It seems to me that none of these interpretations [of quantum theory] is at all satisfactory, and in the gap left by the failure to ?nd a sensible way to understand quantum reality there has grown a pathological industry of pseudo-scienti?c gobbledegook. Claims that entanglement is consistent with telepathy, that parallel universes are scienti?c truths, that consciousness is a quantum phenomena abound in the New Age sections of bookshops but have no rational foundation. Physicists may complain about this, but they have only themselves to blame.

But there is one remaining possibility for an interpretation that has been unfairly neglected by quantum theorists despite—or perhaps because of—the fact that it is the closest of all to commonsense. This view that quantum mechanics is just an incomplete theory, and the reason it produces only a probabilistic description is that it does not provide suf?cient information to make de?nite predictions. This line of reasoning has a distinguished pedigree, but fell out of favour after the arrival of Bell’s theorem and related issues. Early ideas on this theme revolved around the idea that particles could carry ‘hidden variables’ whose behaviour we could not predict because our fun- damental description is inadequate. In other words two apparently identical electrons are not really identical; something we cannot directly measure marks them apart. If this works then we can simply use only probability theory to deal with inferences made on the basis of our inadequate information. After Bell’s work, however, it became clear that these hidden variables must possess a very peculiar property if they are to describe our quantum world. The property of entanglement requires the hidden variables to be non-local. In other words, two electrons must be able to communicate their values faster than the speed of light. Putting this conclusion together with relativity leads one to deduce that the chain of cause and effect must break down: hidden variables are therefore acausal. This is such an unpalatable idea that it seems to many physicists to be even worse than the alternatives, but to me it seems entirely plausible that the causal structure of space-time must break down at some level. On the other hand, not all ‘incomplete’ interpretations of quantum theory involve hidden variables.

One can think of this category of interpretation as involving an epistemological view of quantum mechanics. The probabilistic nature of the theory has, in some sense, a subjective origin. It represents de?ciencies in our state of knowledge. The alternative Copenhagen and Many-Worlds views I discussed above differ greatly from each other, but each is characterized by the mistaken desire to put quantum probability in the realm of ontology.

Peter Coles, From Cosmos to Chaos

I am far too ignorant to say how plausible Coles’s thesis is, other than that acausality doesn’t seem any less plausible than decoherence or Everett’s multiple-worlds. And it has the side effect of delegitimizing one of the most overused scientific metaphors of our time. (The most egregious example offhand being Michael Frayn’s Copenhagen.)