Interesting, Professor Merrifield uses a trick I’ve used to understand a hard to understand paper.. find another paper that references it and read their summary
@@Idontneedahandle333 i call it learning. I'm not sure why this seems like phenomenal similarity to some of you. I didn't go to college. This is just consciousness to me. Getting exterior perspective, beyond the echo chamber of your own take on reality. If there's no door, create one. That's all that sets us apart from a student and a teacher. Door users and door framers.
This video is being published on the day the Physics Nobel Prize is awarded for research in this area - total coincidence!!! What were the odds? --- www.bradyharanblog.com/blog/spooky-action-at-a-distance
i've observed this spooky action at a distance phenomenon a long time ago: each time i would want to play w/ a particular toy my brother would want the same one and when i'd chose a new toy behind my back, his preference would change instantaneously. :)
I met David Mermin once. I studied philosophy of physics at Cornell and I used his paper Relativity Without Light in my thesis. I was happy to discover he was a professor there and I went to his office hours to make sure I was understanding it properly and not misstating his premises and conclusions in my paper. Nice guy.
He sounds more like a philosophy prof to me too, this whole video is bad philosophy in my opinion, its certainly not falsifiable science in any meaningful or observable way.
@@michaelfried3123 what do you mean 🤔? People have made countless experiments which all show that the bells inequalities are violated and that the action at a distance really does happen. He even talks at the end about the implications to quantum computing and everything...
I barely graduated high school but I have a desire to understand this kind of stuff. I've had this explained to me a hundred times. This is the first time I felt like it clicked and right as he said, "This is where your head should start to hurt," my head was hurting. I was thinking exactly what he said I should be thinking. And it made sense to me for the first time.
I barely graduated high school but got really into sixty symbol videos many years ago. I’ve since graduate with a physics degree, if you want to know go find out
Thanks a lot for the first explanation I've seen in forever which goes beyond "oooh look one spins one way and the other another! it must be magic!!" (which would be extremely easy to explain with hidden variables) and actually explain why there is a paradox if we use a hidden variable model
Agreed, the best explanation of Bell's inequality, and its experimental test, I have ever seen. Other demonstrations explain Analogies only. However, the explanation in this video was carefully paced until the 14' 00" mark, when the pace increased on got a bit sloppy: unfortunately this is when the most important info was finally revealed.
@@edshort1138 I lost him precisely around the 14:00 mark. Are we still assuming that spin can only be measured as either up or down? I don't see how the 2/6 probability comes about.
Technically there is still a way to save the EPR paper: Super determinism. The bell inequality relies on the measurement being determined after the entanglement and particules separation. But if you have link between measurement and the particule going way back before the experiment then the hidden variables are still a viable solution. But Free will is no longer. as the decision of the measurement could be taken by an operator and then he would be constrained by those hidden variable which means he doesn't have free will to choose the set-up. (I'm pretty sure that would horrify Einstein as much as spooky interaction at a distance).
Couldn't there be something wrong with the experiment itself? Nobody addresses how the particles are sent to the machine or how the measurement is made. It's always a mystery box and a mysterious process to entangle the particles. Why can't they explain that?
@@zualapips1638 He mentioned the measuring tool at the beginning, with the magnetic field which deflects the particles in different directions. It’s just a simple way of describing the experiments done and what is observed. The physical tools used aren’t important to understanding the concept. You can look up the experiments and how it is done if you want.
Wonderful video thus far, almost finished, but I just had to say this is one of the most clear concise explanations of Bell’s Inequality I have seen on the internet.
A commendably clearly explanation in which you demonstrate how Bell's inequality disproves local hidden variable theories, those where the entangled particles "agreed locally" upon a hidden variable before they departed. I really wish you would have made very clear that this does NOT refute all hidden variable theories. Only LOCAL hidden variable theories are refuted by Bell's inequality. If entanglement involves a hypothesised Einstein-Rosen bridge through a compactified dimension the instantaneous "spooky action at a distance" that is required by Bell's inequality may be described (as Einstein desired) by presently unknown "hidden" variables that would describe the unique instantiation under study as well as the reason for a 75%/25% probability ratio. You described this as The QM prediction, but it's actually an experimental determination that was never predicted by QM.
There are no non-trivial hidden variable theories. The only worked out one that I am aware of is Bohm's guide wave, but it's basically nothing else than a backwards way of solving the Schroedinger equation while pretending that an unphysical and unmeasurable guide wave is floating over the waters. That's not even physics.
@@schmetterling4477 In the '70s I thought Pilot Waves were the way to go, but the concept is only correct in it's approach in the sense that it seeks a rational explanation for QM that is inspired by Feinman's Path Integral formalism as well as aspects of d.slit experments that hint at what Bell proved. Bohmian mechanics points at a future theory that could rationally explain QM, but it's missing the physics behind the undescribed process through which entangled particles are constantly aware of the joint state.
@@gilbertanderson3456 Feynman's path integral is a different way of solving the same equations. It doesn't add anything fundamentally new to the basics of quantum mechanics. Bohmian mechanics only points to one thing: Bohm didn't understand the physical reason for the structure of the standard theory. Neither did von Neumann and I suspect that you don't understand it, either. That can be solved: think really hard about WHY quantum mechanics is the way it is instead of trying to find a replacement for it. There is none. It's no different from the non-existence of a quadrature of the circle or the foolish quest for a perpetual motion machine. It's all a waste of time on the wrong idea.
Great video! Not sure if I totally agree with the conclusion that "information" really is travelling from one electron to the other instantaneously. First, the measurement on one spin has no effect on the density matrix (which describes the statistics of any possible measurement outcome) of the other. Also, in different reference frames, due to the relativity of simultaneity, different observers will disagree on which electron's spin is measured first. I would say what's really spooky here is the fact that the spins are measured in the way quantum mechanics predicts *in spite of* no information being sent between them!
There's no reason you couldn't update the density matrix on particle B if you measure particle A in spin up, and know ahead of time the relative angle between the two detectors. This would give the same result.
_"First, the measurement on one spin has no effect on the density matrix (which describes the statistics of any possible measurement outcome) of the other."_ How can this be? After all, if one particle is measured spin-UP, then the probability of the other particle being measured spin-DOWN assuming the machines are set to the same of the 3 settings, rises from 50% to 100%. If you could explain how this is negated to result in no effect on the statistics of any possible measurement outcome, I would be much obliged. _"Also, in different reference frames, due to the relativity of simultaneity, different observers will disagree on which electron's spin is measured first."_ This doesn't disprove Spooky Action nor "information", in at least one definition of the term, travelling Faster Than Light from one particle to the other, though. All it would change is the *direction* the observer, .....well, observes..... the "information" travelling in. The "information" travelling Faster Than Light doesn't change with the reference frame. What is in fact true, however, is that the "information" being exchanged between particles is only "information" in the most narrow definition possible of the term. No actual communication, of the type that could break Causality under the Theory of Relativity, can be exchanged in this manner. Mostly because it is impossible to predict which state (Spin-UP vs. Spin-DOWN; red light vs. green light) the particles will be in before the first one arrives at its designated machine.
@@AhsimNreiziev I agree with just about everything you've said. However, I have a question. How does the unpredictability of which spin the particles will be in "before the first one arrives at it's designated machine" rule out the seemingly FTL communication between the particles?
@@ML-hl1uh There are 2 types of "communication". The very basic kind that determines things like properties of Entangled Particles (such as position, momentum, Spin etc.), and more "advanced" communication that allows for what we call "information" to be transferred. "Information" is anything that conveys a state of the world more advanced than a Quantum State. Importantly, the second kind of communication breaks Causality when it happens Faster Than Light, while the first kind doesn't. Now, because you can't predict which state each particle will be measured in when it arrives at the machine, you can't use it to *encode* anything that might convey "information". Thus, this Entangled Particle FTL communication doesn't, and can't, break Causality as in the Theory of Relativity.
@@AhsimNreiziev I probably should have been more clear/specific in my original comment. If we use QM to describe the state of the two electrons, along with the detectors/observers which measure their spins, then the interaction of one of the detectors with its associated electron will have no effect on the density matrix of the other electron or the other detector. In the case that you _are_ one of the observers, then because you become entangled with the measured electron, there is a correlation between the measurement result and your knowledge of the state of the other electron, and I would probably agree with @anywallsocket, but I still probably wouldn't call that information transfer.
This presupposes that the hidden variables would result in the 1/3rd distribution. But it's entirely possible that the hidden variables also affect the particles themselves, and lead to a distribution in line with what is observed. In other words, we don't have a complete picture of what is going on yet. So rather than invoke non-locality, we could strive to see what else is impacting this. Also, and this part is very important, entangling particles is difficult, and only a fraction of the particles used in the experiments are validated as being entangled. The results from the other particles that are deemed not entangled are thrown out. But if we add those results back in we may have a clearer picture.
That's why it's called Bell's _Inequality_. It would be possible for hidden variables to generate a correlation greater than 1/3 - the extreme case would have "RGG" and "GRR" as the only two results, with a correlation of 50% - but not for it to be less than 1/3, which is the case when all the results in the table (including RRR and GGG) have equal probability. However, it's not possible for them to give a correlation of less than 1/3, and the experimental results show a correlation of 25%.
