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Chaos: The real problem with quantum mechanics

161 points by firebaze 4y ago

Konohamaru 4y ago
The best written science article I've read in my life.
- mrwnmonm 4y ago
  I hope you are being sarcastic.
  - Konohamaru 4y ago
    No really. He covers all the important information without bogging down the reader in details, but did it in such a way so that the interested reader can use the post as a map if he wants to find out those details.
armchairhacker 4y ago
> But the vast majority of physicists today think the collapse of the wave-function isn’t a physical process. Because if it was, then it would have to happen instantaneously everywhere. Why can't WFC be a physical process? Yes, when a photon on the Moon is measured it immediately changes the "wave function" of a photon on Earth from 50/50 to 100/0. But the wave function was always a probability, and probabilities always allow for hidden information. To the observer, entangled or not the calculation is still 50/50. And you can't e.g. "force" 1,000 entangled photons all to be positive to create an unlikely unusual scenario. WFC collapse or no, both observers experience their own independent 50/50 photon collapse. It doesn't matter which observer measures first or if there is no "first" at all. The WFC may or may not be instantaneous because it doesn't matter. The fact that the particles are entangled doesn't affect observer A until he's able to observe observer B and vice versa. For all we know all of our particles could be entangled with other particles halfway across the universe, it can't affect us until the speed of light reaches us so we can observer ourselves that the other particles are entangled. Also why Hyperion isn't blurred, despite the fact that all of the particles which affect it are too small to be measured, is because Hyperion isn't too small to be measured. The particles aren't too small to be "measured" by Hyperion when they affect Hyperion, and just because Hyperion is further away from us doesn't mean it behaves and differently. And by seeing Hyperion's chaotic orbit we still can't predict those "unmeasurable" particles.
- mtlmtlmtlmtl 4y ago
  Well, to be fair, Sabine does in fact conclude at the end that it must be a physical process, and the fundamental problem [to be solved] in QM is understanding that physical process.
- zarzavat 4y ago
  What is happening physically when something is measured to distinguish it from something that is not being measured?
  - armchairhacker 4y ago
    1) entangled particles are collapsed “instantaneously”. But it’s not really instantaneous because those particles can’t reach the initial observer/measurement until the speed of light. 2) Superpositions are collapsed which apparently causes different behavior than if they’re collapsed later. e.g. the double slit experiment, where measuring the electrons before the slit causes the interference pattern to disappear. This and Bell’s theorem are very unintuitive but they don’t necessarily break the speed of light. What if electrons are shot through a very long double slit, where they may or may not be measured early on but the observers at the end don’t know this? This still doesn’t break the speed of light because once the electrons create the interference pattern which the observers can measure to determine if they are entangled, the electrons are already local to the observers. Bell’s theorem just shows there is no one “hidden state” in entangled electrons before they are measured. The entanglement seems to create the relation “chargeA = !chargeB” without setting “A” or “B”, but when A is finally resolved, it still takes the speed of light for this information to reach B.
    - lawrenceyan 4y ago
      It’s so efficient. I love it.
    - XorNot 4y ago
      It's worth noting that "instantly" is presumed, but not guaranteed. The speed of entanglement has been measured [1] with a lower bound of 1550 * c. [1] https://www.nature.com/articles/s41598-019-48387-8 https://www.nature.com/articles/s41598-019-48387-8
spekcular 4y ago
My QM knowledge is quite rusty, but given what I remember, I don't understand how certain claims in this article can be correct. Hossenfelder seems to be referring to some well-known papers on Hyperion and decoherence. For a review, see: https://arxiv.org/abs/quant-ph/0605249 https://arxiv.org/abs/quant-ph/0605249 There are lots of references there that you can follow, including a debate on whether decoherence theory is really necessary to explain what's going on. But as far as I can tell, no party in this debate ever claims the Hyperion example implies that "the chaotic motion of Hyperion tells us that we need the measurement collapse to actually be a physical process." The decoherence arguments about Hyperion do not assume this (as far as I know). Can someone please explain? Am I misunderstanding?
- andi999 4y ago
  Havent read the paper, but I think when she objects to 'averaging' she means the tracing out the environment; which I think is ok. Especially since all lokal measurement give the same result on the reduced density matrix.
- xmcqdpt2 4y ago
  No you are correct. There is at this point like 40 years of quantum chaos research. I dipped my toes into it a bit in grad school. In the eighties it was believed that chaos might be the key to understanding the quantum-classical transition. It's not a very cool area of research anymore, mainly because it hasn't really led anywhere. We know that when applying decoherence to quantum mechanical systems we recover the original classical (and potentially chaotic) equations of motion. This basically "solves" the chaos problem but doesn't actually help with measurement, because it doesn't cause collapse of the classical probabilities. This is what is referred to as "superselection". In terms of cat analogies, the quantum wavefunction is a superposition of amplitudes a|dead> + b|alive> and these amplitudes cannot be chaotic because the Schrödinger equation is linear. When the system becomes decoherent, it becomes a classical probability distribution p(alive) that evolves under potentially chaotic classical motion. However it's still probabilistic, the cat remains neither alive nor dead. We haven't "measured" anything. The confusion (and this is what Schlosshauser talks about) is that for some people (famously Ballentine) who follows the ensemble theory of quantum mechanics, there is no meadurement problem at all once we have a classical probability distribution. This view is not very popular however. So anyway the point is that the existence of classical chaos can be straightforwardly explained by decoherence without any collapse at all.
joe_the_user 4y ago
Well, Just Duckduckgoing, I found a 2005 article by some Microsoft Research people reputing to explain the phenomena described without decoherence. https://arxiv.org/abs/quant-ph/0503170 https://arxiv.org/abs/quant-ph/0503170
graycat 4y ago
