Abstract Einstein was not in the audience at Bohr’s Como lecture, and their debate was joined in earnest at the fifth Solvay conference in Brussels in October 1927. All of quantum theory’s founders were present. Einstein excused himself for not having mastered the theory, and introduced a simple electron diffraction thought experiment for which he offered two conceptions. In the first, the wavefunction does not describe individual events and is purely statistical. In the second, the wavefunction does describe individual events, its modulus-square giving the probability of detecting the next diffracted electron at a specific position. In his view, the second conception could not stand, as it implies a ‘very peculiar mechanism of action at a distance’. Outside the conference room Einstein peppered Bohr with thought experiments devised to reveal the theory’s confusions or contradictions. The exchanges between them went on like a game of chess, with Bohr emerging the victor.
Abstract Einstein was not in the audience at Bohr’s Como lecture, and their debate was joined in earnest at the fifth Solvay conference in Brussels in October 1927. All of quantum theory’s founders were present. Einstein excused himself for not having mastered the theory, and introduced a simple electron diffraction thought experiment for which he offered two conceptions. In the first, the wavefunction does not describe individual events and is purely statistical. In the second, the wavefunction does describe individual events, its modulus-square giving the probability of detecting the next diffracted electron at a specific position. In his view, the second conception could not stand, as it implies a ‘very peculiar mechanism of action at a distance’. Outside the conference room Einstein peppered Bohr with thought experiments devised to reveal the theory’s confusions or contradictions. The exchanges between them went on like a game of chess, with Bohr emerging the victor.
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 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.
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 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.
Abstract Einstein receive a letter from Bose and developed his idea into Bose–Einstein statistics. He also used De Broglie’s idea to clarify wave-particle duality. De Broglie also inspired Schrödinger to develop his equation in quantum mechanics. Bothe and Geiger ruled out Bohr’s BKS theory experimentally. Heisenberg came up with wave mechanics on the island of Heligoland. Born and Jordan realised that matrices were the mathematical key to quantum mechanics. Schrödinger developed an equivalent formalism. Heisenberg formulated his uncertainty principle. The Solvay Conference in Brussels in October 1927 was the scene for the famous Einstein–Bohr showdown, in which Bohr refuted Einstein’s thought experiment calculated to show that quantum mechanics was incomplete, a subject to which Einstein would return years later in the EPR paper. In Brussels, Einstein met Elisabeth Queen of the Belgians, a violinist with whom he would play chamber music many times. Einstein collaborated with Emil Rupp on experiments to explore quantum effects. Rupp turned out to be a charlatan who duped Einstein with fabricated results. Einstein became involved with the academic politics of the Hebrew University of Jerusalem, and clashed with its head, Judah Magnes.