Editing Bell test (section)

== Experimental assumptions ==
In addition to the theoretical assumptions, there are practical ones. There may, for example, be a number of "accidental coincidences" in addition to those of interest. It is assumed that no bias is introduced by subtracting their estimated number before calculating ''S'', but that this is true is not considered by some to be obvious. There may be synchronisation problems &mdash; ambiguity in recognising pairs because in practice they will not be detected at ''exactly'' the same time.

Nevertheless, despite all the deficiencies of the actual experiments, one striking fact emerges: the results are, to a very good approximation, what quantum mechanics predicts. If imperfect experiments give us such excellent overlap with quantum predictions, most working quantum physicists would agree with [[John Stewart Bell|John Bell]] in expecting that, when a perfect Bell test is done, the Bell inequalities will still be violated. This attitude has led to the emergence of a new sub-field of physics known as [[quantum information theory]]. One of the main achievements of this new branch of physics is showing that violation of Bell's inequalities leads to the possibility of a secure information transfer, which utilizes the so-called [[quantum cryptography]] (involving entangled states of pairs of particles).