Reply To: Retrocausality is intrinsic to quantum mechanics

Aurelien Drezet

Dear Daniel, Your example remind me aslo the old paper by elitzur [] where retrocausality is also involved. This is of course connected to the work by Pres. My question concerning your claim that QM is retrocausal goes like that: 1) what do you mean by QM 2) how can you prove that this version of QM is retrocausal.
To 1) I think you mean QM from the macroscopic observer point of view (i.e., Bohr?). such an observer dont care about the ontology of the real staff (like Bohmian could do instead). So, in this orthodox version of QM you will only collect clicks on your detectors and makes statistics. But then there is no proof of retrocausality since you can only observe the presence or absence of entanglement between Alice and Bob by making correlations with Jim. If Jim is missing data you will just observe a lot of uncorrelated points at A and B. We could thus claim that it is only your post analysis which showed that A and B were correlated even if it looks magical. Clearly, you cant use this scheme to transmit faster than light signal which could then be equivalent to backward causation and convince me. This is my answer to 2) It seems that you are thinking in a ontological way like Bohmian or Rod Sutherland do. Then it seems that you are going beyond the ‘macroscopic observer view’ of QM. Now if you take an ontological view like the one of Rod Sutherland you have a retrocausal theory from the ground (I still dont konw if the theory is correct or not but let admit it here). Still this retrocausality will stay hidden like in your example and I dont think that there is any example demonstrating retrocausality from the view of macroscopi observer otherwise this could look like a time machine?
I precise also that I am not convinced by the point of Travis Norsen. Bohmian mechanics neeed a special foliation to explain the delayed entanglement. This is not very elegant to go back to the old aether concept after 1 century of relativity isn’ it ? I would like to knwo the point of view of Travis on that point as well.

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