Sabine Hossenfelder on consciousness and the collapse of the wave function

November 20, 2022 • 12:10 pm

In the video below, physicist Sabine Hossenfelder deals with the deeply weird nature of quantum mechanics—in this case, can human consciousness cause collapse of the wave function? This is connected with famous experiments like the “double slit experiment” or the Gedankenexperiment of Schrödinger’s cat—scenarios where the apparent outcome of a study depends on whether someone is looking at it and measuring the outcomes. For example, if you let photons from a single source go through two slits in a plate, and don’t observe which slit they go through, they form an interference pattern on a screen on the other side, implying that light is a wave, and is going through both slits at once. But if you put a detector at each slit, observing which one each photon goes through, you now get a mirror of the two-slit pattern on the screen: the photons go through one slit and not both. The results, then,  differ depending on whether you’re looking and measuring. As Wikipedia notes:

The double-slit experiment (and its variations) has become a classic for its clarity in expressing the central puzzles of quantum mechanics. Because it demonstrates the fundamental limitation of the ability of the observer to predict experimental results, Richard Feynman called it “a phenomenon which is impossible […] to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery [of quantum mechanics].

This kind of result has deeply troubled physicists for years, for it implies that our own brains somehow influence quantum physics and the behavior of particles. How can that be? As Sabine says, if consciousness can do that, it must have physical effects on reality, which doesn’t seem tenable. (The idea also leads to all kinds of quantum hokum à la Deepakity.) And would the consciousness of a worm suffice? How can the nature of reality depend on whether someone is looking at it? Well, there are many solutions proposed, including the many-worlds hypothesis, but I’ll let you read the book at the bottom to get the full story.

This all derives from a persisting dichotomy in quantum mechanics: is it telling us something about what is real, or only giving us a mathematical analysis that, while it works, doesn’t give us the ability to visualize what’s really going on on the particle level?  Bohr and his famous “Copenhagen interpretation” of QM espoused the latter: the “shut up and calculate” version. Einstein and others believed that there is a fundamental reality to nature that must be graspable by our brains, and is only approximated by quantum mechanics.  Or so I interpret.

At any rate, I found Sabine’s discussion somewhat confusing, mainly because you have to know a bit about quantum mechanics and its history before you can understand her presentation. I did, however, like her dismissal at the end of the video of the Penrose/Hamaroff idea that consciousness doesn’t cause the collapse of the wave function, but rather the opposite: the collapse of the wave function, working on “microtubules”in the brain, is itself responsible for consciousness.  Right now there’s no evidence for this, or for the panpsychism that Hossenfelder also dismisses.


I just finished this book, which is really all about the observer effect and whether quantum mechanics tells us something about what is real in the world. It’s not too hard going, and is a fascinating story going from Heisenberg up to modern disputes about the many-worlds hypothesis. And it’s heavily historical, showing how the charisma and intelligence of Neils Bohr all but shut down the debate for many decades. Of all the books on quantum mechanics that I’ve read, this is the clearest, and the one that best describes the disputes over what QM means. I recommend it highly. Click on the screenshot to go to the Amazon site.

(h/t Steve)

40 thoughts on “Sabine Hossenfelder on consciousness and the collapse of the wave function

  1. The whole topic amounts to: wavefunction collapse is mysterious and not understood; consciousness is mysterious and not understood; therefore wavefunction collapse and consciousness are intimately related. Not sure this follows.

      1. …for it implies that our own brains somehow influence quantum physics implies that things are the other way round.

      2. 25 years ago or so I attended a symposium at Cambridge on consciousness, organised by the Journal of Consciousness Studies. Most of the well-known names in the field attended — Patty Churchland, Dan Dennett, Gerald Edelman, and Penrose himself; along with a bevy of bemused grandees such as Oliver Sacks and Freeman Dyson. Penrose, inter alia, gave a lecture on an early version of his conjecture about ‘quantum consciousness’. The main argument against it then, as now, was a lack of any plausible theory. ( Patty Churchland called it ‘hand waving’.) The engines of consciousness lay in these microtubules — that is, known cellular microstructure, but microstructure that was not unique to synapses; indeed, not unique to any aspect of vertebrate neuroanatomy. Similar microtubules exist, for example, in gut villi, and neutrophils — but this does not mean that neutrophils are even semi-conscious when activated against invasive pathogens.