She mentions correlation. What could she mean by correlation? Please, I'd prefer the most detailed and mathematically precise and advanced view.
- drdeca 4y ago
  I believe this is referring to the entanglement between parts of the system
- bowsamic 4y ago
  Correlation between two quantum observables indicates how, on average, measurements of them are related. Positive correlation means that generally you measure both variables to have the same sign, more strongly correlated being closer to a straight line, i.e. for perfect correlation a measurement of one variable totally determines the other. Negative correlation means that if you measure one to be positive you will probably measure the other one to be negative and vice versa. For two quantum operators a and b, for simplicity on the same Hilbert space H for which one state is |psi>, which is also chosen to be the current state of the system, the correlation is given by, <(a - <a>) (b - <b>)> / (sigma_a sigma_b) where <o> = <psi|o|psi> for any operator o, and sigma_o = sqrt(<o^2> - <o>^2) is the standard deviation of the quantum operator
  - graycat 4y ago
    Thanks. Okay, good to see that quantum mechanics defines its use of correlation as <(a - <a>) (b - <b>)> / (sigma_a sigma_b) Good. Glad to see the actual definition. That is, with usual quantum mechanics notation, this is the usual Pearson correlation coefficient and, thus, appropriate to call correlation. Fine. Good to see that this is just what physics is talking about. My concern has been, does physics say "correlation" when really they mean some case of what we might call the usually much stronger functionally dependent? That is, for complex valued random variables X and Y, they are functionally dependent provided there exist functions f and g so that Y = f(X) and X = g(Y). With this functionally dependent situation, the correlation could be anything from -1 to 1 but usually we won't care because having either of X or Y implies we also have the other exactly. So, as I was reading quantum mechanics, I was wondering if there could be, and open to, two random variables functionally dependent but without correlation 1 or -1 so that, really, talking about mere correlation would be too weak and, thus, not really appropriate. Well, in the case of correlation 1 or -1, there exists non-zero, complex a so that Y = aX in which case instead of mere correlation it would be better to use the stronger functionally dependent. As I understand the situation, usually quantum mechanics uses correlation for examples of entanglement where it appears that, yes, the stronger functionally dependent would hold, and, thus, be more appropriate. That is, the usual uses of correlation outside of quantum mechanics, say, in statistics of medical research, economics, finance, social science, mean "two random variables not independent and also not functionally dependent" -- having the two random variables be independent (which implies correlation 0) or functionally dependent would be unusual.
wrnr 4y ago
QM may be a linear system but QFT is not.
- xmcqdpt2 4y ago
  What is not linear about QFT is the perturbation theory that is used to predict interactions. The underlying Hamiltonians with interactions included are themselves perfectly linear (but very complicated).
fredgrott 4y ago
A better way to put it, We have two math systems that do not mesh together, one applies to macro and one applies to micro. We have no mathematical construct that tells us when micro ends and when macro begins. My biased guess is that it might be a transformation process and math based on Gravity itself i.e. a reformulation of the Maxwell magnetic equations including gravity. Probably a phase transition in the gravity space that gives the real world transition from micro to macro switch from quantum to classical physics
- mathgenius 4y ago
  This is known as gravitationally induced decoherence. We don't know if there's any truth to this, but people are seriously working on measuring this stuff in the lab. You might like to read what Roger Penrose has to say about it. (Btw, we already know how to combine Maxwell's equations and gravity. This is all classical physics.)
tome 4y ago
There's some interesting discussion about what (probably) motivates this talk at https://www.physicsforums.com/threads/t-hooft-cellular-automaton-interpretation.1014630/ https://www.physicsforums.com/threads/t-hooft-cellular-autom...
mrwnmonm 4y ago
A little bit related > https://www.spiedigitallibrary.org/ebooks/PM/The-Evolution-of-Scientific-Knowledge-From-Certainty-to-Uncertainty/1/The-Evolution-of-Scientific-Knowledge--From-Certainty-to-Uncertainty/10.1117/3.2263362.sup?SSO=1 https://www.spiedigitallibrary.org/ebooks/PM/The-Evolution-o... Not sure why this book is not popular btw, it is written by a Math guru and it is to the point and doesn't have many jumps - https://www.amazon.com/Books-Edward-R-Dougherty/s?rh=n%3A283155%2Cp_27%3AEdward+R.+Dougherty https://www.amazon.com/Books-Edward-R-Dougherty/s?rh=n%3A283... - https://scholar.google.com/citations?user=DvTVkcEAAAAJ&hl=en https://scholar.google.com/citations?user=DvTVkcEAAAAJ&hl=en And as far as I know, the problem with QM is unintelligibility, not chaos.
fredgrott 4y ago
To extend some thoughts, my own bias 1. Universe started with a first phase transition involving gravity 2. Gravity might have another phase transition at the micro and macro quantum boundaries. 3. We are already use to having math systems change and boundaries to phase transitions so its not really radically new to our mathematics tools. Yeah, I do have in my unfinished bucket re-doing my math knowledge and tools as either a MS or PhD. That said I might be wrong in either one of these things or seeing the micro and macro boundaries of quantum and classical as a phase transition in gravity. But, my limited math sense tells me I might have the right idea. The key would start with reworking the Maxwell magnetic equations to account for gravity and to describe the phase transition between micro and macro world environments in terms of going from quantum to classical physics Its a bit hard to picture it at first as the two mathematical systems used are incompatible with each other. One is in the matrices world and one is not. But, we have similar math mismatches in our real world. One part of economics is matrices and one is not and yet the micro and macro economic models fit together somehow. So I think it is eventually reachable to some of us as far as understanding the math. But I just might have it wrong altogether
shireboy 4y ago
> each time a grain of dust bumps into the moon, this very slightly changes some part of the moon’s wave-function, and afterwards they are both correlated Help me out here, though. If this is the explanation, then wouldn’t every moon, planet, etc be chaotic, since presumably they all interact with dust and light?
- lisper 4y ago
  No, the bumps are necessary to produce chaos, but not sufficient.
lisper 4y ago
