Undergrad New paper by physicists Ken Wharton and Nathan Argaman on Retrocausality

[kquantum]

I found this a very interesting article:

Retrocausality may sound like science fiction, but it might be the best way to explain certain features of the quantum world, as detailed in a major new paper by physicists Ken Wharton and Nathan Argaman. Published in Reviews of Modern Physics, Wharton and Argaman's paper analyses possible ways to model measurements of "entangled" particles. One reasonable option, they conclude, is to treat the future choices of experimentalists as inputs, using them to explain past events. This isn't quite time-travel, since those past events remain hidden in quantum uncertainty, but it would be a reversal of the usual direction of causation. The authors conclude that such future-input dependent models warrant further study and development, given that they are more compatible with the theory of relativity than are traditional non-local approaches.

K. B. Wharton and N. Argaman (2020) Bell’s theorem and locally mediated reformulations of quantum mechanics. Rev. Mod. Phys. 92, 021002.
https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.92.021002

 

[Halc]

There seem to be plenty of apparent 'effects before cause' such as any typical delayed-choice quantum experiment.
All of these have local explanations (without FTL travel or retrocausality) by any local interpretation of QM, but they do have FTL and retrocausal explanations by any counterfactual interpretation of QM.

The bottom line seems to be: if you can't send a message faster than light or to the past with your technique, they you haven't conclusively demonstrated retrocausality.

 

[DrChinese]

This version is not behind a paywall:

https://arxiv.org/abs/1906.04313

 

[RUTA]

It’s interesting to note that retrocausal models are still contextual. https://arxiv.org/abs/1708.00137

Abstract:
Realist interpretations of quantum mechanics presuppose the existence of elements of reality that are independent of the actions used to reveal them. Such a view is challenged by several no-go theorems that show quantum correlations cannot be explained by non-contextual ontological models, where physical properties are assumed to exist prior to and independently of the act of measurement. However, all such contextuality proofs assume a traditional notion of causal structure, where causal influence flows from past to future according to ordinary dynamical laws. This leaves open the question of whether the apparent contextuality of quantum mechanics is simply the signature of some exotic causal structure, where the future might affect the past or distant systems might get correlated due to non-local constraints. Here we show that quantum predictions require a deeper form of contextuality: even allowing for arbitrary causal structure, no model can explain quantum correlations from non-contextual ontological properties of the world, be they initial states, dynamical laws, or global constraints.

P. 4: Generally speaking, retrocausal approaches posit the existence of backwards-in-time causal influences to explain quantum correlations. The stated appeal of such approaches is that the consequent explanations retain some element of our classical notion of reality: local causality, determinate ontology, and counterfactual definiteness.

P. 17: We have shown that it is not possible to construct an ontological model that is both instrument and process non-contextual and also accords with the predictions of quantum mechanics. We take both forms of non-contextuality to be very reasonable assumptions if one wishes some aspect of "reality" to be describable in a manner that is independent of the act of experimentation. Thus our work shows that models that posit unusual causal, global or dynamical relations will not solve a key quantum mystery, that of contextuality.