[Physics FAQ] - [Copyright] Updated May 1996 by PEG (thanks to
Colin Naturman). Updated August 1993 by SIC. Original by John
Blanton. In 1935 Albert Einstein and two colleagues, Boris
Podolsky and Nathan Rosen (EPR) developed a thought experiment
to demonstrate what they felt was a lack of completeness in
quantum mechanics. This so-called "EPR Paradox" has led to much
subsequent, and still ongoing, research. This article is an
introduction to EPR, Bell's Inequality, and the real experiments
that have attempted to address the interesting issues raised by
this discussion. One of the principal features of quantum
mechanics is that not all the classical physical observables of
a system can be simultaneously well defined with unlimited
precision, even in principle. Instead, there may be several sets
of observables that give qualitatively different, but
nonetheless complete (maximal possible), descriptions of a
quantum mechanical system. These sets are sets of "good quantum
numbers," and are also known as "maximal