I've always been very attracted to the pilot wave theory and love the fact that you quoted Bell supporting it. Some physicists have argued that pilot wave theory does not add anything to the picture because it only adds a philosophical dress to something (standard quantum mechanics) that does not need such a decoration. Personally, however, I find the philosophical dress, i.e., a deep understanding of what is going on, much more interesting than turning the crank on some quantum mechanics calculator. I do understand why some people are contend with having the math that delivers incredible results, but I find it supremely unsatisfying to be told "don't even try to understand, just turn the crank".
It upsets me how long it's taken me to be aware of your videos. Great work, truly. And thank you for taking the time out so lay folk like myself could learn what we were never taught in school... but really should've.
I've long felt that superpositions were just a way of pretending there are no hidden variables. Instead of admitting there will be things we don't know, throw in all possibilities, then cancel them out after the fact when we know what actually happened. It feels like a statistical trick like ideal gas law. Works fine so no prob, but one builds up from the details to get something practical and the other starts pragmatically and papers over details.
Its similar to how scientists couldnt explain the revolution of mercury around the Sun using newtonian math until einstein theory of relativity helped explain it. Quantum weirdness is most likely something we cant understand because it might be beyond the scope of scientific experimentation. We can only guess using mathematical formulas but never really know the truth.
You don’t need a concept of superposition to “pretend there are no hidden variables” you just have to look for them (or hell even describe what they are) and you come up empty. It’s not pretending something doesn’t exist by failing to mention it when there is no way to observe or talk about what it is in the first place
@@david203 Yes, but I want to understand the exact “real mechanism” that underlies the generation of that superficial “probability distribution” where that real mechanism is fully compatible with things like “Lorentz Invariance”. /s 🤔✌️
@@Mentaculus42 Your comment appears to have been cut off. If your question is that you want the Bohm interpretation to be explained in terms of intuition based on the usual Newtonian physics, that is impossible. The atomic scale of nature does not obey Newtonian physics, just quantum mechanics!
My favorite theory! I think it's totally logical that opening the second door leads to a different path. It's the same with a balloon on water, if you change the shape of the environment, the waves will spread out and then come back and affect the balloon differently. Opening one of the doors is changing the environment, so the waves behave differently than if it was closed.
The pilot wave theory just makes sense. If only we can explain quantum entanglement as easily. Just because we're unable to measure or see something does not mean what's happening is not following specific laws. It's just our inability to currently understand it. But that's what makes it so exciting.
I appreciate that you pause to ask questions of the viewer in the middle of the video. I love to watch your videos while baked and it helps me make sure I'm actually learning the material rather than simply feeling mind-blown for its own sake :D
A few points are worth mentioning on this issue: 1. While some laypeople or beginning physicists complain about Bell's theorem (or even the Kochen-Specker theorem) in regards to Bohmian mechanics, most serious critics choose other lines of attack. For example, Chen and Kleinert have argued that the results of Bohmian mechanics do not agree with those of standard quantum mechanics even for the two slit experiment! (In other words, the picture at 6-24 does not agree with experiment). Neumaier has also pointed out observables made up of time correlations of, say, position operators, do not in general have the same expectation values in Bohmian mechanics as they do in standard quantum mechanics. 2. It is important to note that not even Bohmists try to argue that Bohmian mechanics is fully experimentally equivalent to standard quantum mechanics. The claimed equivalence, even if we ignore the criticisms above, rests on an assumption known as "quantum equilibrium". This assumption states that, in order for Bohmian mechanics to reproduce the Born-rule probabilities of quantum mechanics, the _initial state_ must be distributed in this way as well. This is a highly nontrivial assumption: there is nothing a priori that states that the particles in the beginning of the universe must be distributed according to the absolute-value squared of the wavefunction. Outside of quantum equilibrium Bohmian mechanics has pathological features; in particular, it allows transmission of faster than light signals, which is a problem for any relativistic extension of the theory. The relativistic version isn't just ugly: it simply can't exist! 3. Bohmian mechanics can only describe systems with a fixed number of particles. Processes where particles are created or absorbed, such as when a photon excites the atoms on a phosphorescent screen, are not allowed. The formalism simply isn't equipped to deal with such processes. Since all consistent relativistic theories must allow creation and destruction of particles (for causality preserving reasons), Bohmian mechanics is a dead end of theoretical development. It cannot describe anything happening in a particle accelerator, not just because it's not written in a relativistic form, but because by nature it cannot be relativistic. 4. It's important to note that the "oil droplet theory" and Bohmian mechanics are extremely different. The oil droplet model is really more analogous to a plate attached to a speaker. By playing a tone you can see grains of sand arrange themselves on a plate in a "standing wave" pattern. The difference is that in the oil droplet theory a single drop eventually traverses all of the available surface, and the wavy pattern is seen in the amount of time spent in each spot. Bohmian mechanics does not work like this at all: because the evolution equation for the particle depends on the imaginary part of the wavefunction, if you place the particle in an energy eigenstate (such as the ground state of a hydrogen atom), whose wavefunction is wholly real, it will just sit there. It won't do anything. It won't move at all! The "probability distribution" of particle positions in such a state is given entirely by the initial distribution, which I hope provides some "teeth" to point 2. All in all, I don't think it's premature to discard Bohmian mechanics as a possible theory. Draw inspiration from it if you must, but ultimately, the theory has to agree with experiment... and we've been doing experiments that prove that nature is relativistic for a solid 100 years now.
Thank you for this very thoughtful and interesting comment! There's a lot of things I wanted to cover in this video but they got too complicated for me to understand fully, let alone teach. So I tried to leave it at a basic intro level and make clear that I'm not fully on board with this theory (actually, my favourite interpretation is Many Worlds). 1. Yes, this criticism about the double slit was something I wanted to cover in a video about decoherence. I hadn't hear Neumaier criticism though! Thanks :) I'll look into it. 2. I was very much taking the 'equilibrium' assumption. I'm not sure about what Bohmians think, but I had always thought that this was basically an axiom you should take for BM. It's one of the things I really find unsettling about BM: that the wavefunction has two roles. One representing the probability distribution, and the other deciding how the particle experiences 'force'. 3. Yup! 4. This is true but doesn't take away from the fact that a model like this can reproduce a lot of QM experiments. Pretty cool! Anyway, thanks so much for your comments :)! I really enjoyed reading it. Cool that you know so much about BM.
Looking Glass Universe Thanks for your very nice reply. I'll be sure to stick around so we can talk about many worlds if and when you decide to make a video about it (but I'll tell you in advance I favor Copenhagen, so expect nitpicks :) ). 2. What Bohmians seem to think is that you can prove the equilibrium assumption is satisfied. They seem to believe in something called a subquantum H-theorem (the H-theorem is a sort of generic name for several results that purport to demonstrate the second law of thermodynamics, with varying degrees of success). Their claim is that you can define a sort of "subquantum entropy" that is maximized at equilibrium, and then prove that this entropy always increases. I find that argument unconvincing because, well, the real entropy isn't sitting at its maximum currently, and we see lots of processes that occur far from equilibrium, such as yours truly. " that the wavefunction has two roles. One representing the probability distribution, and the other deciding how the particle experiences 'force'. " Yeah, that's a nice way of putting it. "4. This is true but doesn't take away from the fact that a model like this can reproduce a lot of QM experiments. Pretty cool!" Indeed it's a cool analogue model, and I appreciate that you made the distinction in your video. I really wanted to emphasize the distinction though, because (other!) people say "pilot wave theory" as if it were one monolithic thing, but in fact they can behave very differently. Thanks again for your nice reply!
