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Quantum mechanics and our part in creating reality
- neonate 5y agohttps://archive.is/1DagJ https://archive.is/1DagJ
- dbsmith83 5y agoI'm no physicist, but the QBism interpretation of quantum mechanics smells a lot like "The Secret" type of pseudoscience. Core positions of QBism: 1. All probabilities, including those equal to zero or one, are valuations that an agent ascribes to his or her degrees of belief in possible outcomes. As they define and update probabilities, quantum states (density operators), channels (completely positive trace-preserving maps), and measurements (positive operator-valued measures) are also the personal judgements of an agent. 2. The Born rule is normative, not descriptive. It is a relation to which an agent should strive to adhere in his or her probability and quantum state assignments. 3. Quantum measurement outcomes are personal experiences for the agent gambling on them. Different agents may confer and agree upon the consequences of a measurement, but the outcome is the experience each of them individually has. 4. A measurement apparatus is conceptually an extension of the agent. It should be considered analogous to a sense organ or prosthetic limb—simultaneously a tool and a part of the individual. https://en.wikipedia.org/wiki/Quantum_Bayesianism#Core_positions https://en.wikipedia.org/wiki/Quantum_Bayesianism#Core_posit... I'd recommend reading the wiki page since this article seems to say a lot of words yet not say much.
- oxymoran 5y agoTypical that a non physicist is calling the work of actual physicists pseudoscience just because it “smells” funny to them. What exactly is so absurd about two physical entities interacting with each other to produce an outcome?
- deleted 5y ago[deleted]
- dekhn 5y agoHi. My phd is in biophysics. This is scientific garbage (the proposals are absolutely not supported by any experimental data).
- codethief 5y agoWhich proposals are you referring to exactly?
- dekhn 5y agoAll of its interpretations of QBist "Core Position" on the wikipedia page. Most importantly, nothing I can see in the QBist pages has anything to do with actual experimental work. It's a framework for viewing what the mathematics of human theories of QM "mean" and how to interpret that. However, nothing of what they propose is required to explain what we observe, experimentally. More generally, no "interpretation" of QM is required to apply the theory in generalizable, predictive ways, so all this work isn't really helping us move science or engineering forward.
- codethief 5y ago>>> This is scientific garbage (the proposals are absolutely not supported by any experimental data) >> Which proposals are you referring to exactly? > All of its interpretations of QBist "Core Position" on the wikipedia page. You're making very broad claims here. Whether you find QBism plausible or not, it's certainly not "scientific garbage" and also fully compatible with experimental data (as is any other interpretation of QM). > However, nothing of what they propose is required to explain what we observe, experimentally. So you would say that orthodox views of quantum mechanics (Copenhagen, shut up & calculate, many worlds (as it's becoming increasingly popular)) explain what we observe? > More generally, no "interpretation" of QM is required to apply the theory in generalizable, predictive ways, so all this work isn't really helping us move science or engineering forward. I disagree, once again. Have you actually deeply looked into the issues with QM? Many of them are linked to questions that come up in quantum gravity, so I would argue that getting QM right would be a very good first step in making scientific progress.
- knodi123 5y ago> What exactly is so absurd about two physical entities interacting with each other to produce an outcome? I hardly think that's a fair description of what he's claiming. This sounds almost like the textbook example of the motte and bailey fallacy.
- meroes 5y ago> What exactly is so absurd about two physical entities interacting with each other to produce an outcome? That seems inadequate to explain Bell nonlocality.
- Saptarishi 5y agoI think lots of physicists have a tendency to outrightly reject interpretations which seemingly put humans and other "conscious"(whatever that means) entities on a higher pedestal . It is most probably due to their general dislike of advocation of humans being a superior being than other "animals" by religious organisations, which does inculcate some unhealthy arrogance in people. But i think physicists need to open up a little more. If QBism or other interpretations where reality is subjective were really true, it would probably lead to some "we got it right initially" by some religious organisations, but honestly, that shouldn't stop physicists from pursuing such theories. I think it can be a win-win scenario in the end.
- Koshkin 5y ago> physicists need Except they don't - the science of quantum mechanics with its practical probabilistic "interpretation" has worked pretty well so far. As far as science is concerned, that is.
- dekhn 5y agoInterpreting QM is a waste of time. The current human brain cannot understand QM well enough to mke a physical interpretation. Stop wasting our time with pseudoscience.
- joeberon 5y agoHow do you know that?
- dekhn 5y agoBecause after 100 years of arguing about this, we have a theory which explains everything, but nobody has come up with a reasonable explanation of how the delayed choice quantum eraser could possibly work unless causality works different from human intuition.
- Koshkin 5y agoIsn't this logic some sort of survivorship bias? (OK, the "problem" persisted for a hundred years... Let's just wait for another hundred, and then we'll see?)
