It’s not looking good for objective collapse theories

As noted in the previous post, quantum mechanics is weird. If we try to have a realist understanding of what’s happening, it forces bizarre choices about which aspects of common sense reality we throw under the buss.

The central mystery is the wave function collapse. Quantum particles move like waves, mathematically described by the wave function, but when the particles hit and leave a mark, that is when it’s measured, it’s always as a localized point-like ball, a classical particle. People have been trying to find an explanation for this for almost a century now, which is why we have so many interpretations of what’s happening.

One approach is to regard the wave function as not real, as simply a mathematical contrivance, one that aids in predictions, but doesn’t reflect actual reality. The problem I’ve long had with this move is the very reason we have a wave function in the first place, the interference effects between the portions of the wave. Something is causing those effects.

But once we accept any degree of wave function realism, we hit a dilemma. Where does the rest of the wave, all the other possible outcomes, go on measurement? One answer is that they are simply annihilated from reality. In other words, the wave function collapse isn’t just an epistemic event, but an objective physical one.

I’ve never been particularly enthusiastic about this option. It’s long seemed like too much of an added assumption about how physics works, one not sufficiently motivated by the data. But one strength of the view is that it’s ultimately a testable proposition.

However as Philip Ball discusses in a Quanta article this week, it’s a test that most objective collapse models appear to be failing. Ball notes in his piece that these experimental failures don’t completely close the door on objective collapse models. It’s always possible to tweak the models. But as the tweaks add up, they start to look increasingly less well motivated and more convoluted. That appears to be where we’re getting to with objective collapse theories.

Where does that leave us? Well, pilot-wave theories, where there’s both a particle and a wave the entire time, remain, although that option is arguably already problematic due to the inability to reconcile it with quantum field theory. (And any modifications to quantum field theory would have to be compatible with all the data accumulated from the LHC and earlier experiments, no easy feat.)

There are also superdeterministic theories like the ones Sabine Hossenfelder is trying to find. And there are outright retrocausal theories like the Transactional interpretation. Although both of these seem to need additional assumptions, hidden variables, to work. Adding to the mathematical structure of the theory without disturbing its generalization into quantum field theory seems like a tough challenge.

And of course, there’s always the mad uncle in the basement, simply accepting the mathematical structure as is without any form of collapse. As experiments continue to rule out the other options, this one is becoming increasingly harder to ignore. But, due to its many-worlds implications, it’s probably the option people find the most disturbing, so it’ll likely be resisted for a long time.

Or we can just throw up our hands, give up on realist options, and simply fall back to observable and mathematical predictions. Although I suspect making progress on quantum gravity will require taking into account how the theory can be reconciled with other aspects of physics, and that will likely require a realist approach, at least to some degree.

Unless of course I’m missing something?

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30 thoughts on “It’s not looking good for objective collapse theories

  1. Re “One approach is to regard the wave function as not real, as simply a mathematical contrivance, one that aids in predictions, but doesn’t reflect actual reality. The problem I’ve long had with this move is the very reason we have a wave function in the first place, the interference effects between the portions of the wave. Something is causing those effects.”

    I am of the school that wave functions are mathematical abstracts, not real things, no more that sine waves are light waves or water waves, they are descriptions of the amplitude of some part of the wave-like character of the thing being observed.

    The key point to me is that the wave function has to be squared to get a probability of position of atomic electrons, for example. So, what the heck is the square root of a probability in reality?

    And, of course there was matric mechanics, a different mathematical approach to QM. It was discovered that the two approaches were equivalent, so we didn’t need both. If we decided to use matrix math instead, would we be assuming that the matrices represented something real or were real?

    As to interference, it isn’t caused by the wave forms, it is caused by the underlying water, or fields, or whatever. The shapes just tip us to its happening, they are not the cause.

    Liked by 5 people

    1. The problem is, once we accept that there is an underlying ontology (the underlying water, or fields, or whatever), then we still face the dilemma. When a quantum measurement is made, all but an infinitesimal piece of that underlying water, fields, or whatever, seems to disappear. Where does it go? Is it still there but no longer accessible (many-worlds), a second order of existence (pilot-wave, along with its issues), or some other ontology?

      And of course, if we deny even that underlying ontology, then what produces the observed interference patterns? If there are easy answers, they’re certainly not obvious.

