Can Quantum-Mechanical Description of Physical Reality Be Considered both Complete and Local?

Abstract

This chapter offers an analysis of Bohr’s exchanges with Einstein concerning the completeness and, then, locality of quantum mechanics, most especially Einstein, Podolsky, and Rosen’s article and Bohr’s reply, both published under the same title—“Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?”—in 1935. EPR’s article introduced a thought experiment, the EPR experiment, and offered a particular argument concerning it, EPR’s argument, which led EPR to conclude that quantum mechanics is incomplete, or else nonlocal in Einstein’s sense of entailing instantaneous physical connections, forbidden by relativity. This argument and these conclusions were questioned in Bohr’s counterargument, which offers a different analysis of the EPR experiment and derives different conclusions concerning its meaning and implications. After a general introduction given in Section 8.1, Sections 8.2 and 8.3 focus on those parts of EPR’s and Bohr’s arguments, respectively, that concern the completeness of quantum mechanics. Section 8.4 discusses the question of locality in both arguments. I offer a close overall reading of Bohr’s reply in Chapter 10 where I also discuss Einstein’s arguments that address the statistical nature of quantum mechanics from the perspective of the EPR-type experiments.