Reply To: Quantum causal models, faithfulness and retrocausality (onl. 7/16 @ 11pm UTC+10)

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AvatarPeter Evans

Thanks, Mark – appreciate the input! A couple of comments…

On the footnote comment, I don’t think that dynamical and adynamical explanation should be exclusive. There are plenty of cases in science where two different explanations can be provided for the one phenomenon. For example (I can’t remember where I first heard this; maybe Harvey Brown’s book, or Jim Woodward’s), a helium balloon held by a passenger in a plane that is taking off floats towards the front of the plane. One explanation is that the air in the cabin moves inertially to the rear of the plane, making the front less dense—balloon moves forward. Another explanation is that the plane is an accelerating reference frame, which can be modelled as a gravitational field with the source toward the rear—balloon moves forward. We have a formal relationship between the explanations embodied by Einstein’s equivalence principle.

While the relationship between the 3D vs 4D cases of explanation the comment refers to are slightly different in form to this example, we have no reason to forgo our 3D explanations in favour of a 4D one (despite the beneficial elements of the 4D one). Keeping in mind that we humans are without exception dynamical beings (we experience the world dynamically in time), it seems disingenuous to deny the possibility of a causal (dynamical) explanation.

Keep in mind, also, that anything one says about global constraints and retrocausation must also be said about ordinary causation. Seeing as we’ve been able to produce very successful (albeit incomplete, according to this forum) dynamical theories modelling the world, and we regularly employ causal/interventionist concepts as we explore the world, if the world turned out to obey global constraints as per RBW, we should be able to provide a story joining the two explanations together. If we could do that for ordinary causation, there seems to be no reason it wouldn’t work for retrocausation.

Thus there’s no reason why retrocausality, dynamics or interventions should be “superfluous”. Yes, a properly retrocausal picture, like Ken’s Lagrangian framework and your RBW, is best represented as adynamical, but one would hope a dynamical picture can be extracted therefrom (of the sort that can give us causal and retrocausal explanations). Dynamics, causation, interventions, and so on look a bit different to what we would usually think (and it is an interesting, and largely incomplete, task to spell this out), but they are not, by my lights, inconsistent with the adynamical picture.

I’m just missing the connection, though, between this footnote comment and the issue of faithfulness. Could you please give a bit more detail for how these relate?



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