And in case it wasn't already obvious, that URL indicates Doug was at the University for a long time. The University stopped letting even its staff pick a username years ago, maybe even decades ago and the default assigned usernames are... a bit dull.
With article titles like these, i just had to share it on HN!
Somebody should work on the above two webpages to make them more readable with html+pdf formats. That would make these more accessible to the "interested layman".
me neither! How does the Einstein Rosen Podosky Paradox work? can the unknown that's being collapsed not be a pre-determined value that therefore is not traveling faster than the speed of light?
>can the unknown that's being collapsed not be a pre-determined value that therefore is not traveling faster than the speed of light?
This is known as a "hidden variable theory". People will tell you that a local (things can only affect their immediate surroundings) version of the theory is impossible because it would be a violation of Bell's inequality, but there is a loophole that requires accepting the idea of "superdeterminism". This is the idea that where what measurement a scientist chooses to measure is predetermined and correlated with what the particle being measured is going to do.
So if a particle lands on a screen according to distribution p when going through a double slit, but with distribution p' when one of the slits is measured at, conventional QM says that the measurement "collapses the wave function". But a superdeterministic local hidden variable theory would imply that the choice of whether to measure at the slit or not was already set in stone at the same time that the particle "decided" which path to take to land on the screen, more or less.
One of the "coping mechanisms" is to say that information cannot travel faster than light, even if entanglement is propagated instantaneously and measurement acts faster than light. If Alice and Bob share an entangled pair of spins and Alice measures it, Bob has gained no information until Alice communicates (sublight speed) her result. No new information is shared at measurement time. This is known as the no-communication theorem.
I don't think that's correct? Alice knows immediately what Bob's result is going to be as soon as she measure's it. The travel faster than light part that many people (including Einstein) take/took issue with includes this as an effect. More generally put is that if spin is in a superposition until measurement collapses it into a known quantity, then the result of the collapse itself is somehow propagated to the other entangled particle instantaneously.
Yes, Alice knows what Bob's measurement is going to be, but only if they agreed beforehand on what state to prepare ("let's make the |00> + |11> state"). In that case no information traveled because what Alice learned came from the previous discussion (which presumably happened in the break room, sublight speed). If they prepared a random state, then there is no way for Alice to know what the second spin is only using measurements on the first.
So the decision shared with each other at sub-lightspeed prior to measurement is actually the hidden variable everyone is getting hung up on? If this is correct then the superposition is just the cat in the box, and 'superposition' is just that the state is unknown until measured?
Hidden variables are more about finding a way to derandomize quantum physics. The state |00> + |11> can collapse to |00> or |11> when measured. It appears to be that this randomness is baked into reality (God, meet dice, etc), and many people find this a bit distasteful, because it means measurements propagate faster than light (even if Alice and Bob can't communicate that info). If it turns out the theory is incomplete and there are missing/hidden variables, then it means whether it was |00> or |11> was determined from the start, before the measurement was made, and there's no faster-than-light interaction. Experiments around Bell's inequality prove that hidden variables don't exist, unless we start getting into scenarios that are as weird as entanglement itself. So the cat is truly alive and dead at the same time, and superposition is physically happening; this property is called quantum contextuality and is related to Bell/etc but still another discussion.
The important distinction in this case is about FTL existing but not being able to exploit it for FTL communication.
Thanks for taking the time to explain it further. This is a topic that keeps me up thinking about, not because a fundamental randomness is distasteful, but because it doesn't seem to match with what we see, and I'm wondering if we are getting caught up in describing laboratory/pure math isolated states rather than what actually occurs in nature.
In reality the entangled particle will interact with something almost instantly thus collapsing it. The cat is actually dead or alive from the perspective of the microscopic things in the box. A world never witnessed or measured by a being doesn't collapse it's entire history of interactions of every subatomic particle, atom, molecule and emergent property from the start of the universe to 'now' instantaneously upon being viewed. The photons from that world have been hitting earth continuously since earth existed after all.
If you split up an entangled pair of particles and measure them in a the same 50/50 basis simultaneously (sort of like a coin flip) at distantly removed places, the results will be individually random but perfectly correlated when compared with each other. It seems natural to assume that something here was pre-determined. i.e. There's was some kind of hidden information that we haven't found a way to measure yet. The way in which the coin-tosses were going to pan out was determined when the pair of particles were entangled.
Quantum physics makes predictions that suggest this isn't so. You can design experiments (e.g. A Bell inequality test) in which quantum physics predicts correlations that go beyond what would be possible with some hidden local information attached to the entangled particles that we just don't know about. Experiments don't prove theories to be correct. That's not how science works. However, experimental tests of Bell inequalities have pretty conclusively shown that local hidden variable theories are inadequate to explain what's going on.
Yes, it appears what Einstein called "spooky action at a distance" seems to propagate close to instantly. It's important to appreciate that you can't transmit information this way though. We can only make sense of the quantum correlations after communicating other information at classical speeds. Sometimes you see quantum entanglement devices allowing FTL communication in sci-fi, but that's pure horse hockey.
That all being said, I don't understand quantum physics either.
When I learned about causal sets program and algebraic quantum field theory, I finally (somewhat) understood quantum physics.
Tl;dr spacetime does not exist as a global background where things are "placed", it is not ontic. "Things" are first, and spacetime is derived from interaction statistics of "things". This eliminates nearly all naive paradoxes like double slit etc. Now, these "things" are somewhat complicated and non-intuitive (e.g. there are no individual "particles", they are a limit of discrete distributions), but that's a good start.
Sorkin is great. I think causal sets make some things simpler but other more mysterious. I also found t’ Hooft’s automata and Spekkens toy illuminating in different ways.
I am so sorry to hear this. I enjoyed visiting his web page July, when I came upon a couple of emails he had there, which were eye opening as they made some of the philosophical thoughts behind causal sets much clearer. A huge loss, but he did contribute amazing work.
