Home › Forums › 2015 International Workshop on Quantum Foundations › Bohm’s theory › Counterfactual communication protocol › Reply To: Counterfactual communication protocol
Dear Lev, Two quick (and arguably off-topic) points about your previous comment to me above (#2744).
First, you seem to be using the word “beable” to mean something like “hidden variable” (i.e., stuff postulated to exist in addition to the wave function). I understand Bell’s term in a different way, though — as referring to whatever a theory says exists. So for you, as an MWI/Everett guy, it’s not that you don’t “feel a particular need for beables”, but, I think, rather, that you see no need for beables other than the wave function of the universe (which, for you, is the one and only beable). In a way this is just a pointless quibble about how to use a word, but I wouldn’t want there to be any kind of misunderstanding (on the part of other people reading this exchange) about the fact that MWI/Everett does postulate that the universal wave function (and only that!) is physically real, i.e., I’d say, a beable.
And then second (and relatedly) you indicated that you prefer MWI/Everett over Bohm in part because MWI/Everett does not include action at a distance. I have for a long time found this claim (which Everettians always make) very puzzling. “Action at a distance” refers, of course, to the sorts of faster-than-light causal influences (influences outside of the future light cone) that Bell took himself to have established. The point is that it really only makes any sense to apply this notion (or its absence, “local causality”) to physical goings-on in ordinary 3D physical space (or 4D spacetime). But I simply don’t understand how you can claim that MWI/Everett is a local theory in this sense (if that is what you meant to claim?), or what you would even take such a claim to *mean*, when it is so unclear (as I think you acknowledged?) how the beable posited by MWI/Everett (namely the universal wave function) relates to anything like a distribution of matter in 3D space / 4D spacetime. Do you have some specific model/idea in mind for how we go from the quantum state / wave function of the universe, to some kind of story about physical processes in 3D/4D to which notions like “local”, “action at a distance”, etc., can even be meaningfully applied? Or maybe when you say there’s no action at a distance in Everett’s theory, you don’t actually mean that the theory is locally causal (in anything like Bell’s sense) but you instead only mean something formal, like that the equations defining the theory’s dynamics respect Lorentz invariance. That I would probably agree with. But then to me it remains far from clear why I should care about that, or what it has to do with relativity theory (and its claims, e.g., about the structure of 4D spacetime), when it remains completely unclear what if anything the theory is even saying about physical goings on in 4D spacetime. Anyway, can you help me understand what you have in mind with this claim that Everett avoids the kind of nonlocality that is present in Bohm’s theory?