Seems like I’ve been writing a lot about quantum mechanics lately. Apparently so have a lot of other people. One thing that keeps coming up is the reality or non-reality of the quantum wave function. Raoni Arroyo and Jonas R. Becker Arenhart argue for non-reality: Quantum mechanics works, but it doesn’t describe reality: Predictive power is not a guide to reality. (Warning: likely paywall.)
Along similar lines, in an article about what he says are quantum myths, Ethan Siegel argues that superpositions are not fundamental to quantum physics:
Superpositions are incredibly useful as intermediate calculational steps to determine what your possible outcomes (and their probabilities) will be, but we can never measure them directly.
Arroyo and Arenhart take a similar line. They argue that it would be more intellectually honest for wave function realists to call their position wave function pragmatism. As they note in the title of their piece, they don’t see predictive success as a guide to reality.
The question I want to ask these people is, if predictive power, if usefulness, isn’t your guide to what is real, then what is?
It’s worth thinking about why we care whether something is real or not. Is the sound I’m hearing from outside rain? Is the rain real? To say it is is to say I need to take an umbrella with me when I go outside, or be prepared to get wet. To say it isn’t is to say I can walk outside without worry of getting wet. We get similar considerations when trying to decide if a stock rally is real or illusory, or, from an evolutionary perspective, whether the sound in the bushes is a real predator or just a figment of your imagination. Reality is that which makes a difference, something which there’s a possible cost to ignoring.
Admittedly, this is a strange point to make when talking about quantum states. It might seem like whether they’re real has little to no bearing in our daily lives. But they do seem to make a difference for experimenters and quantum computing engineers. They have to take the dynamics implied in these mathematical tools seriously. In the case of quantum computing, it’s the very dynamics that seem to enable what they’re trying to do. Failure to treat them as real has consequences.
Now, I’m a structural realist. I think what we can count on being real in successful scientific theories are the structures they describe, at least to some level of approximation. That doesn’t mean we can count on them being fundamental, or that we know what they may be structures of. This is particularly important to remember with quantum theory, where the structures are all we currently have.
Does that mean that, rather than being structures of objective reality prior to a measurement, they could actually be structures of subjective expectations as the QBists argue? Or of the way the experimental equipment has been set up, as other antirealists argue? I suppose so. But that seems to imply the possibilities are completely set by these expectations or preparations, that if scientists really wanted to, they could get any result they wanted.
In practice, something seems to constrain the possible results. Of course, if I put on the epistemic hat, I could argue that those constraints are the constraints on their thoughts (QBism) or practical equipment limitations (other epistemics), not anything in the quantum realm. But taking this literally, that seems to imply that quantum physics is a big illusion, a side effect of the way scientists think or construct experiments. If so, how could anyone be sure that any scientific measurements beyond human senses are to be trusted?
All of that is before remembering that if we think anything objective at all is happening in the physics prior to a measurement, that there are mathematical theorems which kick in and demonstrate that quantum states must describe something real. Epistemic interpretations of quantum mechanics, such as Copenhagen, QBism, and RQM avoid this be saying there is no such objective physics prior to measurement (or interaction). Which, to me, makes calling them “epistemic” misleading. Qbists in particular argue for a “participatory reality,” a notion they inherited from John Wheeler’s “it from bit” idea.
This selective application of antirealism has always felt like gerrymandering to me. Most of the proponents want to resist the idealism label, but they seem to want to take from metaphysical antirealism just what they need to avoid quantum state realism. It all feels forced.
Interestingly enough, that doesn’t appear to have been Niels Bohr’s take. Historians often argue that he was more of a neo-Kantian than either an instrumentalist or idealist. His take seemed to be that the quantum realm was real, but inaccessible, the noumena always beyond the phenomena. Of course, this predates the theorems I mentioned above, which is what forces stronger stances from contemporary epistemic proponents.
But my issue with the Kantian view is it pushes reality into something utterly and forever unknowable. Reportedly, Kant’s motivations for doing this were to preserve space for God, the soul, free will, and morality in response to the “Crisis of the Enlightenment,” which seemed to call all of those things into question. I suspect neo-Kantians are trying to preserve different things, but that kind of preservation likely remains part of their motivation.