        I recall one lecture at this symposium, on the philosophical topic of neurological supervenience, given by an Oxbridge Don, one Jeremy Butterfield. As I filed into the lecture hall I was waved to by a cheery haematologist sitting in the back row, who happened to be the mum of the conference organiser. She called out to me, ‘Ramesh, come and sit with us medical doctor simpletons in the back!’ So I did, sitting beside her and Sacks. At question time there was a long involved to-and-fro between Penrose and Dr Butterfield, on this ‘quantum consciousness’ and what supervened on what and why — which was largely incomprehensible. All the medics in the back row were glancing at each other, for once knowing what it felt like to be a patient baffled by pretentious medical jargon. After the lecture, I had a brief stroll with Oliver Sacks. He said to me, apropos of this lecture on ‘supervenience’, ‘I can think of one term that sums up this lecture : ‘metaphysical masturbation’ that is in no way pleasurable.’

      3. That’s Penrose’s argument isn’t it? The one he makes in The Emperor’s New Mind. I rejected it when I read that book because he didn’t convincingly demonstrate that that consciousness could not be explained in terms of neurones and their connections to each other.

        1. Yes Jeremy, the same stuff Penrose writes about in ‘the Emperor’s New Mind’ ( based on what I’ve read in book reviews etc.) That book is still sitting on my shelves in pristine condition because I didn’t read more than 50 pages of it, though Penrose’s ‘Road to Reality’ sits beside it with dozens of page corners curled over because it has been thumbed through so often.
          What better description of the conjecture than Oliver Sacks’ ‘metaphysical wanking’, or ‘metaphysical masturbation’? Hossenfelder should use Sacks’ words of dismissal!

  2. I’ve never understood how the observer effect was isolated to consciousness itself. How, practically, was that done? If I look at the data from each slit, the screen should show a particle-like pattern but if I look at only the screen, the pattern will be wave-like?

    It’s like entanglement — I hear about the interesting behavior of entangled particles all the time but what I want to know is how entanglement is achieved. Maybe the particles are blended together on puree?

    1. If I look at the data from each slit, the screen should show a particle-like pattern but if I look at only the screen, the pattern will be wave-like?

      Not exactly. If you know which slit each particle goes through, all you will see is the image of the two slits on the screen. If you don’t know which slit the particle went through, you see an interference pattern. A human being trying to observe the particles at the slits changes the way the particles behave at the screen.

      It even works if you send the particles through one by one. You’ll only see a dot on the screen where the particle lands, but, as long as you don’t look at which slit it went through, the pattern of dots that builds up as you fire more particles through the slits will look like an interference pattern. If you rerun the experiment but watching the slits to see which one each particle goes through, the new pattern that builds up will just be the two slits.

      1. This just occurred to me, and I haven’t read about it :

        What do we know about the light source?

        Or what is being assumed about the light source?

        Not all light sources, of course, are equal.

          1. OK I didn’t know that but the _source_ instrument is not just in our heads – there has to be some thing making the photons… or electrons … or, I mean, could it be muons? Any particle?

            1. If the source is a source of photons, the photons generated need to be all of the same wavelength to see an interference pattern because otherwise there would be lots of interference patterns that would all blur together to our eyes. They are still there, just all mashed together.

          2. …[adding to invisibje comment in haste …]

            … or even the slit size compared to the particle size … they must be macroscopic slit and sub-atomic particle…?

      2. Your description is the way I understand it — so, if the experiment is run with counters at each slit and the data going to a computer, and then a person looks at the slit data and then the screen, they would see first: the slit data (photon passage/slit/time) and second: the point-like pattern on the screen. But if the person first looks at the screen they will see the wave-like pattern … and what does the slit data look like?

  3. I see no evidence that consciousness causes quantum collapse, nor vice versa. However, I don’t see anything at all problematic in the idea that

    [consciousness] must have physical effects on reality,

    Of course it does, just as tornadoes, ocean waves, and living organisms have effects on reality – all of which are large-scale real physical processes.

    1. I think the problem goes deeper than that. Consciousness does have another effect on reality in the form of language affecting the brain states of another person which I don’t think can be described at a reductionist level. Consciousness is a tricky problem because it doesn’t make sense at a dualist or physicalist perspective.

    2. Indeed, merely moving my fingers around to type this response shows how consciousness ’causes’ things to happen.

  4. Hope Ms. Hossenfelder puts out an audio version of her book, read by the author herself. I dig her accent — and her sardonic inflections.

    1. Give me a break and don’t tell me what how I should write people’s names. You can use titles on your own site if you have one. I call Trump “Donald” and Biden “Joe”, so I can call her “Sabine” if I want.

