Reply To: Causality and quantum mechanics (Online 7/15 @ 10 p.m. to Midnight UTC-7)

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Ken Wharton

Hi David and Matt,

Apologies for taking so long to get to this very interesting piece! Some notes:

– This is probably my own personal bias showing, but at the end of the first column, I thought at first that you were talking about running the experiment in two different time-directions. So you might help people like me here if you just note that you’re talking about switching A and B.

– How much of this analysis requires “maximally mixed” states to be ontic, rather than epistemic? It seemed to me that it didn’t matter in this analysis; do you agree?

– While I appreciate the distinction you’re making between causation and correlation, I’m not sure you want to claim that your “correlator” is “weaker than being a cause”. The language you use implies there’s no causation for a correlator-C, but that’s like telling me I can’t have a causal influence on a random unknown bit if I’m giving a choice of flipping it or not. In Huw’s interventionist account of causation, I’d still “have a causal influence” on the outcome, while in your language it would be “weaker than a cause”.

– Even though your *definitions* of different C’s depend on starting with a maximally-mixed state, wouldn’t those C’s “maintain” their status (as causal, correlator, etc.) whether or not they were part of this particular measurement-chain that started with I? I would think that they would, but this raises the same issue as above. Any given correlator-C can clearly become an ordinary cause if the initial preparation is no longer maximally mixed, and can become known to the C-controller. Since nothing has changed about C itself in this scenario, I would think this would be more evidence that your “correlation” *includes* (ordinary) causation, and is not mutually exclusive of it.

– David, I can’t believe you didn’t cite your own paper (our “action duality” piece) along with [6] and [7]! 🙂

– Any explicit insight you have as to non-maximally entangled states in this framework would be much appreciated; that’s what I’m working on myself these days.

Best, Ken

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