BB #73: Wavefunction Collapse

I’m two-thirds through my second Paul Halpern book this month. Earlier I read his book about cosmology, Edge of the Universe: A Voyage to the Cosmic Horizon and Beyond (2012), which was okay. Now I’m reading The Quantum Labyrinth: How Richard Feynman and John Wheeler Revolutionized Time and Reality (2017), which I’m enjoying a bit more. In part because cosmology has changed more since 2012 than quantum physics has since 2017. (Arguably, the latter hasn’t changed much since the 1960s.)

I wrote about Halpern’s book, Einstein’s Dice and Schrödinger’s Cat (2015), last year. As the title implies, it focuses on two great names from physics. Quantum Labyrinth (as its title also implies) also focuses on two great physics names.

But today’s Brain Bubble (as the title implies) is about wavefunction collapse.

I’m not normally much into history; my other interests don’t leave time for it. Rather to my surprise, though, I’ve found the two Halpern books quite engaging (the cosmology one less so). It may be that my long-time interest in quantum physics (since before quarks) makes me more interested in its evolution.

Lately I’ve been studying quantum math, so my interest and focus has been stronger than usual. (Somewhat like baseball or fiction, it offers an escape from what’s become an angry, polarized, very tribal world. On the flip side, theoretical physics, like philosophy, can spiral in on itself and get lost in fantasy and mathematics.)

I don’t know that I’ll review either of the recent books. Halpern is easy and enjoyable to read; I would recommend his books to anyone with an interest in fairly entry-level accounts. (He’s written on diverse topics.) I didn’t write much about his Einstein and Schrödinger book, either. I just don’t have much to say other than “well-done and very accessible.”

§ §

As to the matter at hand, a rumination about wavefunction collapse, it’s inspired by the bit in Quantum Labyrinth about the perceived issues with it — specifically with regard to the Schrödinger equation.

That equation describes how a quantum system evolves over time in a strictly continuous and linear fashion. When such a system interacts with another quantum system, this causes an abrupt and non-linear jump (a “collapse”) in the function, and there is (currently) no math describing it.

Some physicists have a major problem with this. For many the problem is so serious that it’s a central motivating factor for embracing the Many Worlds Interpretation of quantum mechanics because of its central tenet: “No Collapse!”

It’s true that exactly what happens during an interaction is currently a gap in our understanding. It’s also true that it seems to involve some of the harder-to-swallow aspects of quantum mechanics (such as randomness and non-locality).

Yet I have always wondered what the big deal is. Despite everything I’ve learned (so far), nothing has illuminated exactly why it’s such a big deal. In contrast, I see many reasons why it’s not.


Firstly, quantum mechanics is, at best, an incomplete theory. It’s even barely possible that it’s a wrong theory, although it’s hard to imagine that a theory with such explanatory and predictive power would be completely wrong.

The most obvious aspect of its incompleteness is its conflict with our theory of gravity, our other “best” theory. That isn’t the only gap, though. There is much we don’t understand about how the quantum world works. (Including to what extent the classical world can be said to be quantum.)

That interpretations of quantum mechanics math even exist demonstrates just how big is the gap in our understanding. None of our other sciences have this issue of having to interpret what apparently successful mathematics means. Usually the math derives from the physical meaning.

So point #1 is that, given these big gaps, worrying that “collapse” is without explanation seems premature. We just don’t understand it, yet.


Secondly, “collapse” involves apparent true randomness and apparent non-locality, two possibly true aspects of reality that some find hard to accept. (I’m not only fine with them, I rather like living in a universe that has them as features.)

Shine a photon at a screen, and nothing we know tells us which electron in the screen will absorb the photon. It appears to be truly random. We have no idea why a given electron will absorb the photon, even after the fact. Knowing which electron still doesn’t tell us why.

All the other electrons might have absorbed the photon, and when they don’t, it seems something — probability, possibility, a pilot wave, something — that was there suddenly, instantly, isn’t. Something non-local seems to occur.

Certainly if one resists randomness or non-locality, “collapse” is a challenge.

Point #2, though, is that many experiments demonstrate this quantum non-locality, and all the experiments demonstrate the random nature of QM. These as yet mysterious, non-intuitive, hard-to-swallow aspects appear experimentally and thus, at least in our reality, have to be taken as factual. As such, their appearance in “collapse” is almost a given, not a problem.


Thirdly, the Schrödinger equation itself is both incomplete and inadequate. That it doesn’t completely describe reality isn’t at all surprising.

The equation isn’t relativistic, so right off the bat it only works in a single frame of reference. (Quantum field theory is the relativistic formulation of quantum mechanics.)