In a podcast, Alain Aspect (Nobel Prize winner) explained that he does use the power of visualization and his imagination to generate new ideas, but that he always needs to check them with actual calculations because no mental picture can be an accurate representation of quantum physics.
Quantum _mechanics_ cannot be understood, it is full of paradoxes. It contradicts classical EM and special relativity, among other things. A toy theory that was an important step to what came later.
Feynman's own QED is a part of QFT, but this is no longer quantum mechanics. Special relativity and quantum physics are reconciled since then. Now, we only need to reconcile GR and QFT, but this leap was so far beyond our attempts to scale it. Yet, QED/QFT/SM can be "understood" as there are fewer obvious paradoxes that plagued QM.
With the meaning that Feynman meant it was true then and now. From QED:
>The next reason that you might think you do not understand what I am telling you is, while I am describing to
you how Nature works, you won't understand why Nature
works that way. But you see, nobody understands that. I
can't explain why Nature behaves in this peculiar way.
Heresy! Feynman was the last Prophet of Physics, no one can ever figure out the things he didn't know. If people could discover things after Feynman, those things could get into textbooks, and then mere students could know things that Feynman did not -- which is clearly absurd.
That pre-determined value idea is exactly local hidden variables, and Bell's inequality rules it out, Aspect's 1982 CHSH experiment measured the violation.
To be precise, Bell's inequality rules out a local hidden variable theory. Pilot wave theories/Bohmian mechanics is an attempt to describe a nonlocal hidden variable theory of quantum mechanics.
Intuitive notions of “weird” aren’t necessarily a good guide here. We already know time doesn’t behave the way we intuitively imagine, because of relativity: there can’t be universal agreement on what is past, present, or future. Once you’ve accepted that, retrocausality seems much less strange.
Similarly, superdeterminism is simply the application of the determinism that was believed to apply to physics before QM, to QM itself. In a way, one might have expected it to be the default interpretation.
No? Superdeterminism says that there’s no way to pick your experimental choices in a way that reveals things because any possible random number sources you could use have contrived correlations that prevent that? Why would one ever consider that as “the default”?
The strong belief before QM was discovered was that the universe was deterministic - that given sufficient knowledge of a physical system's present state, you could accurately predict its specific future states (not just possible future states.)
Laplace expressed this in "A Philosophical Essay on Probabilities" in 1814: "We ought then to regard the present state of the universe as the effect of its anterior state and as the cause of that which is to follow. [...] For [an intelligence that has sufficient information] nothing would be uncertain, and the future, as the past, would be present to its eyes."
Superdeterminism essentially extends this idea of deterministic physical evolution to quantum mechanics. It could be considered an appropriate default simply because it was previously considered to be, not only the default, but the strongly believed truth.
> Superdeterminism says that there’s no way to pick your experimental choices in a way that reveals things because any possible random number sources you could use have contrived correlations that prevent that
You're arguing against a consequence of superdeterminism, not its motivation. Its motivation is as I've described.
The word "contrived" is doing some heavy lifting in your statement. Nothing needs to be contrived in superdeterminism, even if it seems that way to an observer within the universe.
The explanatory problem you've alluded to only arises because we're trying to understand the universe from within the universe. The universe is under no obligation to make itself sensible to us.
Essentially, you're saying little more than that you don't like the idea of superdeterminism.
Can you explain how determinism applied to quantum mechanics results in superdeterminism? I feel like you've just skipped over an important step here. Determinism isn't a controversial idea, and indeed in QM the wavefunction is fully deterministic anyway, it's only interpretations which require a collapse where non-determinism appears. I can understand roughly why the many worlds in MWI are a consequence of assuming the wavefunction is reality and that there is never a collapse, I do not understand how you get to the consequences of superdeterminism from applying determinism to quantum mechanics.
(And yeah, preference for any of these interpretations will essentially boil down to what idea you like the most, or more likely what idea you dislike the least. With QM you pick your reasonable base assumptions and then take the uncomfortable conclusions that result)
Superdeterminism so far seems to be prone to Occam's razor.
Actual models of superdeterminism (e.g. Donadi–Hossenfelder (2022)) seem inelegant and mathematically more complex than MWI. Which doesn't mean it's physically wrong or "weirder than MWI".
I don't understand the superdeterminism idea. Wasn’t that already the classical/Newtonian view - that everything was predetermined, a universe of billiard balls following their destiny exactly?
Newtonian is just plain determinism. One thing causes another, but does not imply things are fixed in any particular way.
Superdeterminism implies that things are fixed in advance in such a way that the things we "choose" to measure always looks as if there are no local hidden variables (e.g. Bell's inequality) even though there are.
It's quite deeply weird. It's basically looking at the seemingly impossible correlations that occur in quantum mechanics and saying that they happen because the decision about what to measure is correlated with the state of the system somehow (Bell's inequality assumes that these are independent). This is very strange in a universe where we apparently could base that decision on many different seemingly unrelated processes. (including processes that have been causally seperated for near the lifetime of the universe, e.g. by choosing the measurements based on noise in the CMB).
No, they are completely different. Determinism is the idea that if you have a perfect snapshot of the universe at one time, you could run that snapshot forwards or backwards using the laws of physics and have a complete history of the entire universe. It's a valid scientist idea, but Bell's Inequality experiments pretty much prove it false by showing that either realism or locality is false, and you kind of need both to have determinism.
Meanwhile, superdeterminism is the idea that you can still have realism and locality by claiming that Bell's Inequality experiments are invalid because the universe could somehow "know" you are performing a Bell's Inequality experiment and rig it to get the "wrong" answer. Superdeterminism is equivalent to saying that we can't prove smoking causes lung cancer, because the universe might rig any science experiments to make it look like smoking causes cancer. Anytime you ask why the universe would do that or how you can prove anything in such a universe, they shrug their shoulders. It's a completely BS idea that got traction because specific people pushed it and others don't understand quantum physics enough to know how unserious of an idea it is.
