Reply To: Are retrocausal accounts of nonlocality conspiratorial? A toy model.

[Nathan Argaman]

Hi Travis and Justin,

I’ve been meaning to get aroud to responding to you for quite a few days now, and I feel that perhaps I should apologize for taking so long. But then one of the first items in my response is to say that I liked your description, Travis, with “falling off the back burner.” So perhaps I’ll leave it at that.

I agree essentially with everything you said, Justin, in your reply to my previous post. The only exception is that I would like to follow Bell’s use of lambda, even though he assumed local causality and I am now discussing retrocausal models. And I would like to use retrocausality to save locality. Thus, I would say that lambda is a set of parameters or functions that describes everything that happens to the particles before they are detected, and not just their properties or attributes at the source. As Travis points out, that is not the only possibility (the way Bell used them, different possibilities may be equivalent, but now they aren’t).

Next, let me respond to Travis’ post. Although I clearly found the discussion of the scholarpedia article quite frustrating (and I still think you should at the very least mention the fact that you’re assuming the causal arrow of time in the main text, and not just in a footnote), at least you know what you’re doing! The foremost example of dismay for me was when I read the original piece by Shimony, Horne and Clauser on this [Dialectica 39,97 (1985)]. I had just given a talk at the Perimeter Institute on this (pirsa.org/06110017), the first time I had described my vague ideas to an audience with experts on the matter, and they directed me to this. The article briefly describes a situation where Alice and Bob do not care to decide for themselves which settings to use, and instead consult their secretaries, and somebody has prearranged with the manufacturer of their measurement devices to give the secretaries lists of parameter settings according to a data table of his choice, and to have the devices reproduce results from additional lists. Of course, you can then get anything you want! You can see the original reproduced in this link:
https://books.google.co.il/books?id=Aee0XfBUDZQC&pg=PA163&lpg=PA163&dq=Shimony+Bell+secretary&source=bl&ots=ByiclUvzfl&sig=GlTX4igWLrMmBMpBITjPLUGEVPk&hl=iw&sa=X&ved=0CEEQ6AEwBGoVChMIi6i3gLPlxgIVRLwUCh1megCb#v=onepage&q=Shimony%20Bell%20secretary&f=false
Now that is what earned this type of description the title “conspiratorial,” and for good reason. If you read through their discussion, you find that they were taking the causal arrow of time for granted all along, and in that context, indeed correlations between the device settings and the hidden variable must be conspiratorial. Bell responded, saying that such conspiracies would undermine any scientific inquiry. And that is absolutely right. I was very annoyed to find the idea of retrocausation essentially branded as unscientific in this way. The line of thought seems to be roughly this:
(a) It is suggested that retrocausation could lead to certain unexpected correlations, but
(b) Retrocausation itself is unexpected.
(c) Assume, then, the causal arrow of time, i.e., the absence of retrocausation.
(d) One finds that in this case the said correlations can only occur if something conspiratorial and unscientific occurs.
(e) The upshot is that retrocausation is branded as conspiratorial.
Am I wrong, Travis?

I really think that the word “conspiratorial” should only be used to describe theories or descriptions in which it is denied that the device settings are free variables (free variables are a well-defined mathematical notion, and therefore this conforms with the principle of not bringing in human beings; unfortunately, it seems that most of the community has proceeded to bring in the notion of free will, which is philosphically complicated, and thus does not improve our chances of making progress in quantum theory). But, of course, every author is entitled to his choice of words, so what can I do?

One more thing, Travis – if you want to take a look at another toy-model which, although it doesn’t necessrily reproduce anything of QM, at least would seem to alleviate your fear that the very definition of things would “crumble away,” I suggest you take a look at Ken’s work:
http://www.mdpi.com/2078-2489/5/1/190 , referenced in his post # 2834 within the discussion of his own contribution here.

Now, you have gone on and continued to have a very interesting discussion to which I would also like to respond, but let me end this post here, and then begin another one soon.

Best, Nathan.