More importantly it doesn’t describe particle creation or annihilation, so it has no way to describe the situation above of an electron absorbing a photon. Neither can it describe the light source that emitted the photon.

Creation and annihilation are “collapse” events, and they lie completely outside the Schrödinger equation’s ability to describe.

On the other hand, something like a particle passing through a Stern-Gerlach device in a spin measurement experiences a sudden change in its wavefunction but isn’t absorbed until it’s somehow detected. (Or not! The silver atoms first used weren’t absorbed by their target (glass), but just built up to a visible clump.)


Finally, I see some analogy between classical equations and quantum ones.

Consider the classical equations that describe a thrown baseball or orbiting planet. They predict where the ball or planet will go. As with the Schrödinger equation, these equations describe the evolution of the object.

What they don’t do is describe the baseball hitting a passing pigeon or the planet being hit by a giant asteroid. Or any of myriad other possibilities.

These possibilities can be described, but only by adding on to the existing math.

So likewise quantum evolutions. The “collapse” is always due to some interaction that is “unexpected” from the point of view of the evolving quantum system.

No doubt this can be described by adding to the existing math. Once we understand what the existing math even means and what’s really going on when it comes to quantum systems.

§ §

Bottom line, “collapse” is, I agree, currently unexplained and mysterious, but since QM is also currently unexplained and mysterious, I don’t see what the big deal is.

For what it’s worth, I’ve speculated on what I think might be going on with “collapse.” See Wave-Function Collapse and Wave-Function Story.

Stay collapsed, my friends! Go forth and spread beauty and light.

About Wyrd Smythe

The canonical fool on the hill watching the sunset and the rotation of the planet and thinking what he imagines are large thoughts. View all posts by Wyrd Smythe

10 responses to “BB #73: Wavefunction Collapse

  • Wyrd Smythe

    It wasn’t entirely clear in the post, but I found that his cosmology book, largely in virtue of having been published in 2012, was a bit out of date, especially with regard to dark matter and dark energy.

    His mention of the LHC hoping to find the Higgs Boson (which was indeed found in 2012) made me smile a little. 🙂

  • Wyrd Smythe

    The maths aside, the physical phenomenon of interaction is a central mystery of QM, and it’s closely aligned with the wave-particle duality mystery. What really goes on between the laser that emits a “photon” and the photo-diode that detects it?

    At both ends we see a point-like interaction between what we call “particles” (an “electron” emits or absorbs a “photon”). But between them (and we have no way to experimentally check this) we have a wave that goes from emitter to detector. The quantum description here says everything about the particle’s momentum but nothing about its position.

    Ironically, while they’re the only thing we can detect and measure, I’ve come to think that “particles” are figments, and the reality is nothing like the imagined tiny sphere. I think at the quantum level, it really is all just waves. Quantum Field Theory; wavelets in fields.

  • SelfAwarePatterns

    It seems like the measurement problem is a Rorschach test of sorts, flushing out a least four types of reactions.

    1. QM is weird and seems to have major implications for our understanding of reality. Reality may be vaster than we ever thought. Or sparser. Or there might be retrocausation. Or something stranger.

    2. QM is weird and seems to have major implications for reality, and my conclusions are right and anyone who disagrees is an idiot.

    2b. QM is weird and– Hey I can use it as an excuse to bring in my favorite magical thinking. Consciousness causes the collapse. Which means it’s fundamental. Which means that dualism or idealism is true after all. We’re special and at the center of reality. It’s all about us after all. Yay! QM rocks!

    3. Let’s not panic just because the particle physicists can’t seem to get their act together. If we just look at things a certain way, perhaps while hanging upside down while looking through a mirror and wearing rose colored glasses… There, see, reality is fine. Wait, don’t look in that direction or you’ll break reality! Um, never mind. Instead let’s just go instrumental, but be very precise about it so no one accuses us of idealism. All we care about is the math anyway. There. We’re going to be okay. Everything is fine. No need to panic. We’re fine. Just fine.

    I wonder how amusing these debates will be for people reading about them centuries from now.

    • Wyrd Smythe

      Why does it have to be a debate? Why can’t it just be a discussion about the points raised?

      I can’t tell from the way you wrote your comment, but it feels uncomfortably as if you’re putting this post in your category #3? (I don’t think my views quite fit in any of them, although #1 comes closest.)

      • SelfAwarePatterns

        Well, it never has to be a debate, but debate seems to be what frequently happens. 🙂

        The options I listed are obviously parodies. The positions held by real intelligent people typically have a lot more nuance and sophistication, although I think the parodies catch an element of truth. Your post obviously inspired the list, but I didn’t mean to categorize it. (At least not consciously.)

