
Ulrich Mohrhoff joined the group Workshop on Wigner’s Friend 2018 9 months ago


Ulrich Mohrhoff commented on the post, Quantum Nonlocality Explained (Open Peer Review Paper) 4 years, 7 months ago
In my previous comment I claimed that “Quantum mechanics itself implies that standard assumptions of spatiotemporality must be rejected.” I agree with the referee that this claim was too strong. Virtually every interpretation of quantum mechanics (including those which modify the theory’s formal apparatus or postulate unobservable beables) doe…[Read more]

Ulrich Mohrhoff commented on the post, Quantum Nonlocality Explained (Open Peer Review Paper) 4 years, 8 months ago
Author’s responses:
I have read the manuscript “Quantum Nonlocality Explained”, submitted to IJQF. The author’s overall thesis appears to be that, in an interpretation of quantum mechanics in which certain standard assumptions of spatiotemporality are rejected, the quantum correlations (which Bell argued prove the existence of nonlocal, i.e.,…

Ulrich Mohrhoff wrote a new post, Quantum Nonlocality Explained 4 years, 8 months ago
The preposterous title of this post is also the title of my contribution to the Special Issue on Quantum Nonlocality and Reality — 50 Years of Bell’s theorem.
Abstract: Quantum theory’s violation of remote outcome independence is assessed in the context of a novel interpretation of the theory, in which the unavoidable distinction between the classical and quantum domains is understood as a distinction between the manifested world and its manifestation.
The originally submitted manuscript is available via this link. An extensively revised version was uploaded on December 6, 2014. In the latest version, uploaded on February 11, 2015, a few erroneous (but inconsequential) lines have been removed.
UPDATE 11 March 2016: This paper has morphed into “Quantum mechanics in a new light”, which has been published in Foundations of Science, DOI: 10.1007/s1069901694876.

Report of referee A:
I have read the manuscript “Quantum Nonlocality Explained”, submitted to IJQF. The author’s overall thesis appears to be that, in an interpretation of quantum mechanics in which certain standard assumptions of spatiotemporality are rejected, the quantum correlations (which Bell argued prove the existence of nonlocal, i.e., fasterthanlight, causation) can instead be understood in a different way. It is not really clear to me what this different way is supposed to be. That is, I cannot tell whether the author thinks that his interpretation provides a *local* explanation of the correlations, or instead one that is, while still nonlocal, superior in some way to the explanations provided by the several extant realistic versions of QM. Probably he thinks that the very idea of clearly distinguishing local from nonlocal explanations is invalid, insofar as it presupposes standard notions of spatiotemporality. But then it is not clear to me what the point is.
Overall, I cannot recommend the paper for publication, for the simple reason that I find it utterly incomprehensible. The part I found clearest was the passage at the end of section 4 in which the author makes the point that the usual causal story involved in two subsequent spin measurements on a single particle is timeasymmetric. This reminded me of the work of, for example, Huw Price and Ken Wharton, and I expected the paper to turn to general notions of timesymmetry and retrocausation and perhaps somehow apply the same kind of analysis to the case of two spin measurements on spatiallyseparated (and spinentangled) particles. But instead, in the following section on “Quantum Nonlocality”, the author instead retreats to the (to me) incomprehensible philosophical word play that had dominated the first several sections of the paper. But to me, the idea that “the causality responsible for quantum theory’s violation of remote outcome independence need not be of the familiar spatiotemporal kind” does not provide anything I would call an *explanation* of quantum nonlocality. I’m sure the author thinks that his fleshingout of the particular “kind” of nonspatiotemporal causation that he discusses does provide an explanation of something. But as I said, all of this is, to me, completely incomprehensible; it is like the meaningless word play of the continental philosophers and is simply not in the same universe as what I would regard as an explanation of the Bellinequalityviolating quantum correlations that is appropriate in physics.