    2. I think your point is petty, misplaced and unfair. Using a first name doesn’t imply any lack of respect, and using a first name is considered more polite than a surname in many situations. In the UK, referring to someone by their surname alone – even in an article – is often considered rude, impersonal and objectionable. Aa brit, calling her Sabine sounds much more respectful than calling her Hossenfelder.

      1. This is not meant as a criticism of commenter No. 8 ( whose long moniker appears like half-solved German Enigma code ), but I am sure many watchers of North American and UK science fiction soap operas of the past 25 years will notice the convention that ‘an attractive young woman in the series almost always has an IQ of 160+, is a PhD in astrophysics or ‘quantum-something’, and is addressed as ‘DOCTOR’ basically all the time.’
        But you can have an Asian computer geek on the same series, male, and this person is usually not a Dr. ( But an Asian female in the series is quite often a ‘Dr’ or a medical doctor.)
        ‘Stargate’ series– young blonde DR astrophysics ( always addressed as ‘doctor’ to drive home the socially conscious point), the very recent ‘Picard’ series on Bezosflix – woman doctor genius. The Picard series decided to slap on lots of dialogue in Spanish and ‘forgot’ about Asian languages even though this plot point was set in California. Drop-in characters in Dr Who series — brilliant genius usually female and addressed in dialogue as ‘doctor’ etc etc.

      2. Strangely, this has changed over time in England. When I was applying for Cambridge in the early 1970s, letters to me started “Dear Mr Trudgeon”. When I was accepted, the notification letter from the senior tutor at my college started “Dear Trudgeon”. It seemed rude to me as a 17 year old, but my parents assured me that it was intended as a sign of my increased status. Nowadays I’m with Bullet-tooth Tony in “Snatch” – “You can call me Susan if it makes you happy”

  5. Speaking of quantum physics, here’s an article by Tim Maudlin on what many people misunderstand about the implications of the work of the 2022 Physics Nobel Prize Awardees John Clauser, Alain Aspect and Anton Zeilinger:

    “The 2022 Physics Nobel Prize is misunderstood even by the Nobel prize committee itself. What the work of John Clauser, Alain Aspect and Anton Zeilinger has shown, building on John Bell’s ideas, isn’t that quantum mechanics cannot be replaced by a deterministic, hidden variables theory. What it has shown is that quantum mechanics, as well as all of physics, is non-local. “Spooky action at a distance”, what Einstein had found disturbing about quantum mechanics, is real and emerging technologies depend on it, argues Tim Maudlin.…”


    Here’s also a recommendable video interview with Maudlin, who is one of the leading philosophers of (quantum) physics:

  6. “A physical theory should contain a physical /ontology/: What the theory postulates to exist as physically real. And it should also contain /dynamics/: laws (either deterministic or probabilistic) describing how these physically real entities behave. In a precise physical theory, both the ontology and the dynamics are represented in sharp mathematical terms. But it is exactly in this sense that the quantum-mechanical prediction-making recipe is not a physical theory. It does not specify what physically exists and how it behaves, but rather gives a (slightly vague) procedure for making statistical predictions about the outcomes of experiments. And what are often called “alternative interpretations of quantum theory” are rather alternative precise physical theories with exactly defined physical ontologies and dynamics that (if true) would explain why the quantum recipe works as well as it does.

    A precisely defined physical theory, in this sense, would never use terms like “observation,” “measurement,” “system,” or “apparatus” in its fundamental postulates. It would instead say precisely /what exists/ and /how it behaves/. If this description is correct, then the theory would account for the outcomes of all experiments, since experiments contain existing things that behave somehow. Applying such a physical theory to a laboratory situation would never require one to divide the laboratory up into “system” and “apparatus” or to make a judgment about whether an interaction should count as a measurement. Rather, the theory would postulate a physical description of the laboratory and use the dynamics to predict what the apparatus will (or might) do. Those predictions can then be compared to the data reported.

    So far, then, we have distinguished three things: a physical theory, a recipe for making predictions, and the sort of data or phenomena that might be reported by an experimentalist. What is usually called “quantum theory” is a recipe or prescription, using some somewhat vague terms, for making predictions about data. If we are interested in the nature of the physical world, what we want is instead a theory—a precise articulation of what there is and how the physical world behaves, not just in the laboratory but at all places and times. The theory should be able to explain the success of the recipe and thereby also explain the phenomena.”

