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Steve Gull, in unpublished work available on his Cambridge University homepage, has outlined a proof of Bells theorem using Fourier theory. Gulls philosophy is that Bells theorem can be seen as a no-go theorem for a project in distributed computing (with classical, not quantum, computers!). We present his argument, correcting misprints and filling gaps. In his argument, there were two completely separated computers in the network. We need three in order to fill all the gaps in his proof: a third computer supplies a stream of random numbers to the two computers, which represent the two measurement stations in Bells work. At the end of the day, one can imagine that computer replaced by a cloned, virtual computer, generating the same pseudo-random numbers within each of Alice and Bobs computers. Gulls proof then just needs a third step: writing an expectation as the expectation of a conditional expectation, given the hidden variables.
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Historically, Ehrenfests theorem (1927) is the first one which shows that classical physics can emerge from quantum physics as a kind of approximation. We recall the theorem in its original form. Next, we highlight its generalizations to the relativistic Dirac particle, and to a particle with spin and izospin. We argue that apparent classicality of the macroscopic world can probably be explained within the framework of standard quantum mechanics.
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