Fallen Star Features yeah, people try to come up with relativistic extensions of BM roughly every 5 years, but nothing truly compelling has ever appeared. Look at the example you posted, for example: they abandoned the determinism of Bohmian mechanics in favor of a theory where particles just have a probability to appear or disappear. That's a rather sharp departure from the philosophy of Bohmian mechanics, even if it's right -- and I'm not convinced that it is, for two reasons: 1. These sorts of classical theories in which things "pop" into and out of existence tend to be rather pathological and violate conservation laws. This is a problem with Ghirard-Rimini-Weber theory, another proposed classical model for quantum mechanics. 2. We already know that position observables are not good observables for all particles. For example, there is no position operator for photons because the Newton-Wigner approach fails whenever the little group is not a representation of the spin group. Photons have spin 1, so by all rights there should be three physical states corresponding to spin 1, 0 and -1, but as it turns out, the spin of massless particles can only have two possible states, 1 and -1 in the case of the photon. So the little group is not a representation of the spin group and there is no position operator. Since there is no position operator, there is no wavefunction, and their approach fails for realistic systems. It's hard to overstate just how successful the field point of view has been in fundamental physics. Any relativistic extension of Bohmian mechanics has to fight an uphill battle reproducing all those results that field theory yields naturally, and at the end of the day, because of its inherent nonlocality, will be forced into a sort of catch-22: either it's not really relativistic and requires a privileged frame that is "hidden" from us, or it is really relativistic and has trouble with causality because absent quantum equilibrium messages can be sent to the past.
Fallen Star Features You might be interested in this: physicsforums(dot)com/insights/stopped-worrying-learned-love-orthodox-quantum-mechanics/ That's a text written by Hrvoje Nikolic, the author of one of the papers you linked. Here he essentially admits that his attempts to find a relativistic generalization of Bohmian mechanics have failed. He now reconciles relativity with Bohmian mechanics by postulating that the world really isn't relativistic at its most fundamental scales, and that the apparent relativity is an emergent feature of this nonrelativistic system. This is possible, but there's no evidence for it. We have tested Lorentz invariance at extremely high energies (surprisingly, even above the Planck scale) and found no violations. This disfavors the model in favor of ordinary quantum mechanics.
Bohemian mechanics. Is this the real life? Is this just fantasy? Caught in a landslide, no escape from reality Open your eyes, look up to the skies and see I see a little silhouetto of a man Scaramouche, Scaramouche, will you do the Fandango Thunderbolt and lightning, very, very fright'ning me Bohemian Gravity Easy come, easy go, will you let me go? Bismillah! No, we will not let you go (Let him go) Bismillah! We will not let you go (Let him go) Bismillah! We will not let you go (Let me go) Will not let you go (Let me go) Will not let you go (Let me go) Ah, no, no, no, no, no, no, no (Oh mamma mia, mamma mia) Mama mia, let me go Bohemian Uncertainty Principle Nothing really matters, anyone can see Nothing really matters Nothing really matters to me Any way the wind blows
There is no good answer, in the same way this question isn't answered in other interpretations like many worlds. But it is the thing that causes the quantum force.
I haven't seen a theory that puts it exactly this way, but what about some sort of fluctuations in a Dirac style aether? In his later conversations on the topic with Einstein they seem to have come to some sort of quantum mechanicalized alteration of the Lorentz aether that caused it to work well with general relativity as well. Fluctuations in a material like this could account for low level waves that push the particle, and it would have incredibly complex fluids dynamics because of its massless state.
In the undivided universe Bohm talks about active information. It's only the form of the wave which tells the particle what to do. The analogy he made is of a automatic pilot controlled by radiowaves
Non-locality is explained with pilot wave. The pilot wave feels the effect of one particle and transmits that information to the other particle without the particles being local. The pilot wave spans all of existence. If you have 2 balls floating in a pool and one of the balls is pushed downwards such that it creates a ripple in the pool, that ripple will disturb/communicate with the other ball on the other side of the pool without the balls being near each other.
@@david203you will never get a response because all of the LGU vids are total misinformation, just do a google search on any of these topics and you will discover this to be the case. I'm just waiting for the LGU vid that says dinosaur footprints can be found right beside human footprints!
I'm really glad you made a new video! Clearly there's a market for science explanations, clearly you have a niche people like, keep it up if you have the time!
The great thing about De Broglie Bohm Pilot Wave interpretation is that it accepts outside reality, agrees with predictions of quantum formalism, and is not logically inconsistent (Copenhagen) and is not utter madness (many worlds)
Welcome back, we missed you. Personally I'm glad that there are valid competing theories on how the universe works, because as soon as we "figure it out" we'll choose to stop learning.
Ehhh, not a big fan of the "science must have two sides" thing. It either fits reality or it doesn't. It's like when people pit evolution and creationism together -- it's not really a debate.
David Ralphsky The problem with the 'evolution vs creationism' argument is that they aren't mutually exclusive. But the thing about 'Quantum vs Bohmian' is that they both have valid ideas about how the universe works and are exclusive. Only one can be right, but having multiple sides keeps us looking at the problem rather than just assuming that we understand it all.
my question is -- how is it that they came to the conclusion of superposition in the first place. it makes so much more sense that a guiding wave might be directing particles.
Detect those guiding waves then, interfere with them, predict how strong or far they are. Prove it! The freaky thing about entanglement is that it doesn't care about Light Speed.
Perhaps it has to do with the double-slit experiment being accidental in the first place? "Hey look at this. What the hell is going on? It almost seems like the particle is interfering with itself. That's odd man, like it seems like it's doing both at the same time." "... What if it actually did that though?" And then further experimentation only seemed to prove that idea. (Perhaps because it is true)
LightSource Yes it doesn’t care about lightspeed but there is no additional information gained or transmitted once you collapse the wave function into that singular state. It makes a lot of sense if you consider that it is impossible to put say a negative charge In the exact same place as another negative charge, They would just repel, something has got to give. And what “gives” When you force Two Electrons to be in the exact same place is that they have to occupy a new shared state (you have forced them to be one thing after all - When they are simply two things). When you do this they occupy a realm of existence where that particular property is undefined the property is called spin, And it’s an analog of angular momentum and clockwise and anticlockwise but off axis with an eccentricity each of them random, but each of them opposing. And this has nothing to do with gravity therefore space is a irrelevant. Trying to apply the property of lightspeed to an electron spin is a meaningless statement to attempt to impose. Spin isn’t the same as angular momentum it is something entirely different it’s just the fourth quantum state. Along with quantum number which indicates energy. And the other two which you can look up. I think we should be teaching a periodic table that organises atoms into electronic spin states now because it is “more better” at grouping.
Great fair video on QM and the merits & conundrums of Bohm-de Broglie theory. To resolve, it seems necessary to truly understand the "entanglement" theories.
11:22 "tradgectories"? Someone has clearly been to tired when editing that part of the video! :D But hey! Great video! It reminds me to continue reading about mathematical physics in my free time.
Wow, I am so excited about this video right now. It's so incredibly well put together, amazing work! Favorited instantly. You are truly one of a kind, such a clear thinker, not to mention beautiful. Now I just really have to study entanglement and pilot wave nonlocality. It's the only bit I am still confused about.
I really like the classical pilot wave theory that Derek from Veritassium showed in his video, and I really dislike the Copenhagen interpretation of quantum mechanics, but still I have a fundamental problem with QM pilot wave theory: if there really is a medium upon which there are waves that the particles interact with, shouldn't we be able to somehow detect and measure that? I guess my basic question is, what is this medium and via which forces do particles interact? I just think that Bohmian mechanics leaves more questions open than what it solves (not that Coppenhagen interpretation doesn't).
TravelerInTime The medium for PWT would be Spacetime itself. All fields are contained within Spacetime and contains Spacetime. Both GR and QFT treats Spacetime as a physical entity.
