13 ms·
Does superdeterminism save quantum mechanics?
- Strilanc 5y agoFrom watching the video and reading one of the papers, I get the sense that the theory being described doesn't work in the usual way. For example, reading the paper it talks about "future inputs" determining what happens, which seems impossible if you need to have the entire state specified for each time slice without need to reference other time slices. Instead of having a specific state for time t, and being able to evolve it forward/backward to other times, it is instead applying constraints across spacetime? In principle, allowing yourself that kind of flexibility could be enough to model quantum mechanics. But I'm not sure why I'd want to do it that way instead of the existing ways. It's not particularly philosophically appealing to me, and objectively speaking it looks like they don't yet have a concrete mathematical model that actually reproduces quantum mechanics. But maybe I'm just ignorant of the latter part's existence.
- SuoDuanDao 5y agoI'm no expert in this field, but aren't the existing assumptions around time being independent at the slice we want to take a major reason why QM and General Relativity can't be reconciled? If so, that would seem like a good reason to look at alternative ideas in this space.
- naasking 5y agoI think that's more or less correct. GR suggests "time" isn't independent, we instead have 4-dimensional "spacetime". The idea that future inputs can influence past configurations can be perfectly sensible in this context. It's like a restricted form of consistent closed timelike curves. There was some development in this direction years ago: The Logic of Quantum Mechanics Derived from Classical General Relativity, https://arxiv.org/abs/quant-ph/9706018 https://arxiv.org/abs/quant-ph/9706018
- myridium 5y agoWhy is GR required? Already in standard QFT (Minkowski metric; flat spacetime; special relativity) the propagator 'violates causality'. Although that phrasing is misleading; it doesn't mean there's any logical inconsistency. 'The future affects the past' you might say. Yes, well, all information about the future is derivable from information about the present. So actually those 'future influences' are determined by the present. In the same way, 'locality' is almost a moot concept, because the analyticity of fields implies that the value of fields at remote locations is determined entirely by the field locally.
- naasking 5y agoMaybe GR isn't required. It seems like the simplest path to understanding how this could work for those who aren't familiar with QM though.
- bollu 5y agoI don't follow the comment about analyticity. I thought fields were real analytic, which meant one needed to use a power series to expand them, which has a potentially infinite amount of information in the Taylor coefficients? So I don't see how the local data "effectively" captures non local information.
- evanb 5y agoI think you may be over-simplifying. We have relativistic quantum-mechanical theories, and we can formulate quantum field theories on curved background spacetimes.
- Koshkin 5y agoBut isn't the spacetime of SR flat?
- 323 5y agoYou might want to read about "block time" or "block universe". In this theory, everything is already pre-computed, like an uncompressed video file. So you can skip to whatever frame you want since there is no state. > It is sometimes referred to as the "block time" or "block universe" theory due to its description of space-time as an unchanging four-dimensional "block", as opposed to the view of the world as a three-dimensional space modulated by the passage of time. https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time) https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time...
- zikzak 5y agoPeople who meditate often begin to slowly realize that ideas arise without concious thought. We imagine we are "thinking" but there really is no break in causality where we somehow choose how we want the future to unfold. Our brains are no more exempt from cause and effect than a marble rolling downhill is. It is a mistake to confuse the finger pointing at the moon with the moon itself. We don't preceive everything, our senses are a filter that allows us to navigate but there's no more free will here than a plant turning to follow the sun. Fortunately, we don't experience reality this way. If we did, life would cease to be meaningful.
- thulle 5y ago> there's no more free will here than a plant turning to follow the sun That's a bold claim without presenting anything really backing it up?
- dtjb 5y agoWhile limited, studies using FMRI brain scans can detect "decisions" being made before they're consciously processed. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0025304 https://journals.plos.org/plosone/article?id=10.1371/journal...
- superdetermined 5y agoAs a complete layman, Sabine Hossenfelder's description here about Quantum Mechanics and Super Determinism is exactly that explanation that I came up with that made the most sense to me way back in college. And I have noticed that the idea of Super Determinism really bothers people on some fundamental level that I never really understood.
- d--b 5y agoI can’t agree more with the OP about free will and stuff. The main problem of superdeternimism though is that it both explains everything and nothing. It’s like giving up.
- midjji 5y agoExactly so, its an interesting philosophical idea,but its by definition invalidates the scientific method, and all forms of meaningful reason. The correct answer to the question of if you are dreaming a dream from which you could never wake up isnt perhaps that explains why my math doesnt make sense, its: by premise that can not matter.