But the cost of doing so is to remove the practical aspects I noted above when deciding what’s real or not. In my view, it removes any utility from the concept of reality, except for talking in terms of theology or overall metaphysics.
Which may be why Arroyo and Arenhart want to use the word “pragmatic” instead. I think a better strategy is to retain our grounded everyday meaning for “real,” but admit that we never know whether we’ve reached ultimate reality. But this is coming from someone who doesn’t share the Kantian or neo-Kantian concerns.
Overall, my theory of reality is pragmatic. But I continue to wonder, for the people arguing against that take, what standard are they using?
What do you think? Are there issues with a pragmatic take on reality I’m overlooking? If so, what would be a better standard?
SelfAwarePatterns 
My experience and education in QM is rooted in chemistry. One of the most common applications is for the energies of atomic electrons. In that procedure in order to get positional probabilities for atomic electrons we had to square the wave function. This means that the wave functions represent the square roots of positional probabilities. If those, then are real what do they describe.
Wave functions seem to be linked to predictions. Some predictions are inexact, such as the 50:50 prediction regarding sad death of Schrödinger’s cat. When the box is opened, the wave function is not a physical thing that collapses, what collapses is the prediction, which settles on a 100% dead or 100% alive and the 50:50 prediction no longer exists.
I am so old when I started studying QM we addressed Matrix Mechanics. Schrödinger’s Wave Mechanics had easier math, so MM died a quick death. And if wave functions represent some sort of reality (other than a route to a prediction) doe matrices also? What does a collapsing matrix look like?
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The thing to remember about matrix mechanics is that it was demonstrated early on that it’s mathematically identical to wave mechanics. Note that’s mathematically identical, not just empirically. They always provide the same answers.
On matrices and reality, my understanding is that matrix mechanics were formulated with an explicit decision not to attempt to describe reality, only relate observables. But that means it’s not really accounting for what happens in between those observables. Wave mechanics does make that attempt. As a result, it has something to say, at least in principle, for every step in the evolution of the system.
Wave mechanics also account for the interference effects, something I don’t see in the (admittedly basic) write ups on matrix mechanics on the web.
Interestingly, matrix mechanics were developed in early 1925 and wave mechanics later that year, published in 1926. So I don’t think your age was why someone taught you matrices. And my understanding is that they can be a easier path to quantum field theory, so your instructor(s) may have had that in mind? Or maybe they just preferred matrices.
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Re “On matrices and reality, my understanding is that matrix mechanics were formulated with an explicit decision not to attempt to describe reality, only relate observables. But that means it’s not really accounting for what happens in between those observables. Wave mechanics does make that attempt.“
Schrodinger pulled wave functions out of a hat, that is by intuition. Any subsequent “relation to observables” came from attempts to do what Schrodinger did not. He just wanted mathematical simplicity and functionality. At least that is what I have read/viewed.
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Schrodinger seemed a bit cagey about how he figured out his equation, citing intuition. Which reportedly annoyed Heisenberg, who had meticulously ground out his matrices solutions.
But we know Schrodinger was trying to find the mathematics for Louis de Broglie’s matter wave hypothesis, an intuitive leap of de Broglie’s based on Einstein demonstrating the wave/particle duality of light. And it seems likely Schrodinger was influenced by the Hamilton–Jacobi equation.
However he did it, aside from needing to be generalized for relativistic scales, it’s stood for a century now with no one able to falsify or incontrovertibly extend it.
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I’m a little confused. It sounds like you, like me, are neo-Kantian, but you don’t want to be called that because you, like me, don’t share Kant’s motivations. Is that right?
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Uh, no. I’m not a Kantian, neo or otherwise. Not sure what I might have said to imply I was. I don’t think reality is unknowable. Maybe not all of reality is knowable, but reality in general is, at least as far as I can see.
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Heh. You’re playing around with two definitions of reality:
Ok, I’m labeling you as crypto-Kantian.
🙂
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[unless you’re saying #1 is the “real” reality]
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Reality is vast, and some aspects are more accessible than others. But in general I think it’s knowable. It certainly seems that if any portion of it can be known, it’s the ones who think it can be who are much more likely to acquire that knowledge.