You can imagine the general idea by imagining the state space of a bunch of billiard balls: their position and velocity in a 6D space.
This is a metaphor and not the state or experiment that superdeterminism seeks to answer. I am also speaking well outside the areas of physics I was trained in. So huge grain of salt.
In classical determinism, the trajectories of all billard balls can be derived precisely from their initial conditions. Due to sensitivity to initial conditions and our ability to know them precisely, we can see chaotic mixing behavior where the trajectory of even two billiard balls that start at nearly the same place become more and more uncorrelated as time goes on as they bounce around and into each other. One expects that many accessible observables and functions loose detectable correlations as this billiard ball universe goes on and the billiard balls go on to roughly fill the full 6D state space up to conservation of momentum.
Now imagine the weirder scenario, that there exists some function and statistical comparison you can make between state variables from sets of billiard balls. Although these state variables themselves seem uncorrelated after enough time has passed, there are these properties that always hold with perfect correlation even after infinite chaotic time bouncing around. The points in state space that the balls cover is restricted to some manifold where these statistical properties are true when checked. The system cannot evolve in a way where those correlations of bulk quantities would disappear.
In this toy metaphor it’s not so horrifically odd. Superdetermism gets more flak because: (i) the state space and property in question is so much weirder and more complicated than the kinematic example, the correlations are between objects that measure and the objects being measured! (ii) if these properties are always true under any check we can make there is no way to falsify. Then it doesn’t matter if the behavior is from some unimaginable underlying universal state space geometry or local quantum effects. This same argument could also be applied more generally and inappropriately to reduce any experiment to “that’s just the way the structure of the universe is”.
I've got a feeling that our intuitive ick around spooky action at a distance is due to out intuitive view on locality and the nature of space, maybe time too, being wrong. IOW remote is really not remote.
Perhaps we've got it backwards and quantum entanglement is what defines "locality" rather than mysteriously existing in the face of it.
Second this book, but you need a source before this to study QP successfully. This requires a lot of UG maths and physics knowledge that I think most would not have.
But I do believe that is atleast in part Feynmans point. The way we have explored QM for the past... 120 years (? Wow is it really that old!?) is you don't need to understand it, here are the rules and tools to carry out extraordinary calculation.
I believe the likes of Sean Caroll are trying to bring understanding back to physics and meet philosophy.
It really depends on your goal. If you wish to use it day to day then you do need to understand it but yes you can use the handy Dirac notation to let you calculate lots without ever going too deep.
See also, Atomic Physics for Everyone: An Introduction to Atomic Physics, Quantum Mechanics, and Precision Spectroscopy with No College-Level Prerequisites. - https://news.ycombinator.com/item?id=46961595
I take issue with "understand". I agree QM can not be understood in terms of everyday experience. One must build experience, language and proper metaphor for the understanding. For example, in the intro Ross uses the example of explaining a waterfall to someone who never saw it. He says that can be done but he relies on implicitly the listener knowing what people on Earth may take for granted. That understanding of a waterfall can only happen if the listener already has some understanding of fluid flow and gravity. We do, but say a newly found alien friend from a dry environment that had never experienced fluid flow would not have the mental building blocks to understand it. Feynman gave a famous interview where he said, essentially, "no, I can't explain it to you because you are too ignorant" (he said it more politely). Going the other direction, Physics steeped enough in quantum theory do understand QM enough to have meaningful discussions free (at times) of rigorous math. They do this because they have a shared language, vocabulary, metaphor. Sure, they must rely on math and experiment to ground that understanding in truth but I guarantee they do not communicate understanding (solely) in math and measurement data.
You can imagine waterfall of sand - the fluidity here comes from all those small sand particles moving simultaneously.
>>>Physics steeped enough in quantum theory do understand QM enough to have meaningful discussions free (at times) of rigorous math.
That sounds a lot like gate keeping and has no actual backing - to understand QM you still need to understand Physics, as mechanics of both of them are explaining each other - the scale is the only difference.
The idea is that you can discuss using hand waving while drinking coffee, but after that you must write the complete mathematical calculation, so there is no gate keeping.
Most of the times the formal version with equations agree with the hand waving, but sometimes you have nasty surprises and must learn to hand wave better.
That’s not the meaning of “understand” that was being used. This article points out that nobody understands QM well enough, not even the experts. (Do note the author is an expert!) By “I Don’t Understand”, what he actually means is that QM is incomplete in the same way that Newtonian Mechanics is incomplete; it doesn’t explain physics well enough to understand or explain what’s really there. This is, of course, why there’s an ongoing debate among the experts about what QM even means and how to interpret it.
A useful analogy might be understanding quantum mechanics versus understanding a computer. In the early days of computing, an engineer might plausibly have known every component in a computer, understood how these components worked, and understood why each one was there. As computers got more complicated, no longer could anyone understand the entire system on that level. But still, as an individual engineer, you can understand the system at a high-level, and for each lower-level component, you can have an approximate idea of why it's there, what it does, and how to learn it in more detail if you ever have to. Any "why" question that you might have about it has a straightforward answer that can be stated in a few sentences.
With quantum mechanics, there's a lot that you have to accept when you learn the subject without understanding why. Why complex numbers? Why infinite-dimensional Hilbert spaces? Why non-commutative algebra? You can kind-of, with great effort, make arguments that all of these are at least reasonable. But nobody really understands "why" at a level beyond "because the theory works".
"I really can't do a good job, any job, of explaining magnetic force in terms of something else you're more familiar with, because I don't understand it in terms of anything else that you're more familiar with"
His point was that fundamental forces cannot be understood as "like" everyday objects, because we don't "understand" everyday objects except as applications of fundamental forces. Using those things to explain fundamental forces would just be circular. He can tell you that a stretching rubber band is due to the electric field, but he can't then turn around and "explain" that the electric field is like a stretching rubber band!
Fundamental forces just are, and you understand them by studying them.
Yes, this sounds like the interview that I was remembering.
>Fundamental forces just are, and you understand them by studying them.