In HUT Holographic Universe Theory (HUT) Physics, The faster than Light 'Communication" is explained due to two "realities" , A 'Higher reality" where all the particles actually exist and there is no "space" in terms of separation or distance between them (some variants allow 1 or two dimensions as such) and a "Lower reality" which our perceptions interpret certain key attributes of the particles as discrete POINTS in a (consciously constructed shared illusion) 3/4 dimensional universe. Thus, two particles may be light years "apart" in our lower reality, but in contact in the HIGHER REALITY, thus APPEAR to communicate FTL with respect to our LOWER REALITY. -----
I have always taken a layman interest in quantum mechanics, specifically the strangeness of the double slit experiment and Bell's Inequality. The first book I read that really grabbed my attention was Quantum Reality by Nick Herbert. Over the years I have tried to grasp Bell's experiment and consequences - the probabilities of the 'assume the hidden variable' were never really explained clearly. This video really helps that understanding. Here is my question. When the measurement of the particle is made at one of the detectors, does the measurement actually 'flip' the particle's polarity to its up/down measured value or does the measurement just say "here is how the particle is oriented" when we measured it. I'm not sure if this question makes sense, but to me (not knowing the real technical details of how this works), it's an important question. First, it could mean that when the particles are entangled, it was done in a specific way to polarize the particles in a certain direction. In other words, do we know the intended polarization of the particles when they are created? Second, if the detector is 'flipping' the particle polarity, then THAT implies that this is 'causing' the second particle to flip to the polarity described by quantum mechanical theory (math). The reason I ask is that this would REALLY make things strange. I seem to remember reading something like that years ago, that what is really strange about this is that when particle A is 'flipped', it instantaneously 'causes' particle B to flip. Thank you kindly.
Thank you! After watching like 5 videos, this one finally actually made it 'click'. The way I understood it is that (note: I am a total noob, so please let me know if i got it wrong): 1. they chose 120degree of eachother because then every switch combination will have 120 degrees of eachother (120/240, 240/360, 360/120), so it simplifies it to different switches or the same 2. the result we get that, for different switches, the electrons show 25% same spin and 75% different is impossible if the two eletrons had a predefined plan for each switch they conjured together. That's can be seen by looking at all possible plans, there are 8 such possible plans that have the condition that if they get same switch they must be opposite (which is experimentally verified). When we do it we see it's impossible to get such low probability of them being the same for different switches.. 3. This is because, the key thing here is that the electron does not know how it will be measured when its making the plan. The way it is measured determines how the other electron will behave. That's only possible in quantom mechanics is weird. It's as if it has a plan that is "if I get switch A and you get siwtch B, do same spin 25% and opposite 75%", but that's impossible since they don't know how they'll be measured (that's in the future). 4. Thus somehow something very weird happens. Either the electron like, knows in advance the future - what the switch will be at when it'll be measured. Or it instantly communicates how it was measured to the other. Or something elese (idk). But definetely not a "locally-real" behavior. it seems to me bell (and others) looked at the quantom equations and saw this probability is lower than is possible to make with a concrete/"locally-real" plan (AKA 'hidden variable) of the electrons, and thus there must be something very weird going on there and hidden variable doesn't explain it all as einstein argued.
Isn't the problem in the presumption, that the way this hidden variable would be generated is dependent on the experiment set up? Like in reality it would have not only "prepare answers" for these 3 positions of detector, but for all continuum of possible positions. And even more, why should these answers for all possible positions be completely independent from one another? (as I think calculation presented in the video presumes)
The information is not traveling instantaneously, the particles are already carrying that information with them. It's not changing on the fly. The results you see changing are based on the information the particle already has.
That is a common interpretation but it is wrong. The key to understanding quantum mechanics is the insight that nature does not know the state any better than we do. In effect... state is an after the fact quantity. It does not even exist before the measurement.
I think what you were trying to ask at the end, and what I'd like to see answered, is: Are there any examples of entanglement seen or suspected in nature (the universe)? Like perhaps there is something that happens in neutron stars or quasars or whatnot that could be best explained by quantum entanglement?
I read a few articles on the recent Nobel prize, and they didn't make any sense to me. This video does a great job of framing the problem in lay terms, and the problem makes a lot more sense now. Thank you!
I have never liked this idea that the information is getting from one place to another faster than light. Like, there's no question entanglement is real, but in my mind, it makes much more sense to think of entangled particles as sharing something, instead of communicating. Like deep down they are using two sides of the same "thing", instead of having each an individual "thing" independent from the other. And that makes me feel that there is always two sides of that thing, and we just don't get to observe the other side for some reason (the corresponding antiparticle could be on the other side of the universe, or inside a black hole).
As another commenter has suggested, maybe they _are_ the same thing. With talk of multi-verses and extra dimensions this makes possible sense to me as a 'real' physics explanation. Kind of puts me in mind of Pauli's exclusion principle; there the electrons seem to 'communicate' as well, although this may not be an instantaneous change; I don't know enough about that to comment. But I do remember a lecture by Prof. Brian Cox which seemed to imply that if an electron changes state in one atom, then all other atoms in the universe also change states (not sure I if just misinterpreted what he was saying, though). And I've heard of a (maybe tongue-in-cheek) theory that there actually is only one electron in the universe, but it simultaneously exists in many different places and states. For sure, we certainly don't understand everything yet - not even close. And who knows what will be changed in 'common conception' of the universe in another few centuries. (Assuming we survive that long.)
That’s just an interesting point that I’ve always pondered. If information can’t travel faster than light then how can we have this instantaneous transfer of information. But I suppose he’s completely right that actually your not really transmitting any information as the initial state is itself random. Still feels a bit wishy-washy but that makes a lot more intuitive sense to me.
well that was so lovely, thank you. the spin part in the beginning made my head spin but then came the payoff of a very intuitive explanation why reality is probabilistic was amazing.
Watching Sixty Symbols videos after I have just graduated from Nottingham, nostalgia/bittersweetness fuel. Thanks to everyone for making my time studying physics as fun as I had hoped it would be when I was a young schoolboy watching these videos in awe, inspired to one day study physics. My childhood dream came true in your department; and who knows, one day, if I'm lucky, I might be back! 🥲
I remember a few years ago I wanted to understand QM better, and while my understanding did improve, I couldnt get my head around bells inequality. I understood the gravity, but not how it actually works. This clip made me understand it even before explaining it fully. Great work.
Excellent explanation. To me the answer would require the apparent two particles are actually the same particle in another (fourth or fifth) dimension. Image this particle randomly (or at least unpredictably) orienting its spinning. When measured , its random spinning is fixed and when re measured gives the predicted result.
This is basically correct. The contradiction comes from trying to project 4 degrees of freedom down onto 3. The probabilities being a function of cos^2(theta) already ignores imaginary phases. Moreover, we're told many hints along this direction, such as the fact that elementary particles cannot epistemologically be distinguished. Also, the spins we measure are always projections onto our 3d measuring devices. Then there's the weakest link in Bell's argument: locality. We would like to believe that things are separated to the extent that there is space between them, but relativity dismantles simultaneity -- therefore when one entangled half is 'measured', the other half is measured in a frame of reference which shrinks the physical gap between them. And yes, you could construct entangled pairs far enough apart that even light itself could not hypothetically 'witness' their simultaneous measurement, but we are also forgetting about our linear notion of time. Entangled pairs are created in total isolation, with the degree of entanglement proportional to how little noise there is, therefore it isn't a stretch to suppose that when we witness the evolution of a system, what we are witnessing is nothing more than the irreversible entropy seeping into the system. This has other thermodynamic backing, but in terms of QM it implies that time evolve for systems that remain entangled, and therefore in 4D, the 'distance' or proper time between the two events is not at all as big as the shadow we measure here in 3D.
I like this idea. There is so little we _really_ know about the universe(s?) that this seems as plausible as anything else put forward so far. Yes, it's totally unintuitive and a little bonkers; but so are most quantum mechanical explanations and observed behaviours. I've even heard a theory that there's only _one_ electron in the universe, and it's just 'very busy'. If this was true for all particle types (or even just a the right set of quarks) this might offer an explanation too. Who knows what we'll find out in the future? Maybe yet again making what we know today seem utterly naïve and primitive.
A nice follow-up video on this would be to talk about how Many Worlds and Superdeterminism might still allow for hidden variables but with different other counterintuitive tradeoffs. Many Worlds would be the hypothesis that when the two boxes make their measurements they actually are splitting into different worlds with different results and it's only when the two boxes' lightcones in particular worlds intersect that they both agree on the results. In that scenario everything is still done locally and can have hidden variables but at the cost of the creation of multiple simultaneously branching worlds from the measurements. Superdeterminism deals instead with the notion that the selection of the switches on the boxes might not be independent of the states of the entangled particles. Basically if the settings on the boxes are somehow linked by a prior condition to the states of the particles when the particles initially become entangled then the measurement and then states aren't independent and the stipulations for the inequality aren't valid. The difficulty with this approach is that it's difficult to imagine that the method of random selection of the switches can never be truly independent of the states of the particles. For instance, if you're randomly selecting switches using astronomical measurements of distance quasar fluctuations then for those fluctuations to be tied to the states of the just now created entangled particles on Earth means that information was initially passed down billions of years ago when the stuff in the quasars was physically interacting with the stuff creating the entangled particles. It's not impossible but it's hard to grasp how that would be the case.
I thoroughly enjoy hearing professor Mike Merrifield explain and reflect on phenomena even, as in this case and most others, I have absolutely no idea what he's talking about. 😊
Have you considered that a person *attempting to teach* might be, in fact, deeply saddened or frustrated by a student's proud admission that, while they enjoyed the lecture, they learned nothing? That such a statement is not praise, but rather a blatant insult?