- naasking 5y ago> Exactly so, its an interesting philosophical idea,but its by definition invalidates the scientific method, and all forms of meaningful reason It doesn't, and Sabine specifically addresses this point.
- astrange 5y agoThe explanation of superdeterminism she gives here isn’t a “full” superdeterministic theory (nothing actually happens over time, there are no physics, the universe is just a movie being played back, etc) and she does say it only applies at the quantum level. So there’s still room for science.
- midjji 5y agoJust means she hasn't thought of the inevitable consequences. Besides, the paradox she is resolving isn't a paradox, she just does not understand the answer in standard QM.
- astrange 5y agoSeems like if you “thought of the consequences” and “understood QM” here you’d have a theory of everything all ready to go.
- graycat 5y agoUh, the OP frequently mentions "statistical independence", and I am uncomfortable with that: Independence is a property of a set of more than one random variable and is defined in probability, often used in statistics, but not defined in statistics. There is a polished, elegant, and thorough treatment of such independence, including of uncountably infinite sets of random variables, in J. Neveu, Mathematical Foundations of the Calculus of Probability.
- PeterWhittaker 5y agoIn the context of Bell’s Theorem, statistical independence is understood to mean that, if extant, hidden variables are not correlated with how measurements are being performed. Bell’s Theorem is only correct if this assumption holds. Hossenfelder is arguing that the assumption is incorrect: that Bell’s Theorem is incorrect precisely because there ARE hidden variables and that these ARE correlated with measurement settings. She also argues that all mentions of free will in all related discussions are meaningless red herrings that have distracted physicists from properly interpreting Bell’s Theorem and observed violation of Bell’s Inequality. Superdeterminism, arguably misnamed, simply argues that QM is deterministic, where Bell and others have argued it is not.
- graycat 5y agoAt least for now, I'm willing to f'get about issues of "free will". Thanks, I will keep trying to make sense out of Bell's work. I keep getting stuck trying to read quantum mechanics: One place was the claim that the wave functions form a Hilbert space. Nope: As I read in W. Rudin, Real and Complex Analysis, a Hilbert space is a complete inner product space where complete means that every Cauchy convergent sequence is convergent. Well, while the wave functions are likely points in a suitable Hilbert space, they can't be complete, e.g., they can converge to a point in the space, i.e., a function, that is not continuous and, thus, not differentiable in contradiction to the assumption that all wave functions are differentiable. I admit that this is a small point, but I was trying to take quantum mechanics seriously and be careful. Closer to the OP, another place I got stuck was in the approaches of physics to independent and uncorrelated: In probability theory those two are not the same: For two real valued random variables, independence implies uncorrelated. As in W. Feller, in the case of two real valued random variables with joint Gaussian probability density function, uncorrelated implies independence. Generally, however, uncorrelated does not imply independence. Independence is a much stronger property than uncorrelated. Maybe eventually I will figure out what physics means by "uncorrelated", especially for Bell's work. To me, we can take the Ace of Hearts and the Ace of Spades, shuffle them, and deal them out, face down, one each to Bob and Sally. Bob can go a light year away. Sally then looks at her card and knows right away, nothing faster than the speed of light needed, what Bob's card is. We know all the associated probability distributions for Bob and Sally. And we know that as soon as the cards are dealt what each of Bob and Sally have is determined -- so far unknown but still determined. I'm guessing that this Bob-Sally thought experiment may have something to do with entanglement, the EPR (Einstein, Podolsky, Rosen) paradox, "spooky action at a distance", collapse of quantum mechanics wave functions, and Bell's results -- but I need to keep studying.
- 6gvONxR4sf7o 5y agoSuperdeterminism needs some kind of simplicity, for lack of a better word. To take her vaccine trial analogy further, imagine that you randomly assign a group of 100 people to a treatment and control cell (50-50). It could happen that all 50 people in the control cell just happened to be the 50 most a priori healthy people in the group. But it’s extremely unlikely. Following the analogy, superdeterminism says it happens anyways. But the level of coincidence involved invokes such an absurdly complex series of coincidences, that your coin flip comes up heads on these particular people, that occam’s razor might as well spontaneously cease to exist. Are there any superdeterministic theories that maintain the level of simplicity that the universe is posited to have without it?
