ABSTRACT: 82 years ago Einstein, Podolsky, and Rosen
published a paper with the aim of showing that the wave function in
quantum mechanics does not provide a complete description of reality.
The gedanken experiment showed that quantum theory, as interpreted by
Niels Bohr, leads to situations where distant particles, each with their
own “elements of reality”, could instantaneously affect one another.
Such action at a distance seemingly conflicts with relativity. The hope
was that a local theory of quantum mechanics could be developed where
individual particles are governed by elements of reality, even if these
elements are hidden from us. This concept is known as local realism.
1964 John Bell, continuing Einstein’s line of investigation, showed
that the predictions of quantum mechanics are fundamentally incompatible
with any local realistic theory. Bell’s theorem has profoundly shaped
our modern understanding of quantum mechanics, and lies at the heart of
quantum information theory. However, all experimental tests of Bell’s
theorem have had to make assumptions that lead to loopholes.