Does Bells Inequality rule out local theories of quantum mechanics?
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 sets of commuting observables.” Observables from different sets are “noncommuting observables”. A well known e