I dont think it implies its detectable, it implies ut is hidden and the observations we have already seen are evidence for it. Whatever "it" is. A field? Informational? I like something about the informational approach but its got so many flaws. Therein each particle contains knowledge of the process of the wave. The wave is just knowledge and doesnt necessarily have to exist. Thats weird, but then so are nonlocal particles. In fact yes its nonlocal, near "omnipresent" information but if we observe that in other situations, then why not? At least then we may say there is "one less type" of quantum strangeness and take nonlocal information as an axiom of fundamental particle behaviour. Each electron contains some knowledge of all electrons and i thought that was well accepted so why not "contains information on how it should move based on surrounding particles"? Of course, it may just be a hidden variable again...a hidden field...a hidden force...it doesnt say anything about what it is, only that it predicts well, but we dont need to know until we found it?!
The answer to that question depends upon what type of “Pilot Wave Theory” is being referred to. A reasonable place to start is “Pilot Wave Theory in the Twenty-First Century” which is freely available online in its entirety. That very topic is a focal point of what differentiates various types of “Pilot Wave Theories”. And generally that “something” is a foundational “thing”! From “Pilot Wave Theory in the Twenty-First Century”: “Pilot wave theory vindicates an ontological belief about the nature of quantum phenomena, wherein corpuscles and waves are two very real physical entities, coexisting and interacting at all times. The wave guides or pilots the quantum corpuscle, and in turn, the corpuscle reenforces the wave, acting as a moving oscillator. This physical picture of the quantum world is very different from that put forward by the Bohrian complementarity view, according to which the undulatory and corpuscular aspects always present themselves in a mutually exclusive way. Louis de Broglie ontology is also distinct from that put forward by David Bohm; specifically, Bohmian mechanics does not posit the physical existence of a particle-generated quantum wave: the pilot-wave is the wave function of standard quantum theory and only in de Broglie's ontology would it make sense to discuss the possibility of a quantum wave detection. Something that is addressed in this volume (Croca, ch. 17) and that has also been recently treated in another publication (Croca et al.)” .
Great video! One critique: the bohmian particle is not "affected by all the other possible places it could be". That is simply wrong for pilot wave theory. The particle does not have any other "possible" places because its a deterministic theory. You're placing standard QM rhetoric where it doesn't belong. What the bohmian particle is affected by is not any "possibilities" but a concrete field that pushes it around in space. That field in QM is called the "wave function".
Sounds good, except that the wave function doesn't exist in standard quantum mechanics. It's a purely abstract, mathematical construct that can not be measured. Bohm didn't understand that and he mistook it for something real. The result is complete intellectual nonsense that nobody uses because it doesn't work.
One of the reasons I *LOVE* pilot wave theory is that it beautifully unites QM with the findings of chaos theory - another area where randomness and order are weirdly intertwined. The more we learn about complex systems, the more we understand how fields are a macroscopic description of quanta the same way that temperature is a macroscopic description of molecular motion. It's all layers of emergence. It explains why the gestalt of seemingly random individual events can be predicted statistically with a wave function - because the wave function describes a literal feature of spacetime. A literal ripple of spacetime quanta, much like a ripple in water is a macroscopic description of the motion of water molecules in response to a disturbance. It all makes sense in a very Einsteinian way: matter telling spacetime how to ripple, and spacetime telling matter how to move.
FANTASTIC VIDEO! Thank you. It's good to bring these wild concepts back to reality a bit. What can we prove. We shouldn't assume things we can't actually directly measure or properly infer. The fact that measuring the particle will affect it is super important. It's like trying to measure a runners location by standing blindfolded in his path so you can tell when he goes by, of course you will affect his path!
Also, while we are theorizing...what about simulation theory? The program is playing out all possible paths (within its processing power for each plank frame that is being rendered), and then collapsing into the chosen outcome. Are we playing this game?, is it in control of the possibilities or are we? Dream on you dreamers ;)
For the question why a partical "gets shy": It makes perfect sense if you look at it from a design perspective. As a coder myself this is the kind of optimization i would do if i would design a simulation. I wouldnt calculate every interaction but only interactions that actualy matter (get measured). So you can see superposition and uncertainty as a optimization process which cuts out unnecessary calculations. Only if a measurement is taken the calculations are done and the final position is determined.
This is a very good thought- but I think I disagree. I do quantum computing and in particular looking at why a classical computers can't simulate classical computers. And from that you see that superposition is actually incredibly hard to keep track of!
It's hard to keep track of from a classical stand point. I just wanted to point out the analogy. As classical logic is build on top of "weird" quantum behavior there is enough reason to consider the possibility that for the mechanism of the universe it could be easier to keep track of waves and do the actual mechanics backwards from the point of measurement to the previous point of measurement.
I agree because it gives the system flexibility to fix internal contradictions. Both keeping track of the precise positions of every particle in the universe and maintaining the consistency of that system when it is also chaotic and doing all of this in real time is a bafflingly difficult task. If, on the other hand, you have the flexibility to back-calculate and fudge your numbers a little bit, you don't have to keep track of every real position at all times and instead you can just calculate the outcome. With entanglement, it's even easier because one property covers more than one particle.
Thorium CatBit - Big problem: You now have to keep track of the whole universe at all times - doesn't make any sense as a programmer to do that rather than having mostly local influences.
Thanks for the video. I love seeing the interpretations that challenge QM being represented so well, and in general I love your channel and found your videos very instructive. I have noticed something when thinking hard about the interpretations of the double slit experiment, something that I can't shake off my head but that I haven't been able to find out if someone already talked about, or, if it doesn't make sense, why it doesn't. The Copenhagen interpretation of QM says that the wavefunction is not a "real thing". That the fact that the particle goes through all the possible paths at the same time is something that only happens "virtually", and that until measurement occurs, there is no interaction. This has always struck me as an incomplete explanation. 1. Given that the double slit experiment can be reproduced even with a device that sends one photon at a time, that means that the wavefunction of that photon needs to be aware of the slits to interfere with itself and change the likelihood of the photon hitting one particular spot. That awareness means that, on some level, the wavefunction and the particles on the barrier interact. Not only that: if we are proposing that the wavefunction's shape is influenced by the particles in the surroundings, and we are also saying that the wavefunction is a description of all the possible paths the particle could take, then it implies that, at some level, there is interaction between the wavefunction and the entire universe, only with weaker and weaker force in bigger distances. Does it makes sense so far? 2. If 1 is correct, then that means that even QM implies that the wavefunction has reality, and this "subliminal" (not-measurable) interactions exist. Again, if they wouldn't, the wavefunction would not be affected by the particles in space. It follows that the wavefunction could potentially be interacting with other wavefunctions that are also happening in the same space, since those also have reality. Why wouldn't it? If we know some "invisible aspects" of the photon are affected by the shape of the surrounding objects, both in QM and Bohmian M, then what is stopping us from thinking that invisible aspects of other particles are also interacting with the wavefunction? 3. If 2 makes sense, and the wavefunctions can potentially interact, wouldn't that interaction be a potential source of hidden variables that explain the apparent randomness? Isn't it reasonable to think that the same aspects of the photon that we can't see directly but that are clearly affected by the shape of the slits are also interacting with other things that we can't see, because their energy levels are not enough to be measured directly? 4. And finally: isn't it possible that a measurement just happens to be the point where a continuous wave surpasses a certain threshold that makes it change the state of the other particles in a degree that we can actually measure? Isn't it possible that there is no such thing as an individual photon, but rather what we called a "photon" being emitted is the electromagnetic field being perturbed to the point that we can measure it? Do we need to assume that the electromagnetic field is, when we are not emitting a photon, at rest? What if the electromagnetic (and other quantum fields) are more like an ocean which always have waves, and a photon is more like a tsunami? The waves would affect the tsunami in a way that would seem random to us, and ripples of the tsunami that we can't measure would affect other tsunamis in ways that would, again, seem random to us. Could the apparent randomness of QM be a side effect of such ripples coming from everywhere, a kind of "white noise" of the field? This to me seems to be neither Bohmian Mechanics (which if I understand correctly, postulates that the particle is being driven by a wave, but really exists as something being carried by the wave, and not just as an artifact of measurement) and certainly different than QM, since QM (at least Copenhagen) dismisses the physical reality of the wavefunction. Is there a theory around Quantum Mechanics that approaches it in this way? It seems to be hidden variables approach, but I don't know which one. Thanks a lot for reading :)
love, love, love this. Understood double split when I was younger but always curious... "spooky" maybe not as it turns out... this gives glimpses of a possible new understanding for me. Thanks.
