I was not surprised to see Matt Leifer's entry win first place in this year's FQXi essay contest. Yes, it's a good essay, well argued and worthy of a contest prize.
More important to me personally, however, is that it represents what I observe is a longtime Perimeter Institute and FQXi bias toward probability models based on Bayesian philosophy. For those not familiar with the difference between what are called Bayesian and Frequentist models -- a Bayesian assumes a definite probability on the interval [0,1], requiring a measure of personal belief in the correct probability outcome for a given problem. A frequentist model is objective, based on the average of a sufficient number of independent Bernoulli trials (throws of the dice) such that one's confidence in the correct probability for a given problem increases with the number of trials.
My reaction to Matt's conclusion that "My main argument is that, on the subjective Bayesian interpretation of probability, 'it from bit' requires a generalized probability theory" alternates between "of course," and "so what?"
The fact is, that a generalized probability theory based on Bayesian principles is oxymoronic. One gets from it what one assumes in the first place, and cannot get otherwise. So to conclude, "A subjective Bayesian analysis of noncontextuality indicates that it can only be derived within a realist approach to physics" is simply saying that realism is in the mind of the observer and nowhere else. In no philosophy except standard quantum theory is "realism" defined this way.
"At present, this type of derivation has only been carried out in the many-worlds interpretation," says Matt. Either he misunderstands what Everett's interpretation is actually saying, or he is trying to co-opt many-worlds to coat his theory in a pseudo-objective patina. The fact is, there is no collapse of the wave function in Everett's interpretation; therefore, no probability can be assigned to an outcome. Leifer concludes:
" ... but I expect it can be made to work in other realist approaches to quantum theory, including those yet to be discovered."
The only viable realist approach to quantum theory that I know of, that both forbids collapse of the wave function and fulfills the predictions of quantum measurement correlations demanded by standard quantum theory, is Joy Christian's measurement framework.
Very early on, I was concerned that Joy had sneaked Bayesian assumptions in by the back door -- which shows the extent to which even I have been indoctrinated -- in which case I would have dismissed the framework. It's clear now that no such probabilistic abracadabra infringes on the results.
The choice function of Bell-Aspect and CHSH type quantum experiments rests subjectively with the experimenter. The choice function in Joy's framework rests with random input to the continuous functions of nature independent of the experimenter. *That's* realism.
Tom