@@Hermaniac8 Yours is a fair perspective, but it places me in the class room. I am actually quite removed but delighting in the process. I have no doubt that professor Merrifield's student's are exceptionally and richly informed. Additionally, in my viewing experience humor, subtle and not so, is never lost to Mike. In one video a questioner asked him what was the base trigger for lightening in clouds. When Mike responded that we really don't know the questioner was flummoxed, clearly unbalanced to hear that such a common and observable phenomena was not completely understood. Regaining his equilibrium the questioner responded, "That's ridiculous!" Mike's response was a healthy dose of his infectious laughter. So, while finding no fault in your comment as a general perspective I nonetheless believe professor Merrifield would read my comment and smile.
Here on TH-cam there is a class on quantum mechanics by MIT and in the bell's inequality lecture the professor said we shouldn't be surprised that electrons don't behave like cheese. We should be surprised that cheese behave like cheese.
Great explanation, Mike! At 15:00 I think the row of all three red and all three green is not possible, because the spin has to point somewhere, so it is aligned with at least one Stern-Gerlach experiment. So you would get 1/3 exactly.
Yup. I've struggled to understand precisely that for some time. I haven't found any satisfactory answer to how three red or green probability is valid.
it is one possibility of pre-determined outcomes. it only seems illogical if you assume that the electron has a definitive spin direction. that is correct for a single-electron-wavefunction, but not necessary for a pair of entangled electrons.
Not really. Let's say the (first) particle is exactly aligned with the detector in Position 1, so it has 100% chance of firing the detector in that position. It therefore has a 25% chance of firing the detector in Position 2, and a 25% chance of firing the detector in Position 3 - there's a non-zero chance of a "three reds" result. If one of the detector positions was 180° out from another position, then this would be a valid point. But that's not the case.
I am optimistic enough to say that this is nothing we can use yet. The people figuring out how to utilize this will definitely deserve a Nobel prize. At some point humanity will have spooky communicators.
@@johnkeck it's absolutely an explanation, although others did refine it and make it more rigorous. Unlike say the "just use the Born rule" non explanation of say the Copenhagen "interpretation"
this is the first time this has made sense to me. Thank you! Have hidden variables been disproven in other apparently random conditions like radioactive decay? If so I need to go make a significant amendment to a video I published a few years ago...
the fact he assumes particles to all have consciousness doesn't bother you at all? his explanation was philosophy, not falsifiable science in any meaningful way.
@@michaelfried3123 he doesn't assume the particles have consciousness what are you talking about? What you are talking about is a slight anthropomorphisation of the problem to make it easier to understand. When he says the particles decide amongst themselves what he is actually saying is that there may be some way that the particles are set together in a certain way. It is easy to remove this characterisation do not get distracted by this because it is unimportant to the problem.
@@jimpim6454 you obviously didn't watch the video, or if you did, you didn't pay close attention to the words he used. he certainly does assume particles have consciousness by the grammar and words he uses. philosophical BS at best comes from this so called "expert".
@@michaelfried3123 The purpose of using those words is to make it easier to understand ffs. Why are you assuming he's a bad faith actor? Isn't it much easier to just assume he wants the audience to understand the concept?
6:11 isn't this backwards? If you have a magnetic gradient that causes |+z> to go upward and |-z> to go downward, then flipping the gradient upside down (changing its sign) should cause |+z> to go downward and |-z> to go upward. Now suppose your left-going particle is found in |+z>, i.e. normal SG apparatus causes it to go upward. That would mean its partner must be in |-z>, and so the upside-down SG will cause it to also go upward. And the opposite case would be both of them going downward, even though one of those is with the gradient and the other is against it.
Brady's making the same mistake again in the end that Mike already tried to address: No, the particles in the Milky Way wouldn't "react" in any observable sense. You wouldn't see it. They would behave exactly the same from our point of view whether whatever happened in the Andromeda galaxy affected them or not. And they most certainly wouldn't be obliterated. No communication means no communication, not even by obliteration ;)
What I love, is that it is not really 'instantaneous' transfer. From some reference frames it happened first at one end, and from other reference frames the other end was first (and from some it really was simultaneous). So which direction does the message go? As there are no observable differences between these two cases then we should try to not regard these as indistinguishable, but instead view them as completely equivalent. If that doesn't make your brain fizzle, then nothing will.
Hmm just be careful about simultaneity. If you take two events in any reference frame, and measure the distance between the two events and the time between the two events in that reference frame, then calculate c²t² - x², if c²t² - x² is less than or equal to 0, then there is no reference frame in which the events are simultaneous. That quantity c²t² - x² is called the “spacetime interval”, and it’s the same no matter what reference frame you’re in. It’s worth learning about!
This is why we split the separation between events into 3 cases; space-like, time-like, and light-like. No matter what Lorentz transformation you do, space-like separations remain space-like, time-like remain time-like (and the direction of causality remains the same), and light-like remain light-like.
The brain fizzle is because you are arguing with time while assuming a "relativistic" universe. But that will be the same independently if you talk about entangled particles or anything else. It is just the basic of relativity. And that is also why, in relativity people talk so much about intervals and space-time. And the same thing happens when talking about space by itself. Another way to think about it, is to assume that every time you mention time, you will be using an "unreliable" (reliable for you, but others will disagree) measure tape. The "reliable" measure tape would be the interval which is composed of time and space in a certain relation.
@@jackm3692 I think you have the sign backwards -- if two simultaneous (dt=0) events occur with nonzero spatial separation (dx!=0) then the interval (squared) would be negative. It's when c²t² - x² > 0 that the events are never simultaneous and are causally ordered. Metric conventions are a pain the the rear. (And to Stevo's point, the EPR paradox involves just such a spacelike separation of events where c²t² - x² < 0 and the superluminal "signal" can "travel" in either, or neither, direction depending on your reference frame.)
I've still yet to see anybody explain how the quantum probabilities are derived. They just always skip over that part. does QM predict a 25% correlation?
If you consider the many-world perspective, there is no instantaneous information being transmitted, just yourself being entangled with one of the lamps, which means that you are also entangled with the other lamp.
Thank you for making this video, I am only part way in, but already want to make a comment. Regarding the discreteness of state discovered via the Stern-Gerlach experiment, I have a proposition solely for the curious of mind. Perhaps the magnetic force acts not just in space, but in time as well. Imagine the field attracts parallel-aligned poles towards the present, and repels for perpendicular poles into the past/future where we never detect them!
It's a paradox only when we insist on seeing the entangled pairs as two separate point particles. We've known since the 20s that matter is made of waves, this behaviour is entirely consistent with how waves propagate. The real mystery is why the wavefunction collapses to a single point when we do a measurement. I've seen some nice thoughts on the measurement being a sort of Fourier transform, similar to when we focus multiple light rays into a single point through a lens. The nature of the rays never changes, it's just our measurement making it appear different.
I first learned about this decades ago and because of the content and that it was published in the same year I was born I wanted to learn more and understand it better. I thought, as my understanding of physics grew, I would eventually have one of those "epiphany moments" when it finally made sense. The only epiphany I have had is I'm not going to live long enough for that.
i'm confused here, in the image with the colored circles, each of those is taken as an equal probability. so if we take the 4 rows where red comes out of detector 1 setting the possibilities are it comes red or green on detector 2 and 3 with 50% probability, but earlier in the video it showed that when you have that tilted scenario it comes out as 25/75% probability of matching or not, wouldnt you need to apply those probabilities and then adjust the 2/6 results downward for the fact that its not 50/50 whether they match or dont but 25/75?
I think you are confusing the probability of the results and the probability of the experiment configuration. The 75/25 is the probabilistic results prediction of quantum mechanics, you don't know what an individual particle will do only overal statistical behaviour. If there is a hidden variable then for any given particle pair there is no probability involved. The test has three configurations, the detectors can be in the same alignment, 120 degrees apart or 240 degrees apart so the particles have to have "decided" what to do in each of the three possible configurations. The test is repeated many times so each configuration happens 1/3 of the time. Since the configuring changes after the particles separate so that no light speed communication has time for them to communicate they have ot have "choosen" what they will do for each possible configuration before reaching the detectors. There is no probability within one row, its saying e.g. if the detectors are aligned it's red, 120 its red, 240 its green and so on, there is nothing to adjust. Its 1/3 for each experiment configuration because that is how the experiment is designed. The particles can't influence the probability of the experiment configurations, indeed to be sure they did tests where the configuration was determined by light for quasars millions of years old so it could've been influenced by the recently entangled pair. There could be different probabilities of which configuration the particles "choose" before they seperate, but since all of them have a probability of 2/3 or higher it doesn't matter and doesn't effect the discrepancy between the prediciton and the result since it happens which ever preset results the particles could have.
What I find interesting is that when the poarticle inters the experiment, it has presumably an infinate reange of orientations. And yet, the experiment forces an expression as if it could only have one of two. You'd think that that might have some bearing on what the entagnled does, but apparently not. And the fact that you can get two reds or two greens by turning one of the aparatuses upside down is just very strange indeed.
Did you make this video for the occasion of the 2022 Nobel Prize in physics being awarded to scientists who worked on this problem or is this a spooky coincidence?