It is important to note that there is a hidden agenda in this essay: Sabine is a superdeterminist, and so her presentations have to be viewed through that lens. As a superdeterminist, she is committed to idea that classical reality is "actually real" (for some value of "actually real" -- see below). And so Hyperion's chaotic behavior is actually real, and QM cannot account for that. All of which is true. But there is an alternative view of classical reality which is that it is not "actually real" (the scare quotes are important here), that it is all just a sort of shared illusion among sentient beings. And QM can account for that, i.e. the math of QM can (and does) describe a set of mutually entangled observers all of which agree on an observation, notwithstanding that the observation has not actual referent in the model. And that is actually what we observe. We do not directly observe Hyperion. What we observe is our own subjective perception of seeing Hyperion, and having everyone around us report their own subjective perception of seeing Hyperion. The "actual existence" of a classical entity, i.e. an actual physical referent for "Hyperion" seems like a plausible explanation for this, but what QM tells us is that this explanation is wrong. But Sabine, as a committed superdeterminist, rejects this idea. But she's not being up-front about that. The problem with QM is not chaos, it is the fact that it is incompatible with classical intuition. The chaos thing just brings this incompatibility into very sharp focus.
- progrus 4y ago
  Question: How often have you seen Quanta Magazine write a disclaimer that their latest story is from a school of superstring theorists? It’s PR, this is just how it is. I do wish Sabine would state the axiom “reality is real” up front though, because I think people should be trusted to consider that one on their own.
- otikik 4y ago
  I must be super deterministic as well because the alternative you describe sounds … unuseful to me. If we can have illusions like that then all the conclusion you extract from that are also subject to the same effect: it’s not necessarily true that QM can account for it; we could also be “allucinating”collectively that they can account for it. Or, we might not exist at all and all perceptions are all fake. Once you introduce a malicious devil like that it always goes “full universe”. Say, this religious group knocks on your door, tells you that Earth is 2022 years old. You point to dinosaur fossils. They say the Devil put them there to trick us. But then, you follow, our whole existence might as well be fake. The Devil could have created both of us 5 minutes ago, with fake memories of a life that never existed, just so we could have this conversation. And we will both vanish when I close this door (blam!). The usual counter is that the devil has a very specific amount of power: triceratops head is ok, humans is too much. But even accepting that, how can you know you are a human? It might be the Devil tricking you again, maybe you are a teacup that thinks they are human.
layer8 4y ago
In the Many Worlds view, does this mean Hyperions motion is nonchaotic overall (i.e. considering the ensemble of the Hyperions in all branches) but chaotic in (most of) the individual branches? Not sure that makes sense.
- progrus 4y ago
  It works because of the big hand-wave that underpins MWI: Which universe do you end up in? It’s random!
  - layer8 4y ago
    > It’s random! It’s not. You end up in all of them. You branch. There is no hand-wave. It’s like if you have a VM with a program running in it, and you clone the VM. Which VM does the running program end up in? In all of them, of course. And the fact that the program branches/forks in that way is not observable to the program. All clones of the running program believe they are the same running program as their earlier self in the original VM. If the program was running a conscious AI, the consciousness would split (multiply).
    - progrus 4y ago
      Which parts have the story you are experiencing? It’s random, isn’t it? I mean at this point you might as well just start arguing that nobody can reason or argue anything.
      - layer8 4y ago
        Honestly, I don’t quite understand what problem you see. The obvious answer is that each you has been experiencing the branch they are in, and will continue to split into more yous that will each again experience the branch they are in. It seems that you’re assuming that there is only a single linear you with a single subjective future, and can’t conceive of your subjective experience forking. But the point is that the perceived linearity of the self is only an illusion, stemming from the vantage point of any given you at any given point in time looking at his/her respective past at that point in time (which for each of them indeed looks linear). Your future branches are all equally real futures of your current self. Your current self will end up in all of them, but of course each of those future yous will only remember their shared past (your current present) and not have any perception of the other branches. The fact that we never subjectively experience the branching (because we are merely a content of the branch, just like the running program is merely a content of the forking VM and does not notice that it is being forked) may be why some people have difficulties with the idea of their subjective experience splitting into separate futures. Again, take the program/VM analogy. What would you expect the program to experience? The answer is that the experience will differ depending on which clone you consider (assuming that the VMs diverge like the MW branches diverge), yet all of the clones used to be the same running program. All the clones are equally real continuations of the original running program, just like in MW the different yous are equally real continuations of their former single consciousness (but now are separate consciousnesses). You are right that we can’t reason about which future we will end up in, because we will end up in all physically possible futures. That can indeed be a philosophical conundrum. Decisions we make are only effective in the branch they are made, and there will presumably always be (equally real and existing) branches where they are not made. That shouldn’t detract from making desirable decisions though, because once we make them, we are necessarily in the branch where we made them, and it’s only our unlucky former future selves who didn’t make them that are now in the less desirable branches.
ithkuil 4y ago
If the Hilbert space is infinite-dimensional, wouldn't that allow for a linear chaotic system?
rsp1984 4y ago
What I don't understand about this example with Hyperion is a) Wouldn't Hyperion's orientation be influenced much more by Saturn and its many moons on their many orbits than by dust and photons? b) Wouldn't it then boil down to "just" an n-body problem (for which we know no closed form predictions exist -- yet is still perfectly "classical" in nature)? In other words, why involve dust and photons and wave functions and entanglement when the answer could simply be "it's an n body problem so we simply can't predict its orientation"?
