The Most Embarrassing Graph in Modern Physics

Scientists don’t always agree with each other. Yes, I know; shocking but true. In cases of collegial disagreement, it’s often fun to quantify the extent of opinion by gathering a collection of experts and taking a poll. Inevitably some killjoy will loudly grumble that “scientific questions aren’t decided by voting!”, but that misses the point. A poll of scientists isn’t meant to decide questions, it’s meant to collect data — mapping out the territory of opinion among people who have spent time and effort thinking carefully about the relevant questions.

There’s been a bit of attention given recently to one such poll, carried out by Maximilian Schlosshauer, Johannes Kofler, and Anton Zeilinger at a quantum foundations meeting (see John Preskill at Quantum Frontiers, Swans on Tea). The pollsters asked a variety of questions, many frustratingly vague, which were patiently answered by the 33 participants.

This plot gives the money shot, as they say in Hollywood:

Quantum Poll

It’s a histogram of the audience’s “favorite” interpretation of quantum mechanics. As we see, among this expert collection of physicists, philosophers, and mathematicians, there is not much of a consensus. A 42% percent plurality votes for the “Copenhagen” interpretation, while the others are scattered over a handful of alternatives.

I’ll go out on a limb to suggest that the results of this poll should be very embarrassing to physicists. Not, I hasten to add, because Copenhagen came in first, although that’s also a perspective I might want to defend (I think Copenhagen is completely ill-defined, and shouldn’t be the favorite anything of any thoughtful person). The embarrassing thing is that we don’t have agreement.

Think about it — quantum mechanics has been around since the 1920’s at least, in a fairly settled form. John von Neumann laid out the mathematical structure in 1932. Subsequently, quantum mechanics has become the most important and best-tested part of modern physics. Without it, nothing makes sense. Every student who gets a degree in physics is supposed to learn QM above all else. There are a variety of experimental probes, all of which confirm the theory to spectacular precision.

And yet — we don’t understand it. Embarrassing. To all of us, as a field (not excepting myself).

I’m sitting in a bistro at the University of Nottingham, where I gave a talk yesterday about quantum mechanics. I put it this way: here in 2013, we don’t really know whether objective “wave function collapse” is part of reality (as the poll above demonstrates). We also don’t know whether, for example, supersymmetry is part of reality. Wave function collapse has been a looming problem for much longer, and is of much wider applicability, than the existence of supersymmetry. Yet the effort that is put into investigating the two questions is extremely disproportionate.

Not that we should be spending as much money trying to pinpoint a correct understanding of quantum mechanics as we do looking for supersymmetry, of course. The appropriate tools are very different. We won’t know whether supersymmetry is real without performing very costly experiments. For quantum mechanics, by contrast, all we really have to do (most people believe) is think about it in the right way. No elaborate experiments necessarily required (although they could help nudge us in the right direction, no doubt about that). But if anything, that makes the embarrassment more acute. All we have to do is wrap our brains around the issue, and yet we’ve failed to do so.

I’m optimistic that we will, however. And I suspect it will take a lot fewer than another eighty years. The advance of experimental techniques that push the quantum/classical boundary is forcing people to take these issues more seriously. I’d like to believe that in the 21st century we’ll finally develop a convincing and believable understanding of the greatest triumph of 20th-century physics.

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77 Responses to The Most Embarrassing Graph in Modern Physics

  1. vmarko says:

    @ Torbjörn Larsson:

    “The mistake was to believe that we will not be able to understand the universe, or that invisible bearded men had anything to do with it.”

    Just a note — keep in mind that there is a sharp difference between “understanding the basic laws of elementary physical systems” and “understanding any phenomenon that occurs in the Universe”. There are all sorts of things that make reductionism trip over and stop to a halt at one point or another (uncertainty relations, deterministic chaos, Goedel’s incompleteness theorems, etc…). Even Sean admits that understanding the basic laws does not imply understanding of the complex phenomena. 😉

    And of course, invisible bearded men don’t have anything to do with neither science nor religion. The fact that some people draw images of God as an old bearded man have an interpretation similar to a physicist who draws a tiny ball on the blackboard and says “this is an electron” — neither is true in a literal sense, and both exist only to depict some more abstract concept.

    Best, :-)
    Marko

  2. doc c says:

    @ Torbjorn,

    Produce someone who can visualize or otherwise experientially integrate QM, and I’ll yield my comment as a deepity.

    Saying that we will be able to understand the universe has as much validity as saying that an invisible bearded man created it. Neither is falsifiable at present. How do we disprove that the natural evolution of intelligent beings enables them to survive long enough for their full understanding to arise?

    Krauss never explained how something arises from nothing, only how our universe could arise from the quantum vacuum. That is a great achievement, as he rightly claims, but it is far from solving the entire problem of understanding how nature originated, in the typical meaning of originated.

