I( can't believe that. That's much too concrete to be real. So Martin Klein of Yale University quotes Niels Quantum theory, of which Bohr was one of the main progenitors, is anything but too concrete. This attitude of Bohr's may reflect both what he saw in quantum theory and what he gave to it, and it could be a basis for the famous controversy between him and Albert Einstein that lasted more than three decades. In their lifetimes neither made the other budge. They died good friends but conceptually unreconciled. Their colleagues, pupils and followers have ramified and continued the argument. Many of them and others gathered recently at the American Academy of Arts and Sciences in Cambridge, Mass., for Symposium Commemorating the Centennial of Niels Bohr. A series of experiments done near Paris has put a definite advantage in Bohr's court with respect to a very important part of the argument, the challenge historically known as the Einstein-Podolsky-Rosen (EPR) paradox. Einstein is famous for remarks about God not throwing dice. These epigrams led to a general belief that his disagreement with quantum mechanics was based on problems of determinism and causality, an unhappiness with the uncertain, statistical quality of quantum mechanical predictions. Not so, said Einstein himself (in his correspondence with Max Born, cited by N. David Mermin of Cornell University in Ithaca, N.Y, in the April 1985 PHYSICS TODAY). The most basic unhappiness, prior to Einstein's admitted dislike of the statistical aspects, was over reality, the reality of physical attributes and properties.
I( can't believe that. That's much too concrete to be real. So Martin Klein of Yale University quotes Niels Quantum theory, of which Bohr was one of the main progenitors, is anything but too concrete. This attitude of Bohr's may reflect both what he saw in quantum theory and what he gave to it, and it could be a basis for the famous controversy between him and Albert Einstein that lasted more than three decades. In their lifetimes neither made the other budge. They died good friends but conceptually unreconciled. Their colleagues, pupils and followers have ramified and continued the argument. Many of them and others gathered recently at the American Academy of Arts and Sciences in Cambridge, Mass., for Symposium Commemorating the Centennial of Niels Bohr. A series of experiments done near Paris has put a definite advantage in Bohr's court with respect to a very important part of the argument, the challenge historically known as the Einstein-Podolsky-Rosen (EPR) paradox. Einstein is famous for remarks about God not throwing dice. These epigrams led to a general belief that his disagreement with quantum mechanics was based on problems of determinism and causality, an unhappiness with the uncertain, statistical quality of quantum mechanical predictions. Not so, said Einstein himself (in his correspondence with Max Born, cited by N. David Mermin of Cornell University in Ithaca, N.Y, in the April 1985 PHYSICS TODAY). The most basic unhappiness, prior to Einstein's admitted dislike of the statistical aspects, was over reality, the reality of physical attributes and properties.
The 1935 paper by Einstein, Podolski and Rosen represented the culmination of a long debate that had begun soon after quantum theory was developed in the 1920s. One of the main protagonists in this discussion was Niels Bohr, a Danish physicist who worked in Copenhagen until, like so many other European scientists of his time, he became a refugee in the face of the German invasion during the Second World War. As we shall see, Bohr's views differed strongly from those of Einstein and his co-workers on a number of fundamental issues, but it was his approach to the fundamental problems of quantum physics that eventually gained general, though not universal, acceptance. Because much of Bohr's work was done in that city, his ideas and those developed from them have become known as the ‘Copenhagen interpretation’. In this chapter we shall discuss the main ideas of this approach. We shall try to appreciate its strengths as well as attempting to understand why some believe that there are important questions left unanswered. When Einstein said that ‘God does not play dice’, Bohr is said to have replied ‘Don't tell God what to do!’ The historical accuracy of this exchange may be in doubt, but it encapsulates the differences in approach of the two men. Whereas Einstein approached quantum physics with doubts, and sought to reveal its incompleteness by demonstrating its lack of consistency with our everyday ways of thinking about the physical universe, Bohr's approach was to accept the quantum ideas and to explore their consequences for our everyday ways of thinking.
The 1935 paper by Einstein, Podolski and Rosen represented the culmination of a long debate that had begun soon after quantum theory was developed in the 1920s. One of the main protagonists in this discussion was Niels Bohr, a Danish physicist who worked in Copenhagen until, like so many other European scientists of his time, he became a refugee in the face of the German invasion during the Second World War. As we shall see, Bohr's views differed strongly from those of Einstein and his co-workers on a number of fundamental issues, but it was his approach to the fundamental problems of quantum physics that eventually gained general, though not universal, acceptance. Because much of Bohr's work was done in that city, his ideas and those developed from them have become known as the ‘Copenhagen interpretation’. In this chapter we shall discuss the main ideas of this approach. We shall try to appreciate its strengths as well as attempting to understand why some believe that there are important questions left unanswered. When Einstein said that ‘God does not play dice’, Bohr is said to have replied ‘Don't tell God what to do!’ The historical accuracy of this exchange may be in doubt, but it encapsulates the differences in approach of the two men. Whereas Einstein approached quantum physics with doubts, and sought to reveal its incompleteness by demonstrating its lack of consistency with our everyday ways of thinking about the physical universe, Bohr's approach was to accept the quantum ideas and to explore their consequences for our everyday ways of thinking.
Albert Einstein once said that he does not believe in a God who plays dice. He was referring to the fundamental principle that quantum theory permits only statistical assertions concerning the values of physical quantities. This issue, namely, whether the description of Nature in statistical terms is complete or even consistent, was the subject of a very lively debate-dialogue between Einstein and Niels Bohr in the years 1920-1930. Nowadays there is no debate as the principles of quantum theory have been verified countless times in experiments. In this lecture (which requires no previous background) I shall discuss both classical and quantum probabilities. Although the meaning of probability remains the same in both contexts, the method of calculating them is different. I shall explain the strange but beautiful manner in which quantum probabilities are calculated, explaining the mathematical foundations in an elementary manner. The meaning of probability
The famously controversial 1935 paper by Einstein, Podolsky, and Rosen (EPR) took aim at the heart of the flourishing field of quantum mechanics. The paper provoked responses from the leading theoretical physicists of the day, and brought entanglement and nonlocality to the forefront of discussion. This book looks back at the seminal year in which the EPR paper was published and explores the intense debate it unleashed. These conversations in print and in private correspondence offer significant insight into the minds of pioneering quantum physicists including Niels Bohr, Erwin Schrödinger and Albert Einstein himself. Offering the most complete collection of sources to date – many published or translated here for the first time – this text brings a rich new context to this pivotal moment in physics history. Both researchers and students in the history and philosophy of science, and enthusiasts alike, will find this book illuminating.
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.