    (Maudlin, Tim. Philosophy of Physics: Quantum Theory. Princeton, NJ: Princeton University Press, 2019. pp. 4-6)

    1. Tim Maudlin is a philosopher. Meanwhile the proof is in the pudding, since quantum field physicists do what philosophers cannot do, successfully explore and explain nature.

      The main problem here, and that goes for the entire discussion in and under this article, is that quantum mechanics is a classical approximation of modern quantum field physics. As far as I understand the latter doesn’t even *do* wavefunction collapse as a necessary fundamental process of the fields, e.g. of the equivalent formulations Feynman’s path integral formulation composes the probabilities without it.

  7. I loved the Becker book, in fact mentioned it in a recent post about what books people are/were reading. He points out that the Copenhagen interpretation is a resurfacing of dualism. Good stuff.

  8. I’ve read Sean Carroll’s book on the subject – figured you might have as well since he’s the sit physicist :). Very good, explains the different hypotheses and then his own favorite – Everrett’s many worlds… all of this is above my pay grade, but fun!

    1. An article by Stuart Hameroff:

      “Consciousness is the collapse of the wave function: Quantum mechanics and the organic light of consciousness

      Quantum mechanics suggests that particles can be in a state of superposition – in two states at the same time – until a measurement take place. Only then does the wavefunction describing the particle collapses into one of the two states. According to the Copenhagen interpretation of quantum mechanics, the collapse of the wave function takes place when a conscious observer is involved. But according to Roger Penrose, it’s the other way around. Instead of consciousness causing the collapse, Penrose suggested that wavefunctions collapse spontaneously and in the process give rise to consciousness. Despite the strangeness of this hypothesis, recent experimental results suggest that such a process takes place within microtubules in the brain. This could mean that consciousness is a fundamental feature of reality, arising first in primitive bio-structures, in individual neurons, cascading upwards to networks of neurons, argues Roger Penrose collaborator Stuart Hameroff.”

  9. Comment from one with no relevant qualifications: there is no actual wave, so nothing to collapse. The equations just describe your uncertainty. When you make an observation, the function collapses only in the sense that your uncertainty goes away

    1. no, sorry, the “double slit experiment” proves exactly that it’s not a mere question of uncertainty of our knowledge

  10. Sweet old memories… I spent years on these subjects at the university…

    “This all derives from a persisting dichotomy in quantum mechanics: is it telling us something about what is real, or only giving us a mathematical analysis that, while it works, doesn’t give us the ability to visualize what’s really going on on the particle level?”

    This is true for all physics (and, to some extent, to all science), although it’s much more evident for quantum mechanics. And, if we consider past theories, the answer can only be: physics is just a useful machinery for predicting numbers. Nothing more. Is Newtonian mechanics “telling us something about what is real”? Absolutely not. A theory is like a play where characters (entities) behave according to some rules. All the characters in Newtonian mechanics don’t exist: absolute time, absolute space, point particles, action at a distance, etc. Yet the theory works very well in a very large set of contexts. A similar analysis could be made for other theories (heat, electromagnetism, etc). If you think this is true for past theories but not for current theories, well, … believe that, if you want.

    A funny thing: people from hard sciences often say that soft sciences can’t produce “real” knowledge. However, in the future we may easily discover that quarks and muons don’t exist (in the sense that they are just useful placeholders for more fundamental entities), but questions like “has species A evolved from species B?” have a definite meaning and a unique, true answer. It may be difficult to find the right answer, but in principle you can answer this question with absolute certainty. I know nothing closer to “truth” than this.

  11. It’s quite simple really :-), we don’t have a realistic interpretation of QM, so every claim we make about it , is unjustified. Consciousness,on the other hand, gives us just enough sense of reality to keep us reasonable safe in a limited number of environments. It does that for bacteria just as it does it for humans.

    Consciousness is not a good source for truth,it never has been; it’s a source for illusions. Science is about finding out how thing really work; and these things are never intuitive.

    It’s not even strange that at limits of what we can observe, our observations are stranger than we did imagine. Nobody ever has observed a collapse of a wave-function ; it’s just a fictional mathematical object.

    I’m a scientific realist, but that doesn’t mean that we have to give in to scientific speculation; we do not have to have opinions about things we don’t know.

  12. Another excellent book on this subject is Anil Ananthaswamy’s “Through two doors at once”. Remember, the language of physics is mathematics. But it’s only the language, it isn’t what’s out there (sorry, Max Tegmark).

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