This is largely the point I was trying to make. One must understand QM using non-everyday ideas developed with math and measurement. But once those ideas are held, similes/metaphor (sometimes actual isomorphs) can be useful parts of that understanding and its communication between those that share the basis for that understanding.
Or we understand just enough to make things and instruments that only work on (and up to) the layer that we understand.
Ancient humans could build boats 5000 years ago and expand throughout the planet, but they didn't know about water being made up of hydrogen+oxygen, or the tides being caused by the moon, etc.
Their calculations served them on the layer they operated on.
Mostly because people around the mediterranean sea didn't have to care, tides being so small there. Yet the Greek had fairly advanced models of tide schedules.
Pretty sure peoples that were experiencing bigger tides and depended on it e.g for fishing figured out the relationship with the moon pretty quickly, whatever esoteric reason they may have plastered upon it.
The difference is that the part we do not understand about QM is rather fundamental to its interpretation, while in classical physics it is more a problem of understanding its consequences in complex scenarios.
No, I do not claim I am expert at understanding at how LLMs operate, but there is a huge difference - we can measure changes in models and even identify what part of model is used - it is clearly a niche thing to do and not particularly interesting to many people(and not to me as well, unless those LLMs will be able to replicate brains - in future, then I would be biting my nails that I have ignored the basics), but there is no such issue on dissecting and identifying how bits are shuffled around, unlike with QM.
For QM the main issue is that we are barely able to see results of that black box and have to make guesses even about observable results, because what we see is result of particle long gone and the result has been a mess of paths that it took. And basically we are operating at identifying single particle, while clearly the path that particle took was defined by other particles and "gravity"? from interacting with other particles bumping it around. I'm even less knowledgeable when it comes to QM terminology, but I get impression that most of the commenters here simply are parroting things they have read or being taught without actually trying to understand and taking into account all the unresolved problems in QM, which is why so many of them sounds so confident is my guess. Because knowing limitations of my brain I would be not so confident of anything, only because of massive load of unresolved issues that QM has.
>It sounds all superior and mysterious to quote Feynman here,
It isn't about being superior, mysterious, or clever. The following "nobody understands" type of quips and thought experiments are different ways of saying our intuitions don't help us understand it :
- "God does not play dice with the universe.", Albert Einstein
- "Shut up and calculate", N. David Mermin
- "Schrödinger's cat" being both alive and dead
- various interpretations/analogies explaining quantum physics leading to absurdities or contradictions
Yes, humanity has harnessed quantum mechanics with mathematic frameworks and repeatable experiments to make useful things... but that's a different layer of "understanding" than the deeper levels in the above quotes.
"Nobody understands what gravity is." ... Wait, if nobody "understands" gravity, how did we send people to the moon?!?
Because those are different usages of the word "understand".
"Understand" means "Have a reasonable metaphor for."
Our monkey minds evolved to throw rocks at birds, and our metaphors are based on concepts like position, velocity, and temperature. We added first-level abstractions like energy and cause-and-effect, then built higher level abstractions on those basic concepts.
QM clearly doesn't work like that. It's probabilistic, possibly non-local, possibly subjective, possibly a holographic projection of some underlying reality that is nothing like this one, and its relationship with causality is slippery.
We have a mathematical UI for it, but that's not at all the same thing as understanding the machinery on the other side of the UI.
All the idea of valence and conduction bands depends on quantum effects. The holes are quantum effects, the electrons are not plain electrons and in particular they have an effective mass that is not equal to the mass of a plain electron traveling in vacuum.
When you ask what time it is, the answer ultimately comes from an atomic clock that uses quantum state selection. You could argue that any sort of fluorescent lamp or LED is quantum-driven, based on bandgap thresholds or ionization of gas. Same for anything involving solar PV electricity generation.
The example the author gives, transistors that somehow rely on quantum tunneling to produce gain, is not a good example at all. In fact it's downright wrong. The essay could have been titled "I don't understand transistors."
Listen, people were able to make calendars by observing skies and assuming that Sun was orbiting Earth. It is not exactly the same, but very much how people understand QM - they do not need to known mechanics, but observing end results is enough to "understand" how it functions.
Also billions of people understand how to operate mobile phones, but "understanding how they operate" would be rather stretch and even the biggest specialists of QM have understanding only on how to interpret end results in QM - at best and that is basically it.
Quite frankly, I'm confused about these bold statements. I assume there seems to be some knowledge background of what you are saying - it very much reminds me what stupid strawman arguments I had in high school with my schoolmates then as a part of learning process, but rather far from actual wisdom.
I think the disconnect here is the use of the word "understand". What Feynman presumably meant was really "interpret" not "understand", and theories are not made to be interpreted - they are made to make experimental predictions.
Many people of course, Feynman obviously included, understand the theory in the sense of knowing how to correctly apply it to make predictions.
Somewhat related: a book that really helped me is Picturing Quantum Processes
by Bob Coecke. It's a visual representation of quantum processes, which really helped me understand the concept
It stands out as not too common a sight for books, so having two like this, more or less in the same style, on the same topic, both posted in this thread, is amusing. Maybe it's not that rare and I'm just not reading enough books from academics for whom a book is like a weird long paper with hand-holding for amateurs.
Physicists use LaTeX and less often plain TeX a lot as you say because of writing papers. I think that the basic LaTeX book document style provides a workable set of features, and that lets the author just focus on the content. I'd imagine that commercial publishers e.g. OUP would redefine the basic macros to produce output in their house style.
Finished reading this book not too long ago, one of my top three textbooks. An absolute joy to read full on great insight.
Not sure how it feels to a beginner, but to someone with a good deal of familiarity in the field it put everything in such a nice tight conceptual package.
"IS QUANTUM PHYSICS CORRECT AND COMPLETE?" is reductive, there are more quantum denominations: Copenhagen, QBism, RQM, consistent histories, Many-worlds, Bohmian mechanics, and various spontaneous collapse people. I might've missed a few.
