The Quantum Debate: From Einstein to Bell and Beyond

Alain Aspect

In 1935, with co-authors Podolsky and Rosen, Einstein discovered a weird quantum situation, in which particles in a pair are so strongly correlated that Schrödinger called them “entangled”. By analyzing that situation, Einstein concluded that the quantum formalism is incomplete. Niels Bohr immediately opposed that conclusion, and the debate lasted until the death of these two giants of physics. In 1964, John Bell discovered that it is possible to settle the debate experimentally, by testing the now celebrated "Bell's inequalities", and to show directly that the revolutionary concept of entanglement is indeed a reality. A long series of experiments, started in 1972, have produced more and more precise results, in situations closer and closer to the ideal theoretical scheme.After explaining the debate, and describing some experiments, I will show how this conceptual discussion has prompted the emergence of the new field of quantum information, at the heart of the second quantum revolution.

David C. Cassidy

David C. Cassidy

Guang-Liang Li

Bell inequalities are intended to formulate mathematically the argument of the thought-experiment proposed by Einstein, Podolsky and Rosen (EPR) in the Einstein-Bohr Debate. Devised to test Bell inequalities against quantum mechanics for resolving the Einstein-Bohr debate, Bell experiments are purportedly modern versions of the EPR experiment. However, there exists a fatal logical flaw in Bell experiments. Because of the logical flaw, Bell experiments differ essentially from the EPR experiment, and quantum correlation in the EPR experiment is not "quantum entanglement" in Bell experiments; the latter is not physically meaningful. In addition to the logical flaw in Bell experiments, a physical constraint imposed on measuring individual quantum objects is violated by all Bell inequalities, which makes Bell inequalities physically meaningless. Unlike Bell experiments, the EPR experiment will not violate any physical constraint, and the EPR argument has no logical flaw. Consequently, the experimental invalidation of Bell inequalities is not evidence for falsifying the two fundamental hypotheses for scientific research, i.e., locality and realism, underlying the EPR experiment, and by no means can Bell experiments resolve the Einstein-Bohr debate. Stemming from abandoning either locality or realism or both, the so-called new applications of quantum mechanics, including various quantum information technologies, are all ineligible and doomed to failure, for they attempt to exploit physically meaningless "quantum superposition" or "quantum entanglement", treating them as physical resources "out there" in the real world.

Jim Baggott, John L. Heilbron

Abstract Our drama lies not only in the clash of ideas, but also in the human passions and social contexts in which the ideas were conceived, debated, refined, accepted, or rejected. Like artists and musicians, the creators of quantum mechanics approached their work with the full range of human emotions. In 2022, Clauser, Aspect, and Zeilinger were at last recognized by the Nobel institution, ‘for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science’. Their prize came exactly 100 years after those of Einstein and Bohr. Experiment moved the debate to a new level, but it has by no means removed or resolved the fundamental question. There will be no Nobel prize for an answer. That will not shut off discussion. Our drama will continue beyond our telling of it and is unlikely to reach its final scene before science ceases or the world ends.