I think the confusion about why this isn't a problem is highlighted at the end of the video; you can't "do something" with certainty to either of the particles. You can't force your particle to be spin up and force their particle to be spin down. What you can do to the particle is measure it in some way; the point of this video is that this really does do something to the particle and its entangled pair (it changes their state, and there's no way they could have already been in that state in some hidden way). But quantum measurements are a very special type of "doing something". Individually, measuring each particle doesn't look special; each individual particle's measurements looks the same as a particle that wasn't entangled, so you can't get any information from anywhere else out of it. It's only when you compare the results of entangled pairs that you see the results are correlated. The point is that they are correlated in a way that can't be explained by "local hidden variables".
I still feel like there must be some physics going on that we have yet to understand. Something so far ahead of us that we cannot yet conceive of a way to even prove that we are missing something. Any sufficiently advanced physics is indistinguishable from magic.
This does have all the hallmarks of our base assumptions about the experiment being somehow incorrect. An assertion is being made that the initial spin is entirely random. An assertion is being made that the magnetic field isn't changing the spin. An assertion is being made that the measurements are completely quantized. An assertion is being made that there are no halfway states that could be incorrectly measured as entirely up or down, left or right. I'm sure there are experimental reasons for these assumptions. But for me personally, I don't find that the absolute nature of these assumptions have been completely addressed. Not that they have to address them for my benefit, but it's clear that we are missing something.
Bells experiment assumes that the experimenters have a free choice in configuring their experiment (Choosing the spatial orientation of their detectors). This assumption sounds insane to me because if there are hidden variables and the universe does work like a deterministic 'machine' then why would the experimenters be special (in that they don't work like machines but have free choice)? When are we finaly going to loose the 'human = special' assumption in physics. It has turned out to be wrong so often already....
I've missed why in the counter-experiment if A1 is red B2 would be green. They're at an angle, so the particles aren't symmetrical and the setup doesn't account for all possible results, as explained earlier in the video. Which would bring the probability closer to the observed while still keeping the model.
I've been struggling to understand Bell's Theorem for decades (I'm only a software developer not a physicist) and if Prof. Merrifield says "i struggle to understand it", I think I might be doomed.
I really can't stop feeling that the colors of the rotated arrows are wrong, but I don't know for certain. I thought that the color signified basically at what direction the magnetic field is in. And if the entangled particles have opposing results with respect to the field (which I assume), if the left left arrow is red over green with a result of green, I would think that if the other arrow instead was green over red, this would result in red?
This breaks down for me (logically) when he's trying to explain by assuming each particle somehow has consciousness. Sounds more like rubbish philosophy to me, quantum mechanics is not falsifiable in any observational way, so to me its philosophy at best, certainly not real science, especially because it possesses maths made up out of whole cloth. I can prove ANYTHING I want by manipulating statistics, just give me the time, clever maths don't PROVE a thing about quantum theories.
Ok, this video certainly explains it far better than any other I've watched. Well done for that. What I still don't understand is how instantaneous transfer of information and the probabilistic nature of things are related. Even if instantaneous transfer of information seems a necessary assumption, this would still be compatible with hidden variables, wouldn't it? The question of probabilistic vs. deterministic seems a philosophical one, or indeed a modelling choice, but not an empirical one. Am I missing something here?
@@schmetterling4477 What do you mean? Isn't that the whole point of the spooky action? - Or is your point that the instantaneous transfer of information is not an observation, but a theoretical statement a.k.a. interpretation?
It is claimed here that the "spooky action at a distance" really can't be used for communication as the signals are random. Ok sure, but can we look at it a little bit different? What if we use the random signals for coordination of behavior? Say that we are two separated actors, two military units of an army out in space. We are preparing an attack and have two options: strategy 1 or strategy 2, equally reasonable from a strategic perspective, let's say, but both units have to follow the same strategy to be effective. Then the random quantum signal lets both units select either strategy 1 or strategy 2 in a coordinated way. Instantaneously, without further contact, while also avoiding to reveal their presence by alternatively using radio communication.
This is a totally classical (non-quantum) scenario. You just fire red or blue light from a source, randomly, and they pick the signal and act coordinated. Nothing quantum and nothing faster-than-light is going on here.
How can the chance be 2/6 if the switches are in different positions? The 2 cases where the results are opposed are exactly the cases where the switches woud be in the same positions, which we EXPLICITLY EXCLUDED. Removing the possibility of switches being the same leaves 2 rows with 4/4 and 6 rows with 0/4, result ing in exactly the 25% we measure. The particles do not need to know what happens on the other side because by forcing different settings we remove the cases "after the fact". It's still the same row, we just prevent some of the outcomes, no spooky action required. Is the explanation in the video wrong or did i just misunderstand something?
Bell’s Inequality only rules out local hidden variables. There still could be global hidden variables. Although if true, it is unfalsifiable, so maybe moot from a scientific point of view.
What should be looked into is the apparent 'conspiring' going on amongst macroscopic nature. Talking about 'information instantly passing from electron to another' seems wrong-headed. After all, our quantum conceptualisation of electrons do not even carry use information - they're defined purely in terms of probabilistic properties. Trying to stuff hidden variables in such quantum objects was doomed from the start. 4am and I'm high (on lack of sleep), so don't know if that made any sense.
Consider the following... 1."Particles" are merely an analogy for the underlying wave like nature of the energy, which itself is a two dimensional view of a higher dimensional construct. 2. Entangled particles are two parts of the same quantum system, they are not separate but both parts of the whole, and there is no information required to be passed from one part to another part of what is the same thing. 3. Quantum calculations such as cos²(Θ/2) reflect the geometry of the energy, which appears probabilistic in nature.
Why is it so hard to believe that there is a non-spatial dimension that is relating the two particles when we entangle them? No speed-of-light required. The particles are still right next to each other in this dimension.
because it is indeterminate in the present and thus inherently unproveable except after the fact. If you study the "weak measurement" experiments of Yakir Aharonov then he does - his research group proves there is a guiding field from the future.
It's 4am and i have work in 3 hrs buy spooky action at a distance is keeping me up. I'm completely baffled. The universe is a mystery and this is closest we got to magic!
Interesting, Professor Merrifield uses a trick I’ve used to understand a hard to understand paper.. find another paper that references it and read their summary
And if you can't understand their summary, go find this youtube video that summarizes their summary!
It's summaries all the way down!
yep, the classic 😅
That's how I've educated myself for free.
@@Idontneedahandle333 i call it learning. I'm not sure why this seems like phenomenal similarity to some of you. I didn't go to college. This is just consciousness to me. Getting exterior perspective, beyond the echo chamber of your own take on reality. If there's no door, create one. That's all that sets us apart from a student and a teacher. Door users and door framers.
This video is being published on the day the Physics Nobel Prize is awarded for research in this area - total coincidence!!! What were the odds? --- www.bradyharanblog.com/blog/spooky-action-at-a-distance
Spooky
The fates align
λ(x)
To be honest it looks like i was a spooky action at a distance (in a way) :>
That depends on how many videos you had at the ready
i've observed this spooky action at a distance phenomenon a long time ago: each time i would want to play w/ a particular toy my brother would want the same one and when i'd chose a new toy behind my back, his preference would change instantaneously.
:)
On the other hand, I've experienced spooky dookie at a distance. Anytime a glass of milk is opened, my rectum fills with diarrhea
And then you'd get in a tangle...
We need to kidnap u and research on you then 😈, but that's kinda cute 🥺
Did we have the same brother??? That would be really spooky 🙃
@@a.randomjack6661 All electrons are equal.
I met David Mermin once. I studied philosophy of physics at Cornell and I used his paper Relativity Without Light in my thesis. I was happy to discover he was a professor there and I went to his office hours to make sure I was understanding it properly and not misstating his premises and conclusions in my paper.
Nice guy.
He sounds more like a philosophy prof to me too, this whole video is bad philosophy in my opinion, its certainly not falsifiable science in any meaningful or observable way.
@@michaelfried3123 what do you mean 🤔? People have made countless experiments which all show that the bells inequalities are violated and that the action at a distance really does happen. He even talks at the end about the implications to quantum computing and everything...
ok?
I barely graduated high school but I have a desire to understand this kind of stuff. I've had this explained to me a hundred times. This is the first time I felt like it clicked and right as he said, "This is where your head should start to hurt," my head was hurting. I was thinking exactly what he said I should be thinking. And it made sense to me for the first time.
I went to school for nuclear engineering and I can assure you my experience is the same as yours!
My head wasn't hurting...For sure it wasnt in the right state. :(
Your fd bud. Join the construction force like the rest of us.
Oh this was a fun one to get the head around. Reality really is weird when you divide it down finely.
I barely graduated high school but got really into sixty symbol videos many years ago. I’ve since graduate with a physics degree, if you want to know go find out
Always happy to see a long sixty symbols video.
its comical when you realise its all bs
@@residentfelon im gonna take it from a random youtube commenter
@@residentfelon the Nobel prize foundation begs to differ.
@@residentfelon Wow that's the best scientific paper I've ever read. I hope your genius will be recognised.
Thanks a lot for the first explanation I've seen in forever which goes beyond "oooh look one spins one way and the other another! it must be magic!!" (which would be extremely easy to explain with hidden variables) and actually explain why there is a paradox if we use a hidden variable model
Absolutely the best explanation of Bell's inequality in TH-cam! Thank you
Agreed.
He incorrectly describes a disproof of local hidden variables as a disproof of hidden variables.
Agreed, the best explanation of Bell's inequality, and its experimental test, I have ever seen. Other demonstrations explain Analogies only. However, the explanation in this video was carefully paced until the 14' 00" mark, when the pace increased on got a bit sloppy: unfortunately this is when the most important info was finally revealed.
