The fifth Solvay conference is usually remembered for the clash that took place between Bohr and Einstein, supposedly concerning in particular the possibility of breaking the uncertainty relations. It might be assumed that this clash took the form of an official debate that was the centrepiece of the conference. However, no record of any such debate appears in the published proceedings, where both Bohr and Einstein are in fact relatively silent. The available evidence shows that in 1927 the famous exchanges between Bohr and Einstein actually consisted of informal discussions, which took place semiprivately (mainly over breakfast and dinner), and which were overheard by just a few of the participants, in particular Heisenberg and Ehrenfest. The historical sources for this consist, in fact, entirely of accounts given by Bohr, Heisenberg and Ehrenfest. These accounts essentially ignore the extensive formal discussions appearing in the published proceedings. As a result of relying on these sources, the perception of the conference by posterity has been skewed on two counts. First, at the fifth Solvay conference there occurred much more that was memorable and important besides the Bohr–Einstein clash. Second, as shown in detail by Howard (1990), the real nature of Einstein's objections was in fact misunderstood by Bohr, Heisenberg and Ehrenfest – for Einstein's main target was not the uncertainty relations, but what he saw as the non-separability of quantum theory.
The fifth Solvay conference is usually remembered for the clash that took place between Bohr and Einstein, supposedly concerning in particular the possibility of breaking the uncertainty relations. It might be assumed that this clash took the form of an official debate that was the centrepiece of the conference. However, no record of any such debate appears in the published proceedings, where both Bohr and Einstein are in fact relatively silent. The available evidence shows that in 1927 the famous exchanges between Bohr and Einstein actually consisted of informal discussions, which took place semiprivately (mainly over breakfast and dinner), and which were overheard by just a few of the participants, in particular Heisenberg and Ehrenfest. The historical sources for this consist, in fact, entirely of accounts given by Bohr, Heisenberg and Ehrenfest. These accounts essentially ignore the extensive formal discussions appearing in the published proceedings. As a result of relying on these sources, the perception of the conference by posterity has been skewed on two counts. First, at the fifth Solvay conference there occurred much more that was memorable and important besides the Bohr–Einstein clash. Second, as shown in detail by Howard (1990), the real nature of Einstein's objections was in fact misunderstood by Bohr, Heisenberg and Ehrenfest – for Einstein's main target was not the uncertainty relations, but what he saw as the non-separability of quantum theory.
ASPECTS OF THE DEBATE The debate between Niels Bohr and Albert Einstein concerning the interpretation of quantum mechanics extended from the fifth Solvay Conference in 1927 until the end of Einstein's life. The most dramatic exchange occurred in 1935, when Einstein, in collaboration with B. Podolsky and N. Rosen, published a paper in Physical Review entitled “Can quantum-mechanical description of physical reality be considered complete?”, concluding with a negative answer, and Bohr replied in the same journal, with a paper of the same title but giving a positive answer. Their arguments were restated, in some respects with greater clarity, in the Library of Living Philosophers volume on Einstein in 1949. The disagreements between Bohr and Einstein concerned not only the physical question expressed in the common title of their papers, but also philosophical questions about physical reality and human knowledge. Much light was thrown upon the Bohr–Einstein debate by the theorem of J. S. Bell (1964) and the experiments which it inspired. Bell showed that any physical theory which applies to a pair of spatially separated systems (as considered in the thought experiment of Einstein, Podolsky, and Rosen) and satisfies a certain locality condition will, in certain circumstances, disagree statistically with quantum mechanics. Consequently, the supplementation of the quantum mechanical description envisaged by Einstein and his collaborators (usually referred to as a “hidden variables theory”) must either violate the locality condition or clash with quantum mechanical predictions.