Yes this is a particular interest of mine, the various interpretations of QM. Most physicists subscribe to the Copenhagen interpretation, but I still find it has philosophical quandaries.
He mentioned many-worlds.
Bohmian mechanics has been shown to be inadequate.
Blokhinstev's ensemble interpretation, which I like, is unattractive to many.
Situation: There are 12 major interpretations of quantum mechanics.
Quantum Bayesianism (QBism): We need to eliminate the interpretational conundrums that have beset quantum theory. A quantum state should not be thought to offer a description or representation of physical reality – instead it represents the degrees of belief an agent has about the possible outcomes of measurements.
Situation: There are 13 major interpretations of quantum mechanics.
This makes me wonder if we could also argue that there were multiple denominations of classical mechanics. Newton's laws, Hamiltonians and Lagrangians come to mind. I recall that people including Newton were also unsettled by Newton's law of gravity ('action at a distance')[1] and tried to come up with more 'intuitive' theories. The one where the law of attraction arises from being bombarded by particles from the universe (screening) was an amusing one that doesn't work due to thermal effects [2].
> The one where the law of attraction arises from being bombarded by particles from the universe (screening) was an amusing one that doesn't work due to thermal effects [2]
It's useful, not metaphysically real. (Hot take btw) This is called Instrumentalism. The belief that it's real is called Scientific Realism. However over and over again, science can't cover edge cases, and we find better fitting models. The Copernician revolution is a good example of this dichotomy.
2. Academia basically forces you to believe the doctrine or you fail the class. From philosophy to physics to sociology. If you read the philosopher survey, you will find trendy things being quite high. It's a religion in itself.
Bonus 3: Philosophical Pragmatism and Instrumentalism generally solves this, but is intellectually a dead end. There is a reason analytic philosophy continues despite gaping holes in linguistics (late Wittgenstein) that ruin it. But at the same time, best fits might be missing a new paradigm. I wish I could tell people to ask AI to explain Hegel to understand, but I think people need to read it themselves.
Tl;dr: quantum mechanics is the best we have. It's definitely wrong, but it's the most useful we have.
> 2. Academia basically forces you to believe the doctrine or you fail the class.
Yes, but if you can make a reliable experiment that disagree with the doctrine, it will change, even if everyone hates the idea. In particular https://en.wikipedia.org/wiki/Wu_experiment
I disagree. Science is what we do to find out what is the case, i.e. real. The fact that it also has useful applications is directly tied to the extent to which the findings are real. It works because it describes something real.
If you read late Wittgenstein or Karl Popper, you will find that science is a useful simplification. Rorty is boring and not useful, but he kills any sort of Realism.
The 3 gigantic holes:
1. It's all language. (Wittgenstein)
2. The edges of systems do not connect with each other.
3. There are exceptions to everything.
I know that might seem a bit generic, but these are the major flaws in the philosophy of science.
I was a true believer too.
If you ever want to learn a ton about science, read Popper. He tortures himself, but he's also scientific meta.
I guess that depends on what you mean by "real". I've always taken the scientific method to be about creating theories that correctly predict experimental outcomes, which is to say that utility is primary.
I guess if/when we discover a theory of everything then we could claim "this is real/reality", but what would that even mean other than modelling reality/outcomes with 100% fidelity?
Things being might be real in a specific point in spacetime, but that they are real is independent of time. However what Science "claims to be real"[0] is dependent of time. You can't know that the realness is the final understanding. The closest you can come to believing things are real, is that you can't think of an experiment that falsifies them. But you can't really know for sure, that falsifying is impossible. How do you solve that? I don't have that problem, because I agree with your parent, but this is what I thinks contradicts your understanding of Science.
[0] I personally don't think Science concerns itself whether things are real, only whether the result of model and realness match, but that's what we are discussing here.
The key aspects of quantum physics can be explained very simply. The issue is going in depth without those basics. I often find if someone doesn't get Quantum Physics, it's that source or you need the steps explaining more in-depth. Often sources assume your base knowledge and that is where many fall flat.
I loved the book QED: The Strange Theory of Light and Matter by Feynman as a child. Funny enough I always saw QM from a path integral PoV, a decade before I got to learn the formalism
Unpopular opinion I think, but I still believe the physics world was wrong to chase the Copenhagen interpretation.
The math does indeed work, and many experiments and practical uses seem to show that there is something to quantum broadly. But to throw determinism out the window and believe that quantum is fundamentally probabilistic, and that one can never really run scientific experiments because observing state collapses superposition, has always seemed asinine to me.
I could be completely wrong, but it's always seemed obvious to me that the need for probabilities in quantum is a clear indicator that something is missing in the theory. I'm never surprised when a person can't understand quantum as its described today.
It has been shown that you can keep determinism (Bohm etc), but what follows is not necessary something you'll find more intuitive or cleaner or more logical.
I haven't been sold by pilot-wave theory, adding hidden variables to attempt to get rid of randomness feels like a cheat rather that a realistic view of how reality would work.
Unrelated, but I also wish scientists properly used the term "theory".
It's completely counterintuitive, but that's how it works experimentally. For example:
Measure the spin of electrons in direction X (that's done with a weirdly shaped magnet). You'll get either +1 or -1 in a conveniently chosen unit system. That's already weird, you'll never measure +0.5 for example. Keep only the +1 electrons. You can measure them again and again, you'll always get +1 in the X direction.
Now measure those electrons in the Y direction, you'll also get either +1 or -1.
But now, if you measure in the X direction again, you'll get +1 or -1 with 50% probability; although before measuring in the Y direction, these electrons always had spin +1 in the X direction.
Oh I get that experiments prove out. What has always been unintuitive to me to the point of seeming wrong is that said spin is random and lives in a probability cloud that is probabilistic only until we observe it.
The math works and the experiments work, but it feels like a broken clock situation. It happens to correlate well, but the understanding and models are missing something in the actual underlying physics that, if understood, would throw the whole randomness part out the window.