If me being open to the mere possibility that some aspects may never be known makes you want to see me as a secret Kantian, well, if it makes you feel better. But based on what I’ve read, “Kantian” implies a stronger stance.
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Ah, ok. The Kantian stance is there will always be some reality that can never be known. We can usually go down a level, but it always takes more energy, and at some point you reach the level where there is not enough energy in the universe to go further.
Would you say “reality” is everything above that bottom energetic level, even if there are still levels we haven’t reached?
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When I think of Kantianism, I think of the distinction between “appearances” (which seem to encompass more than just sensory perceptions) and “things in themselves.” It’s the distinction between structure and relations, which are knowable, and non-relational intrinsic properties, which supposedly are not. I’ve never understood what the “things in themselves” concept was supposed to be. Given that all the structure and relations is in the first concept, I suspect the second is redundant.
Brian Cox, when talking with Neil deGrasse Tyson recently, noted that probing below the Planck scale requires so much energy that a black hole gets created. So if there’s meaningful reality below that scale, then, at least right now, it seems unknowable. Although who knows what future experimentalists could come up with. (See John Bell as an example of someone figuring out a way to learn something previously seen as unknowable.)
In any case, I see it all as reality, but none of it as “things in themselves.”
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“…that seems to imply that quantum physics is a big illusion, a side effect of the way scientists think or construct experiments.”
Exactly; this is not an either or statement, it’s both. First, it is a side effect of the way human beings think and second, it is also the way scientists construct experiments. The double-slit is the quintessential example of both the rationale used to interpret the findings as well as the engineering controls used to construct the test apparatus. Both are fundamentally flawed.
“If so, how could anyone be sure that any scientific measurements beyond human senses are to be trusted?”
It’s all about utility, that’s the answer to your question, right? Is a given tool useful for what we are trying to accomplish? If it is, then we’ve accomplished what we set out to achieve because we have empirical evidence of its effectiveness as a tool.
The flint Clovis Tip is the quintessential example. It is a useful tool for killing large mammals, but other than that, what does it tell us about the true nature of reality? The same assessment applies to the Schrodinger equation as well. It’s great tool for making predictions, but like the Clovis tip, that tool tells us nothing about the true nature of reality.
Uncertainty is the psychological hurdle that we have to overcome, not trying to pigeon hole the majesty of reality itself into a mechanistic framework because it makes us feel better.
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Right, but if we can’t use predictive accuracy to assess what we know about reality, then what standard should we use?
Is actual reality something so far beyond our reach that even talking about it is pointless? If not, what enables us to have those discussions?
And what label should be use for these concepts that provide high utility? Aside from the data showing it, at what point would we say it stops working, and why?
Feel free to answer or ignore any of these you’d like. I’m just putting down the questions that occur to me as I consider your points.
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Talking about actual reality is not pointless however, what enables us to have those discussions is recognizing that the models of reality we have inherited, namely idealism and the antithesis of materialism are historical artifacts.
If we cannot or will not set those artifacts aside and move on, then the discussion ends. Every time I bring up this conundrum, all I get is an incredulous stare. And I know why I get that stare, it’s because individuals are emotionally and psychologically invested in either materialism or idealism to the point, that they can’t even imagine that there is another way.
“And what label should be use for these concepts that provide high utility?”
We should call them what they are, they are tools, magnificent tools. Anthropology 101: Homo Sapiens are tool makers. All of our scientific knowledge without exception is derived from inventing, using and making tools. In all seriousness, does it make sense to you that inventing, using and making tools should be the standard by which we assess what we know about reality?
I
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Looks like part of your reply might have been cut off Lee.
“If we cannot or will not set those artifacts aside and move on, then the discussion ends.”
I think for people to set aside things like that, they need an alternative. If we rule out materialism and idealism, and I think you ruled out neutral monism the other day, what are we talking about? Some other variant of panpsychism? I know you used to talk about pansentientism.
“Tools” might work for some things. But if I’m just wondering whether the rain is real, or a storm that might be heading for me, are those tools? We definitely can use tools to learn about them, but they themselves seem like something else.