- dekhn 5y agoI think the dual choice quantum eraser experiment basically shows that to have a reasonable understand of quantum mechanics, we have to suspend much of our common belief and intuition about temporal causality, and it's quite clear at this point humans are not good at reasoning about temporal causality, as anybody who has been in a journal club session about relativity or EPR or paxos will know.
- kgwgk 5y agoQuantum mechanics may go against common sense in some aspects but temporal causality is not one of them. https://philarchive.org/rec/ELLWDC https://philarchive.org/rec/ELLWDC “Why Delayed Choice Experiments do NOT imply Retrocausality” - David Ellerman “There is a fallacy that is often involved in the interpretation of quantum experiments involving a certain type of separation such as the: double-slit experiments, which-way interferometer experiments, polarization analyzer experiments, Stern-Gerlach experiments, and quantum eraser experiments. The fallacy leads not only to flawed textbook accounts of these experiments but to flawed inferences about retrocausality in the context of delayed choice versions of separation experiments.”
- jonathanstrange 5y agoWait a minute. As a non-physicist who only knows QM from popular science texts, I always thought that wave function collapse does not require any human intervention and that this can be shown. Isn't "measurement" just an interaction of one physical system with another? If so, why would anyone include subjective degrees of belief in a formulation of QM? Could a physicist please clarify this?
- monktastic1 5y agoWhen one system measures another, there is no collapse, only entanglement. The superposition just grows. As trillions of environmental particles entangle with the system, that superposition becomes in practice -- but not in principle -- impossible to detect or exploit. This is called decoherence, and it is often wrongly used to explain away the issue. When does "collapse" happen in principle? There's no clear answer. Yet, when you observe a system yourself, you are free to say it has one result (at least, in "your world / branch" if we use MWI lingo). So there is (possibly) a sense in which you are the only observer -- at least, w.r.t. the place you think of as "the world." (And of course when we say "you observe," we mean "you experience". If only your toe measures it, you may treat your toe as an external measuring device. This is how "consciousness" enters the picture, though nobody agrees on what exactly it means.)
- phkahler 5y ago>> When does "collapse" happen in principle? There's no clear answer. It does not happen at all. There is no measurable distinction between a particle whose wave function has collapsed and one that hasn't. If there were a discernable difference the "spooky action at a distance" when an entangled pair is collapsed could be used for faster than light communication. >> When one system measures another, there is no collapse, only entanglement. This is the first time I've seen this explanation. To me it feels like an attempt at resolving the issue, but I think not. The right answer AFAICT is that we must embrace non-locality. But that's still another sort of punt.
- monktastic1 5y ago
- katabasis 5y agoCarlo Rovelli's book Helgoland[1] is a short and accessible account of the various philosophical interpretations of quantum phenomena, along with their shortcomings. Highly recommended to anyone interested in the topic. Rovelli is a proponent of what he calls the "relational interpretation" of QM, which basically states that particles only have properties when they interact with other systems (and may be better thought of as events than persistent objects). Entanglement is a general phenomenon that describes the relationship between two interacting systems and a third which hasn't interacted yet. Put another way, something can be real in relation to A but not to B. However, the correlation that entanglement guarantees ensures that previously isolated systems will see the same things if they do eventually intersect. It's different from QBism because there is no special privileging of human observers; all physical systems exist in direct interaction with some systems, are in superpositions in relation to others, etc. [1]: https://bookshop.org/books/helgoland-making-sense-of-the-quantum-revolution/9780593328880 https://bookshop.org/books/helgoland-making-sense-of-the-qua...
- raphlinus 5y agoThis sounds to me not unlike the "zero worlds interpretation" in Ron Garret's talk. Are you familiar with it and would you happen to know if it's roughly the same or whether there are substantial differences? [1]: https://blog.theangry.dev/2017/01/05/ron-garrets-the-quantum-conspiracy-what-popularizers-of-qm-dont-want-you-to-know-google-tech-talk/ https://blog.theangry.dev/2017/01/05/ron-garrets-the-quantum...
- katabasis 5y agoIf "zero worlds" means there is no unified single reality that all physical systems relate to (just like there is no universal frame of reference for motion according to relativity) then I think we're in similar territory. I'm not familiar with Garret, but Rovelli's book contains a great discussion of the "quantum eraser" experiment in that blog post, where quantum interference causes a split laser beam to recombine in different ways whether or not a detector is present. This is something you can observe with tabletop equipment apparently, a pretty visceral demonstration that quantum phenomena are a real part of our world.
