Title: The Einstein-Podolsky-Rosen Argument in Quantum Theory (Stanford Encyclopedia of Philosophy)
Headings: The Einstein-Podolsky-Rosen Argument in Quantum Theory
The Einstein-Podolsky-Rosen Argument in Quantum Theory
1. Can Quantum Mechanical Description of Physical Reality Be Considered Complete?
1.1 Setting and prehistory
1.2 The argument in the text
1.3 Einstein’s versions of the argument
2. A popular form of the argument: Bohr’s response
3. Development of EPR
3.1 Spin and The Bohm version
3.2 Bell and beyond
Bibliography
Academic Tools
Other Internet Resources

Content: The experiment imagines a box that contains a clock set to time precisely the release (in the box) of a photon with determinate energy. If this were feasible, it would appear to challenge the unrestricted validity of the Heisenberg uncertainty relation that sets a lower bound on the simultaneous uncertainty of energy and time. ( See the entry on the Uncertainty Principle and also Bohr 1949, who describes the discussions at the 1930 conference.) The uncertainty relations, understood not just as a prohibition on what is co-measurable, but on what is simultaneously real, were a central component in the irrealist interpretation of the wave function. Jammer (1974, p. 173) describes how Einstein’s thinking about this experiment, and Bohr’s objections to it, evolved into a different photon-in-a-box experiment, one that allows an observer to determine either the momentum or the position of the photon indirectly, while remaining outside, sitting on the box. Jammer associates this with the distant determination of either momentum or position that, we shall see, is at the heart of the EPR paper. Carsten Held (1998) cites a related correspondence with Paul Ehrenfest from 1932 in which Einstein described an arrangement for the indirect measurement of a particle of mass m using correlations with a photon established through Compton scattering. Einstein’s reflections here foreshadow the argument of EPR, along with noting some of its difficulties. Thus without an experiment on m it is possible to predict freely, at will, either the momentum or the position of m with, in principle, arbitrary precision. This is the reason why I feel compelled to ascribe objective reality to both.