> [the] spin is random and lives in a probability cloud that is probabilistic only until we observe it.
My mental model of it is kinda reversed. The maths assign a specific, deterministic state to each electron between each measurement. However, the "left" state is equal to "(up + down) / sqrt(2)". It then follows that when we measure an electron that is in the "left" state along the vertical direction, we get 50% up and 50% down: the probabilistic behavior happens when measuring, which "forces" an electron that was in the "left" state to become either "up" or "down".
I agree though that it would be less frustrating if there was some property of the electrons that would allow to predict in which state it'll collapse.
He also wrote another similar popular article on Relativity, I DO Understand Relativity - https://news.ycombinator.com/item?id=50220891
With article titles like these, i just had to share it on HN!
Somebody should work on the above two webpages to make them more readable with html+pdf formats. That would make these more accessible to the "interested layman".
Yes but it's a very large institution. Thousands of staff, tens of thousands of students across a bunch of campuses.
The author also wrote a sequel; I DO Understand Relativity - https://news.ycombinator.com/item?id=50220891
This is known as a "hidden variable theory". People will tell you that a local (things can only affect their immediate surroundings) version of the theory is impossible because it would be a violation of Bell's inequality, but there is a loophole that requires accepting the idea of "superdeterminism". This is the idea that where what measurement a scientist chooses to measure is predetermined and correlated with what the particle being measured is going to do.
So if a particle lands on a screen according to distribution p when going through a double slit, but with distribution p' when one of the slits is measured at, conventional QM says that the measurement "collapses the wave function". But a superdeterministic local hidden variable theory would imply that the choice of whether to measure at the slit or not was already set in stone at the same time that the particle "decided" which path to take to land on the screen, more or less.
The important distinction in this case is about FTL existing but not being able to exploit it for FTL communication.
In reality the entangled particle will interact with something almost instantly thus collapsing it. The cat is actually dead or alive from the perspective of the microscopic things in the box. A world never witnessed or measured by a being doesn't collapse it's entire history of interactions of every subatomic particle, atom, molecule and emergent property from the start of the universe to 'now' instantaneously upon being viewed. The photons from that world have been hitting earth continuously since earth existed after all.
Quantum physics makes predictions that suggest this isn't so. You can design experiments (e.g. A Bell inequality test) in which quantum physics predicts correlations that go beyond what would be possible with some hidden local information attached to the entangled particles that we just don't know about. Experiments don't prove theories to be correct. That's not how science works. However, experimental tests of Bell inequalities have pretty conclusively shown that local hidden variable theories are inadequate to explain what's going on.
Yes, it appears what Einstein called "spooky action at a distance" seems to propagate close to instantly. It's important to appreciate that you can't transmit information this way though. We can only make sense of the quantum correlations after communicating other information at classical speeds. Sometimes you see quantum entanglement devices allowing FTL communication in sci-fi, but that's pure horse hockey.
That all being said, I don't understand quantum physics either.
Tl;dr spacetime does not exist as a global background where things are "placed", it is not ontic. "Things" are first, and spacetime is derived from interaction statistics of "things". This eliminates nearly all naive paradoxes like double slit etc. Now, these "things" are somewhat complicated and non-intuitive (e.g. there are no individual "particles", they are a limit of discrete distributions), but that's a good start.
- Richard Feynman
Feynman's own QED is a part of QFT, but this is no longer quantum mechanics. Special relativity and quantum physics are reconciled since then. Now, we only need to reconcile GR and QFT, but this leap was so far beyond our attempts to scale it. Yet, QED/QFT/SM can be "understood" as there are fewer obvious paradoxes that plagued QM.
>The next reason that you might think you do not understand what I am telling you is, while I am describing to you how Nature works, you won't understand why Nature works that way. But you see, nobody understands that. I can't explain why Nature behaves in this peculiar way.
Superdeterminism and retrocausality both allow for local hidden variables - it’s just that they don’t satisfy Bell’s assumptions.
Similarly, superdeterminism is simply the application of the determinism that was believed to apply to physics before QM, to QM itself. In a way, one might have expected it to be the default interpretation.
Laplace expressed this in "A Philosophical Essay on Probabilities" in 1814: "We ought then to regard the present state of the universe as the effect of its anterior state and as the cause of that which is to follow. [...] For [an intelligence that has sufficient information] nothing would be uncertain, and the future, as the past, would be present to its eyes."
Superdeterminism essentially extends this idea of deterministic physical evolution to quantum mechanics. It could be considered an appropriate default simply because it was previously considered to be, not only the default, but the strongly believed truth.
> Superdeterminism says that there’s no way to pick your experimental choices in a way that reveals things because any possible random number sources you could use have contrived correlations that prevent that
You're arguing against a consequence of superdeterminism, not its motivation. Its motivation is as I've described.
The word "contrived" is doing some heavy lifting in your statement. Nothing needs to be contrived in superdeterminism, even if it seems that way to an observer within the universe.
The explanatory problem you've alluded to only arises because we're trying to understand the universe from within the universe. The universe is under no obligation to make itself sensible to us.
Essentially, you're saying little more than that you don't like the idea of superdeterminism.
(And yeah, preference for any of these interpretations will essentially boil down to what idea you like the most, or more likely what idea you dislike the least. With QM you pick your reasonable base assumptions and then take the uncomfortable conclusions that result)
Actual models of superdeterminism (e.g. Donadi–Hossenfelder (2022)) seem inelegant and mathematically more complex than MWI. Which doesn't mean it's physically wrong or "weirder than MWI".
A theory that says that unicorns exist but only go places where no one will discover them (even though they aren’t invisible), is dumb.
A scientific theory should be compatible with experimentation.
Superdeterminism implies that things are fixed in advance in such a way that the things we "choose" to measure always looks as if there are no local hidden variables (e.g. Bell's inequality) even though there are.