The Bohr-Einstein debate, the most interesting intellectual contest in science of this century, began in the late afternoon of October 24,1927, at the Fifth Solvay Conference in Brussels, Belgium. 50 (Einstein had not attended the meeting in Como a month before, at which Bohr first introduced complementarity.) The theorists Bohr, Born, de Broglie, Brillouin, Dirac, Einstein, Ehrenfest, Heisenberg, Pauli, Planck, and Schrödinger were in attendance, as well as the experimentalists Bragg, Compton, Madame Curie, and Debye. The eminent Dutch theorist H.A. Lorentz, the grandfather of relativity (after whom the theory’s space-time transformations were named), chaired the sessions. The organizers had chosen “Electrons and Photons” as the official title of the conference, but a better one might have been: “Quantum Mechanics: What Does it Mean?” As Einstein’s opinion had become widely known, fireworks were expected. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Between 1927 and 1936 no one had a greater influence on Bohr's thinking than Einstein. It was Einstein's unremitting criticism which provided the severest test of Bohr's interpretation of quantum physics, and which forced him to clarify and refine his arguments. The debate between Bohr and Einstein concerning the interpretation of quantum physics is generally recognised as one of the great intellectual disputes in the history of science. What was the nature of the disagreement between them, and what were the arguments with which each defended his position? The fifth Solvay Conference, 1927 Einstein was not present at the Volta Centennial Conference at Como in September 1927, where Bohr first presented his theory of complementarity; Einstein first learned of Bohr's interpretation of quantum mechanics at the fifth Solvay Conference of Physics at Brussels in October 1927. In the discussion following Bohr's paper Einstein examined an imaginary experiment in which an electron passes through a slit in a diaphragm and impinges at a point on a hemispherical screen. This experiment, Einstein suggested, could be interpreted in either of two ways: the de Broglie–Schrödinger waves represent either ( a ) an ensemble of electrons spread out in space (but not an individual electron), or ( b ) a wave-packet corresponding to an individual electron. There is, he noted, a difficulty with the latter interpretation.
The Bohr-Einstein debates of the 20th century represent the most famous intellectual conflict in the history of quantum mechanics. For three decades, Albert Einstein and Niels Bohr clashed over the completeness of quantum theory, the nature of reality, and the role of the observer. Neither convinced the other, and the debate ultimately ended in a pragmatic stalemate: the Copenhagen interpretation was adopted, and metaphysical questions were banished from physics. We apply the Category Error Detector (CED) to this historical debate to demonstrate that both physicists were committing a shared category error. They were attempting to force the invariant, deterministic structure of the Abstraction axis into the localized, probabilistic framework of the Contingency axis. They lacked the two-axis geometry required to see that they were both right, but describing different layers of the manifold. We argue that the Solvay Conferences were the exact historical inflection point where Structural Rationalism should have been born. The failure to do so resulted in a century of theoretical aporia, culminating in the current crisis of unfalsifiable models and particle phantoms.
Abstract This conference was lauded by Heisenberg as, “officially, the completion of the quantum theory,” while Langevin remarked it was, “where the confusion of ideas reached its peak.” The conference was held just as the theory had reached maturity, only two years after Heisenberg’s matrix mechanics was invented. De Broglie argued for his pilot wave theory, which was shot down by Pauli using an incorrect argument and in later years was re-introduced as the de Broglie–Bohm theory. Heisenberg and Dirac debated the meaning of superposition and the “collapse” of the wave function. Bohr and Einstein engaged in their legendary debate. In the conference proceedings, we see the main contributors to the new theory attempt to come to terms with its enigmas.
The Bohr--Einstein debate is one of the more remarkable protracted intellectual exchanges in the history of physics. Its influence has been lasting: One of the few clear patterns in a 2013 survey about quantum foundations was that the physicists who believed Bohr to be correct were apt to say that Einstein had been wrong. The exchanges began when Bohr and Einstein first met in 1920, continued at the Solvay conferences of the following decade, reached a dramatic crescendo with the EPR paradox in 1935, and continued thereafter. Not every episode in this long story has been investigated equally. In particular, one late statement attributed to Bohr has received much more intense examination than Einstein's equally pithy reply.