Saving Bohr

Dan Thomas

Michael D. Gordin

Françoise Balibar

SUMMARY. — The idea of complementarity may be viewed as the core of Bohr's strategy, in 1927, to save both observation and definition. To this end, Bohr sought to incorporate, within the new quantum theory, the usual concepts of space and time, as well as the invariance principles and their associated conservation laws. At the time, Bohr saw himself as following in the footsteps of Einstein, who, in 1905, used a similar strategy to resolve the apparent contradiction between the constancy of the velocity of light and galilean invariance. By clarifying Bohr's deliberately vague notions, Dirac made the search for invariance transformations the aim of quantum physics. Dirac's work thus illustrates the importance of Bohr's of 1927 for the future development of theoretical physics.

Hrvoje Nikolić

In 1930, Einstein argued against the consistency of the time–energy uncertainty relation by discussing a thought experiment involving a measurement of the mass of the box which emitted a photon. Bohr seemingly prevailed over Einstein by arguing that Einstein's own general theory of relativity saves the consistency of quantum mechanics. We revisit this thought experiment from a modern point of view at a level suitable for an undergraduate readership and find that neither Einstein nor Bohr was correct. Instead, this thought experiment should be thought of as an early example of a system demonstrating nonlocal 'EPR' quantum correlations, five years before the famous Einstein–Podolsky–Rosen paper.

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