- samus 4y ago
  My guess is that this is an example of the struggle between proponents of different interpretations of Quantum Mechanics. There are rather a lot of them, even though they all try to explain the same theory. The whole issue eerily reminds me of the debates between proponents of different theories of the relationship between God and Jesus (trinitarians, nontrinitarians and so on). Unless they yield testable predictions, there will not be an end to them.
- bufferoverflow 4y ago
  QM is far worse than an N-body problem. You can trivially model an interaction of 2 or 3 particles as bodies, at a given precision. But when you consider them as waves, you have to compute an insane amount of information. Example: https://youtu.be/0kXGb0_-1iY https://youtu.be/0kXGb0_-1iY And precision is another undefined thing. Is particle's speed / position continuous or quantized? Or in case of QM, is there a resolution to the waves? Or is it all infinitely precise?
- unrealp 4y ago
  Perfect. This is exactly what I thought when I watched the video yesterday. There will also be local variations in saturn's gravity.
newpavlov 4y ago
Personally, I am firmly in the "superdeterminism" camp. To me it's the most elegant interpretation of QM without any mystical measurements magically dependent on "consciousness" and whole universes created on each interaction. If you want to learn basics about it, I recommend watching this video: https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc Do not mind the (joking) clickbait title, the talk itself is quite good even if you only vaguely remember QM.
bigbillheck 4y ago
Hossenfelder links to this paper discussing Hyperion: https://michaelberryphysics.files.wordpress.com/2013/07/berry337.pdf https://michaelberryphysics.files.wordpress.com/2013/07/berr... whose Appendix A starts: "Caricaturing Hyperion as a homogeneous sphere...." Given that one of Hyperion's distinguishing features is that it's very far from being a sphere, this seems like a particularly bad assumption.
mathgenius 4y ago
> But the vast majority of physicists today think the collapse of the wave-function isn’t a physical process. Because if it was, then it would have to happen instantaneously everywhere. I'm a physicist and this does not pass the sniff-test. Part of the problem is we don't know what a "physical process" is. And the second sentence just does not follow from the first (if we even knew what the first sentence meant).
SideburnsOfDoom 4y ago
So to be clear, the article discusses the "wave-function" the "superimposition of states", not of an electron moving through slits, or even of a cat in a box; but of Hyperion, moon of Saturn, diameter 200 km; and what this means for predicting it's motion of over time? Because after a while the superimposed states produce a outcome that can only be explained via Quantum Mechanics, like with the experiments of electrons through slits? I suppose it must be valid to model this large system with Quantum mechanics. And that's partly the point of the article?
effie 4y ago
The main claim that the Schroedinger equation isn't consistent with chaotic behaviour of observables because it is linear in psi seems poorly thought out. As one commenter on youtube pointed out, the Schroedinger equation is linear in psi, but the Liouville equation from statistical physics is also linear in rho and nobody suggests this somehow makes it inconsistent with classical systems exhibiting chaos. The mistake is that mathematical linearity is in equation for psi/rho, and this is then incorrectly changed into assuming linearity of equations for observables. The observed chaos is not in psi/rho, but in observables, say, positions and momenta. The actual problem here is the age-old measurement problem, i.e. the psi function does not tell us result of experiment, only probabilities of possible results, so psi function can't be complete description of state of things in reality.
axilmar 4y ago
Before discussing chaos in QM, I'd like someone more knowledgeable than me to explain a few things to me, if you don't mind, of course: 1) how do we know particles act as/are waves? the double slit experiments does not seem to be proof of that: a) if we rotate the slits 90 degrees, then the interference pattern also rotates 90 degrees in the same direction...does that mean the wave also rotates 90 degrees? does this mean the wave is 3d? and if so, why is the interference pattern not a checkerboard? b) if we enlarge the slits, the interference pattern goes away; the more we enlarge the slits, the more the interference pattern disappears. This means that in our original experiment, the slits were too small for the particle and the particle hits both slits simultaneously, and hence the interference pattern. Why should then the particle be a wave? putting a detector means to make the two slit equipment one slit effectively, making the interference pattern disappear. How can then one reach a conclusion that particles are waves? 2) how do we know that entanglement is the result of 'spooky action at a distance' and not the result of creating two entangled particles? couldn't it be that the particles are created with correlated spins and no communication ever occurs between them? Why am I asking these simple questions and not contribute to the discussion meaningfully, you might ask? well, it seems QM has all the markings of an strange theory, that works for some cases, does not work for some others, and it requires magic for some others. Those things make me think that the basics of QM may be invalid, so I am really questioning those basics. I am sure I am 100% wrong, so please do illuminate me on the questions above; I've tried to ask before, and in different sites, the worst responses being 'go away lame person! how you dare questioning are beautiful intellect!!!', and the best responses being lots and lots of math that don't really answer my basic questions. I am just looking for simple straightforward answers.
- eterevsky 4y ago
  Regarding waves and interference, have a look at this video: https://www.youtube.com/watch?v=TshYfYIxR9E https://www.youtube.com/watch?v=TshYfYIxR9E. It shows how the interference patterns actually look. Yes, the wave is 3D and the interference patterns can be kind of like checker board. We are usually considering a 2D example because it is simpler to visualize and analize. > how do we know that entanglement is the result of 'spooky action at a distance' and not the result of creating two entangled particles? A very high-level explanation is that we know this because quantum computers work (even though right now we can't build them big enough to be useful) and it can't be explained by any classical effects.