      Liked by 3 people

      1. I don’t see any easy answers, but “God did it” or “wave functions are real” are in the same category, IMHO. We can withhold judgement and clearly state the questions we want answered for the physicists coming behind to answer. Then we move on to problems we can contribute to.

        Liked by 2 people

        1. To add some specificity to Steve’s assessment: “the notion that either God and/or wave functions are real” is a false assumption that is derived from projecting our own experience of consciousness onto a fundamental reality.

          God is the theological version of a mind whereas wave function is the so-called scientific version of the same projection which is again, based upon our own abilities as a mind to hold all possible outcomes in a superposition until an intellectual measurement is made, a measurement which collapses all of those possibilities into single, discrete outcome.

          Liked by 1 person

  2. Not sure if this gets touched on in the Quanta article or not as I haven’t read it yet, but one interesting implication of the failure of objective collapse models is that Orch OR is almost certainly wrong (if we didn’t already possess enough evidence in the form of biological implausibility). I used to really like the theory as a teenager, now I’m mostly embarrassed to even bring it up. 🙂

    I think Penrose’s motivations for quantum consciousness mainly rest on his misguided belief that the mind is non-computational as opposed to problems with phenomenal consciousness or anything like that. So, I’m not sure if he’s willing to give up his pet theory in spite of the now overwhelming evidence against it. If the latter concern was the main motivator, then one could just switch to some other kind of non-interactionist theory of phenomenal realism. But it’s hard to see how non-computationalism could be true for a physicalist (which I presume Penrose is?) unless you think quantum processing is involved.

    Liked by 2 people

    1. A lot of people find Penrose’s Orch OR theory enticing. I might have found it so myself when I was younger. When I finally did hear his theory, in a Google talk he gave many years ago, I was pretty surprised. At the time, he didn’t really characterize it as physicalist. As I recall, he was fine with computation for a lot of what happens in the brain, but not for consciousness itself (presumably phenomenal consciousness).

      I was about to say that the article mentioned his gravity induced objective collapse theory but not Orch OR specifically. But when I went back to check my memory, I noticed a sidebar about it I missed on the first reading. Yeah, it would pretty much rule out his model.

      Of course, he’s currently working on a new version of his collapse model. As Ball noted, you can always tweak falsified theories.


      1. Thanks for the link Jim: read the article and the comments. Not sure why everyone is so freaked out about quantum processes being responsible for consciousness☺️

        Liked by 1 person

      2. Yeah I would be super cautious about extrapolating based on findings of quantum phenomena in the brain, even if such phenomena are found to be robust/real and well-organized.

        That’s a big leap that’s being made there. It’s like inferring that the brain is a digital optical computer based on the finding that brain EM radiation emissions are predictably correlated with certain brain functions. As we know, that’s just a consequence of the brain’s electromagnetic activity, and not some central characteristic of its computation.

        Liked by 1 person

        1. “As we know”

          That EM fields are not a central characteristic of its computation isn’t something I know. What makes you so sure?

          There might be good reasons to doubt the research or its conclusions but I don’t think it can be dismissed as easily as “we know” especially since there is no good account yet of the details about how any of it works.


          1. ‘As we know’ is too strongly worded, I agree. ‘As far as we know’ is what I meant to say (I think?). Also, I wasn’t referring to the EM field of the brain, but to EM radiation. From what I understand, CEMI theories equate computational elements with the patterns of EM field modulation in our brain, but I don’t think anyone (as far as I know!) believes that the actual radiation being emitted by our brain (either because of black body radiation, or because of EM field effects) plays a substantial role in computation, at least not in a primary sense.

            As for secondary effects, I would imagine that most of the EM field modulation in our brain happens due to the movement of charged particles in the brain.


          2. Flowing charged particles generate EM fields. These fields are not strong enough to affect anything outside the brain but are strengthened by many neurons firings synchronously. The synchronous firings – known correlates of cognition – are a key part of the argument for EM fields being involved.

            There are many researchers who think these EM fields do affect the computations performed by the brain. McFadden and Pockett are the most well-known at present. But even Karl Popper had a version of this theory.

            This page references the theory and has six references of research showing EM fields do have impact on neuronal firings.