@@edshort1138 I lost him precisely around the 14:00 mark. Are we still assuming that spin can only be measured as either up or down? I don't see how the 2/6 probability comes about.
Well... minutephysics has a great explainer too.
Excellent explanation and also very timely, given the Nobel prize announcement this morning.
Exactly! That's remarkable! (Almost somewhat spooky...)
Technically there is still a way to save the EPR paper: Super determinism. The bell inequality relies on the measurement being determined after the entanglement and particules separation. But if you have link between measurement and the particule going way back before the experiment then the hidden variables are still a viable solution. But Free will is no longer. as the decision of the measurement could be taken by an operator and then he would be constrained by those hidden variable which means he doesn't have free will to choose the set-up. (I'm pretty sure that would horrify Einstein as much as spooky interaction at a distance).
Yes, I would like to see that addressed.
Couldn't there be something wrong with the experiment itself? Nobody addresses how the particles are sent to the machine or how the measurement is made. It's always a mystery box and a mysterious process to entangle the particles. Why can't they explain that?
@@zualapips1638 He mentioned the measuring tool at the beginning, with the magnetic field which deflects the particles in different directions. It’s just a simple way of describing the experiments done and what is observed. The physical tools used aren’t important to understanding the concept. You can look up the experiments and how it is done if you want.
Wonderful video thus far, almost finished, but I just had to say this is one of the most clear concise explanations of Bell’s Inequality I have seen on the internet.
Congratulations on creating the best video on Bells Inequality on youtube! I finally understood it. Thankyou!
false.
A commendably clearly explanation in which you demonstrate how Bell's inequality disproves local hidden variable theories, those where the entangled particles "agreed locally" upon a hidden variable before they departed.
I really wish you would have made very clear that this does NOT refute all hidden variable theories. Only LOCAL hidden variable theories are refuted by Bell's inequality. If entanglement involves a hypothesised Einstein-Rosen bridge through a compactified dimension the instantaneous "spooky action at a distance" that is required by Bell's inequality may be described (as Einstein desired) by presently unknown "hidden" variables that would describe the unique instantiation under study as well as the reason for a 75%/25% probability ratio.
You described this as The QM prediction, but it's actually an experimental determination that was never predicted by QM.
There are no non-trivial hidden variable theories. The only worked out one that I am aware of is Bohm's guide wave, but it's basically nothing else than a backwards way of solving the Schroedinger equation while pretending that an unphysical and unmeasurable guide wave is floating over the waters. That's not even physics.
@@schmetterling4477 In the '70s I thought Pilot Waves were the way to go, but the concept is only correct in it's approach in the sense that it seeks a rational explanation for QM that is inspired by Feinman's Path Integral formalism as well as aspects of d.slit experments that hint at what Bell proved. Bohmian mechanics points at a future theory that could rationally explain QM, but it's missing the physics behind the undescribed process through which entangled particles are constantly aware of the joint state.
@@gilbertanderson3456 Feynman's path integral is a different way of solving the same equations. It doesn't add anything fundamentally new to the basics of quantum mechanics. Bohmian mechanics only points to one thing: Bohm didn't understand the physical reason for the structure of the standard theory. Neither did von Neumann and I suspect that you don't understand it, either. That can be solved: think really hard about WHY quantum mechanics is the way it is instead of trying to find a replacement for it. There is none. It's no different from the non-existence of a quadrature of the circle or the foolish quest for a perpetual motion machine. It's all a waste of time on the wrong idea.
Great video! Not sure if I totally agree with the conclusion that "information" really is travelling from one electron to the other instantaneously. First, the measurement on one spin has no effect on the density matrix (which describes the statistics of any possible measurement outcome) of the other. Also, in different reference frames, due to the relativity of simultaneity, different observers will disagree on which electron's spin is measured first. I would say what's really spooky here is the fact that the spins are measured in the way quantum mechanics predicts *in spite of* no information being sent between them!
There's no reason you couldn't update the density matrix on particle B if you measure particle A in spin up, and know ahead of time the relative angle between the two detectors. This would give the same result.
_"First, the measurement on one spin has no effect on the density matrix (which describes the statistics of any possible measurement outcome) of the other."_
How can this be? After all, if one particle is measured spin-UP, then the probability of the other particle being measured spin-DOWN assuming the machines are set to the same of the 3 settings, rises from 50% to 100%. If you could explain how this is negated to result in no effect on the statistics of any possible measurement outcome, I would be much obliged.
_"Also, in different reference frames, due to the relativity of simultaneity, different observers will disagree on which electron's spin is measured first."_
This doesn't disprove Spooky Action nor "information", in at least one definition of the term, travelling Faster Than Light from one particle to the other, though. All it would change is the *direction* the observer, .....well, observes..... the "information" travelling in. The "information" travelling Faster Than Light doesn't change with the reference frame.
What is in fact true, however, is that the "information" being exchanged between particles is only "information" in the most narrow definition possible of the term. No actual communication, of the type that could break Causality under the Theory of Relativity, can be exchanged in this manner. Mostly because it is impossible to predict which state (Spin-UP vs. Spin-DOWN; red light vs. green light) the particles will be in before the first one arrives at its designated machine.
@@AhsimNreiziev I agree with just about everything you've said. However, I have a question. How does the unpredictability of which spin the particles will be in "before the first one arrives at it's designated machine" rule out the seemingly FTL communication between the particles?
@@ML-hl1uh
There are 2 types of "communication". The very basic kind that determines things like properties of Entangled Particles (such as position, momentum, Spin etc.), and more "advanced" communication that allows for what we call "information" to be transferred. "Information" is anything that conveys a state of the world more advanced than a Quantum State.
Importantly, the second kind of communication breaks Causality when it happens Faster Than Light, while the first kind doesn't.
Now, because you can't predict which state each particle will be measured in when it arrives at the machine, you can't use it to *encode* anything that might convey "information". Thus, this Entangled Particle FTL communication doesn't, and can't, break Causality as in the Theory of Relativity.
@@AhsimNreiziev I probably should have been more clear/specific in my original comment. If we use QM to describe the state of the two electrons, along with the detectors/observers which measure their spins, then the interaction of one of the detectors with its associated electron will have no effect on the density matrix of the other electron or the other detector. In the case that you _are_ one of the observers, then because you become entangled with the measured electron, there is a correlation between the measurement result and your knowledge of the state of the other electron, and I would probably agree with @anywallsocket, but I still probably wouldn't call that information transfer.
This presupposes that the hidden variables would result in the 1/3rd distribution. But it's entirely possible that the hidden variables also affect the particles themselves, and lead to a distribution in line with what is observed.
In other words, we don't have a complete picture of what is going on yet. So rather than invoke non-locality, we could strive to see what else is impacting this.
Also, and this part is very important, entangling particles is difficult, and only a fraction of the particles used in the experiments are validated as being entangled. The results from the other particles that are deemed not entangled are thrown out. But if we add those results back in we may have a clearer picture.
That's why it's called Bell's _Inequality_. It would be possible for hidden variables to generate a correlation greater than 1/3 - the extreme case would have "RGG" and "GRR" as the only two results, with a correlation of 50% - but not for it to be less than 1/3, which is the case when all the results in the table (including RRR and GGG) have equal probability.
However, it's not possible for them to give a correlation of less than 1/3, and the experimental results show a correlation of 25%.
Waking up to a new sixty symbols video is such a rare treat
In HUT Holographic Universe Theory (HUT) Physics, The faster than Light 'Communication" is explained due to two "realities" , A 'Higher reality" where all the particles actually exist and there is no "space" in terms of separation or distance between them (some variants allow 1 or two dimensions as such) and a "Lower reality" which our perceptions interpret certain key attributes of the particles as discrete POINTS in a (consciously constructed shared illusion) 3/4 dimensional universe. Thus, two particles may be light years "apart" in our lower reality, but in contact in the HIGHER REALITY, thus APPEAR to communicate FTL with respect to our LOWER REALITY. -----
I have always taken a layman interest in quantum mechanics, specifically the strangeness of the double slit experiment and Bell's Inequality. The first book I read that really grabbed my attention was Quantum Reality by Nick Herbert. Over the years I have tried to grasp Bell's experiment and consequences - the probabilities of the 'assume the hidden variable' were never really explained clearly. This video really helps that understanding. Here is my question. When the measurement of the particle is made at one of the detectors, does the measurement actually 'flip' the particle's polarity to its up/down measured value or does the measurement just say "here is how the particle is oriented" when we measured it. I'm not sure if this question makes sense, but to me (not knowing the real technical details of how this works), it's an important question. First, it could mean that when the particles are entangled, it was done in a specific way to polarize the particles in a certain direction. In other words, do we know the intended polarization of the particles when they are created? Second, if the detector is 'flipping' the particle polarity, then THAT implies that this is 'causing' the second particle to flip to the polarity described by quantum mechanical theory (math). The reason I ask is that this would REALLY make things strange. I seem to remember reading something like that years ago, that what is really strange about this is that when particle A is 'flipped', it instantaneously 'causes' particle B to flip. Thank you kindly.
Bell also assumes statistic independence. Why are most videos ignoring that?
Because somehow many scientists are afraid of having to give up free will. Disappointing to see
i don't think can blame einstein for not liking that.