- 6gvONxR4sf7o 5y agoI don’t understand QBism well enough to really comment, but from the outside it seems like QM interpretations are taking the measurement problem increasingly seriously. I like that the writer is up front in how all we really know right know is ‘shut up and calculate’ and wish that it had been taught with such honesty when I was taught it in school, rather than basically doing everything from the copenhagen interpretation and pretending that that isn’t fundamentally philosophically weird. The observer and measurement in the ‘shut up and calculate’ school is much more believable than in the copenhagen school where people (or at least things people do, like taking measurements and observing observables) are suddenly jarringly special for the first time in a physicist’s training.
- simiones 5y agoModern Copenhagen is basically an evolution from "shut up and calculate". It also doesn't given (human/conscious) observers any special role in QM - it is the measurement apparatus that has a special role instead. Basically the initial approach was ontological: science is about what can be measured, when quantum properties are measured we need to apply the Born rule to predict outcomes, it makes no sense to discuss the scientific properties of what is by definition not measured, so shut up and calculate. Later, the approach was more metaphysical: since our math doesn't work if we assume that particles have definite properties, we conclude that particles don't have definite properties; instead, when we measure their properties in a particular basis, the particles randomly acquire some definite property with a probability corresponding to the amplitude of the wave function.
- spywaregorilla 5y agoWas the human conscious part ever a serious belief among actual physicists historically? I'm no physicist but it seemed obvious to me immediately that that could not possibly be the case.
- dekhn 5y agoYes. Through grad school the physics PhDs kept bringing it up. I believe Wigner was the only Wise One who actually pursued it (https://en.wikipedia.org/wiki/Wigner%27s_friend https://en.wikipedia.org/wiki/Wigner%27s_friend) Since Wigner was a Wise One (https://en.wikipedia.org/wiki/Wigner%27s_theorem https://en.wikipedia.org/wiki/Wigner%27s_theorem) people took the idea seriously, but these days, most physicists will simply ask you to show them a comprehensible and reproducible experiment that demonstrates the requirement of a human observer and reject your belief based on the absence of data and occam's razor.
- Strilanc 5y agoI've never found epistemic interpretations compelling (like QBism, which is what the article is about). I'll try to explain why. First, the stuff we do with quantum mechanics just seems sort of... really obviously objective? It's not like Bell tests work for me but not for you, or quantum computers factor numbers for me but not for you. If I sell you a machine to produce a specific superposition, and it produces the wrong one, you can tell. Yes you need to run it multiple times and do statistics, but ultimately anyone can check that the machine is doing the wrong thing. Second, two agents can't actually disagree on what the superposition of a state is, to any appreciable degree, without one of them being provably irrational (modulo some weak-sauce assumptions we take for absolute granted in classical mechanics). [1] Third, note that (w.l.o.g) diagonally polarized photons are superpositions of horizontally and vertically polarized photons. This suggests that, in an interpretation where superpositions are less real than classical states, slightly rotating a polarizing filter radically changes the conceptual machinery used to understand a photon passing through the filter. That seems... silly? There is a rotational symmetry in the system that should be natural in the model (e.g. see how special relativity reifies Lorentz boosts). Fourth, although this is ironically subjective, I've never read an epistemic explanation of some quantum phenomenon and thought "Ah, that makes it clearer!". But that has happened with collapse interpretations, with path integral interpretations, and with many-worlds. [1]: https://en.wikipedia.org/wiki/PBR_theorem https://en.wikipedia.org/wiki/PBR_theorem
- TheOtherHobbes 5y agoYou're confusing statistics with events. Superpositions are statistical distributions. Only statistics are wholly predictable. Individual events are wholly unpredictable. You can have two statistical views of the same experiment in which each individual event is different but the statistics agree. You can have a distribution of views in which events are somewhat different to varying degrees and the statistics still agree. Each view will experience itself as unique in specifics while agreeing that the distribution of events is identical. That doesn't solve the problem. It's hard to get random processes to define an identical distribution without having classical mechanics as a foundation. Basic QM hand-waves this away with "Here's some math that defines the distribution and..." But that's like "Starting with this universe we can..." It so happens that the statistics correlate spatially with various field potentials. Which is interesting, but... Why is there a distribution at all? Why are there creation/destruction operators? Where does the "code" that defines this mechanism live? How do particles know they should follow it? Do particles even exist, or are they just something random and constrained a field does every so often? How do fields know the physical configuration of an experiment has changed and sometimes that information appears to travel FTL? (Even though it can't be used for signalling.) How does a particle keep track of how many other entities it's entangled with and in what ways? Where does that information live? (Bell suggests it's not inside the particle itself. So where is it?) Is all of this shaped by some kind of hidden causal propagation mechanism which also defines how relativity works? And so on. A complete explanation would answer all of these questions - and others - with ease. Clearly we're nowhere near that.