Is the life-world reduction sufficient in quantum physics?

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Is the life‑world reduction sufficient in quantum physics? Michel Bitbol1  Accepted: 29 September 2020 © Springer Nature B.V. 2020

Abstract According to Husserl, the epochè (or suspension of judgment) must be left incomplete. It is to be performed step by step, thus defining various layers of “reduction.” In phenomenology at least two such layers can be distinguished: the life-world reduction, and the transcendental reduction. Quantum physics was born from a particular variety of the life-world reduction: reduction to observables according to Heisenberg, and reduction to classical-like properties of experimental devices according to Bohr. But QBism has challenged this limited version of the phenomenological reduction advocated by the Copenhagen interpretation. QBists claim that quantum states are “expectations about experiences of pointer readings,” rather than expectations about pointer positions. Their focus on lived experience, not just on macroscopic variables, is tantamount to performing the transcendental reduction instead of stopping at the relatively superficial layer of the life-world reduction. I will show that quantum physics indeed gives us several reasons to go the whole way down to the deepest variety of phenomenological reduction, may be even farther than the standard QBist view: not only reduction to experience, or to “pure consciousness,” but also reduction to the “living present.” Keywords  Philosophy of physics · Phenomenology · Quantum physics · QBim · Husserl · Crisis of the European science · Wigner’s friend paradox · Non-locality

1 Introduction Quantum mechanics was born from a quick and thorough ontological tabula rasa, between the years 1924 and 1926, just after the ontological patchwork that characterized the birth of quantum theory from 1900 to 1924. There were two versions of the tabula rasa: replacing an old ontology with a new one, or permanently suspending ontologies. De Broglie and Schrödinger proposed to substitute a new ontology that included their so-called “matter waves,” for the old corpuscular ontology. * Michel Bitbol [email protected] 1



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Heisenberg was more radical when he introduced his matrix mechanics of 1925. He performed the well-known “reduction to observables,” namely a reduction of the representational scaffolding of the new theory to the variables that can be directly measured in atoms: the frequencies and intensities of spectral lines. Heisenberg thereby suspended traditional ontologies without replacing them with anything. As for Bohr, he advocated a sort of middle way between replacing and suspending ontologies. On the one hand he held on to the idea of “quantum objects” that can be approached by complementary representations. Yet, on the other hand, he tended to reduce physics to what can be handled in a laboratory or said in dialogues between scientists. This is what he implied by declaring that quantum theory is nothing else and nothing more than a “symbol