    The creationist problem is that they forget that the God who they worship denied us direct access to him when he kicked our progenitors out of the Garden. Everything that follows in the Bible, by definition therefore, is a guess. What we were not denied access to is knowledge of our natural world. We’ve come a long way in that regard, but direct knowledge of a loving creator still remains closed off. There really is no Judeo-Christian religious argument against science in the natural world.

  3. Gizelle Janine says:

    “And of course, invisible bearded men don’t have anything to do with neither science nor religion. The fact that some people draw images of God as an old bearded man have an interpretation similar to a physicist who draws a tiny ball on the blackboard and says “this is an electron” — neither is true in a literal sense, and both exist only to depict some more abstract concept.”

    Vmarko: in QM, I’d say because of the majority thinking we’ll live on a cloud and that a bearded man in the sky knows all, it might just be true in some sense. In QM it’s all about probablities. Who knows. Maybe I’ll see the Rat Pack playing poker.

  4. Bob Iles says:

    @VMarko

    “You don’t want to think about an electron as a particle, but rather as an excitation of the electron field, just like a photon is an excitation of the electromagnetic field. Particles don’t exist in nature, fields do.”

    OK, I’m starting to get a handle on this but then my question is, what is it that excites a field, thereby causing us to observe particles? In addition, I assume this is part of the Standard Model, correct? So that a string theorist would perhaps say that it’s the vibration of strings that produce particles & maybe a LQG-ist would say it’s something else. Or am I off-base here?

  5. vmarko says:

    @ Bob Iles:

    The Standard Model is one particular example of a quantum field theory (i.e. a theory of fields that are quantized). A nontrivial qft is a theory where one field can interact with another (or even with itself). Excitations of the fields (i.e. particles) are one of the products of those interactions.

    As for the string theory, the “real thing” is called String Field Theory, i.e. a theory of fields of strings. An elementary excitation of such a field is a string, instead of a particle. Now, each string is considered to be of small length, and it appears to us as a point particle experimentally. Furthermore, a string can vibrate in various ways, thereby appearing as a particle of this or that type. In QFT you introduce one field per each type of particles. In string field theory you introduce only one string-field which has oscillating strings as excitations, thereby generating “particles of all types” simultaneously. That is the string theory unification idea.

    Finally, Loop Quantum Gravity has nothing to do with all this — it deals with the quantization of the gravitational field, i.e. the manifold of “spacetime points” on which all other fields (or string-fields) may live. The LQG framework does not aim to do any unification like ST does. Rather, it aims at coupling the ordinary Standard Model QFT to quantum gravity. The matter fields are the same as in the SM, but the underlying manifold has a different structure (it actually isn’t a manifold anymore).

    But we’re drifting off-topic here… 😉

    HTH, :-)
    Marko

  6. Bob Iles says:

    @ VMarko

    Thank you for the explication. I was unaware of the term String Field Theory, altho I HAD heard of Superstring Theory & M Theory. Presumably the latter two should be more strictly Superstring Field Theory & M Field Theory. And I’ll forget about LQG for now, at least. (Smolin be danged! [g])

  7. xiaokj says:

    @Nicholas Malaya:
    So many posts in, and nobody has yet to refute the claim.

    People must first realise that the entirety of Classical Thermodynamics can be reduced to the postulate of the existence and properties of the Entropy function, where the properties are mainly that it is first order in some variables and their conjugate variables, what we call extrinsic and intrinsic variables.

    Statistical Thermodynamics gives this Entropy function an interpretation, such that we can simply just define the Entropy function, or rather the partition function, in Quantum Mechanics, and come to the astonishing conclusion that the entirety of Statistical Thermodynamics is devoid of assumptions once Quantum Mechanics is accepted.

    @ Classical Observation:
    Although I do not agree with the interpretation, that is this Google fellow that is not a physicist, but manage to argue that you only require the measurement apparatus to be perfectly correlated with the quantum system in order to measure. So the foundation is refuted.

    @ Atoms Observing Universe:
    Variations of this problem is actually related to the Schroedinger’s Cat paradox. As a general rule, thought experiments are extremely fraught of disasters, and should be left to the masters. If you read Feynman Lectures Vol 3, he talks about the Ammonia Maser instead of the Schroedinger’s Cat, and upon easy reflection it is obvious that the Schroedinger’s Cat is a classical system, explainable with classical probability, and has absolutely nothing to do with quantum probabilities and quantum superposition and quantum measurement. As an analogy, it is a gigantic time waster for all those brilliant minds to spend upon.

    No, nothing is special of the minds of observers. Instead, something along the lines of entanglement is a better approach to this problem.

    @ Quantum Fields:
    Steven Weinberg’s book made an explanation as to why it is a relief to realise that Quantum Field Theories are themselves mean field approximations…

    My view on this is that, as of right now, the Standard Model is the most fundamental that we have, so that is it. Let String Theory struggle its way out from being a proto-theory before we even discuss it.