Mahasiddhic Sceptic the Pronoid Vegan Because QM doesn't work with special relativity. In this case the "wave" giving the Quantum force transmits information faster than light. This gets you into trouble because simultaneous events in one frame are not in another, so you could do things like: entangling two particle, separating them, changing the quantum state of the wave function and making a sort of code language and sending todays lottery ticket numbers to the other experimenter, but then in some other reference frame the event of receiving the message will actually happen before you send the signal!
Adolfo Holguin But QM can be relativized with Quantum Field Theory, which is the single most accurate theory of all time. My limited understanding of the subject is that to relativize Bohmian mechanics, which Bell did, you have to give up the determinism that was at the heart of the motivation behind the theory. I'm hoping she makes a video on that, as I really don't understand that and I'm not totally sure I'm right about it.
Adolfo Holguin You're a bit off. QM is perfectly consistent with relativity (special relativity, at least). Entanglement doesn't break the rules of relativity - it doesn't permit any signals to be transmitted faster than light, only correlations between measurements which can't be directly observed. Bohmian mechanics' problem with relativity stems from the fact that BM posits a single universal wave function whose shape is determined by the instantaneous positions and momenta of all the particles within the universe. I.e., it requires an absolute reference frame where one can definitively state the relative distances and speeds of every particle in the universe at a given moment. Special relativity doesn't allow that - like, it REALLY doesn't allow that. Not that it's necessarily impossible to marry BM and relativity - but it would probably make the theory even weirder and more needlessly complex than it already is.
Copydot Old Fashioned QM is NOT Lorentz covariant (It treats time and space on different footings). What I wanted to say was that QM breaks causality (the wave function will be non zero outside your light cone so you can design experiments to send information back and forward in time depending on the frame of reference). And you seem to misunderstand Special Relativity. It doesn't state that the universe doesn't have an absolute frame of reference, but rather that physics is the same in all frames (physics doesn't prefer a frame, but the universe might!) In fact there is a very special frame of reference, the CMB rest frame (where the CMB looks uniform) which can be thought as the rest frame of universe. The problem with Pilot Wave theory is that it pretty much requires you to throw away Lorentz covariance and build a theory where physics is different in different places.
+Adolfo Holguin Dude I never thought of it that way. But I think it can still be reasoned via the uncertainty principle. I mean, the particle is still bound by its light cone but since you can't really know where the particle is, you can't know where the light cone is either. And thus the light cone too is spread out throughout the universe. That doesn't necessarily imply the probability of finding the particle outside the light cone is nonzero. Just a thought.
If Bohemian mechanics is true, doesn't this say some fundamentally different things about our universe? Things like atomic randomness wouldn't be a thing. I also don't think quantum computing would work like they want it to. It would mean that the world is not inherently probabilistic?
I am no exepert but i think the uncertainty princeple still works in this theory so particals do have a position but we cant know exectly where they are soo there is still randomnos kinda
Pilot wave theory is deterministic, meaning there are no probabilities involved. If you know the current state you know all future states. However, since we are physically limited to never know the current state of the universe, we can only use approximations and assign probabilities to events - meaning experimentally we can't do any better than conventional quantum mechanics.
(as i understand it) quantum computing works by setting up quantum circuits in a way that causes the wave form to cancel out any wrong answers and output only the answer to the desired query. and pilot wave still has the wave form. so i think it would still work
Check out the "heligone" channel / user on TH-cam... He has some amazing walking droplet experiments that mimic radioactive decay and quantum tunneling... in vibrating silicon anyway :)
Halberdier I think having weird rules is mor intuitive than having weird particles. A knight in a game of chess moves unintuitive but it appears more natural transforming it into a wave or multyplying. Well, that's how I feel anyway.
While PWT is 'weird' due to non locality and the 'hidden' variable of the theory, it is 'weird' in an entirely different manner than the Copenhagen Interpretation (QM). The Copenhagen Interpretation is 'weird' because it is illogical (Ontological Probability is a logically incoherent and untenable notion) and contradicts everything we know about nature through Science, which tells us that everything that happens has causes and is causally determined. PWT is only 'weird' because people are unfamiliar with it. It ISN'T weird insofar as it is illogical nor is it weird as in it contradicts causal determinism. PWT actually explains the weirdness it proposes. The Copenhagen Interpretation doesn't explain the weirdness it proposes. These are SIGNIFICANT differences between the 'weirdness' of both interpretations. I know which of the two I am a proponent of..the one that is logically coherent. (Keep in mind PWT is an actual and full fleged Scientific Theory, while the Copengagen Interpretation can't even be considered a proper Scientific Hypothesis, because it doesn't explain what it proposes.) Looking Glass Universe
I beg to differ. The Shrodinger's Cat Thought Experiment clearly shows the ABSURDITY of the notion of ontological probability that underpins the Copenhagen Interpretation.
You're mostly correct, except that something doesn't have to explain what it proposes to be a proper scientific hypothesis, but it does have to be falsifiable... if your hypothesis asserts "there can exist no reason for a coin flip to land heads rather than tales or tales rather than heads, it is random" then the whole theory is falsified upon demonstration that actually, explanations that are perfectly consistent with our really existing universe are really existing... which, duh, as if people could really believe "if the universe doesn't tell me, it must be because it doesn't know".
Lovely Looking Glass Universe thank you for all the great content on quantum mechanics! I am sure you have your reasons on why pause on making more of these amazing videos but if I may ask: a video on decoherence would be most appreciated :)
Absolutely. Re-watching them helps me understand the concepts better, too, since I've never studied physics at the university level... I just find it fascinating.
This video was incredibly easy to understand!! I really love your videos although i tend to scratch my head a fair bit, and i agree with you saying that bohmian mechanics made it look like superposition isnt the only interpretation, i grew to really dislike superposition
Hadn't heard about Pilot wave theory before, I thought that quantum theory is the only widely accepted theory for the particles. Thanks for introducing it. Well explained and very interesting. I loved it :)
Great video and I'm glad this interpretation is alive and coming into mainstream. P.S. Veritasium did a great video on this interpretation a few months back, too!
Great video! Very logical and clear to understand - just like a Pilot Wave Theory ;) I find just once small detail missing - the actual pilot-wave wasn't shown in the diagrams like at 3:59. For newcomers to quantum mechanics (and wave theories) it can help clarify the main concept.
The Pilot Wave is imaginary. What is real is the deterministic paths of particles from source through one slit to the screen. These paths are based on the Schrödinger equation plus the initial positions of each particle.
Just finished the video, it's awesome! One question though, if they both produce the same results in all possible experiments, will we ever know if either of these is correct? Is either of these correct at all?
Don't be sorry. It's not your fault. But thanks for another interesting video! You really inspire me to think more critically about Physics in general.
+Quim Last Hi. No theory is ever correct. Every theory is just that: a theory. The schooling process gives illusion we know exactly. We don't. There is no such thing as the exact knowledge. There are just interpretations. Interpretations, also known as theories. There's actually one extremely important theorem in mathematics, called Goedel's theorem. There are two of them, actually. In rather vague words, it says that every theory is incomplete or inconsistent. There's a problem that cannot be solved within any given theory, or there's a problem that has two solutions, such as "yes" and "no". There are Nobel prizes being awarded for theories that were vastly expanded just a year after awards being given out. There is no exact theory. Oh, by the way, the Goedel theorems come from -- logic. The Goedel statements are larger than mathematics. They concern logic. Stop using logic, it's incomplete or inconsistent :D Cheers :D
Really nice presentation. QM is a very interesting field PRECISELY because there are numerous possibles interpretations for what is observed during experiments. The more experiments conducted, the more interpretations/theories spring out.