161 points by firebaze 4y ago

Konohamaru 4y ago

The best written science article I've read in my life.

mrwnmonm 4y ago
I hope you are being sarcastic.
- Konohamaru 4y ago
  No really. He covers all the important information without bogging down the reader in details, but did it in such a way so that the interested reader can use the post as a map if he wants to find out those details.

armchairhacker 4y ago

> But the vast majority of physicists today think the collapse of the wave-function isn’t a physical process. Because if it was, then it would have to happen instantaneously everywhere. Why can't WFC be a physical process? Yes, when a photon on the Moon is measured it immediately changes the "wave function" of a photon on Earth from 50/50 to 100/0. But the wave function was always a probability, and probabilities always allow for hidden information. To the observer, entangled or not the calculation is still 50/50. And you can't e.g. "force" 1,000 entangled photons all to be positive to create an unlikely unusual scenario. WFC collapse or no, both observers experience their own independent 50/50 photon collapse. It doesn't matter which observer measures first or if there is no "first" at all. The WFC may or may not be instantaneous because it doesn't matter. The fact that the particles are entangled doesn't affect observer A until he's able to observe observer B and vice versa. For all we know all of our particles could be entangled with other particles halfway across the universe, it can't affect us until the speed of light reaches us so we can observer ourselves that the other particles are entangled. Also why Hyperion isn't blurred, despite the fact that all of the particles which affect it are too small to be measured, is because Hyperion isn't too small to be measured. The particles aren't too small to be "measured" by Hyperion when they affect Hyperion, and just because Hyperion is further away from us doesn't mean it behaves and differently. And by seeing Hyperion's chaotic orbit we still can't predict those "unmeasurable" particles.

mtlmtlmtlmtl 4y ago
Well, to be fair, Sabine does in fact conclude at the end that it must be a physical process, and the fundamental problem [to be solved] in QM is understanding that physical process.
zarzavat 4y ago
What is happening physically when something is measured to distinguish it from something that is not being measured?
- armchairhacker 4y ago
  1) entangled particles are collapsed “instantaneously”. But it’s not really instantaneous because those particles can’t reach the initial observer/measurement until the speed of light. 2) Superpositions are collapsed which apparently causes different behavior than if they’re collapsed later. e.g. the double slit experiment, where measuring the electrons before the slit causes the interference pattern to disappear. This and Bell’s theorem are very unintuitive but they don’t necessarily break the speed of light. What if electrons are shot through a very long double slit, where they may or may not be measured early on but the observers at the end don’t know this? This still doesn’t break the speed of light because once the electrons create the interference pattern which the observers can measure to determine if they are entangled, the electrons are already local to the observers. Bell’s theorem just shows there is no one “hidden state” in entangled electrons before they are measured. The entanglement seems to create the relation “chargeA = !chargeB” without setting “A” or “B”, but when A is finally resolved, it still takes the speed of light for this information to reach B.
  - lawrenceyan 4y ago
    It’s so efficient. I love it.
  - XorNot 4y ago
    It's worth noting that "instantly" is presumed, but not guaranteed. The speed of entanglement has been measured [1] with a lower bound of 1550 * c. [1] https://www.nature.com/articles/s41598-019-48387-8 https://www.nature.com/articles/s41598-019-48387-8

spekcular 4y ago

My QM knowledge is quite rusty, but given what I remember, I don't understand how certain claims in this article can be correct. Hossenfelder seems to be referring to some well-known papers on Hyperion and decoherence. For a review, see: https://arxiv.org/abs/quant-ph/0605249 https://arxiv.org/abs/quant-ph/0605249 There are lots of references there that you can follow, including a debate on whether decoherence theory is really necessary to explain what's going on. But as far as I can tell, no party in this debate ever claims the Hyperion example implies that "the chaotic motion of Hyperion tells us that we need the measurement collapse to actually be a physical process." The decoherence arguments about Hyperion do not assume this (as far as I know). Can someone please explain? Am I misunderstanding?

andi999 4y ago
Havent read the paper, but I think when she objects to 'averaging' she means the tracing out the environment; which I think is ok. Especially since all lokal measurement give the same result on the reduced density matrix.
xmcqdpt2 4y ago
No you are correct. There is at this point like 40 years of quantum chaos research. I dipped my toes into it a bit in grad school. In the eighties it was believed that chaos might be the key to understanding the quantum-classical transition. It's not a very cool area of research anymore, mainly because it hasn't really led anywhere. We know that when applying decoherence to quantum mechanical systems we recover the original classical (and potentially chaotic) equations of motion. This basically "solves" the chaos problem but doesn't actually help with measurement, because it doesn't cause collapse of the classical probabilities. This is what is referred to as "superselection". In terms of cat analogies, the quantum wavefunction is a superposition of amplitudes a|dead> + b|alive> and these amplitudes cannot be chaotic because the Schrödinger equation is linear. When the system becomes decoherent, it becomes a classical probability distribution p(alive) that evolves under potentially chaotic classical motion. However it's still probabilistic, the cat remains neither alive nor dead. We haven't "measured" anything. The confusion (and this is what Schlosshauser talks about) is that for some people (famously Ballentine) who follows the ensemble theory of quantum mechanics, there is no meadurement problem at all once we have a classical probability distribution. This view is not very popular however. So anyway the point is that the existence of classical chaos can be straightforwardly explained by decoherence without any collapse at all.

joe_the_user 4y ago

Well, Just Duckduckgoing, I found a 2005 article by some Microsoft Research people reputing to explain the phenomena described without decoherence. https://arxiv.org/abs/quant-ph/0503170 https://arxiv.org/abs/quant-ph/0503170

graycat 4y ago

She mentions correlation. What could she mean by correlation? Please, I'd prefer the most detailed and mathematically precise and advanced view.