Thank you! After watching like 5 videos, this one finally actually made it 'click'. The way I understood it is that (note: I am a total noob, so please let me know if i got it wrong):
1. they chose 120degree of eachother because then every switch combination will have 120 degrees of eachother (120/240, 240/360, 360/120), so it simplifies it to different switches or the same
2. the result we get that, for different switches, the electrons show 25% same spin and 75% different is impossible if the two eletrons had a predefined plan for each switch they conjured together. That's can be seen by looking at all possible plans, there are 8 such possible plans that have the condition that if they get same switch they must be opposite (which is experimentally verified). When we do it we see it's impossible to get such low probability of them being the same for different switches..
3. This is because, the key thing here is that the electron does not know how it will be measured when its making the plan. The way it is measured determines how the other electron will behave. That's only possible in quantom mechanics is weird. It's as if it has a plan that is "if I get switch A and you get siwtch B, do same spin 25% and opposite 75%", but that's impossible since they don't know how they'll be measured (that's in the future).
4. Thus somehow something very weird happens. Either the electron like, knows in advance the future - what the switch will be at when it'll be measured. Or it instantly communicates how it was measured to the other. Or something elese (idk). But definetely not a "locally-real" behavior.
it seems to me bell (and others) looked at the quantom equations and saw this probability is lower than is possible to make with a concrete/"locally-real" plan (AKA 'hidden variable) of the electrons, and thus there must be something very weird going on there and hidden variable doesn't explain it all as einstein argued.
Uh yeah, you got it wrong, buddy. Sorry. Go study "math" and get smarter.
Great timing, considering who received the 2022 physics Nobel prize just about a hour ago! :)
Isn't the problem in the presumption, that the way this hidden variable would be generated is dependent on the experiment set up? Like in reality it would have not only "prepare answers" for these 3 positions of detector, but for all continuum of possible positions. And even more, why should these answers for all possible positions be completely independent from one another? (as I think calculation presented in the video presumes)
The information is not traveling instantaneously, the particles are already carrying that information with them. It's not changing on the fly. The results you see changing are based on the information the particle already has.
That is a common interpretation but it is wrong. The key to understanding quantum mechanics is the insight that nature does not know the state any better than we do. In effect... state is an after the fact quantity. It does not even exist before the measurement.
I think what you were trying to ask at the end, and what I'd like to see answered, is: Are there any examples of entanglement seen or suspected in nature (the universe)? Like perhaps there is something that happens in neutron stars or quasars or whatnot that could be best explained by quantum entanglement?
You can create an entangled state in lab. There is a hypothesis that our brains have tubules that are entangled and probably much more.
Interesting that the 120 degree tilt causes 25% / 75% outcomes. Naively, I would think it'd be 33% / 66% to match the 1/3 of a circle.
The "Alright!" at 0:20 is seriously so funny to me. The cameraman's excitement for a quick physics lesson is so wholesome 🥰🥰
ok?
I read a few articles on the recent Nobel prize, and they didn't make any sense to me. This video does a great job of framing the problem in lay terms, and the problem makes a lot more sense now. Thank you!
I have never liked this idea that the information is getting from one place to another faster than light.
Like, there's no question entanglement is real, but in my mind, it makes much more sense to think of entangled particles as sharing something, instead of communicating. Like deep down they are using two sides of the same "thing", instead of having each an individual "thing" independent from the other. And that makes me feel that there is always two sides of that thing, and we just don't get to observe the other side for some reason (the corresponding antiparticle could be on the other side of the universe, or inside a black hole).
As another commenter has suggested, maybe they _are_ the same thing. With talk of multi-verses and extra dimensions this makes possible sense to me as a 'real' physics explanation.
Kind of puts me in mind of Pauli's exclusion principle; there the electrons seem to 'communicate' as well, although this may not be an instantaneous change; I don't know enough about that to comment.
But I do remember a lecture by Prof. Brian Cox which seemed to imply that if an electron changes state in one atom, then all other atoms in the universe also change states (not sure I if just misinterpreted what he was saying, though).
And I've heard of a (maybe tongue-in-cheek) theory that there actually is only one electron in the universe, but it simultaneously exists in many different places and states.
For sure, we certainly don't understand everything yet - not even close. And who knows what will be changed in 'common conception' of the universe in another few centuries. (Assuming we survive that long.)
Indeed, it is only convention to describe entangled pairs as individual particles rather than collective parts of the singular wavefunction.
That’s just an interesting point that I’ve always pondered.
If information can’t travel faster than light then how can we have this instantaneous transfer of information. But I suppose he’s completely right that actually your not really transmitting any information as the initial state is itself random. Still feels a bit wishy-washy but that makes a lot more intuitive sense to me.
A serious but understandable description of the problem. Thanks for taking the time to explain this in detail.
well that was so lovely, thank you. the spin part in the beginning made my head spin but then came the payoff of a very intuitive explanation why reality is probabilistic was amazing.
Hearing "quite young" and "early 60's" in the same description makes me feel just that little bit better about myself.
Oh gosh. He meant it in the sense that Bell died quite young (he was 62).
@@anythingandeverythingandall I know. It makes me feel better better about aging because 62 can be considered young.
Watching Sixty Symbols videos after I have just graduated from Nottingham, nostalgia/bittersweetness fuel. Thanks to everyone for making my time studying physics as fun as I had hoped it would be when I was a young schoolboy watching these videos in awe, inspired to one day study physics. My childhood dream came true in your department; and who knows, one day, if I'm lucky, I might be back! 🥲
ok?
I had to watch this multiple times, but this is the clearest explanation I've seen on this subject. Well done!
So I’ve heard and read about this many times and this is the first time I actually understand it
This only rules out local hidden variable hypothesis; non-local hidden variable hypothesis could still be true
Physics is so beautiful, thank you for this video!
I remember a few years ago I wanted to understand QM better, and while my understanding did improve, I couldnt get my head around bells inequality. I understood the gravity, but not how it actually works. This clip made me understand it even before explaining it fully. Great work.
Love watching Mike explain stuff, what a rare treat!
false.
@@Triantalex What's false? I don't love it?
Excellent explanation. To me the answer would require the apparent two particles are actually the same particle in another (fourth or fifth) dimension. Image this particle randomly (or at least unpredictably) orienting its spinning. When measured , its random spinning is fixed and when re measured gives the predicted result.
This is basically correct. The contradiction comes from trying to project 4 degrees of freedom down onto 3. The probabilities being a function of cos^2(theta) already ignores imaginary phases.
Moreover, we're told many hints along this direction, such as the fact that elementary particles cannot epistemologically be distinguished. Also, the spins we measure are always projections onto our 3d measuring devices. Then there's the weakest link in Bell's argument: locality. We would like to believe that things are separated to the extent that there is space between them, but relativity dismantles simultaneity -- therefore when one entangled half is 'measured', the other half is measured in a frame of reference which shrinks the physical gap between them. And yes, you could construct entangled pairs far enough apart that even light itself could not hypothetically 'witness' their simultaneous measurement, but we are also forgetting about our linear notion of time. Entangled pairs are created in total isolation, with the degree of entanglement proportional to how little noise there is, therefore it isn't a stretch to suppose that when we witness the evolution of a system, what we are witnessing is nothing more than the irreversible entropy seeping into the system. This has other thermodynamic backing, but in terms of QM it implies that time evolve for systems that remain entangled, and therefore in 4D, the 'distance' or proper time between the two events is not at all as big as the shadow we measure here in 3D.
interesting, and the up or down is just the different part of the same particle
I like this idea. There is so little we _really_ know about the universe(s?) that this seems as plausible as anything else put forward so far.
Yes, it's totally unintuitive and a little bonkers; but so are most quantum mechanical explanations and observed behaviours.
I've even heard a theory that there's only _one_ electron in the universe, and it's just 'very busy'. If this was true for all particle types (or even just a the right set of quarks) this might offer an explanation too.
Who knows what we'll find out in the future? Maybe yet again making what we know today seem utterly naïve and primitive.
A nice follow-up video on this would be to talk about how Many Worlds and Superdeterminism might still allow for hidden variables but with different other counterintuitive tradeoffs.
Many Worlds would be the hypothesis that when the two boxes make their measurements they actually are splitting into different worlds with different results and it's only when the two boxes' lightcones in particular worlds intersect that they both agree on the results. In that scenario everything is still done locally and can have hidden variables but at the cost of the creation of multiple simultaneously branching worlds from the measurements.
Superdeterminism deals instead with the notion that the selection of the switches on the boxes might not be independent of the states of the entangled particles. Basically if the settings on the boxes are somehow linked by a prior condition to the states of the particles when the particles initially become entangled then the measurement and then states aren't independent and the stipulations for the inequality aren't valid. The difficulty with this approach is that it's difficult to imagine that the method of random selection of the switches can never be truly independent of the states of the particles. For instance, if you're randomly selecting switches using astronomical measurements of distance quasar fluctuations then for those fluctuations to be tied to the states of the just now created entangled particles on Earth means that information was initially passed down billions of years ago when the stuff in the quasars was physically interacting with the stuff creating the entangled particles. It's not impossible but it's hard to grasp how that would be the case.
I thoroughly enjoy hearing professor Mike Merrifield explain and reflect on phenomena even, as in this case and most others, I have absolutely no idea what he's talking about. 😊
Have you considered that a person *attempting to teach* might be, in fact, deeply saddened or frustrated by a student's proud admission that, while they enjoyed the lecture, they learned nothing?
That such a statement is not praise, but rather a blatant insult?
