Reply To: Retrocausality is intrinsic to quantum mechanics


“I certainly don’t consider … exceeding the speed of light.” I think that is the problem. The setup/scenario in question here is exactly the sort wherein Bell showed — making a few other assumptions (like that the future cannot influence the past, that experimenters’ choices about what to measure can be considered “free” in the relevant sense, etc.) — that faster than light causation is *required*. So … *of course* … if you just decide a priori, up front, to refuse to consider the possibility of faster than light causal influences, you will end up convincing yourself that there is backwards in time causation, or that free will doesn’t exist, or some such thing. But arguments with unadmitted premises are never good/convincing.

And by the way, if the surprising conclusion one does end up endorsing in this situation is that there are backwards-in-time (but non-super-luminal!) causal influences, one really does not thereby elude causal influences that exceed the speed of light, because one can always “chain” or “zig-zag” backwards- and forwards-in-time influences to produce a net (indirect) influence across spacelike separation. So, while there are admittedly some other ways of looking at this, the idea of trying to avoid nonlocality (in Bell’s sense) by endorsing sub-luminal but retro-causal influences, always struck me as silly. You don’t actually succeed, that way, in avoiding the thing one wanted to avoid.

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