- candiodari 5y agoThe point is that it's only unlikely (or other situations likely) if the events, even from patient to patient, are random. If whether a patient is sick or not determined if they're in the placebo group or the healthy group, you would be testing exactly nothing. The randomness in placing the patient is a required part of the experiment. And more than random, the patient placement must be random and independent from their disease status (misdiagnosed healthy patients get treated too, after all. Generally it works quite well, as there isn't any problem to solve) and whether the treatment will work. And of course superdeterministic theories are "simple". In the same sense that you can model any sequence as a function: just list all observed values for all time. Very simple, very little predictive power when you need it. That also gives you the criticism of superdeterminism: if we do things that way, nothing needs an explanation, as it just can't be simplified from that full specification that we observe ... so there's no point to science. Note that it can still be more complex than we'll ever usefully realise, so whilst it means everything is determined, it does not necessarily (in fact quite unlikely imho) make it predictable for us limited beings. But, in at least one meaning of the word, it's certainly simple. Every function in physics, whether quantum gravity or electroweak forces or the number of puppies your cat will have next year: f(x) = the x'th entry in the table ... (tables, of course, that you generally don't have access to) Which isn't to say this is a strategy that can't work and perform useful functions. Take a robot for example, and look at inverse kinematics. That comes with 3d calculus, volume intersection (robot mustn't self-intersect), and there's not just limits in position but in speed, acceleration and torque as well. You can fully develop this theory. Or you can move the robot, observe all variables and save them to disk, then use nearest neighbour to figure out robot movement. Works like a charm, and doesn't even need to know how many arms the robot has. And while it takes a while, I bet it's a hell of a lot faster than building the theory for even the simplest of robots, never mind multi-armed or nonlinear robots. Plus it's trivial to make a machine learning algorithm do it for you, and the same can't be said of developing the correct theory for a new robot model.
- quantum_mcts 5y agoI'm from the many-worlds interpretation camp, and this "superdeterminism" business always strikes me as ironic. Proponents of hidden variables, in their desire to explain QM effects, arrived at the idea that there is something that permeates the Universe since the Big Bang and participates in every physical interaction. Existence of this something cannot be directly proven - since we are "inside" of it. How about the "wave function of the Universe"?
- effie 5y agoTheir goal is to find the deeper explanation behind wave functions, so obviously going back to wave function, even that of the Universe, is not very appealing to them.
- myridium 5y agoWell if they insist on expressing the dynamics of the universe as the minimisation of a global (or local) action functional, then they are already throwing in the towel because that implies a wavefunction of the universe. I'm suspicious that these fringe quantum-physics-deniers just don't understand the mathematics. They want to be relevant but they don't want to learn, so they post wordy, fluffy blog posts targeted at non-professionals. Like Sabine.
- Koshkin 5y agoExcept she does not "deny" quantum mechanics, and she does understand the math.
- myridium 5y agoTotally agree. It's therapeutic to read this. Last I checked, many-worlds is a consequence of current quantum theory, not a postulate or additional axiom. Yet people treat it like such. Probably because it's 'spooky'. Then indeed it's ironic that they search for alternative explanations which try to say the same thing as many worlds but without saying 'many worlds'.
- nimish 5y agoThere are other possible choices that reject superdeterminism but are still ok: https://arxiv.org/abs/1907.05607 https://arxiv.org/abs/1907.05607 -- you have to abandon either locality or the assumption that observed events exist absolutely Personally I think it's easiest to reject the "absoluteness" of events and subscribe to RQM or QBism. Superdeterminism is a little boring if ultimately plausible.
- meroes 5y ago"If statistical independence is violated, this means that what a quantum particle does depends on what you measure." But in standard QM without superdeterminism, what a particle does already depends what you (i.e. the experimenters) measure - how you set the relative angles of your detectors determines the amount of correlation, even when setting them at spacelike distances after the entangled pair is released (say Alice chooses hers and Bob his without any communication between them. It's the same physical facts and we either take superdeterminism or quantum nonlocality (or other interpretations not at issue here). To me the conspiracy of superdeterminism is too great.
- mrjangles 5y agoYeah this seems like yet another attempt by someone to use different words to explain the exact same quantum theory we have always been using, then trying to claim because they used different words they somehow came up with a special new theory.
- naasking 5y agoWhat you describe is "quantum contextuality". What Sabine is saying is that so-called superdeterminism/giving up statistical independence implies the contextuality that is needed to explain quantum mechanics using hidden variables, and it does so in a simple way if we accept future input dependence.
- myridium 5y ago
- geertj 5y agoHonest question, why did you have to go ad hominem? If you look at her papers she’s obviously well versed in QFT and GR. You may disagree with her philosophical views but making the case that she doesn’t understand QM doesn’t pass the smell test.