Dual slit experiment possible explanation: Via QED, basically anything shot out of the gun would have it's magnetic field interact with the magnetic fields especially of the electrons in the atoms and molecules of the gun itself, the medium the projectile is traveling though, and/or from around the slits themselves. Any newly generated photons would possibly set up hills and valleys of energy. In the case of protons or electrons being shot out of the gun, the newly generated EMR wave would travel faster than the projectile of which the projectile would then follow whatever valley it entered. Even shooting only one electron or proton at a time would still possibly have the interference pattern show up.
Brilliant, balanced analysis, even if you didn't approach explaining Bohm's pilot waves per se and how it attempts to mechanistically a count for delocalization. Next video? Still, I still get stuck on whether mathematical solutions (like Bohm's) need intrinsically to reflect basic processes. I see Schroedinger wave formulation as descriptive, and yielding beautiful results (in computationally tractable contexts) BUT dancing around the fact the computed probability densities are only descriptive and predictive. "Piss off, Bohr", my prejudices scream, and I thank you for taking a shot into this philosophical mine field!
One particle surrounded by a wave. The wave goes through both slits first and creates its pattern of interference which the particle follows at random. The device they used to see through which slit the particle went through actually disrupted the wave and its interference pattern, the particle then made a normal 2 slits pattern.
In the diagram at 5:00, suppose the particle is an electron. From Gauss's Law and Ampere's Law, we can model the moving electron as a moving spherically radial electric field with an associated disk-shaped magnetic field. When both doors are open, the center of the Gaussian Sphere might pass through one door, but a portion of the associated magnetic field passes through the adjacent open door. This unbalances the geometric symmetries of the electric and magnetic fields of the moving electron. According to Maxwell's Equations, this sideways imbalance in the magnetic field causes the resultant trajectory to veer to one side. This is how the E-M fields of one electron interferes with itself. The electric permittivity and magnetic permeability of the material forming the double slit barrier depart from their values in free space.
Here is another way to think about it. Suppose you shoot an electron through the hole of a donut. Let the donut be made out of a material with a magnetic permeability larger than that of free space. As the moving electron approaches the hole, the magnetic field inside the donut builds up, and this changing magnetic field creates a back EMF that slows down the electron. To the extent that the magnetic field collapses after the moving electron passes through the donut hole, the collapsing magnetic field will then accelerate the moving electron. Now comes the fun part. Instead of a complete donut, take a bite out of one side, so that the donut is now more like the capital letter 'C'. As the electron passes through the center of the semi-donut, the forces that created the back EMF that previously slowed down the electron are now circularly asymmetric. The electron won't just slow down on approach and speed up after, it will also be deflected sideways. Opening and closing the door in the double slit is like using a full donut vs one with a bite taken out. Has anyone tested this effect experimentally, replacing the double slit with a donut with a bite taken out of it, to demonstrate how Maxwell's Equations predict the sideways deflection?
A great video. To further clarify - both the Copenhagen interpretation and the pilot wave theory both have unappealing aspects as theories in physical science. In the Copenhagen interpretation, the idea of collapsing wave function has much to do with modeling probabilistic phenomena (i.e., a trial, experiment such as a coin toss). Once an experiment is over, there is no longer a probability distribution. This view introduces a subtle bias - a subjective perspective (that of an observer performing the experiment), and thus leads to the unsettling prospect of "consciousness" or the question of "who is observing." The Pilot wave theory is clearly a version of QM that works. By (1) interpreting the probability distributions of the particles as results of their initial conditions; and (2) with the idea that measuring a minute system disturbs the system, the Pilot wave theory does away with the "collapsing of the wave function," or the measurement problem. But to me, the Pilot Wave theory is a bit annoying. The probability distributions of particles, although reflecting the initial conditions and the pilot waves, are still probabilities that indicate the presence or the absence of each particles. This comes across as a feature that does not stem from some fundamental-ness of the theory but from its attempt to deal specifically with the measurement problem. It smells of contrivance.
If we only look at the "standing wave" solutions, knowing which slit a "particle" goes through becomes equivalent to imposing a boundary condition: That is knowing that a particle goes through slit A is equivalent to closing slit B. Standing wave solutions may also address entanglement and "quantum eraser."
I think both are wrong, like when Galileu started looking at planets like Saturno and it's moons with telescope he thought the moons were moving in harmonical moviments because of his perspective and ALL the formulas of harmonical moviments(HM) could predict what he observed, same way that quantum mecanics works, but then we realise that what was happening wasn't an HM( lateral perspective) but a circular moviment of the moon.What I'm saying is that even quantum mecanics works, it's explanations could be wrong because of the way we're looking at it.( I love your videos....keep making them)
Great vid 👏 highlighting some misunderstandings about Pilot Wave Þeory (PWÞ)! PWÞ is not a mere interpretation of QM; it's a framework ðat can explain a broader range of phenomena. If and only if particles are distributed according to ðe Born Rule (quantum equilibrium) does PWÞ foretell ðe same results as QM. However, wið quantum unequilibrium, a range of awesome phenomena becomes possible, like sending a signal in an eyeblink and violating ðe Uncertainty Principle. Doesn't ðat cause time paradoxes? No, because in PWÞ, Lorentz invariance is an illusion and holds only macroscopically due to quantum equilibrium. If we find matter in quantum unequilibrium or a way to make it, we can refute QM while keeping PWÞ... and do a lot of awesome stuff, as Antony Valentini talks about in Subquantum Information and Computation. So, PWÞ is 1. *testable against QM* and 2. *offers mind-boggling practical applications* to boot. What more can we ask for?
@@TristanLaguz You didn't look carefully enough. In Copenhagen the measurement process is a trivial irreversible energy transfer and the Born rule links the absorption spectrum of the measurement device directly to the possible measurement outcomes. You have nothing of this sort in Bohm. What you do have is an unphysical ghost field that nobody has ever seen, a hard ball that nobody has ever seen, either and a complicated non-linear differential equation that returns absolutely nothing new in comparison to the old linear one. Bohm is total bullshit. ;-)
@lepidoptera9337 In Copenhagen, ðe term "measurement" is not defined. In Copenhagen, ðere are no particles and waves. Raðer, waves and particles are taken to be mere ways of talking about measurement outcomes ... which concept is, as said, not defined. But on ðe oðer hand, ðe very measuring appatatus itself and ðe physicist's brain are made up of ðe very quantum objects ðat are supposed to be mere figures of speech. What a wagonload of circular and illogical literal nonsense 😂! (Yes, not wrong, but nonsense, just like "dgtwp jkjdhhd ddcn".) I quote from ðe Wikipedia article on ðe Measurement Problem in ðe part about Copenhagen: "Exactly how to understand this process remains a topic of dispute." Beautiful Bohmian Mechanics, by contrast, has no MP. I quote from ðe Wiki article on BM: "The theory does not have a "measurement problem", due to the fact that the particles have a definite configuration at all times. The Born rule in de Broglie-Bohm theory is not a basic law." In BM, particles interact wið each oðer þrough ðe wave function. Because our 🧠 are made up of particles, which always have definite positions, we observe definite outcomes in experiments. Oh, right, measurements: What are ðey in BM? Plain old physical processes obeying ðe laws of ðe þeory like any oðers. In short, BM is a well-defined, self-consistent þeory in which we know exactly what we're talking about: particles in well-defined states interacting wið each oðer þrough a field in an equally well-defined state. And most importantly, it foretells precisely what we see. We infer ðe existence of ψ from ðe way particles which we behold directly behave. By contrast, what is Copenhagen even about? What kinds of entities does it posit? What is measurement in Copenhagen? Unlikely BM, Copenhagen is clearly BS. And by extension, any claim ðat Copenhagen explain ðe MP and BM be wrong or nonsense is itself BS. 😉
I'm commeting it here because it's your latest video: I have very troublesome doubts about the quantum eraser, which you covered in previous videos: Take the nomenclature you used, M1 and M2 as measuring devices: 1) What would happen if you place M1 far enough away so that you can first know whether you are having an interference pattern or not? If you saw the interference, then you could turn the device on and know which slit the photons went through, and you have already seen the interference pattern so it's very unlikely that it magically changes itself into two clumps. If you don't see the interference pattern, you could keep your device off, and that would mean that the mere threat of measurement collapsed the state. Either way, it's very unsettling, so I'd like to know the experimental results. 2) Is this not allowing faster-than-light communication? The observer of the double-slit experiment can know whether M1 is turned on or off, because we get interference if it's off and two clumps if it's on. That would in theory allow to send messages faster than light. If anyone know the answer to these two, I'd be very glad, I've been trying to wrap my mind about it for too much.