drdeca 4y ago
I believe this is referring to the entanglement between parts of the system
bowsamic 4y ago
Correlation between two quantum observables indicates how, on average, measurements of them are related. Positive correlation means that generally you measure both variables to have the same sign, more strongly correlated being closer to a straight line, i.e. for perfect correlation a measurement of one variable totally determines the other. Negative correlation means that if you measure one to be positive you will probably measure the other one to be negative and vice versa. For two quantum operators a and b, for simplicity on the same Hilbert space H for which one state is |psi>, which is also chosen to be the current state of the system, the correlation is given by, <(a - <a>) (b - <b>)> / (sigma_a sigma_b) where <o> = <psi|o|psi> for any operator o, and sigma_o = sqrt(<o^2> - <o>^2) is the standard deviation of the quantum operator
- graycat 4y ago
  Thanks. Okay, good to see that quantum mechanics defines its use of correlation as <(a - <a>) (b - <b>)> / (sigma_a sigma_b) Good. Glad to see the actual definition. That is, with usual quantum mechanics notation, this is the usual Pearson correlation coefficient and, thus, appropriate to call correlation. Fine. Good to see that this is just what physics is talking about. My concern has been, does physics say "correlation" when really they mean some case of what we might call the usually much stronger functionally dependent? That is, for complex valued random variables X and Y, they are functionally dependent provided there exist functions f and g so that Y = f(X) and X = g(Y). With this functionally dependent situation, the correlation could be anything from -1 to 1 but usually we won't care because having either of X or Y implies we also have the other exactly. So, as I was reading quantum mechanics, I was wondering if there could be, and open to, two random variables functionally dependent but without correlation 1 or -1 so that, really, talking about mere correlation would be too weak and, thus, not really appropriate. Well, in the case of correlation 1 or -1, there exists non-zero, complex a so that Y = aX in which case instead of mere correlation it would be better to use the stronger functionally dependent. As I understand the situation, usually quantum mechanics uses correlation for examples of entanglement where it appears that, yes, the stronger functionally dependent would hold, and, thus, be more appropriate. That is, the usual uses of correlation outside of quantum mechanics, say, in statistics of medical research, economics, finance, social science, mean "two random variables not independent and also not functionally dependent" -- having the two random variables be independent (which implies correlation 0) or functionally dependent would be unusual.

wrnr 4y ago

QM may be a linear system but QFT is not.

xmcqdpt2 4y ago
What is not linear about QFT is the perturbation theory that is used to predict interactions. The underlying Hamiltonians with interactions included are themselves perfectly linear (but very complicated).

fredgrott 4y ago

A better way to put it, We have two math systems that do not mesh together, one applies to macro and one applies to micro. We have no mathematical construct that tells us when micro ends and when macro begins. My biased guess is that it might be a transformation process and math based on Gravity itself i.e. a reformulation of the Maxwell magnetic equations including gravity. Probably a phase transition in the gravity space that gives the real world transition from micro to macro switch from quantum to classical physics

mathgenius 4y ago
This is known as gravitationally induced decoherence. We don't know if there's any truth to this, but people are seriously working on measuring this stuff in the lab. You might like to read what Roger Penrose has to say about it. (Btw, we already know how to combine Maxwell's equations and gravity. This is all classical physics.)

tome 4y ago

There's some interesting discussion about what (probably) motivates this talk at https://www.physicsforums.com/threads/t-hooft-cellular-automaton-interpretation.1014630/ https://www.physicsforums.com/threads/t-hooft-cellular-autom...

mrwnmonm 4y ago

A little bit related > https://www.spiedigitallibrary.org/ebooks/PM/The-Evolution-of-Scientific-Knowledge-From-Certainty-to-Uncertainty/1/The-Evolution-of-Scientific-Knowledge--From-Certainty-to-Uncertainty/10.1117/3.2263362.sup?SSO=1 https://www.spiedigitallibrary.org/ebooks/PM/The-Evolution-o... Not sure why this book is not popular btw, it is written by a Math guru and it is to the point and doesn't have many jumps - https://www.amazon.com/Books-Edward-R-Dougherty/s?rh=n%3A283155%2Cp_27%3AEdward+R.+Dougherty https://www.amazon.com/Books-Edward-R-Dougherty/s?rh=n%3A283... - https://scholar.google.com/citations?user=DvTVkcEAAAAJ&hl=en https://scholar.google.com/citations?user=DvTVkcEAAAAJ&hl=en And as far as I know, the problem with QM is unintelligibility, not chaos.

fredgrott 4y ago

To extend some thoughts, my own bias 1. Universe started with a first phase transition involving gravity 2. Gravity might have another phase transition at the micro and macro quantum boundaries. 3. We are already use to having math systems change and boundaries to phase transitions so its not really radically new to our mathematics tools. Yeah, I do have in my unfinished bucket re-doing my math knowledge and tools as either a MS or PhD. That said I might be wrong in either one of these things or seeing the micro and macro boundaries of quantum and classical as a phase transition in gravity. But, my limited math sense tells me I might have the right idea. The key would start with reworking the Maxwell magnetic equations to account for gravity and to describe the phase transition between micro and macro world environments in terms of going from quantum to classical physics Its a bit hard to picture it at first as the two mathematical systems used are incompatible with each other. One is in the matrices world and one is not. But, we have similar math mismatches in our real world. One part of economics is matrices and one is not and yet the micro and macro economic models fit together somehow. So I think it is eventually reachable to some of us as far as understanding the math. But I just might have it wrong altogether

shireboy 4y ago

> each time a grain of dust bumps into the moon, this very slightly changes some part of the moon’s wave-function, and afterwards they are both correlated Help me out here, though. If this is the explanation, then wouldn’t every moon, planet, etc be chaotic, since presumably they all interact with dust and light?