Meanwhile, superdeterminism is the idea that you can still have realism and locality by claiming that Bell's Inequality experiments are invalid because the universe could somehow "know" you are performing a Bell's Inequality experiment and rig it to get the "wrong" answer. Superdeterminism is equivalent to saying that we can't prove smoking causes lung cancer, because the universe might rig any science experiments to make it look like smoking causes cancer. Anytime you ask why the universe would do that or how you can prove anything in such a universe, they shrug their shoulders. It's a completely BS idea that got traction because specific people pushed it and others don't understand quantum physics enough to know how unserious of an idea it is.
This is a metaphor and not the state or experiment that superdeterminism seeks to answer. I am also speaking well outside the areas of physics I was trained in. So huge grain of salt.
In classical determinism, the trajectories of all billard balls can be derived precisely from their initial conditions. Due to sensitivity to initial conditions and our ability to know them precisely, we can see chaotic mixing behavior where the trajectory of even two billiard balls that start at nearly the same place become more and more uncorrelated as time goes on as they bounce around and into each other. One expects that many accessible observables and functions loose detectable correlations as this billiard ball universe goes on and the billiard balls go on to roughly fill the full 6D state space up to conservation of momentum.
Now imagine the weirder scenario, that there exists some function and statistical comparison you can make between state variables from sets of billiard balls. Although these state variables themselves seem uncorrelated after enough time has passed, there are these properties that always hold with perfect correlation even after infinite chaotic time bouncing around. The points in state space that the balls cover is restricted to some manifold where these statistical properties are true when checked. The system cannot evolve in a way where those correlations of bulk quantities would disappear.
In this toy metaphor it’s not so horrifically odd. Superdetermism gets more flak because: (i) the state space and property in question is so much weirder and more complicated than the kinematic example, the correlations are between objects that measure and the objects being measured! (ii) if these properties are always true under any check we can make there is no way to falsify. Then it doesn’t matter if the behavior is from some unimaginable underlying universal state space geometry or local quantum effects. This same argument could also be applied more generally and inappropriately to reduce any experiment to “that’s just the way the structure of the universe is”.
Perhaps we've got it backwards and quantum entanglement is what defines "locality" rather than mysteriously existing in the face of it.
If anyone is interested in self-studying quantum physics, QFT for the Gifted Amateur [1] is very well regarded.
1: https://academic.oup.com/book/36442?login=false
It is much more shut up and calculate.
But I do believe that is atleast in part Feynmans point. The way we have explored QM for the past... 120 years (? Wow is it really that old!?) is you don't need to understand it, here are the rules and tools to carry out extraordinary calculation.
I believe the likes of Sean Caroll are trying to bring understanding back to physics and meet philosophy.
https://web1.eng.famu.fsu.edu/~dommelen/quantum/
>>>Physics steeped enough in quantum theory do understand QM enough to have meaningful discussions free (at times) of rigorous math.
That sounds a lot like gate keeping and has no actual backing - to understand QM you still need to understand Physics, as mechanics of both of them are explaining each other - the scale is the only difference.
Most of the times the formal version with equations agree with the hand waving, but sometimes you have nasty surprises and must learn to hand wave better.
With quantum mechanics, there's a lot that you have to accept when you learn the subject without understanding why. Why complex numbers? Why infinite-dimensional Hilbert spaces? Why non-commutative algebra? You can kind-of, with great effort, make arguments that all of these are at least reasonable. But nobody really understands "why" at a level beyond "because the theory works".
The famous interview I know is when he said:
"I really can't do a good job, any job, of explaining magnetic force in terms of something else you're more familiar with, because I don't understand it in terms of anything else that you're more familiar with"
His point was that fundamental forces cannot be understood as "like" everyday objects, because we don't "understand" everyday objects except as applications of fundamental forces. Using those things to explain fundamental forces would just be circular. He can tell you that a stretching rubber band is due to the electric field, but he can't then turn around and "explain" that the electric field is like a stretching rubber band! Fundamental forces just are, and you understand them by studying them.
>Fundamental forces just are, and you understand them by studying them.
This is largely the point I was trying to make. One must understand QM using non-everyday ideas developed with math and measurement. But once those ideas are held, similes/metaphor (sometimes actual isomorphs) can be useful parts of that understanding and its communication between those that share the basis for that understanding.
It sounds all superior and mysterious to quote Feynman here, but the fact is many people absolutely do understand quantum mechanics.
Ancient humans could build boats 5000 years ago and expand throughout the planet, but they didn't know about water being made up of hydrogen+oxygen, or the tides being caused by the moon, etc.
Their calculations served them on the layer they operated on.
Mostly because people around the mediterranean sea didn't have to care, tides being so small there. Yet the Greek had fairly advanced models of tide schedules.
Pretty sure peoples that were experiencing bigger tides and depended on it e.g for fishing figured out the relationship with the moon pretty quickly, whatever esoteric reason they may have plastered upon it.
Nobody takes this to mean that classical physics is generally incomprehensible.
We can build black boxes and exploit the behavior of what we see.
But we can’t always go to deeper and deeper layers of understanding.
QM is not a black boxes we built but one could perhaps say it’s a black box that we see.
For QM the main issue is that we are barely able to see results of that black box and have to make guesses even about observable results, because what we see is result of particle long gone and the result has been a mess of paths that it took. And basically we are operating at identifying single particle, while clearly the path that particle took was defined by other particles and "gravity"? from interacting with other particles bumping it around. I'm even less knowledgeable when it comes to QM terminology, but I get impression that most of the commenters here simply are parroting things they have read or being taught without actually trying to understand and taking into account all the unresolved problems in QM, which is why so many of them sounds so confident is my guess. Because knowing limitations of my brain I would be not so confident of anything, only because of massive load of unresolved issues that QM has.