        More generally, my impression is that you’re in 1, until a specific option is discussed (MWI, RQM, etc) to which you usually seem to have a pretty negative reaction. I put Philip Ball and Jim Baggott in 3, two people you usually find resonance with. Again, all my subjective impressions. You might be in a category I didn’t think of.

        Myself, I think I was in 3 for a long time, but have gradually gotten more comfortable with 1 in recent years. Although there are some options (2b) I’ll admit to giving very little credence.

      • Wyrd Smythe

        One trick for discussion is just asking questions. It’s possible the answers might be interesting. Or focus on some non-controversial aspect. If there’s a lurking bone of contention, just nibble at the meat around it. 🙂

        Your parodies weren’t obvious to me. What came through was the meta and the mocking. Given that #3 was the longest and most detailed, it seemed like the pocket shot. Here you write “I put Philip Ball and Jim Baggott in 3, two people you usually find resonance with.” That seems to amplify the sense. Given the mockery in #3, you seem to be calling us idiots. Maybe I’m just reacting to the apparent cynicism.

        I think I would put just about everyone I’ve read, books, papers, even many blogs, in some version of #1. Certainly anyone informed. Some do fall into your #2b, but at least some of those understand it’s mere speculation. (I just read half of, and then gave up on, Lisa Randall’s book about how dark matter might have killed the dinosaurs. Talk about speculation. To form the dark matter disk required, there need to be different species of dark matter particles that interact with each other. Yet it’s not clear DM even is particles. MOND is gaining credence.)

        I’m not sure what constitutes a “pretty negative reaction” in your book. Certainly there are things I give “very little credence” to. (In some cases, zero.) But I get the sense you mean an emotional reaction? Of course we have emotions, we can’t not. The question is whether one also has reasons and logic. Those can be discussed. Or debated. 😉 I don’t think vehement beliefs should block reasonable discussion of the grounding for those beliefs.

        FWIW, I come from an arts background where a more emotional expression of one’s views is the norm. I’ve been in rousing yelling matches that ended in shared beers and laughs. It’s natural for me to express myself vehemently, but it’s all bark. I suppose if there’s any central theme, it’s that I strongly oppose gnostic views. Certainty without facts is a bit of a red flag to me, I admit. I have a well-exercised and very muscular “Yeah, but” mechanism! 😀

  • Wyrd Smythe

    Finished Quantum Labyrinth. A definite thumbs up on both his “pair of scientists” books. I really enjoyed the one about Einstein and Schrödinger, and likewise this one about Wheeler and Feynman.

    The latter gentleman especially always interested me. I have a couple of his books. QED, especially, is a cornerstone. I very much share his lack of convention, sense of humor, fascination with physics, disdain for sweeping speculative theories, blunt manner, and appreciation of young people. (We even share that fascination with picking locks.)

    Wheeler I didn’t know that much about. He promoted the term “black hole,” and coined the phrase “it from bit.” He brought Everett to the world’s attention (although it was DeWitt who made him famous). And really into the sweeping speculative theories that Feynman never cared much for (he was more aligned with the experimental side).

  • Wyrd Smythe

    Now I’m reading Lee Smolin’s Three Roads to Quantum Gravity. I generally agree with Smolin’s views, although I’m finding things in this book that I question. Mostly it’s that I’m not sympathetic to relational views of reality, which is what Smolin is promoting here. There is also that was published in 2001 which is fairly old when it comes to cosmology and particle physics.

    (I’ve started taking notes, so I’ll almost certainly post about the book when I finish.)

  • Wyrd Smythe

    I finished Smolin’s quantum gravity book (oh, yeah, there will be posts) and just got started on his 2013 book, Time Reborn. I think I’m going to enjoy this book. A lot.

    In the Preface I read:

    “More to the point, I no longer believe that time is unreal. In fact, I have swung to the opposite view: Not only is time real, but nothing we know or experience get closer to the heart of nature than the reality of time.”

    Oh, that’s hysterical! It’s what I’ve been saying all along! 😀

    In the Introduction he writes:

    “The notion that our universe is part of a vast or infinite multiverse is popular — and understandably so, because it is based on a methodological error that is easy to fall into.”

    He’s talking about how many of our theories need a multiverse to explain the “coincidence” of ours. The infamous Anthropic Principle.

    Kant felt time was our most fundamental intuition, and I’ve always thought that meant something about physical reality. I’ve written a number of posts arguing time is fundamental, axiomatic. Smolin presents his view that time is real as controversial, which just shows the uphill battle I’ve faced talking about it. The radical notion that time is, gasp, real.

  • Wavefunction Collapse | Logos con carne

    […] collapse, see the paired Wave-Function Collapse and Wave-Function Story posts from May of 2020 and BB #73: Wavefunction Collapse from August of 2021. They may not add much, but you may find them […]

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