lisper 4y ago
No, the bumps are necessary to produce chaos, but not sufficient.

lisper 4y ago

It is important to note that there is a hidden agenda in this essay: Sabine is a superdeterminist, and so her presentations have to be viewed through that lens. As a superdeterminist, she is committed to idea that classical reality is "actually real" (for some value of "actually real" -- see below). And so Hyperion's chaotic behavior is actually real, and QM cannot account for that. All of which is true. But there is an alternative view of classical reality which is that it is not "actually real" (the scare quotes are important here), that it is all just a sort of shared illusion among sentient beings. And QM can account for that, i.e. the math of QM can (and does) describe a set of mutually entangled observers all of which agree on an observation, notwithstanding that the observation has not actual referent in the model. And that is actually what we observe. We do not directly observe Hyperion. What we observe is our own subjective perception of seeing Hyperion, and having everyone around us report their own subjective perception of seeing Hyperion. The "actual existence" of a classical entity, i.e. an actual physical referent for "Hyperion" seems like a plausible explanation for this, but what QM tells us is that this explanation is wrong. But Sabine, as a committed superdeterminist, rejects this idea. But she's not being up-front about that. The problem with QM is not chaos, it is the fact that it is incompatible with classical intuition. The chaos thing just brings this incompatibility into very sharp focus.

progrus 4y ago
Question: How often have you seen Quanta Magazine write a disclaimer that their latest story is from a school of superstring theorists? It’s PR, this is just how it is. I do wish Sabine would state the axiom “reality is real” up front though, because I think people should be trusted to consider that one on their own.
otikik 4y ago
I must be super deterministic as well because the alternative you describe sounds … unuseful to me. If we can have illusions like that then all the conclusion you extract from that are also subject to the same effect: it’s not necessarily true that QM can account for it; we could also be “allucinating”collectively that they can account for it. Or, we might not exist at all and all perceptions are all fake. Once you introduce a malicious devil like that it always goes “full universe”. Say, this religious group knocks on your door, tells you that Earth is 2022 years old. You point to dinosaur fossils. They say the Devil put them there to trick us. But then, you follow, our whole existence might as well be fake. The Devil could have created both of us 5 minutes ago, with fake memories of a life that never existed, just so we could have this conversation. And we will both vanish when I close this door (blam!). The usual counter is that the devil has a very specific amount of power: triceratops head is ok, humans is too much. But even accepting that, how can you know you are a human? It might be the Devil tricking you again, maybe you are a teacup that thinks they are human.

layer8 4y ago

In the Many Worlds view, does this mean Hyperions motion is nonchaotic overall (i.e. considering the ensemble of the Hyperions in all branches) but chaotic in (most of) the individual branches? Not sure that makes sense.

progrus 4y ago
It works because of the big hand-wave that underpins MWI: Which universe do you end up in? It’s random!
- layer8 4y ago
  > It’s random! It’s not. You end up in all of them. You branch. There is no hand-wave. It’s like if you have a VM with a program running in it, and you clone the VM. Which VM does the running program end up in? In all of them, of course. And the fact that the program branches/forks in that way is not observable to the program. All clones of the running program believe they are the same running program as their earlier self in the original VM. If the program was running a conscious AI, the consciousness would split (multiply).
  - progrus 4y ago
    Which parts have the story you are experiencing? It’s random, isn’t it? I mean at this point you might as well just start arguing that nobody can reason or argue anything.
    - layer8 4y ago
      Honestly, I don’t quite understand what problem you see. The obvious answer is that each you has been experiencing the branch they are in, and will continue to split into more yous that will each again experience the branch they are in. It seems that you’re assuming that there is only a single linear you with a single subjective future, and can’t conceive of your subjective experience forking. But the point is that the perceived linearity of the self is only an illusion, stemming from the vantage point of any given you at any given point in time looking at his/her respective past at that point in time (which for each of them indeed looks linear). Your future branches are all equally real futures of your current self. Your current self will end up in all of them, but of course each of those future yous will only remember their shared past (your current present) and not have any perception of the other branches. The fact that we never subjectively experience the branching (because we are merely a content of the branch, just like the running program is merely a content of the forking VM and does not notice that it is being forked) may be why some people have difficulties with the idea of their subjective experience splitting into separate futures. Again, take the program/VM analogy. What would you expect the program to experience? The answer is that the experience will differ depending on which clone you consider (assuming that the VMs diverge like the MW branches diverge), yet all of the clones used to be the same running program. All the clones are equally real continuations of the original running program, just like in MW the different yous are equally real continuations of their former single consciousness (but now are separate consciousnesses). You are right that we can’t reason about which future we will end up in, because we will end up in all physically possible futures. That can indeed be a philosophical conundrum. Decisions we make are only effective in the branch they are made, and there will presumably always be (equally real and existing) branches where they are not made. That shouldn’t detract from making desirable decisions though, because once we make them, we are necessarily in the branch where we made them, and it’s only our unlucky former future selves who didn’t make them that are now in the less desirable branches.

ithkuil 4y ago

If the Hilbert space is infinite-dimensional, wouldn't that allow for a linear chaotic system?