@@Hermaniac8 Yours is a fair perspective, but it places me in the class room. I am actually quite removed but delighting in the process. I have no doubt that professor Merrifield's student's are exceptionally and richly informed. Additionally, in my viewing experience humor, subtle and not so, is never lost to Mike. In one video a questioner asked him what was the base trigger for lightening in clouds. When Mike responded that we really don't know the questioner was flummoxed, clearly unbalanced to hear that such a common and observable phenomena was not completely understood. Regaining his equilibrium the questioner responded, "That's ridiculous!" Mike's response was a healthy dose of his infectious laughter. So, while finding no fault in your comment as a general perspective I nonetheless believe professor Merrifield would read my comment and smile.
Here on TH-cam there is a class on quantum mechanics by MIT and in the bell's inequality lecture the professor said we shouldn't be surprised that electrons don't behave like cheese. We should be surprised that cheese behave like cheese.
Wut
I have a deep love for Mike Merrifield that I can't quite explain. He's clearly a genius, I love listening to him. :)
Alphabet...
Great explanation, Mike!
At 15:00 I think the row of all three red and all three green is not possible, because the spin has to point somewhere, so it is aligned with at least one Stern-Gerlach experiment. So you would get 1/3 exactly.
Yup. I've struggled to understand precisely that for some time. I haven't found any satisfactory answer to how three red or green probability is valid.
it is one possibility of pre-determined outcomes. it only seems illogical if you assume that the electron has a definitive spin direction. that is correct for a single-electron-wavefunction, but not necessary for a pair of entangled electrons.
Not really. Let's say the (first) particle is exactly aligned with the detector in Position 1, so it has 100% chance of firing the detector in that position. It therefore has a 25% chance of firing the detector in Position 2, and a 25% chance of firing the detector in Position 3 - there's a non-zero chance of a "three reds" result.
If one of the detector positions was 180° out from another position, then this would be a valid point. But that's not the case.
I am optimistic enough to say that this is nothing we can use yet. The people figuring out how to utilize this will definitely deserve a Nobel prize. At some point humanity will have spooky communicators.
Everett had an explanation even before Bell came up with this, and in fact was one of the inspirations for Bell
Kenny Everett was a clever guy (wink )
You mean the "Many Worlds" non-explanation? I don't know what Bell said about Everett, but I do know he admired Bohm.
@@johnkeck it's absolutely an explanation, although others did refine it and make it more rigorous. Unlike say the "just use the Born rule" non explanation of say the Copenhagen "interpretation"
Such clarity! Easily the best explanation I've seen on YT!
this is the first time this has made sense to me. Thank you! Have hidden variables been disproven in other apparently random conditions like radioactive decay? If so I need to go make a significant amendment to a video I published a few years ago...
the fact he assumes particles to all have consciousness doesn't bother you at all? his explanation was philosophy, not falsifiable science in any meaningful way.
@@michaelfried3123 he doesn't assume the particles have consciousness what are you talking about? What you are talking about is a slight anthropomorphisation of the problem to make it easier to understand. When he says the particles decide amongst themselves what he is actually saying is that there may be some way that the particles are set together in a certain way. It is easy to remove this characterisation do not get distracted by this because it is unimportant to the problem.
@@jimpim6454 you obviously didn't watch the video, or if you did, you didn't pay close attention to the words he used. he certainly does assume particles have consciousness by the grammar and words he uses. philosophical BS at best comes from this so called "expert".
@@michaelfried3123 The purpose of using those words is to make it easier to understand ffs. Why are you assuming he's a bad faith actor? Isn't it much easier to just assume he wants the audience to understand the concept?
@@Google_Censored_Commenter if you wanna live a naive life, feel free, I refuse to.
4:40 This is when the video begins to give incomprehensible answers. How do you create the pair of electrons that are coupled together?
The bell inequality breaks local hidden variable, but not now local theory like pilot-wave theory.
pilot wave theory is non-local actually, from what I hear, not like I do the math lol
6:11 isn't this backwards? If you have a magnetic gradient that causes |+z> to go upward and |-z> to go downward, then flipping the gradient upside down (changing its sign) should cause |+z> to go downward and |-z> to go upward. Now suppose your left-going particle is found in |+z>, i.e. normal SG apparatus causes it to go upward. That would mean its partner must be in |-z>, and so the upside-down SG will cause it to also go upward. And the opposite case would be both of them going downward, even though one of those is with the gradient and the other is against it.
Doesn't matter... it's all sci fi anyway...
@@kwimms I mean I have literally done this experiment but go off
Brady's making the same mistake again in the end that Mike already tried to address: No, the particles in the Milky Way wouldn't "react" in any observable sense. You wouldn't see it. They would behave exactly the same from our point of view whether whatever happened in the Andromeda galaxy affected them or not. And they most certainly wouldn't be obliterated. No communication means no communication, not even by obliteration ;)
What I love, is that it is not really 'instantaneous' transfer. From some reference frames it happened first at one end, and from other reference frames the other end was first (and from some it really was simultaneous). So which direction does the message go? As there are no observable differences between these two cases then we should try to not regard these as indistinguishable, but instead view them as completely equivalent. If that doesn't make your brain fizzle, then nothing will.
Excellent excellent point, I'd never considered this before! Relativity of simultaneity and spooky action at a distance make for a mean one-two punch.
Hmm just be careful about simultaneity. If you take two events in any reference frame, and measure the distance between the two events and the time between the two events in that reference frame, then calculate c²t² - x², if c²t² - x² is less than or equal to 0, then there is no reference frame in which the events are simultaneous. That quantity c²t² - x² is called the “spacetime interval”, and it’s the same no matter what reference frame you’re in. It’s worth learning about!
This is why we split the separation between events into 3 cases; space-like, time-like, and light-like.
No matter what Lorentz transformation you do, space-like separations remain space-like, time-like remain time-like (and the direction of causality remains the same), and light-like remain light-like.
The brain fizzle is because you are arguing with time while assuming a "relativistic" universe. But that will be the same independently if you talk about entangled particles or anything else. It is just the basic of relativity. And that is also why, in relativity people talk so much about intervals and space-time. And the same thing happens when talking about space by itself.
Another way to think about it, is to assume that every time you mention time, you will be using an "unreliable" (reliable for you, but others will disagree) measure tape. The "reliable" measure tape would be the interval which is composed of time and space in a certain relation.
@@jackm3692 I think you have the sign backwards -- if two simultaneous (dt=0) events occur with nonzero spatial separation (dx!=0) then the interval (squared) would be negative. It's when c²t² - x² > 0 that the events are never simultaneous and are causally ordered. Metric conventions are a pain the the rear. (And to Stevo's point, the EPR paradox involves just such a spacelike separation of events where c²t² - x² < 0 and the superluminal "signal" can "travel" in either, or neither, direction depending on your reference frame.)
I've still yet to see anybody explain how the quantum probabilities are derived. They just always skip over that part. does QM predict a 25% correlation?
That's the best explanation of Bell's Inequality. Very clear. Well done!
If you consider the many-world perspective, there is no instantaneous information being transmitted, just yourself being entangled with one of the lamps, which means that you are also entangled with the other lamp.
Strangely enough, I take great comfort from both the randomness of QM and quantum non-locality. It makes the universe a much more interesting place!
??
This is one of those episodes you have to watch a dozen times, so fascinating
Really incredible that Nobel Prize for physics was announced today!!
Thank you for making this video, I am only part way in, but already want to make a comment. Regarding the discreteness of state discovered via the Stern-Gerlach experiment, I have a proposition solely for the curious of mind. Perhaps the magnetic force acts not just in space, but in time as well. Imagine the field attracts parallel-aligned poles towards the present, and repels for perpendicular poles into the past/future where we never detect them!
It's a paradox only when we insist on seeing the entangled pairs as two separate point particles. We've known since the 20s that matter is made of waves, this behaviour is entirely consistent with how waves propagate. The real mystery is why the wavefunction collapses to a single point when we do a measurement. I've seen some nice thoughts on the measurement being a sort of Fourier transform, similar to when we focus multiple light rays into a single point through a lens. The nature of the rays never changes, it's just our measurement making it appear different.
I first learned about this decades ago and because of the content and that it was published in the same year I was born I wanted to learn more and understand it better. I thought, as my understanding of physics grew, I would eventually have one of those "epiphany moments" when it finally made sense. The only epiphany I have had is I'm not going to live long enough for that.
Your entangled double in Andromeda probably gets it. Only one of you can.
Thank you so much ❣️
Best explanation of the experiment and the phenomenon I've seen/read in quite a while.
I read a better one once... back in the 90's. It was way better actually.
i'm confused here, in the image with the colored circles, each of those is taken as an equal probability. so if we take the 4 rows where red comes out of detector 1 setting the possibilities are it comes red or green on detector 2 and 3 with 50% probability, but earlier in the video it showed that when you have that tilted scenario it comes out as 25/75% probability of matching or not, wouldnt you need to apply those probabilities and then adjust the 2/6 results downward for the fact that its not 50/50 whether they match or dont but 25/75?
Yes, you would. But for some reason, nobody thought of that...
Exactly! I also don't understand why the options in the table are all regarded as equal probability.
I think you are confusing the probability of the results and the probability of the experiment configuration.