    For the record, I am closer to a Transactional Interpretation supporter. But I will fight for all the interpretations that are consistent with experiments, which is a whole lot. Copenhagen, however, is as Dr Sean Carroll said, not an interpretation at all. It is a set of rules to follow; ritualistic, and senseless. Interpretations are not trying to work against it, but to explain those rules that Copenhagen is about.

  8. Dianelos Georgoudis says:

    I think the interpretation of QM is a different kind of problem than the confirmation of supersymmetry. Supersymmetry is part of physics, for it makes a claim about a deep order in the structure of physical phenomena. Granted that claim is not yet proven, but that’s not rare in advanced physics.

    The interpretation of QM on the other hand belongs to metaphysics, for, as Matt Leifer writes above it asks “what must the world be like in reality in order for quantum theory to be true?” But what the world is like is provably irrelevant to physics. For example, if we found out that we live in a computer simulation ( which is a serious hypothesis, see http://www.simulation-argument.com), or if we found out that Berkeley’s subjective idealism is true and matter does not actually exist, then not one sentence in physics books would have to be changed, or at least not one formula. As Rick says, physics is about mathematically modeling experimental results (or in general physical phenomena), and that’s it. Incidentally Berkeley’s subjective idealism allows for a very economical interpretation of QM, namely that God solves QM’s equations in his head as it were, and directly produces for us the respective quantum phenomena. Physicists of course try to find mechanistic interpretations, and are qua physicists not allowed to suggest weird religious explanations. On the other hand Everett’s picture of the world is weirder than most religious dogmas.

    By the way, I’d like to correct Matt on a point. Strictly speaking the question is not about how to interpret the theory of QM, but about how to interpret quantum phenomena. The distinction is significant, for quantum phenomena are given data, and are independent of any future developments of physical theory. I think one can describe a small set of quantum phenomena which are as difficult to interpret in Matt’s sense (i.e. of how the world must be like to produce them) than the whole of QM. If I am right in this then no future theoretical or experimental developments will help us solve the embarrassing problem of interpretation.

  9. Patrick Murphy says:

    Wave(surface) collapses to a string(line) and finally from a string to a point(particle) seeing were still guessing

  10. what would Witten do? says:

    Isn’t the question of the interpretation of quantum mechanics the same as the question of the ontology of quantum mechanics?

    Many-Worlds, Bohmianism, Transactional, etc… all give an account of *what it is that exists* before, during, and after measurement. (As far as I can tell Copenhagen doesn’t answer the question of what the world must be like if it is accurately modeled by quantum mechanics.)

    We know quantum systems (excitations of fields or whatever) possess some properties independently of the measuring apparatus, while other properties (e.g. the location of an electron) are not properties of the system under study but properties of the system-plus-measuring apparatus. Other features are here to stay, too, e.g. probability. This ‘neo-realism’ doesn’t require extra universes, pilot waves, or travelling backwards in time. I don’t see what the problem is.

  11. As Penrose said, their can be more interpretations of QM than scientists doing it since some can believe in more than one interpretation at the same time. :-)

  12. Dianelos Georgoudis says:

    Phillip,

    If I were a scientific realist I would choose the many minds interpretation, since it is the one interpretation which takes literally what QM says: Matter is and stays a wave of the superposition of many physical states. It follows that in every physical state which entails a consciousness producing brain, that consciousness exists and will experience only that one physical state when it looks around. Such a realist interpretation is the most economical possible, and perfectly comports with our own experience of quantum phenomena.

    It is true that the many minds interpretation does not escape the weird implications of the many worlds interpretation, but at least it avoids the splitting of the universe business. And, incidentally, there is nothing in QM about there being more than one universe.

  13. Chris says:

    Could it be that we have 129% response to this question that make this graph embarrassing?

  14. Pingback: Quantum mechanics is an “embarrassment”

  15. Mark E. Dougherty says:

    Here is the secret:

    “If you seek mind, you find only things.
    If you seek things, you find only mind.
    Therefore, there is only no-mind and no-thing
    and they are both the same thing.”

  16. Sean Meaney says:

    String Theory invalidates Religion and Evolution because All life is the Same life at Superposition.

  17. not-Carroll says:

    The many-minds interpretation is troubling because it implies that one brain can have several minds associated with it. That would be bizarre, it is not Dualism and not Materialism and not even Idealism.

    The survey didn’t cover many interpretations. The ones that were mentioned were not defined the same way by everyone. The participants had a bias compared to the rest of physicists and philosophers. Also, there is not even a consensus that there *is* a problem in the foundations.