What happens when the slits are moved further apart? What if it was a matter that each electron created a field of probability with a given radius which when the slits are smaller than the given radius you get an interference pattern but when the slits are moved further apart, larger than than the radius of probability, the interference pattern doesn't develop?
Yes you're right. If it's far apart, in QM you'd say that the particle goes through both but the weight of the second one is much less. In BM you'd say the particle is less effected by the other slit now.
The detectors would have an energy field that is one way when on and a different way when off. The interaction of this energy field, or lack thereof, with whatever is passing through it would possibly give the indication observed.
In the double slit experiment you get the interference pattern, I understand how the pilot wave theory can explain the resulting pattern. But when doing the double slit experiment and using a sensor to observe which slit the particle passes through, the interference pattern disappears (and there's the more complex quantum entanglement experiments) . How does observing which slit the particle passes through, eliminate the pilot wave / particle interaction in Bohmian mechanics? How would Bohmian mechanics explain the results we see when sending through quantum entangled pairs and using quantum erasers to observe the results?
It's always a pleasure to see a new video from you. I hope everything is well with you. Regarding Bohmian mechanics, or whatever you want to call it, I'm afraid that I still just don's see the point. Sure, QM is weird, but so what? Why would one expect humans to intuitively understand things on such a small scale that we could not detect them until recently (meaning that evolution could not have given our brains such intuition)? Why would one expect things on that scale to be just like things on human scales? I also think that BM raises its own questions. What exactly is waving in the pilot wave? How does it interact with the "real" particles it is piloting?
I have a counter to your question: why would we *not* expect things on a small scale to behave (roughly) like they do on bigger scales? In particular, why would we *not* expect things to be in 1 place at 1 time, and *not* expect that every effect has a cause?
Partly because in the real world we can easily see things that are different at different scales, even when those scales are close to human scale. For example, have you ever seen a movie that used model ships? You can easily tell that they are models, because water behaves differently at different scales. Fractals would not be as surprising as they are if scale invariance were common. More generally, though, your questions get things backwards. We should not make assumptions about how things are without evidence. The default position should be neutral with regard to scale. We should not assume that things are the same on every scale, nor should we assume that things are different. We should not assume at all.
Hey Michael, good to hear from you! I have to agree with Ahsim on this one though, why would you presuppose weirdness? Also, as I tried to explain in this video, I don't support one theory or the other. I just want people to understand that both theories work and have the same experimental evidence. I don't see why then people choose to believe QM (rather than accepting either could be true) while making it sound like the other people are the dogmatic ones.
@@LookingGlassUniverse This would be more due to Philosophical issues concerning Science than ofc rather than Science issues. As Adam Becker points out in his book "What is Real?" “And Philosophers of Physics today almost unanimously reject the Copenhagen Interpretation (Logical Empiricism of a sort has made a comeback since 1980, but scientific realism is still the standard position among philosophers of physics - and even the most staunch defenders of empiricism today agree that the sort of positivism deployed in standard defenses of Copenhagen doesn't work). How have many physicists failed to get the memo from philosophers after all this time? Part of the problem is that physicists generally don't know much about philosophy.”
Nice to pick out pilot wave theory as a more than plausible alternative. I liked the hidden variables introduction, the double slit and bell experiments have numerous potential hidden variables which are so often just cast aside as an inconvenience. The strength of pilot wave is the wave part - everything moving creates a forward wave, the bow wave of a boat, the invisible pressure wave in front of a bullet etc etc. Pilot wave theory is saying that this front wave is independent of the particle and will spread out and pass through both slits and create a pattern of interference waves on the other side of the two slits. It is this wave pattern that is altering the direction of particles fired through the slits in rapid succession even if they are alternating between the slits. Most particles don’t pass through the slits remember, they hit the barrier either side of the slits and likely cause oscillating waves, another “hidden variable” made even more important when firing electrons at conductive materials like copper or gold, commonly used for the experiments, probably because insulators don’t produce the same results I’d imagine.
Almost. The pilot wave is not created by the particle as a bow wave, moving faster than the particle is moving to explore the experimental geometry. The physics of the very tiny is stranger than that!
Yeah! I've been looking forward to your take on this. I'm among those who believes that the relevant portion of Bohmian Mechanics has been discredited, but my expertise is not sufficient to be sure I'm right and I'm excited for you to let me know. I've been talking up your channel on other channels whose audience I think would appreciate you, like PBS Spacetime.
It's not a different theory, it's just a different interpretation. Entanglement, or superposition is a fundamental part of the universe and it's up to us to make sense of it.
I got to hear about the theory when it was really really uncool in 2011 When Brian Hiley who collaborated with David Bohm visited us from Birbeck University which was just over the road. I bought his book which was published just before bohm’s death in 1993 called the undivided universe & I’ve tried to understand it many a time without any success but the talk made a lot of sense! Brian believed he was on the verge of a breakthrough looking at the fourth degree stress energy and momentum tensor.. (Something like that) he was combining it with general relativity and was still full of vitality well into his 80s to find these answers!
Am I right in assuming that the titular pilot wave is in the field the particle is in - e.g. the photon is the peak of an excitation of the EM field and the pilot wave is 'the rest of' the excitation we don't see because it doesn't rise to the level we can measure? If so this presumably also explains the Elitzur-Vaidman bomb tester experiment, because the excitation is actually and (semi-)classically filling the whole array and we are only detecting the portion that rises to the level of 'one photon', the location of which will vary depending on the setup of the tester.
An important detail that everybody forget when they believe that a photon is a particle is that it still keep it's frequency/wavelength no matter how we imagine the model. That mean, if the photon is a point particle, it still radiate an energy at a distance equal to its wavelength. Another detail is that the matter used for the slit absorb photons everywhere except in the space where are the slits. Similar to iron exposed to magnetic force, an opaque object which absorb photons remain "magnetized" for some time. A normal magnet exercise a macroscopic force with iron when the magnetic domain are large enough. These magnet don't interact with visible light because of these domain are many order of magnitude too large. However, visible light photon can be deviated by two slits because of these self generated tiny magnetic domains. The photons follow the guide of magnetic loops which, by coincidence, look exactly like interference pattern from wave.
Great video. I believe that the non-local aspects of PWT can be explained best by considering other dimensions (than our traditional 3D universe - I don’t really consider time as an extra dimension as the units of xy&z are in units of spacetime anyway). You can think of this as some dimension (s) smaller than Planck’s Constant (which by definition is the smallest thing we can resolve as it is limited to the wavelength of light). Those dimensions could easily exist and we would have no other wave to measure them but it is quite possible that the non-local aspects in our dimensions are “local” there so it may be too early to say that PWT can’t be classical.
+Looking Glass Universe I have an idea for a test, I'm not sure about all the implications of the results and would like to see what you think. The basics of it would be a stacked double slit experiment, where the second test only gets electrons when the first part of the test results in an interference field. The first test would have no measurement happening to the particle except for where it lands when passing through both slits. The second test would measure the particle only as it passed through the second slit and where it lands. The expected results for the first set of tests would be to see interference evidence when landing after passing through each slit. The second test should result in interference for the first part and no interference for the second... or it could result in no interference at all.