          3. I agree that the EM fields generated by the brain must have some effect on cognition, and I agree that the radiation generated by the brain must have some effect on EM field modulation. I am just questioning the significance of the latter, not the former. Presumably, any radiation generated by the brain is not going to provide a strong enough feedback loop to really affect the brain’s EM propagation. And there’s no reason to think that any such effect isn’t mere noise, as opposed to central to cognition.


        2. Alex,

          There are two important aspects of Penrose’s justification for asserting that mind is not computational. First is the the fact that what we consider as “information” that is processed by the brain does not exist independent of mind. First and foremost, mind generates and constructs that information; once that information is constructed then the mind synthesizes and processes it.

          Second: computationalism is based upon an algorithm that follows objective, well define rules whereas, not only does mind follow objective, well defined rules as well, it is a subjective system that constructs those rules; and if it chooses, it can circumvent any rule that it constructs by simply changing it. So in that sense, mind is sovereign to any notions of rules and is in fact “the very rule itself”. The system of mind is a self-appointed God for lack of a better term.

          A self-appointed God is the nexus of our own subjective experience of consciousness. It is a model explicitly codified by Plato, Aristotle and their Greek Cronies as subject/object metaphysics.


  3. I think I’m largely with Steve here. I think the fact that wave-type mathematics describes something does not require that there is an ontological wave-thing. Consider a box of air. Rap on one side of the box and a wave-type thing happens throughout the box. We call it sound. If you examine the air molecules while this is happening, you’re not gonna see some “wave”, except as a description of how the molecules are interacting.

    And of course it is now one of my pet peeves that the fundamental particles are not in fact particles, i.e., point-like balls. They’re something else whose interactions under certain conditions are describable w/ wave-like mathematics. Here (again?) is my analogous situation: suppose you have a room in outer space, so, zero gravity, with a bunch of batons (yard-long sticks) floating around in it. The room also has air so you can hear sounds. Suppose there are no lights, and the only way you can probe the room is by throwing other batons into it and listening for strikes. Guess what? Every strike will happen at a point. Obviously the batons are not collapsing to particles. That’s just a quirk of how batons interact.

    So I guess we’re still working on the ontology of what interacts in the ways we observe. I was hopeful that string theory was getting there, but maybe not.


    Liked by 2 people

    1. If you’re saying that a sound wave isn’t real, then yeah, I think you guys may be setting the bar for “real” too high. By that standard, no waves are real, not even water ones. At some point it seems like we have to have a discussion about what our pragmatic criteria for “real” is.

      What I think I’m actually hearing from you guys is that the wave isn’t fundamental. I don’t think wave function realism requires it to be so. It could be an emergent topology, one describing relations and interactions of underlying entities. The main thing is that it’s real at some level of abstraction. But that’s all that’s needed to bring in the dilemma about what happens with most of it on measurement. To deny even that level of realism seems to be getting into miracle territory, that the theory could be as predictive as it is without matching reality at some level of description.

      The biggest issue with the baton analogy is coming up with something that actually works with the mathematics and observations. We can always say there’s more hidden ontology that evades the issues, but coming up with that actual ontology is a lot harder than it looks.

      Liked by 2 people

      1. “The main thing is that it’s real at some level of abstraction.”

        That depends upon what you mean by real and equally, what you mean by abstraction. Unfortunately, our current intellectual paradigm of subject/object metaphysics is unable to effectively respond to those type of questions.

        Liked by 1 person

        1. The meaning of “real” can indeed get tricky. Chalmers in his book Reality+ discusses a number of criteria, including causal power and mind independence. I like the causal power one. Is the entity in question causally effected by other systems we consider real? And does it have causal effects on other real systems? If so, I’m inclined to regard it as real, at least in some pragmatic sense.

          Of course there are things people argue for being real that don’t meet those criteria. For example a platonist would likely object to the causal power one since abstract objects are generally regard as acausal. And strong qualia realists might object to the mind independence one. But since I’m not in either of these camps, the criteria work for me, at least currently.

          On abstraction, I think of it in terms of dynamics for which we don’t know all the details, or where it’s just not convenient to keep them all in mind. For example, when writing a web application, the developer usually doesn’t have to think about hardware or network details. Those details are abstracted away behind programming languages and libraries. In another example, we can productively discuss temperature without having to get into all the particle kinetics involved.


          1. I think your comment has demonstrated my point. SOM is a subjective paradigm that is incapable of rendering an objective outcome for the meaning of “real”, whereas reality/appearance metaphysics (RAM) is a model that is more than capable of giving a definitive meaning to the word “real”.