Author’s responses:
I have read the manuscript “Quantum Nonlocality Explained”, submitted to IJQF. The author’s overall thesis appears to be that, in an interpretation of quantum mechanics in which certain standard assumptions of spatiotemporality are rejected, the quantum correlations (which Bell argued prove the existence of nonlocal, i.e., fasterthanlight, causation) can instead be understood in a different way.
Quantum mechanics itself implies that standard assumptions of spatiotemporality must be rejected. It is not clear to me what the referee means by saying that the quantum correlations can be understood in a different way. Different from what? How are they usually understood if not as correlations between outcomes of measurements?
It is not really clear to me what this different way is supposed to be. That is, I cannot tell whether the author thinks that his interpretation provides a *local* explanation of the correlations, or instead one that is, while still nonlocal, superior in some way to the explanations provided by the several extant realistic versions of QM.
Whether the author thinks that his interpretation provides a local explanation of the correlations, can be discovered by reading his manuscript, in which he concludes (on p. 3) that “The spatial differentiation of the physical world is incomplete. Physical space (as distinct from a calculational tool) cannot be modeled as an actually existing manifold of points.” Locality therefore is not an option.
Probably he thinks that the very idea of clearly distinguishing local from nonlocal explanations is invalid, insofar as it presupposes standard notions of spatiotemporality. But then it is not clear to me what the point is.
It is perfectly legitimate, and even necessary for the point being made, to clearly distinguish local from nonlocal explanations, the point being made being that in a world that is incompletely differentiated spacewise, local explanations are impossible.
Overall, I cannot recommend the paper for publication, for the simple reason that I find it utterly incomprehensible. The part I found clearest was the passage at the end of section 4 in which the author makes the point that the usual causal story involved in two subsequent spin measurements on a single particle is timeasymmetric.
I am not in the least surprised that the referee finds the paper incomprehensible. The vast majority of physicists are on very shaky ground when it comes to such metaphysical issues as the relation of the formal apparatus of quantum mechanics to the actual physical world. (This point is lucidly made in Ref. 34 by Dieks, editor of Studies in History and Philosophy of Modern Physics.) Understandably so, since thinking outside the box framed by the settheoretic conception of physical space and time and the atavistic notion that a quantum state represents a kind of evolving instantaneous state in a sense close to the classical sense of “state”, would draw too much time and mental energy away from the often excellent but chiefly mathematical work that they are used to doing and that is expected from them. (Unfortunately thinking inside this box is also what renders the objectification problem insoluble and quantum mechanics semantically inconsistent.) It is thus equally unsurprising that the referee feels most comfortable with Sect. 4 — the only section containing mathematical formulae. (The shortage of mathematical formulae in this paper is readily explained: one cannot get at the physical meaning of a mathematical formalism by writing down more mathematical formulae.)
It is a matter of rare luck to find a referee capable of “getting a feeling” (see the quote by Dieks on p. 16) for the interpretational scheme outlined in this paper. This happened to me with my Ref. 5 [Quantum mechanics and the manifestation of the world, Quantum Studies: Mathematics and Foundations 1 (3–4) 195–202], which is similar in content to the present paper, and which according to the anonymous referee of that journal “describes a unique and refreshingly different view of quantum theory”. The difficulty of course also lies in presenting such a view in the short space of a paper, though I doubt that the present referee would be able to make much sense of my Ref. 12 [Manifesting the Quantum World, Foundations of Physics 44 (6) 641–677], which runs into 37 pages.
This reminded me of the work of, for example, Huw Price and Ken Wharton, and I expected the paper to turn to general notions of timesymmetry and retrocausation and perhaps somehow apply the same kind of analysis to the case of two spin measurements on spatiallyseparated (and spinentangled) particles.
Did it escape the referee that the case of two spin measurements on EPRentangled particles in spacelike relation is discussed in Sect. 4? The lefthand side of Eq. 3 represents the correlations involved in logical order. If these correlations had anything to do with causal connections across spacetime, some of them would be pastdirected and therefore retrocausal. But the central point of the paper is that the usefulness of thinking in causal terms is limited to the manifested world; it cannot be applied to the manifestation of the world, with which quantum mechanics is fundamentally concerned.
But instead, in the following section on “Quantum Nonlocality”, the author instead retreats to the (to me) incomprehensible philosophical word play that had dominated the first several sections of the paper. But to me, the idea that “the causality responsible for quantum theory’s violation of remote outcome independence need not be of the familiar spatiotemporal kind” does not provide anything I would call an *explanation* of quantum nonlocality.
That kind of causality cannot be responsible. In a world that is not completely differentiated spacewise, it can play no explanatory role. I do not claim that this explains quantum nonlocality. I am content with explaining why the familiar spatiotemporal kind cannot explain the nonlocality that is implied by the incomplete differentiation of the spatial aspect of the physical world.
I’m sure the author thinks that his fleshingout of the particular “kind” of nonspatiotemporal causation that he discusses does provide an explanation of something. But as I said, all of this is, to me, completely incomprehensible; it is like the meaningless word play of the continental philosophers and is simply not in the same universe as what I would regard as an explanation of the Bellinequalityviolating quantum correlations that is appropriate in physics.
If my explanation turned out to be correct, looking for what the referee regards as an explanation of the Bellinequalityviolating quantum correlations would be looking for a key lost in a dark place under the lamppost just because there one can see.

