Quantum 2025 – wissenschaftliches Programm

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TUE: Tuesday Contributed Sessions

TUE 7: Entanglement and Complexity: Contributed Session to Symposium I

TUE 7.3: Vortrag

Dienstag, 9. September 2025, 14:45–15:00, ZHG008

Why Quantum Mechanics needs ’Hidden’ Variables — •Wolfgang Paul — Martin-Luther-Universität Halle-Wittenberg, Institut für Physik, 06099 Halle

One early culmination point of the discussion on whether the Hilbert space description of quantum mechanics can be considered complete or not are the famous breakfast and dinner conversations between Bohr and Einstein during the 5th Solvay Conference 1927. While Einstein thought that it should be augmented by ontological objects (hidden variables) Bohr insisted that this can not be done.

Bohr was well aware that he declared the death of a good part at the heart of physics as it had been established for the preceding 300 years: his position denied quantum physics the ability to model the measurement process and reduced it to the accounting of measurement results.

Based on Nelson’s stochastic mechanics approach [1], one can formulate a model of particles with spin as possessing position and orientation degrees of freedom and describe the measurement process in the Stern Gerlach experiment as well as the Einstein-Podolski-Rosen-Bohm thought experiment [2]. The outcome statistics agree with the Hilbert space quantum mechanical predictions, even reproducing the violation of Bell’s inequalities, but in addition the complete measurement process can be followed in a time-resolved manner, so there is no measurement problem any more.

[1] E. Nelson, Phys. Rev. 150, 1079 (1966)

[2] M. Beyer, W. Paul, Found. Phys. 54, 20 (2024)

Keywords: Bell inequalities; entanglement; hidden variables