  18. smally says:

    John Baez has an interesting discussion of QM & Bayesianism here:
    http://math.ucr.edu/home/baez/bayes.html

  19. Michael says:

    If a man trained a dog to do a trick, how many times must he repeat it to learn it, how many times will the dog do this trick in his life time, when will the dog do this trick, if the man does not signal the dog to do the trick will he ever do it on his own, will the dog teach other dogs this trick, how does the dog feel, that he knows this trick. from the dogs perspective is the trick, ‘what I do when I see the man that taught me’?, can a bird do the same trick, does the dog like doing this trick or is it for another purpose such as food or favor, what the mathematically reason the bird can’t do the dog’s trick

    Just because an abstract question can be asked,
    no matter how apparently reasonable or unreasonable, doesn’t mean a 100% answer can/will be derived, but it’s truth will still exists. (light traveled at light speed before we gave it our value.)
    Reality can/will produce strange results when tested, reality “Itself” keeps itself secret from us, with pitfalls, lies, illusions, and traps. its part of what we are by design/creation. The universe is more than what can meet the eye and “our” minds’ eyes’.
    the way/why/how it works evolves moment to moment by influence of our infinite thought creation manifestation processes. You can never define rules that change because you defined them, or falsify themselves because you explain them, or play ‘tricks’ when you examine them.

    The universe is Mental By Nature, and my mind plays tricks on me.
    lol & live (The Real Secret)

  20. Pingback: Sean Carroll: “What is Quantum Mechanics, Really?” : DS 2030

  21. Pingback: Quantum mechanics’ different schools | Macro Exposure

  22. Jim says:

    What about the fact that the percentages add up to 129%? That’s embarassing…

  23. Ned Black says:

    As a lay person I have a problem with mathematics let alone QM.
    I mean, lines with infinite thinness, yeah right!
    does QM allow for that?

  24. DanielS says:

    QM tries to mirror the universe. And the universe is a successfully game because there is out there an experience to design and test successfully games. From inside the game, there is something that comes from the future: the experience of the outside player. The player knows that something is going to happened, but is not quite sure exactly what. Of course, inside and outside, past or future, are false notions. But very useful for the fun of the game.

    The player is never sure about his power. He will always suspect that somebody is playing him. He will always suspect that he is a game in a game. QM tells to all players that they are probably right.

  25. R Hawkins says:

    Some years ago (1990s) I did a degree in physics at Imperial College in London and had the pleasure of doing my final project with Prof Chris Isham. I spent my final year reading lots of papers on the Consistent Histories interpretation and comparing it to the more conventional Copenhagen and Bohm interpretations, we also studied a course in QFT and had a guest lecturer show in a quite simple way how Everett’s Many Worlds interpretation (or at least the plain vanilla version) led to probabilities of events that were greater than 1, even for straight forward events like the double slit experiment.

    This was held up as a reason why the Many World’s interpretation was problematic to say the least. How can an acceptable interpretation lead to calculated probabilities for events that are not consistent with experimental observations?

    Is there some more advanced understanding of Everett’s many world’s model which has been constructed which shows how workable probabilities can be arrived at for the quantum events we see in laboratories all the time while preserving the universe-splitting aspects of the interpretation? I would be interested to read a paper on this.

  26. Dianelos Georgoudis says:

    @ not-Carroll

    On the many minds interpretation physical objects are not like they seem to us when we look around. There is not one pencil I see lying on the desk in front of me, nor one brain that is looking. There aren’t many pencils and many brains either. Reality is not at all like it seems, but is exactly like QM says it is, namely a superposition of all quantum states of the universe according to the distribution of the universe’s wavefuncion.

    Out of the potentially infinite number of superposed states, consider just one, which happens to include the states of a brain and of a pencil. These two states are entangled, in the sense that there is a representation of some of the physical parameters of the pencil in the patterns of neuron firings in that brain. Therefore the conscious experience produced by that *state* of the brain in that particular state of the universal wavefunction is of a concrete pencil lying on the desk.

    In other words the only existents that are concrete or “classical” are experiences. Everything else, including the brains which produce the experiences and the pencil some experiences are about, are abstract superposed quantum states. And exist not in physical space which we experience, but in the space of complex numbers. One’s current experience of the world is produced by a particular state of the universal wavefunction, but has nothing to do with how reality is. Reality consists of one mathematical object (QM’s universal wavefunction) producing myriads of experiences.

    At least that’s my understanding of the ontology of the many minds interpretation of QM. (Being myself a Berkeleyan idealist I don’t buy any of that stuff, but appreciate how well it works from the point of view of the scientific realist. Physical realism is untenable though; there is no physical matter as such but only the experience of physical objects following apparent physical laws.)

  27. Fra Erasmus says:

    Neal Stephenson explores this in Anathem, where the hundreders and thousanders are able to bridge “many worlds” via conscious effort. Although not very rigorous, the thesis for the book is that collapse is a function of intelligent (sic) biological life, or consciousness.