The 75/25 is the probabilistic results prediction of quantum mechanics, you don't know what an individual particle will do only overal statistical behaviour. If there is a hidden variable then for any given particle pair there is no probability involved. The test has three configurations, the detectors can be in the same alignment, 120 degrees apart or 240 degrees apart so the particles have to have "decided" what to do in each of the three possible configurations. The test is repeated many times so each configuration happens 1/3 of the time. Since the configuring changes after the particles separate so that no light speed communication has time for them to communicate they have ot have "choosen" what they will do for each possible configuration before reaching the detectors.
There is no probability within one row, its saying e.g. if the detectors are aligned it's red, 120 its red, 240 its green and so on, there is nothing to adjust. Its 1/3 for each experiment configuration because that is how the experiment is designed. The particles can't influence the probability of the experiment configurations, indeed to be sure they did tests where the configuration was determined by light for quasars millions of years old so it could've been influenced by the recently entangled pair.
There could be different probabilities of which configuration the particles "choose" before they seperate, but since all of them have a probability of 2/3 or higher it doesn't matter and doesn't effect the discrepancy between the prediciton and the result since it happens which ever preset results the particles could have.
Yayy more quantum goodness from our guys at Nottingham university.
I've exhausted all the videos on this channel and I neeeed more
'At this point, your head should start to hurt' 😂😂😂 20:01 Great video! Thank you!
What I find interesting is that when the poarticle inters the experiment, it has presumably an infinate reange of orientations. And yet, the experiment forces an expression as if it could only have one of two. You'd think that that might have some bearing on what the entagnled does, but apparently not. And the fact that you can get two reds or two greens by turning one of the aparatuses upside down is just very strange indeed.
Did you make this video for the occasion of the 2022 Nobel Prize in physics being awarded to scientists who worked on this problem or is this a spooky coincidence?
I think the confusion about why this isn't a problem is highlighted at the end of the video; you can't "do something" with certainty to either of the particles. You can't force your particle to be spin up and force their particle to be spin down.
What you can do to the particle is measure it in some way; the point of this video is that this really does do something to the particle and its entangled pair (it changes their state, and there's no way they could have already been in that state in some hidden way). But quantum measurements are a very special type of "doing something". Individually, measuring each particle doesn't look special; each individual particle's measurements looks the same as a particle that wasn't entangled, so you can't get any information from anywhere else out of it. It's only when you compare the results of entangled pairs that you see the results are correlated. The point is that they are correlated in a way that can't be explained by "local hidden variables".
I still feel like there must be some physics going on that we have yet to understand. Something so far ahead of us that we cannot yet conceive of a way to even prove that we are missing something. Any sufficiently advanced physics is indistinguishable from magic.
ER = EPR?
If only it were that simple for us!
This does have all the hallmarks of our base assumptions about the experiment being somehow incorrect.
An assertion is being made that the initial spin is entirely random.
An assertion is being made that the magnetic field isn't changing the spin.
An assertion is being made that the measurements are completely quantized.
An assertion is being made that there are no halfway states that could be incorrectly measured as entirely up or down, left or right.
I'm sure there are experimental reasons for these assumptions. But for me personally, I don't find that the absolute nature of these assumptions have been completely addressed. Not that they have to address them for my benefit, but it's clear that we are missing something.
So what you're saying is the particles have a VPN for talking to each other, a virtual particle network.
gives a whole new meaning to ExpressVPN doesn't it?
Bells experiment assumes that the experimenters have a free choice in configuring their experiment (Choosing the spatial orientation of their detectors). This assumption sounds insane to me because if there are hidden variables and the universe does work like a deterministic 'machine' then why would the experimenters be special (in that they don't work like machines but have free choice)? When are we finaly going to loose the 'human = special' assumption in physics. It has turned out to be wrong so often already....
Yeah, it's funny how it is just not even mentioned, as if it was self evidently true.
Quantum mechanics is even more confusing when your colour blind.
I've missed why in the counter-experiment if A1 is red B2 would be green. They're at an angle, so the particles aren't symmetrical and the setup doesn't account for all possible results, as explained earlier in the video. Which would bring the probability closer to the observed while still keeping the model.
Very spooky
And it just happens to coincide with the Halloween month.
I've been struggling to understand Bell's Theorem for decades (I'm only a software developer not a physicist) and if Prof. Merrifield says "i struggle to understand it", I think I might be doomed.
"Is there anything happening in the universe because of entanglement?" - yeah, the freaking spacetime itself is made from an entanglement hirarchy :D
Susskind: "Entanglement is the hooks that hold space together"
I really can't stop feeling that the colors of the rotated arrows are wrong, but I don't know for certain. I thought that the color signified basically at what direction the magnetic field is in. And if the entangled particles have opposing results with respect to the field (which I assume), if the left left arrow is red over green with a result of green, I would think that if the other arrow instead was green over red, this would result in red?
in the video it would seem like the particles results are with respect to the spacial directions, not the directs of the fields?
This breaks down for me (logically) when he's trying to explain by assuming each particle somehow has consciousness. Sounds more like rubbish philosophy to me, quantum mechanics is not falsifiable in any observational way, so to me its philosophy at best, certainly not real science, especially because it possesses maths made up out of whole cloth. I can prove ANYTHING I want by manipulating statistics, just give me the time, clever maths don't PROVE a thing about quantum theories.
NPCs are not supposed to know about or directly interact with the underlying program code.
Humans are as clever as they are brutal. Trip
Ok, this video certainly explains it far better than any other I've watched. Well done for that.
What I still don't understand is how instantaneous transfer of information and the probabilistic nature of things are related.
Even if instantaneous transfer of information seems a necessary assumption, this would still be compatible with hidden variables, wouldn't it?
The question of probabilistic vs. deterministic seems a philosophical one, or indeed a modelling choice, but not an empirical one.
Am I missing something here?
Nobody has ever observed instantaneous transfer of information.
@@schmetterling4477 What do you mean? Isn't that the whole point of the spooky action? - Or is your point that the instantaneous transfer of information is not an observation, but a theoretical statement a.k.a. interpretation?
@@ah1548 The whole point of "spooky action at a distance" is that there is no action at a distance. ;-)
It is claimed here that the "spooky action at a distance" really can't be used for communication as the signals are random. Ok sure, but can we look at it a little bit different? What if we use the random signals for coordination of behavior? Say that we are two separated actors, two military units of an army out in space. We are preparing an attack and have two options: strategy 1 or strategy 2, equally reasonable from a strategic perspective, let's say, but both units have to follow the same strategy to be effective. Then the random quantum signal lets both units select either strategy 1 or strategy 2 in a coordinated way. Instantaneously, without further contact, while also avoiding to reveal their presence by alternatively using radio communication.
This is a totally classical (non-quantum) scenario. You just fire red or blue light from a source, randomly, and they pick the signal and act coordinated. Nothing quantum and nothing faster-than-light is going on here.
This video finally made me understand Bell's inequality. Thank you.
How can the chance be 2/6 if the switches are in different positions? The 2 cases where the results are opposed are exactly the cases where the switches woud be in the same positions, which we EXPLICITLY EXCLUDED. Removing the possibility of switches being the same leaves 2 rows with 4/4 and 6 rows with 0/4, result ing in exactly the 25% we measure. The particles do not need to know what happens on the other side because by forcing different settings we remove the cases "after the fact". It's still the same row, we just prevent some of the outcomes, no spooky action required. Is the explanation in the video wrong or did i just misunderstand something?
This is a simple explanation of a very complex concept. Thanks sixty symbols for making it so.
Great video! as a non physics nor a mathematician this is possibly the first time I believe I have understood the Bell's inequality
Bell’s Inequality only rules out local hidden variables. There still could be global hidden variables. Although if true, it is unfalsifiable, so maybe moot from a scientific point of view.
I'm of the view that there aren't hidden variables (in that sense) *and* that quantum mechanics isn't the whole thing.
What should be looked into is the apparent 'conspiring' going on amongst macroscopic nature.
Talking about 'information instantly passing from electron to another' seems wrong-headed. After all, our quantum conceptualisation of electrons do not even carry use information - they're defined purely in terms of probabilistic properties. Trying to stuff hidden variables in such quantum objects was doomed from the start.
4am and I'm high (on lack of sleep), so don't know if that made any sense.
(Aug/Sept 2023)
I've got a physics degree but I could watch a million Bell's inequality videos and still not be able to explain it.
Consider the following...
1."Particles" are merely an analogy for the underlying wave like nature of the energy, which itself is a two dimensional view of a higher dimensional construct.
2. Entangled particles are two parts of the same quantum system, they are not separate but both parts of the whole, and there is no information required to be passed from one part to another part of what is the same thing.
3. Quantum calculations such as cos²(Θ/2) reflect the geometry of the energy, which appears probabilistic in nature.
The universe is not predetermined. It is buffered, so stuff may be altered/synchronized before it's presented. Or something.
wouldn't determinism solve the paradox, and the dots in both examples are in a pattern that's flipped upside down. did anyone else notice that?
That's the point: determinism makes the wrong prediction altogether.
Why is it so hard to believe that there is a non-spatial dimension that is relating the two particles when we entangle them? No speed-of-light required. The particles are still right next to each other in this dimension.
because it is indeterminate in the present and thus inherently unproveable except after the fact. If you study the "weak measurement" experiments of Yakir Aharonov then he does - his research group proves there is a guiding field from the future.
It's 4am and i have work in 3 hrs buy spooky action at a distance is keeping me up. I'm completely baffled. The universe is a mystery and this is closest we got to magic!
Very much happy to see professor Merrifield back in his office 🥰
He should stay there. Close the door and just think about why he lies so much.