollaksen (2017) Proc. Natl. Acad. Sci. 114 (25)]. Key to this explanation is dynamical nonlocality, which naturally appears in the Heisenberg picture as nonlocal equations of motion. This insight led us to develop an approach to quantum mechanics which relies on pre- and post-selection, weak measurements, deterministic, and modular variables. This fundamental change in perspective towards a new ontology points to deterministic properties within the Heisenberg picture as being the primitives instead of the wavefunction, which remains an ensemble property.

Using this new approach in a double-slit experiment, we can verify that the particle, which is localized, goes through only one of the slits. In addition to this corpuscular behavior, a nonlocal property originating from the other, distant, slit has been affected through the nonlocal Heisenberg equations of motion. Although the Heisenberg and Schrödinger pictures are equivalent formulations, nevertheless, the framework presented here has led to new insights, intuitions, and experiments that were missed from the old perspective. For example, this new perspective affects the axiomatic structure of quantum mechanics: under the assumption of nonlocality, uncertainty turns out to be crucial to preserve causality. Hence, a (qualitative) uncertainty principle can be derived rather than assumed.
 
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