It isn't about being superior, mysterious, or clever. The following "nobody understands" type of quips and thought experiments are different ways of saying our intuitions don't help us understand it :
- "God does not play dice with the universe.", Albert Einstein
- "Shut up and calculate", N. David Mermin
- "Schrödinger's cat" being both alive and dead
- various interpretations/analogies explaining quantum physics leading to absurdities or contradictions
Yes, humanity has harnessed quantum mechanics with mathematic frameworks and repeatable experiments to make useful things... but that's a different layer of "understanding" than the deeper levels in the above quotes.
"Nobody understands what gravity is." ... Wait, if nobody "understands" gravity, how did we send people to the moon?!?
Because those are different usages of the word "understand".
Our monkey minds evolved to throw rocks at birds, and our metaphors are based on concepts like position, velocity, and temperature. We added first-level abstractions like energy and cause-and-effect, then built higher level abstractions on those basic concepts.
QM clearly doesn't work like that. It's probabilistic, possibly non-local, possibly subjective, possibly a holographic projection of some underlying reality that is nothing like this one, and its relationship with causality is slippery.
We have a mathematical UI for it, but that's not at all the same thing as understanding the machinery on the other side of the UI.
Anyway, I prefer LEDs as an example.
The example the author gives, transistors that somehow rely on quantum tunneling to produce gain, is not a good example at all. In fact it's downright wrong. The essay could have been titled "I don't understand transistors."
Also billions of people understand how to operate mobile phones, but "understanding how they operate" would be rather stretch and even the biggest specialists of QM have understanding only on how to interpret end results in QM - at best and that is basically it.
Quite frankly, I'm confused about these bold statements. I assume there seems to be some knowledge background of what you are saying - it very much reminds me what stupid strawman arguments I had in high school with my schoolmates then as a part of learning process, but rather far from actual wisdom.
Many people of course, Feynman obviously included, understand the theory in the sense of knowing how to correctly apply it to make predictions.
https://gitlab.com/users/mirtitles/projects
Not sure how it feels to a beginner, but to someone with a good deal of familiarity in the field it put everything in such a nice tight conceptual package.
Uh oh, some people have no sense of humor =\
Blokhinstev's ensemble interpretation, which I like, is unattractive to many.
Quantum Bayesianism (QBism): We need to eliminate the interpretational conundrums that have beset quantum theory. A quantum state should not be thought to offer a description or representation of physical reality – instead it represents the degrees of belief an agent has about the possible outcomes of measurements.
Situation: There are 13 major interpretations of quantum mechanics.
https://xkcd.com/927/
[1] https://en.wikipedia.org/wiki/Action_at_a_distance [2] https://en.wikipedia.org/wiki/Mechanical_explanations_of_gra...
But isn’t that how EM actually works ?
The photon mediates the electromagnetic force
It's useful, not metaphysically real. (Hot take btw) This is called Instrumentalism. The belief that it's real is called Scientific Realism. However over and over again, science can't cover edge cases, and we find better fitting models. The Copernician revolution is a good example of this dichotomy.
2. Academia basically forces you to believe the doctrine or you fail the class. From philosophy to physics to sociology. If you read the philosopher survey, you will find trendy things being quite high. It's a religion in itself.
Bonus 3: Philosophical Pragmatism and Instrumentalism generally solves this, but is intellectually a dead end. There is a reason analytic philosophy continues despite gaping holes in linguistics (late Wittgenstein) that ruin it. But at the same time, best fits might be missing a new paradigm. I wish I could tell people to ask AI to explain Hegel to understand, but I think people need to read it themselves.
Tl;dr: quantum mechanics is the best we have. It's definitely wrong, but it's the most useful we have.
Yes, but if you can make a reliable experiment that disagree with the doctrine, it will change, even if everyone hates the idea. In particular https://en.wikipedia.org/wiki/Wu_experiment
If you read late Wittgenstein or Karl Popper, you will find that science is a useful simplification. Rorty is boring and not useful, but he kills any sort of Realism.
The 3 gigantic holes:
1. It's all language. (Wittgenstein)
2. The edges of systems do not connect with each other.
3. There are exceptions to everything.
I know that might seem a bit generic, but these are the major flaws in the philosophy of science.
I was a true believer too.
If you ever want to learn a ton about science, read Popper. He tortures himself, but he's also scientific meta.
I guess if/when we discover a theory of everything then we could claim "this is real/reality", but what would that even mean other than modelling reality/outcomes with 100% fidelity?
[0] I personally don't think Science concerns itself whether things are real, only whether the result of model and realness match, but that's what we are discussing here.
The math does indeed work, and many experiments and practical uses seem to show that there is something to quantum broadly. But to throw determinism out the window and believe that quantum is fundamentally probabilistic, and that one can never really run scientific experiments because observing state collapses superposition, has always seemed asinine to me.
I could be completely wrong, but it's always seemed obvious to me that the need for probabilities in quantum is a clear indicator that something is missing in the theory. I'm never surprised when a person can't understand quantum as its described today.
Unrelated, but I also wish scientists properly used the term "theory".
Measure the spin of electrons in direction X (that's done with a weirdly shaped magnet). You'll get either +1 or -1 in a conveniently chosen unit system. That's already weird, you'll never measure +0.5 for example. Keep only the +1 electrons. You can measure them again and again, you'll always get +1 in the X direction.
Now measure those electrons in the Y direction, you'll also get either +1 or -1.
But now, if you measure in the X direction again, you'll get +1 or -1 with 50% probability; although before measuring in the Y direction, these electrons always had spin +1 in the X direction.
The math works and the experiments work, but it feels like a broken clock situation. It happens to correlate well, but the understanding and models are missing something in the actual underlying physics that, if understood, would throw the whole randomness part out the window.
My mental model of it is kinda reversed. The maths assign a specific, deterministic state to each electron between each measurement. However, the "left" state is equal to "(up + down) / sqrt(2)". It then follows that when we measure an electron that is in the "left" state along the vertical direction, we get 50% up and 50% down: the probabilistic behavior happens when measuring, which "forces" an electron that was in the "left" state to become either "up" or "down".
I agree though that it would be less frustrating if there was some property of the electrons that would allow to predict in which state it'll collapse.