          2. Probably most (all?) abstractions are real to some degree and unreal to some degree.

            Meaning that when we are dealing with thought there are only relativities and no absolutes.

            Are unicorns real? Yes in some senses. No in others. Reality is unreal. And real.

            Liked by 1 person

          3. This gets into another one of Chalmers’ criteria: genuineness, meaning when we refer to something as “real”, what exactly are we saying is real? Along those lines, unicorns are a real concept, but not a real animal.

            In that sense, the wave function may not be real in terms of a substance (although I’m agnostic on that) but could still be real in terms of structure, relations, and the effects of its interactions.

            Liked by 1 person

  4. I happened to find an interesting 5D interpretation of quantum weirdness. I’m not sure if you have access or not, but will quote some interesting parts.

    A 5D interpretation of quantum physics, however, just might explain it in terms of a higher dimensional classical physics where concepts like realism (not to be confused with the philosophical idea), locality, and independence are all absolute, but only apply approximately in 4D.

    A 5D interpretation of quantum physics, however, just might explain it in terms of a higher dimensional classical physics where concepts like realism (not to be confused with the philosophical idea), locality, and independence are all absolute, but only apply approximately in 4D.

    View at

    The theory makes more sense to me than some of other stuff floating around. It seems a little like Many Worlds but he writes:

    The 4D slices are not “worlds” as in the Many Worlds since they don’t appear from splitting because of quantum measurements. They do represent different worlds in a sense, but it is a much more realistic sense since not all probable worlds exist as slices. Only the most probable worlds do.

    Liked by 1 person

    1. Something got mangled up in the original quote. Let me try again:

      A 5D theory of quantization means that classical become quantum theories by being averaged over a fifth dimension. Such a theory is only nonlocal in 4D since it is a classical theory in 5D and perfectly local.

      In my conception for such a theory, I proposed that the universe is a 5D classical manifold (a word meaning a topologically closed set of points). This manifold is divided into slices sort of like slices in a loaf of bread. Each slice is a 4D universe.

      The 4D universe that we observe is essentially flowing in a 5th dimension, similar to how our 3D universe flows through time. Each “moment” in the 5th dimension is a complete universe both in terms of space and time from Big Bang to heat death.

      Quantum physics happens because of fluctuations that happen in the 5th dimension. These fluctuations, taken in aggregate across the 5th dimension, form the wavefunction but we only experience one 4D slice at a time, so never the whole thing at once. This is consistent with the way quantum measurements work. We never measure the whole wavefunction at once but only get a look by repeating experiments and observing our measurements and calculating probabilities from them.

      Liked by 1 person

      1. Thanks. Medium let me read it. (I’m apparently within my free allotment for the month.)

        His idea is in some sense similar to David Deutsch’s way of looking at many-worlds, that the worlds don’t split from “thicker” ones into “thinner” ones, but all the “thin” ones are there the entire time with the wave function spanning a portion still similar enough for coherent interference.

        His point about 5D locality mapping to 4D non-locality also reminds me of Alyssa Ney’s advocacy for full wave function realism, where locality within all the higher dimensions of the wave function map to non-locality in our 4D view.

        I’m confused on three points however. One is he talks about many-worlds involving hidden variables, but it’s not generally considered a hidden variable approach; everything’s in the wave function, so I’m curious what he’s driving at with that. Second he limits himself to five dimensions, but the wave function is usually considered to have 3N dimensions, where N=number of particles. And finally I didn’t really follow the point about the low probability worlds not existing. What prevents them from existing? (He might have covered it. I largely skimmed the post.)

        Still, pretty interesting. Thanks for sharing it!

        Liked by 1 person

        1. I’m not sure in what sense he means MWI has hidden variables unless he considers all of the potential measurements not made exist in a different world and hence hidden from us. “All Worlds exist simultaneously, having sprung out of a single observation.”

          Liked by 1 person

          1. Usually the phrase “hidden variable” refers to new variables added to the mathematical structure. Something like pilot-wave. Although you could be right about what he’s thinking.

            On the reality of the dimensions, a lot of people seem confident they know the answer, but I don’t think anyone really does. I hope someone figures out a way to test it in our lifetimes.

            Liked by 1 person

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