A few comments in response to the author’s comments on my earlier comments:
“Quantum mechanics itself implies that standard assumptions of spatiotemporality *must* be rejected.”
I don’t agree. There are several extant theories (e.g., spontaneous collapse theories, the de Broglie – Bohm pilotwave theory, etc.) which explain the correlations in a way that doesn’t involve any rejection of what I would think of as “standard assumptions of spatiotemporality”. I mean, they explain the correlations *nonlocally*, as we know from Bell any theory must do, so there are questions about whether and how such theories are compatible with fundamental relativity. But they don’t give up on the project of giving a coherent spatiotemporal physical account, and indeed they succeed (at very least) in proving that this is possible. Given that, I can’t understand why anybody would want to give up on that project.
On a related point, the author writes that “Physical space … cannot be modeled as an actually existing manifold of points.” But this is simply not true. It can. The theories mentioned above allow a perfectly standard “actually existing manifold of points” account of space.
Finally, in response to the author’s paragraph explaining why he doesn’t find it surprising that I found the paper incomprehensible, I don’t think his remarks are on target at all. I work in foundations of physics and am perfectly comfortable with philosophical discussion of theories. The problem with the paper is not that it doesn’t contain enough mathematical formulas, but that what is said is to me incomprehensible. The paper announces in its title that it will “explain” quantum nonlocality. But what I find is instead a very vague and metaphysical story, with at best flimsy evidence supporting it, whose purpose appears to be to reconcile us to the view that nothing like an actual explanation of quantum nonlocality is possible. But there are already theories that provide actual (candidate) explanations. Perhaps the author’s views would be more convincing if he confronted these existing explanations and tried to show why they are inadequate, or how (appearances to the contrary notwithstanding) they exhibit the properties he thinks are required. Because as things stand now, they look like simple counterexamples to a bunch of the ideas (like that normal notions of spatiotemporality are untenable) that seem to motivate his proposals.

