Bell's fifth position
Gerard 't Hooft is searching for a deterministic and local theory to underlie quantum mechanics. By Bell's theorem this should not be possible, but the theorem does have some small print. 't Hooft knows this and says: "one does not have the freedom to do arbitrary measurements at the Planck scale". However, this is no escape, because we still appear to have the freedom to do Bell-type experiments at the macroscopic level, and 't Hooft's theory has to accommodate those experiments too. I am not happy with the solution that the photons know in advance how they are going to be measured since the experimenter's choices were predetermined at the time of the big bang!
I propose another reconcilation of 't Hooft's theory-in-spe with the success of quantum mechanics at explaining the real world: a Bell-inequality violating loophole-free Bell-type experiment can never be carried out because quantum mechanics itself prohibits the required initial conditions - the feasibility to create "to order" a bipartite system of two well separated and well localized components, in close to a Bell entangled state. One could think of this as a kind of uncertainty relation.
I call this point of view "Bell's fifth position" since John Bell listed four possible positions to hold in the light of the theoretical violation of his inequality by quantum mechanics. It turns out that several others hold the same or a similar view : Emilio Santos and Iain Perceval, to mention but two. Bell admitted in a letter to Santos that the fifth position is a logical possibility, though Bell said that he did not expect it to be the answer.
To summarize: it could be that quantum mechanics itself prevents us from carrying out a definitive experiment to prove that there cannot be a local and deterministic theory from which QM emerges. So we will never know; 't Hooft's quest is not doomed from the start; a quantum computer may never succeed in factoring large integers, ... .
To physicists who think this is all stupid I would like to say: well, go ahead then, and perform a loophole free and succesful Bell experiment.
A few years ago no physicist was intending to do a loop-hope free experiment: after all, all the loopholes had been closed, hadn't they? The whole topic was getting distinctively unfashionable. Fortunately I can now report that several prominent groups are thinking very hard about doing it. Maybe in five years, manybe in ten... I certainly agree that it is very important to try. We shall see. (I don't have an opinion about whether or not they will succeed though I do suspect it might take thirty years if it happens at all).
Time, Finite Statistics, and Bell's Fifth Position