Objectivity versus Nonobjectivity in Quantum Mechanics

Ralf Quadt

R. Folman, Z. Vager

Henry Margenau, James L Park

Davide Poderini, Giovanni Rodari, George Moreno +6 more

Quantum Darwinism offers an explanation for the emergence of classical objective features (those we are used to at macroscopic scales) from quantum properties at the microscopic level. The interaction of a quantum system with its surroundings redundantly proliferates information to many parts of the environment, turning it accessible and objective to different observers. However, given that one cannot probe the quantum system directly, only its environment, how to determine whether an unknown quantum property can be deemed objective? Here we propose a probabilistic framework to analyze this question and show that objectivity implies a Bell-like inequality. Among several other results, we show quantum violations of this inequality, a device-independent proof of the nonobjectivity of quantum correlations. We also implement a photonic experiment where the temporal degree of freedom of photons is the quantum system of interest, while their polarization acts as the environment. Employing a fully black-box approach, we achieve the violation of a Bell-like inequality, thus certifying the nonobjectivity of the underlying quantum dynamics in a fully device-independent framework.

J J MacMahon

Andrei Yu. Khrennikov

This paper discusses a possible resolution of the nonobjectivity-nonlocality dilemma in quantum mechanics in 'the light of experimental tests of the Bell inequality for two entangled photons and a Bell-like inequality for a single neutron. My conclusion is that these experiments show that quantum mechanics is nonobjective: that is, the values of physical observables cannot be assigned to a system before measurement. Bell's assumption of nonlocality has to be rejected as having no direct experimental confirmation, at least thus far. I also consider the relationships between nonobjectivity and contextuality. Specifically, I analyze the impact of the Kochen-Specker theorem on the problem of contextuality of quantum observables. I argue that, just as von Neumann's "no-go" theorem, the Kochen-Specker theorem is based on assumptions that do not correspond to the real physical situation. Finally, I present a theory of measurement based on a classical, purely wave model (pre-quantum classical statistical field theory), a model that reproduces quantum probabilities. In this model continuous fields are transformed into discrete clicks of detectors. While this model is classical, it is nonobjective. In this case, nonobjectivity is the result of the dependence of experimental outcomes on the context of measurement, in accordance with Bohr's view.