In my previous comment I claimed that “Quantum mechanics itself implies that standard assumptions of spatiotemporality must be rejected.” I agree with the referee that this claim was too strong. Virtually every interpretation of quantum mechanics (including those which modify the theory’s formal apparatus or postulate unobservable beables) does share those standard assumptions. What I should have said is that quantum mechanics renders the standard assumptions of spatiotemporality unobservable, via the indeterminacy principle, as argued in the paper. (This, by the way, is one reason why the wave function itself is unobservable.) If the theory itself tells me that a feature of its mathematical apparatus is unobservable, I conclude that that feature does not exist except as a feature of the mathematical apparatus. (From the pilotwave theory, I would expect an explanation why the theory’s surreal particle trajectories are unobservable, but such an explanation is not forthcoming. Invoking disturbance without proposing an explicit mechanism of disturbance does not qualify.)
The referee can’t understand why anybody would want to give up on the project of giving a coherent spatiotemporal physical account of the nonlocal correlations. How about this: The fact that the spatial differentiation of the physical world is incomplete (so that physical space cannot be modeled as an actually existing manifold of points) makes it possible to rigorously define “macroscopic object” (as opposed to the FAPP definitions provided by other interpretations) and to draw a rigorous distinction between the classical and quantum domains, a distinction not imposed from outside but implied by the theory itself. That counts for nothing?
To be sure, much effort has been and continues to be directed towards showing how the classical domain emerges from the quantum domain, so that it does not have to be treated as a separate domain. Recent attempts capitalize on decoherence, which, being a quantummechanical phenomenon confined to the unitary propagation of correlations, has no bearing on the existence of the correlata. As the insolubility proofs of the objectification problem have shown, unitary dynamics cannot account for the existence of a domain in which measurements have outcomes. In reality, neither domain can be dispensed with. What happens in the quantum domain can only be described in terms of correlations between measurement outcomes, and in order to describe measurements and their outcomes we need the language of interacting objects and causally connected events, which is applicable only to the classical domain. (See my arXiv:1410.5916 for an indepth discussion of this issue.)
The referee claims that spontaneous collapse theories and the pilotwave theory, among others, succeed in proving that it is possible to explain the nonlocal correlations without giving up on the project of giving a coherent spatiotemporal physical account. Considering that spontaneous collapse theories give up on the project of interpreting standard quantum mechanics, and that the pilotwave theory finds no acceptance outside a small quasireligious community, we seem to have good reason to enlarge the logical space of possible interpretations in the manner described in the paper, by adding to it a logical dimension across which the manifestation of the world (including its spatiotemporal features) takes place.
The referee reiterates that the problem with what is said in my paper is that it “is to me incomprehensible.” This ought to be reason to reject the referee, not the paper. His (or her) previous comparison of what is said therein to “the meaningless word play of the continental philosophers” makes one wonder if he (or she) could make much sense of Plato, Plotinus, Kant, Bergson, Husserl, or Wittgenstein (all engaged in meaningless word play?). The whole point of my paper is to enlarge the logical space of possible interpretations in order to make standard quantum mechanics semantically consistent, i.e., to establish the consistency of the quantummechanical calculus of correlations with the existence of its correlata. If the referee tries to collapse this expanded logical space into “the same universe as what I would regard as an explanation of the Bellinequalityviolating quantum correlations that is appropriate in physics,” it is no wonder that he or she can’t make sense of it.
I admit that the paper did not explain quantum nonlocality in the manner expected by the reviewer. The paper explains quantum nonlocality as a consequence of the process of manifestation, whose end result is the existence of the macroworld, which allows itself to be understood in terms of causal relations across time or spacetime. That process itself cannot be understood in these terms. And because, ontologically, quantum mechanics concerns this process, its correlations cannot be understood in these terms. If one nevertheless tries to so understand them, one behaves like someone who lost his key in a dark place but looks for it under a lamppost just because there he can see.
The paper has been extensively revised in an attempt to make it accessible to a somewhat larger readership. I must thank the referee for forcing me to make the necessary effort. The revised manuscript is available via this link.


Ulrich Mohrhoff replied to the topic Panel Discussion: How to make sense of the wave function? [Friday, EDT (UTC4): 3pm5pm] in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
The reason I’m late to the party is the oddity of my time zone (India), not that I want to have the last word!
To my mind, the wave function is a computing “machine” with inputs and outputs. (I’m happy to note that some of you would agree with this.) Pop in (a) the outcomes of the relevant measurements that were made, (b) the times when they were…[Read more]

Ulrich Mohrhoff replied to the topic Ruediger Schack: QBism and the character of the world in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Dear Ruediger,
Thank you for your patience and helpful answers!
Best,
Ulrich 
Ulrich Mohrhoff replied to the topic Ruediger Schack: QBism and the character of the world in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Dear Ruediger,
Many thanks for your detailed answers to my questions. I have a few comments, numbered 1 to 5 corresponding to your five answers.
1. Actually there are ways to assign probabilities to particle tracks (suitably defined), and your answer seems to accept that, having Alice making bets on Bob’s report about the tracks he saw.
2.…[Read more]