- myridium 5y agoI didn't commit an ad hominem fallacy. I did not say that her blog is invalid because of her character. I was just commenting on her character (actually more so on her work tbh). i.e. an insult is not an ad hominem. This is an ad hominem: "Your argument is wrong because <insult to character>." This is not an ad hominem: "<insult to character. Particularly an insult that they often wrong>"
- akvadrako 5y agoBecause she's accessible and prolific. It doesn't matter if she's wrong, because there are not better qualified physicists who make youtube videos every week.
- gameswithgo 5y agoShe communicates with equations regularly in actual science papers: https://arxiv.org/a/hossenfelder_s_1.html https://arxiv.org/a/hossenfelder_s_1.html
- myridium 5y agoOf course. I assume that in those papers, she demonstrates a similar lack of understanding of the details. Or that she doesn't research on quite the same things she talks about in her public-facing content. Someday I'll get around to reading some of them, and I'll find whether that assumption is wrong.
- rafaelero 5y agoThis is the first time I've read some way of looking at quantum physics that actually make sense. I hope it is indeed correct and all those ~smart people who were putting their ridiculously complex theory of quantum physics at our throats end up being ridiculed.
- myridium 5y agoYou're exactly the target audience for her content :) .
- rafaelero 5y agoI suppose. It does seem pretty logical that statistical independence between measurement and particles could be violated, and I am just a newbie. If someone could explain why people overlooked this fact I would be very interested.
- sigmoid10 5y agoThis reminds me of Feynman's famous quote: "If you think you understand quantum mechanics then you don't understand quantum mechanics." Frankly, I'm baffled how some scientists still clinge to classical physics and absolute determinism, just because they describe our macroscopic world nicely. People have tried to argue against quantum principles 100 years ago and some still do it today, even going so far as to believe that the entire universe conspires against us since the big bang (which is what supetdeterminism boils down to in light of things like entanglement) rather than accept the inconvenient truth: our universe is much stranger than classical physicists could have envisioned.
- deleted 5y ago[deleted]
- raylad 5y agoI got a bit lost at the double slit experiment with superdeterminism. Can someone clarify what is supposed to be going on? * We send one photon at a time through a double slit, don't measure them, and an interference pattern is formed, presumably because the probabilities of the particle going through each slit interfere with each other. * If we measure the position of the particle, it goes through only one slit, and there's no interference pattern created. * Standard QM says that the probability wave function representing the position of the particle "collapses" when measured and the particle then goes through only one slit with no interference when we measure it. * Superdeterminism says that the initial state of the universe determined that we would measure the particle, and therefore it goes through one slit and there's no interference. * What I don't understand is: why would there ever be interference in that case? If it's not probabilities interfering with each other what causes single photon interference in the double slit experiment in superdeterminism?
- Koshkin 5y agoWell, the thing is, neither the standard (non-local) quantum mechanics nor the superdeterminism answer this question, as they both simply talk about a wave function and its taking a different shape depending on what measurement is made; the only difference is that one completely gives up on futher clarification of what the wave function physically represents while the other encourages looking for hidden variables.
- raylad 5y agoI've heard the interference discussed as an "interference of probability amplitudes". But in superdeterminism, it seems as if there are no probabilities in that sense, or am I missing something?
- Koshkin 5y agoSuperdeterminism does not deny probabilities (just like, say, classical mechanics does not deny statistical mechanics).
- alex_young 5y ago> Once you understand what’s going on with the double slit, all the other quantum effects that are allegedly mysterious or strange also make sense. Take for example a delayed choice experiment. In such an experiment, it’s only after the particle started its path that you decide whether to measure which slit it went through. And that gives the same result as the usual double slit experiment. Delayed choice seems pretty silly in relativistic terms to me. If photons are massless, and distances they travel are 0, then there is no such thing deciding to measure the slit after the photon is emitted but before it reaches the slit, right? That's just a figment of our reference frame.
- Koshkin 5y agoBut reference frames do have physical significance (and the distance traveled does depend on one).
- alex_young 5y agoSo, from the photon’s perspective (I know perspective isn’t right, but I’m not sure what else to call it), the distance traveled is 0, and the emitting and measuring happen instantaneously right? What I’m struggling with is what it means to the experiment to move a measurement into the system between these events if they are at the same moment according to the thing being measured.
- Koshkin 5y agoA frame of reference that moves at the speed of light is non-physical. For example, using it you could conclude that objects that have non-zero mass, too, all move at the speed of light...
- deleted 5y ago[deleted]
- thyrsus 5y agoThe post suggests that carefully designed experiments could settle the question. I hope they get performed.