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You either missed my point or deliberately trying to deflect. I never implied that the reality we find ourselves in is a tool.
“I think for people to set aside things like that, they need an alternative.”
That is the natural response of course, but I think the initial first step requires the ability to recognize that both of these historical artifacts are not tenable. And until one reaches that consensus first, no other alternate explanation will be given serious consideration because of the investment made in one of the two alternatives.
How about you Mike, have you given up on materialism as it is currently framed by the scientific community?
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My view remains roughly physicalist Lee, in the sense that I expect things to work by principles we can eventually discover. I’m interested in understanding proposed alternatives, but right now there’s nothing making that urgent.
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I’m a physicalist as well Mike with one important distinction. I have not been radicalized by scientific extremism into believing that reality is mechanical, deterministic and causally closed.
“I expect things to work by principles we can eventually discover.”
Freedom is a principle right? Is freedom something that we can eventually discover? What if the universe was not governed by entailing laws of any kind, and as result if was free to express itself. It that were the case, then we’d have to entertain the idea that the universe is the very definition of life itself.
It should not be dismissed that self organization, a phenomenon responsible for complexity and diversity operates within a larger context of emergence that cannot be fully predicted or explained by the mechanisms of physics. It therefore becomes self-evident that the universe itself possesses life-like properties which make the notion of “life” a more realistic and inclusive rendition of nature in contrast to a mechanistic, determinate and causally closed universe.
Complexity theories increasingly utilize endosymbiosis as a foundational model to argue that life and consciousness are products of cooperative merging rather than just competitive survival. This perspective reframes evolution as a series of “major transitions” driven by symbiotic partnerships. This too is a radical break from the naive idea of a mechanical universe and opens the door to freedom of expression.
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Re:
> Along similar lines, in an article about what he says are quantum myths, Ethan Siegel argues that superpositions are not fundamental to quantum physics
I think this take is confused. While I think it is correct, the argument that is given just does not concern itself with superpositions at all because it seems to talk about a statistical mixture of states. Maybe the language is just chosen poorly/wrong but correcting for that (in the sense that the author meant a superposition of states instead of a statistical mixture) still does not make the point imo.
Here is how I see this: Superposition is not a physical property of some state. It depends on the basis one chooses to describe the problem. As such it can never have an observable consequence.
Tbh, I am unsure what exactly 'fundamental' means here in this context. In layman's terms, I would say that superposition is a fundamental concept in the usual formalism of quantum physics. But it is not a physical property of a state (because it depends on my choice of basis) and as such the question whether it can be measured is ill-posed imo.
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Sounds like you agree with Siegel that superpositions aren't physical but have issues with his language.
My question would be, if they're not physical, where do the interference effects come from?
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I’m not sure structural realism and pragmatism are compatible. For a structural realist, structures are absolutely real, as opposed to objects, which are less real. For a pragmatist, structures are real when you need them to be, and physical objects are just real when you need them to be (that is to say, when useful).
It’s the same with colour. There are those who would argue that colours are not real. But if they’re useful, say for recognizing food or danger, is that enough to make them real in some sense, for some purpose?
On the Kantian thing-in-itself, it was Kant’s position that space, time, and causality are ways that the human mind makes sense of reality, and what lies behind them is unknowable. To the extent that quantum physics presents us with riddles about space, time, and causality, this could still be said to apply. To the extent that our mathematics helps us get around these limitations, it could be said that what seemed unknowable may yet be knowable. But by “knowable” here we mean “knowable through the math,” which still leaves room for “incomprehensible to human intuition.” To that extent, the ting-in-itself would remain opaque or mysterious to us.
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I view structural realism as a pragmatic form of scientific realism. And a structural realist, like any realist, sees structures as approximations of reality, hopefully to ever increasing precisions. To that extent, objects are real, since they’re structures. They’re only not real if by “real” we mean objects in some primitivist sense that overlooks what science knows about molecules, atoms, and the various forces.
I think the right way to see color realism is to understand the scope of that realism. Color exists as a relationship between aspects of the environment and an organism’s evolutionary affordances. It’s our nervous system’s way of enhancing discriminations and deciding which are more important. This is easier to understand if we think about sensations like sweetness, bitterness, hot, cold, etc.