Ulrich Mohrhoff replied to the topic Ruediger Schack: QBism and the character of the world in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Good morning, Ruediger.
I’m glad to have this opportunity to pick your brains about QBism.
I begin with a question that is rhetorical since I answer it myself. Shouldn’t QBists make a distinction between a direct experience and an indirect experience such as the indirect experience of a spin component (via the direct experience of an apparatus…[Read more]

Ulrich Mohrhoff replied to the topic Why ever the wave function, of all things? in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Dear All,
My scheduled time is now up, but I will be happy to respond to any further questions or comments later.
Ulrich

Ulrich Mohrhoff replied to the topic Why ever the wave function, of all things? in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Ken, here I respond to your note concerning the last footnote of my paper, which I reproduce here for the benefit of the others:
“Actually, the diachronic correlations between events in timelike relation are as spooky as the synchronic correlations between events in spacelike relation. While we know how to calculate either kind of correlation,…[Read more]

Ulrich Mohrhoff replied to the topic Why ever the wave function, of all things? in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Ken, on to your next bundle of questions.
The other concern I have has to do with your use of the word “atemporal” near the end. Whenever I see this word accompany terms that normally have temporal meaning, I wonder whether the author is (accidentally or purposefully) imagining a 5th time dimension in which things can “happen” in some order w…

Ulrich Mohrhoff replied to the topic Why ever the wave function, of all things? in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Dear Ken,
Many thanks for your challenging questions. I’ll start with this one:
I’m reading from your approach that we can say nothing about what happens in between those ultimate measurements. So it’s not just interferometer arms in which nothing can be said to happen; it’s also all the space between us and a gravitationallylensing super…

Ulrich Mohrhoff replied to the topic Why ever the wave function, of all things? in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Richard,
You are welcome to ask questions any time, even now, if it’s not too late for you. (I just finished my breakfast.)
Ulrich

Ulrich Mohrhoff replied to the topic Ruediger Schack: QBism and the character of the world in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Dear all,
Maybe my recent critical appraisal of QBism may be of interest to some.
Ulrich 
Ulrich Mohrhoff replied to the topic Why ever the wave function, of all things? in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
So why is there no answer to the question “Which outgoing particle is identical with which incoming one?”? Because the incoming particles (and therefore the outgoing ones as well) are one and the same entity. What’s more, there is no compelling reason to believe that this identity ceases when it ceases to have observable consequences owing to the…[Read more]

Ulrich Mohrhoff replied to the topic Why ever the wave function, of all things? in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
The eigenvalue–eigenstate link is an interpretive principle that saves the appearances in the context of the wavefunction formulation of quantum mechanics. To go beyond a metaphysically sterile instrumentalism, a different interpretive principle needs to be used, as well as as a different formulation of quantum mechanics: Feynman’s. Both the…[Read more]

Ulrich Mohrhoff replied to the topic Why ever the wave function, of all things? in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
I suggest all participants write a few posts under his or her topic, which gives a clear summary of his or her ideas, before the workshop starts. This will be helpful for discussions during the workshop.
OK, here goes. The question I am asking here is this: why focus on the wave function? After all, there are (by a recent count) at least nine…[Read more]

Ulrich Mohrhoff replied to the topic The meaning of the wave function. in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
Richard, thank you for your response to my comments (both at #768).
I realize that our difference (if any) concerns the use we make of the wave function, and that there are different legitimate ways of using the wave function. One can even use the ABL rule (in lieu of the Born rule) to assign probabilities on the basis of both past and future…[Read more]

Ulrich Mohrhoff replied to the topic Ruediger Schack: QBism and the character of the world in the forum First iWorkshop on the Meaning of the Wave Function 4 years, 8 months ago
I can’t seem to find these slides.
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