Scientific method is based on rationality. Einstein reasoned that the laws of the universe should be the same for all observers and that was how he was able to discover relativity. For the laws of the universe to be the same for all observers then there can not be anything that is innately random. Therefore we can conclude that everything has a cause even if things can be so complex to appear random. This is why De Broglie Bohm Pilot Wave theory is on the right track. If we are to have a theory of everything it has to be deterministic.
I'm questioning Bohmian mechanics because of the quantum eraser. It would be too much to explain it in a youtube comment, but PBS Spacetime makes a great video on it
Thanks for putting this so well. I was trying to derive the fundamentals of QM when reading up about it. Turns out I was just finding my way to Bohmian mechanics. :) I hope something like consistent histories might help to fix relativity in Bohmian mechanics?
LGU: Great video. Loved it. On another note, there is one aspect of gravity that no one explains. I understand Einstein's theory about gravity being a warping of space-time. And it makes perfect sense that the moon is orbiting the earth because it thinks it is following a straight line, except it is following a straight line in a warped space-time. But what about a stationary object? Why does a weight on the end of a spring pull toward the earth? How can a warped space-time cause a stationary object to have a force on it? Where does the force come from? Some say the earth is accelerating towards the weight. If that were the case, then a weight on the opposite side of the earth would fly off the earth, not be pulled towards it. I would love to see a video which explains gravity for stationary objects. Full disclosure: I ran this by Science Asylum and he is showing some interest in this. But interests can change over time. No reason why you could not look at the problem also if it interests you. I'd love to see your perspective.
You should read "Quantum mechanics: Historical contingency and the Copenhagen interpretation" of Cushing. And Mara Beller's work about Quantum mechanic. She explains what were the strategies used to impose Copenhague Orthodoxy
Hi, im just getting started on qm and am a complete novice but i was hoping you could help with a conundrum. By assuming a particle has a definite speed and position, doesnt bohm contradict Heisenberg's uncertainty principle? Or am i understanding it incorrectly in thinking that Heisenberg said both cannot be MEASURED to high accuracy but the particle can possess well defined speed n position, and we are just restricted by our ability to measure? Thanks in advance for your reply. Cheers!
There are different states. A dust particle can be here and there and everywhere. Similarly, a dust particle can be standing still, or moving, or moving even faster, or moving in reverse even. These positions and velocities are called states. When we look at a dust particle, it's in one single state: it's exactly here and it moves at the very precise velocity. It is not both here and there, and it is not both still and moving. This is classical. But what if a dust particle was both here and there and over there too, and both standing still as well as moving? Then the dust particle would not be in a single state, it would be in many states at the same time. it would be in not just a single position: it would be in a superposition. Superposition actually means "a sum, an addition". But one can see it as a super-position as well :D So... is a dust particle here and there being still while moving? Yup. If you're not watching it, that is :D Once we turn our eyes towards it, the dust particle collapses to only one state: only one position and only one velocity. How does the collapsing into just one state happen? No one knows!!!!!!!!!!!!! It's the biggest mystery of quantum theory. However, it's not a mystery for de Broglie theory. However, there is the mystery in the pilot wave theory. It's: the pilot wave. What's the pilot wave? No one knows. But there is one thing quantum theory has that is extremely similar to the pilot wave: the quantum vacuum. So, the quantum vacuum could be the pilot wave. So, the pilot wave theory has one mystery less than the quantum theory. And it answers the question: how does the collapse into just one state happen? The collapse doesn't happen, because a particle was never in a superposition. A particle is always at one place with only one velocity. This is the beauty of it. Cheers :D
Anything we do to detect, determine or even deduce, however indirectly, which path the particle will take / is taking / took, causes it to take a classical path. It isn't enough that the particle is free to choose either path. Interference only happens when the setup is such that it is impossible, even in principle, to know which path it took. Something about "measurement," itself, no matter how tricky or indirect, destroys superposition. Google "quantum eraser" for more of a taste of just how puzzling this can be.
ramkrishan charan the observation cannot be passive. So when they say "observe" they don't mean simply looking at it. These systems are so small that they have to be interacted with to make any type of measurement.
Cosmic Atrophy, true it's like firing a canon with a hill that blocks your view and calculating the the speed and trajectory depending on from where the ball would land. At the same time the ball has 8 possible ways to exist in between and you'll never actually "see,verify" it with current technology. Fluiddynamics without the knowlegde of atoms from about 200 years ago is perhaps An example of this.
But if one considers the photon particles are moving in a HELICAL motion - it would depend on which part of each loop the particle happened to be as it reached the slits. Some would pass through one slit and others the other slit - but many would hit the surrounding wall. Once through the slits the particle can create the interference patterns.
I always thought in quantum mecanics a particle isn't even a particle but a wave, but when two waves interact, not interfer, they interact as if they were particles.
If every possible quantum mechanics result is also explained by Bohmian mechanics, does that mean no experiment can tell the difference, and, consequently, we'll never know which interpretation is correct?
I've always been very attracted to the pilot wave theory and love the fact that you quoted Bell supporting it. Some physicists have argued that pilot wave theory does not add anything to the picture because it only adds a philosophical dress to something (standard quantum mechanics) that does not need such a decoration. Personally, however, I find the philosophical dress, i.e., a deep understanding of what is going on, much more interesting than turning the crank on some quantum mechanics calculator. I do understand why some people are contend with having the math that delivers incredible results, but I find it supremely unsatisfying to be told "don't even try to understand, just turn the crank".
Some people like to roll around in bullshit. :-)
It upsets me how long it's taken me to be aware of your videos. Great work, truly. And thank you for taking the time out so lay folk like myself could learn what we were never taught in school... but really should've.
I've long felt that superpositions were just a way of pretending there are no hidden variables. Instead of admitting there will be things we don't know, throw in all possibilities, then cancel them out after the fact when we know what actually happened. It feels like a statistical trick like ideal gas law. Works fine so no prob, but one builds up from the details to get something practical and the other starts pragmatically and papers over details.
Its similar to how scientists couldnt explain the revolution of mercury around the Sun using newtonian math until einstein theory of relativity helped explain it. Quantum weirdness is most likely something we cant understand because it might be beyond the scope of scientific experimentation. We can only guess using mathematical formulas but never really know the truth.
I think your intuition is good. A probability distribution hides the real behavior that causes it.
You don’t need a concept of superposition to “pretend there are no hidden variables” you just have to look for them (or hell even describe what they are) and you come up empty. It’s not pretending something doesn’t exist by failing to mention it when there is no way to observe or talk about what it is in the first place
@@david203
Yes, but I want to understand the exact “real mechanism” that underlies the generation of that superficial “probability distribution” where that real mechanism is fully compatible with things like “Lorentz Invariance”. /s 🤔✌️
@@Mentaculus42 Your comment appears to have been cut off. If your question is that you want the Bohm interpretation to be explained in terms of intuition based on the usual Newtonian physics, that is impossible. The atomic scale of nature does not obey Newtonian physics, just quantum mechanics!
My favorite theory! I think it's totally logical that opening the second door leads to a different path. It's the same with a balloon on water, if you change the shape of the environment, the waves will spread out and then come back and affect the balloon differently. Opening one of the doors is changing the environment, so the waves behave differently than if it was closed.
Yes, that does seem reasonable!
Good intuition!
I find your voice super relaxing. Love the content too. It's like educational asmr to me.
The pilot wave theory just makes sense. If only we can explain quantum entanglement as easily. Just because we're unable to measure or see something does not mean what's happening is not following specific laws. It's just our inability to currently understand it. But that's what makes it so exciting.
So glad to see more videos from you! If this is as well done as all your other videos its going to be fantastic!
Thank you for your videos.
Aw, that is far too kind- thank you so much!