On Kantian thought, right. That’s basically the historical rational for the epistemic interpretations. Although as I noted, the various theorems have constrained that. So now these interpretations deny any reality prior to the measurement (or interaction). (To be fair, that’s long been the stance of many Copenhagenists.) It evades the theorems, but at the cost of mixing in metaphysical antirealism, or “participatory realism” in the words of Chris Fuchs, or “flash ontology” in Carols Rovelli’s language.
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I’m as comfortable as anyone with talking about the “scope” of a realism. But this means I can be comfortable thinking about a participatory realism or a flash ontology when it seems useful, and just as comfortable talking about a wave function when it seems useful. I don’t see alternatives to wave function realism as having a cost, but as presenting an advantage, depending on the uses to be served..
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Advantages and costs seem like two sides of the same coin. If a view has advantages, and I forgo it, then I give up those advantages, in other words, incur costs.
What would you see as the advantages of participatory realism, or of a flash ontology? Are we talking in terms of enhanced predictive power?
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Advantages and costs may be two sides of the same coin, but with pragmatism that’s how it is. what you take as “real” concerns how you weigh the advantages. The only measure of reality is whatever works best for whatever you’re trying to do.
If the wave function provides a good calculation tool, that’s an advantage, but if it fails to address how anything actually happens, perhaps some other approach is more useful for that purpose. Participatory realism offers a way forward for thinking about events as they transition from possibility to actuality; the wave function has nothing at all to say about that. Flash ontology, if this is how Rovelli’s views are being styled at the moment, seems to speak to the quantum foam that some say underlies our ongoing reality; again, the wave function is silent about it.
Pragmatism is entirely agnostic about what’s ultimately real; every nominal realism has its proper scope of application. Even religious talk refers to something real, if it has its uses (as it assuredly does). Talk of colours and smells refers to the real,. Of course we always have in mind the scope of the realism in question, its proper domain of application.
So the fact that the wave function is useful suggests that it’s about something real, but if the argument is purely pragmatic then the sense of “real” is seriously watered down. Other ideas of the real are not automatically displaced or usurped. If you’re hoping by this argument to secure the wave function as the best description of reality for all purposes, across all scopes, for all uses, I don’t think it’s going to work.
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Ultimately we can’t ever grasp fully any reality external to our minds. We can only understand it through the interfaces we have with it. If we grasp a rock in our hand, we are not perceiving the rock (thing-in-itself) directly. We are perceiving the reactions of our sensory neurons in our hand as it makes contact with the rock. That our brains and minds are constructed from the same “stuff” as the external reality allows us through evolved, innate capabilities perfected by learning and experience to create a decent enough simulation of the rock that we feel we are touching the thing itself.
Science can extend the interfaces and formalize them; hence, its pragmatic value for understanding reality and its ability to provide an illusion of objective reality. With most things, this works well because we can match what science tells us with our experiential interfaces, even if science sometimes upsets our preconceived notions. QM presents a conundrum because the reality its science reveals seems to defy our experience rather than augmenting it.
Doesn’t your pragmatic take put you in the “shut up and calculate” camp?
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Consider, what about the rock can we never know, even after extensive scientific investigation? If you say the rock in itself, what does that mean? Most often people mean hidden structure, but hidden structure is knowable, at least in principle. Kantians mean something non-relational and intrinsic, whatever that means. I strongly suspect things in themselves, in the Kantian sense, is an empty concept. But maybe I’m wrong, which is why I keep asking people what they think it means.
Shut up and calculate can have its uses. But it’s a hard stance to maintain. My experience is that most of the people who try inevitably end up talking in terms of the ontology of some interpretation (typically Copenhagen). And if our goal is to actually understand what’s happening in the measurement process, or more broadly how quantum mechanics fits in cosmology, it actively avoids exactly what must be explored. And again, I’ll point out that the theory of quantum computing was developed by quantum state realists. You might be able to use QC while being in the shut-up-and-calculate camp, but before it existed, that camp didn’t have the tools to conceptualize it.
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