Einstein, Bohr, and Bell

Alain Aspect

Andrew Whitaker

1. Bohr and Einstein: Einstein and Bohr 2. The peace before the quantum 3. A glance at relativity 4. The slow rise of the quantum 5. Bohr: what does it all mean? 6. Einstein's negative views 7. Bohm, Bell and experimental philosophy 8. A round-up of recent developments 9. Bohr or Einstein? References Bibliography.

Henry J. Folse

Helen Infeld

Muhammad Suhail Zubairy

The first round of the Einstein–Bohr debates took place when Einstein challenged Bohr’s principle of complementarity at the Solvay conference in 1927 and Bohr successfully defended it. The most serious challenge, however, came in 1935 when a paper by Einstein, Podolsky, and Rosen (EPR) argued that quantum mechanics was incomplete through a gedanken experiment motivating an approach based on hidden variables. In this chapter, EPR’s arguments about the incompleteness of quantum mechanics and Bohr’s reply to them are presented. The ultimate answer came almost 30 years later, almost ten years after Einstein’s death, and was nothing that Einstein would have expected. Bell’s inequality and the subsequent Bell-CHSH inequality, that are satisfied by all theories based on the “self-evident truths” of reality and locality are discussed. The startling results that quantum mechanics violates Bell’s inequality and the experimental results are in agreement with the prediction of quantum mechanics are presented.