rsp1984 4y ago

What I don't understand about this example with Hyperion is a) Wouldn't Hyperion's orientation be influenced much more by Saturn and its many moons on their many orbits than by dust and photons? b) Wouldn't it then boil down to "just" an n-body problem (for which we know no closed form predictions exist -- yet is still perfectly "classical" in nature)? In other words, why involve dust and photons and wave functions and entanglement when the answer could simply be "it's an n body problem so we simply can't predict its orientation"?

samus 4y ago
My guess is that this is an example of the struggle between proponents of different interpretations of Quantum Mechanics. There are rather a lot of them, even though they all try to explain the same theory. The whole issue eerily reminds me of the debates between proponents of different theories of the relationship between God and Jesus (trinitarians, nontrinitarians and so on). Unless they yield testable predictions, there will not be an end to them.
bufferoverflow 4y ago
QM is far worse than an N-body problem. You can trivially model an interaction of 2 or 3 particles as bodies, at a given precision. But when you consider them as waves, you have to compute an insane amount of information. Example: https://youtu.be/0kXGb0_-1iY https://youtu.be/0kXGb0_-1iY And precision is another undefined thing. Is particle's speed / position continuous or quantized? Or in case of QM, is there a resolution to the waves? Or is it all infinitely precise?
unrealp 4y ago
Perfect. This is exactly what I thought when I watched the video yesterday. There will also be local variations in saturn's gravity.

newpavlov 4y ago

Personally, I am firmly in the "superdeterminism" camp. To me it's the most elegant interpretation of QM without any mystical measurements magically dependent on "consciousness" and whole universes created on each interaction. If you want to learn basics about it, I recommend watching this video: https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc Do not mind the (joking) clickbait title, the talk itself is quite good even if you only vaguely remember QM.

bigbillheck 4y ago

Hossenfelder links to this paper discussing Hyperion: https://michaelberryphysics.files.wordpress.com/2013/07/berry337.pdf https://michaelberryphysics.files.wordpress.com/2013/07/berr... whose Appendix A starts: "Caricaturing Hyperion as a homogeneous sphere...." Given that one of Hyperion's distinguishing features is that it's very far from being a sphere, this seems like a particularly bad assumption.

mathgenius 4y ago

> But the vast majority of physicists today think the collapse of the wave-function isn’t a physical process. Because if it was, then it would have to happen instantaneously everywhere. I'm a physicist and this does not pass the sniff-test. Part of the problem is we don't know what a "physical process" is. And the second sentence just does not follow from the first (if we even knew what the first sentence meant).

SideburnsOfDoom 4y ago

So to be clear, the article discusses the "wave-function" the "superimposition of states", not of an electron moving through slits, or even of a cat in a box; but of Hyperion, moon of Saturn, diameter 200 km; and what this means for predicting it's motion of over time? Because after a while the superimposed states produce a outcome that can only be explained via Quantum Mechanics, like with the experiments of electrons through slits? I suppose it must be valid to model this large system with Quantum mechanics. And that's partly the point of the article?

effie 4y ago

The main claim that the Schroedinger equation isn't consistent with chaotic behaviour of observables because it is linear in psi seems poorly thought out. As one commenter on youtube pointed out, the Schroedinger equation is linear in psi, but the Liouville equation from statistical physics is also linear in rho and nobody suggests this somehow makes it inconsistent with classical systems exhibiting chaos. The mistake is that mathematical linearity is in equation for psi/rho, and this is then incorrectly changed into assuming linearity of equations for observables. The observed chaos is not in psi/rho, but in observables, say, positions and momenta. The actual problem here is the age-old measurement problem, i.e. the psi function does not tell us result of experiment, only probabilities of possible results, so psi function can't be complete description of state of things in reality.

axilmar 4y ago

Before discussing chaos in QM, I'd like someone more knowledgeable than me to explain a few things to me, if you don't mind, of course: 1) how do we know particles act as/are waves? the double slit experiments does not seem to be proof of that: a) if we rotate the slits 90 degrees, then the interference pattern also rotates 90 degrees in the same direction...does that mean the wave also rotates 90 degrees? does this mean the wave is 3d? and if so, why is the interference pattern not a checkerboard? b) if we enlarge the slits, the interference pattern goes away; the more we enlarge the slits, the more the interference pattern disappears. This means that in our original experiment, the slits were too small for the particle and the particle hits both slits simultaneously, and hence the interference pattern. Why should then the particle be a wave? putting a detector means to make the two slit equipment one slit effectively, making the interference pattern disappear. How can then one reach a conclusion that particles are waves? 2) how do we know that entanglement is the result of 'spooky action at a distance' and not the result of creating two entangled particles? couldn't it be that the particles are created with correlated spins and no communication ever occurs between them? Why am I asking these simple questions and not contribute to the discussion meaningfully, you might ask? well, it seems QM has all the markings of an strange theory, that works for some cases, does not work for some others, and it requires magic for some others. Those things make me think that the basics of QM may be invalid, so I am really questioning those basics. I am sure I am 100% wrong, so please do illuminate me on the questions above; I've tried to ask before, and in different sites, the worst responses being 'go away lame person! how you dare questioning are beautiful intellect!!!', and the best responses being lots and lots of math that don't really answer my basic questions. I am just looking for simple straightforward answers.

eterevsky 4y ago
Regarding waves and interference, have a look at this video: https://www.youtube.com/watch?v=TshYfYIxR9E https://www.youtube.com/watch?v=TshYfYIxR9E. It shows how the interference patterns actually look. Yes, the wave is 3D and the interference patterns can be kind of like checker board. We are usually considering a 2D example because it is simpler to visualize and analize. > how do we know that entanglement is the result of 'spooky action at a distance' and not the result of creating two entangled particles? A very high-level explanation is that we know this because quantum computers work (even though right now we can't build them big enough to be useful) and it can't be explained by any classical effects.