I appreciate that you pause to ask questions of the viewer in the middle of the video. I love to watch your videos while baked and it helps me make sure I'm actually learning the material rather than simply feeling mind-blown for its own sake :D
A few points are worth mentioning on this issue:
1. While some laypeople or beginning physicists complain about Bell's theorem (or even the Kochen-Specker theorem) in regards to Bohmian mechanics, most serious critics choose other lines of attack. For example, Chen and Kleinert have argued that the results of Bohmian mechanics do not agree with those of standard quantum mechanics even for the two slit experiment! (In other words, the picture at 6-24 does not agree with experiment). Neumaier has also pointed out observables made up of time correlations of, say, position operators, do not in general have the same expectation values in Bohmian mechanics as they do in standard quantum mechanics.
2. It is important to note that not even Bohmists try to argue that Bohmian mechanics is fully experimentally equivalent to standard quantum mechanics. The claimed equivalence, even if we ignore the criticisms above, rests on an assumption known as "quantum equilibrium". This assumption states that, in order for Bohmian mechanics to reproduce the Born-rule probabilities of quantum mechanics, the _initial state_ must be distributed in this way as well. This is a highly nontrivial assumption: there is nothing a priori that states that the particles in the beginning of the universe must be distributed according to the absolute-value squared of the wavefunction. Outside of quantum equilibrium Bohmian mechanics has pathological features; in particular, it allows transmission of faster than light signals, which is a problem for any relativistic extension of the theory. The relativistic version isn't just ugly: it simply can't exist!
3. Bohmian mechanics can only describe systems with a fixed number of particles. Processes where particles are created or absorbed, such as when a photon excites the atoms on a phosphorescent screen, are not allowed. The formalism simply isn't equipped to deal with such processes. Since all consistent relativistic theories must allow creation and destruction of particles (for causality preserving reasons), Bohmian mechanics is a dead end of theoretical development. It cannot describe anything happening in a particle accelerator, not just because it's not written in a relativistic form, but because by nature it cannot be relativistic.
4. It's important to note that the "oil droplet theory" and Bohmian mechanics are extremely different. The oil droplet model is really more analogous to a plate attached to a speaker. By playing a tone you can see grains of sand arrange themselves on a plate in a "standing wave" pattern. The difference is that in the oil droplet theory a single drop eventually traverses all of the available surface, and the wavy pattern is seen in the amount of time spent in each spot. Bohmian mechanics does not work like this at all: because the evolution equation for the particle depends on the imaginary part of the wavefunction, if you place the particle in an energy eigenstate (such as the ground state of a hydrogen atom), whose wavefunction is wholly real, it will just sit there. It won't do anything. It won't move at all! The "probability distribution" of particle positions in such a state is given entirely by the initial distribution, which I hope provides some "teeth" to point 2.
All in all, I don't think it's premature to discard Bohmian mechanics as a possible theory. Draw inspiration from it if you must, but ultimately, the theory has to agree with experiment... and we've been doing experiments that prove that nature is relativistic for a solid 100 years now.
Thank you for this very thoughtful and interesting comment! There's a lot of things I wanted to cover in this video but they got too complicated for me to understand fully, let alone teach. So I tried to leave it at a basic intro level and make clear that I'm not fully on board with this theory (actually, my favourite interpretation is Many Worlds).
1. Yes, this criticism about the double slit was something I wanted to cover in a video about decoherence. I hadn't hear Neumaier criticism though! Thanks :) I'll look into it.
2. I was very much taking the 'equilibrium' assumption. I'm not sure about what Bohmians think, but I had always thought that this was basically an axiom you should take for BM. It's one of the things I really find unsettling about BM: that the wavefunction has two roles. One representing the probability distribution, and the other deciding how the particle experiences 'force'.
3. Yup!
4. This is true but doesn't take away from the fact that a model like this can reproduce a lot of QM experiments. Pretty cool!
Anyway, thanks so much for your comments :)! I really enjoyed reading it. Cool that you know so much about BM.
Relativistic and particle creation/annihilation extensions of Bohmian Mechanics:
arxiv.org/pdf/1205.4102v2.pdf
arxiv.org/pdf/quant-ph/0208072.pdf
Looking Glass Universe Thanks for your very nice reply. I'll be sure to stick around so we can talk about many worlds if and when you decide to make a video about it (but I'll tell you in advance I favor Copenhagen, so expect nitpicks :) ).
2. What Bohmians seem to think is that you can prove the equilibrium assumption is satisfied. They seem to believe in something called a subquantum H-theorem (the H-theorem is a sort of generic name for several results that purport to demonstrate the second law of thermodynamics, with varying degrees of success). Their claim is that you can define a sort of "subquantum entropy" that is maximized at equilibrium, and then prove that this entropy always increases. I find that argument unconvincing because, well, the real entropy isn't sitting at its maximum currently, and we see lots of processes that occur far from equilibrium, such as yours truly.
" that the wavefunction has two roles. One representing the probability distribution, and the other deciding how the particle experiences 'force'. "
Yeah, that's a nice way of putting it.
"4. This is true but doesn't take away from the fact that a model like this can reproduce a lot of QM experiments. Pretty cool!"
Indeed it's a cool analogue model, and I appreciate that you made the distinction in your video. I really wanted to emphasize the distinction though, because (other!) people say "pilot wave theory" as if it were one monolithic thing, but in fact they can behave very differently.
Thanks again for your nice reply!
Fallen Star Features yeah, people try to come up with relativistic extensions of BM roughly every 5 years, but nothing truly compelling has ever appeared. Look at the example you posted, for example: they abandoned the determinism of Bohmian mechanics in favor of a theory where particles just have a probability to appear or disappear. That's a rather sharp departure from the philosophy of Bohmian mechanics, even if it's right -- and I'm not convinced that it is, for two reasons:
1. These sorts of classical theories in which things "pop" into and out of existence tend to be rather pathological and violate conservation laws. This is a problem with Ghirard-Rimini-Weber theory, another proposed classical model for quantum mechanics.
2. We already know that position observables are not good observables for all particles. For example, there is no position operator for photons because the Newton-Wigner approach fails whenever the little group is not a representation of the spin group. Photons have spin 1, so by all rights there should be three physical states corresponding to spin 1, 0 and -1, but as it turns out, the spin of massless particles can only have two possible states, 1 and -1 in the case of the photon. So the little group is not a representation of the spin group and there is no position operator.
Since there is no position operator, there is no wavefunction, and their approach fails for realistic systems.
It's hard to overstate just how successful the field point of view has been in fundamental physics. Any relativistic extension of Bohmian mechanics has to fight an uphill battle reproducing all those results that field theory yields naturally, and at the end of the day, because of its inherent nonlocality, will be forced into a sort of catch-22: either it's not really relativistic and requires a privileged frame that is "hidden" from us, or it is really relativistic and has trouble with causality because absent quantum equilibrium messages can be sent to the past.
Fallen Star Features You might be interested in this: physicsforums(dot)com/insights/stopped-worrying-learned-love-orthodox-quantum-mechanics/
That's a text written by Hrvoje Nikolic, the author of one of the papers you linked. Here he essentially admits that his attempts to find a relativistic generalization of Bohmian mechanics have failed. He now reconciles relativity with Bohmian mechanics by postulating that the world really isn't relativistic at its most fundamental scales, and that the apparent relativity is an emergent feature of this nonrelativistic system. This is possible, but there's no evidence for it. We have tested Lorentz invariance at extremely high energies (surprisingly, even above the Planck scale) and found no violations. This disfavors the model in favor of ordinary quantum mechanics.
"They collectively scratched their heads"
Why am I imagining monkey scientists sitting in a circle, picking each other ?
+. :D :D :D :D :D
You have an active imagination
So bummed I didn't draw this now.
+Looking Glass Universe :D :D :D
2:05 "they scratched their collective heads" lol
Bohemian mechanics.
Is this the real life? Is this just fantasy?
Caught in a landslide, no escape from reality
Open your eyes, look up to the skies and see
I see a little silhouetto of a man
Scaramouche, Scaramouche, will you do the Fandango
Thunderbolt and lightning, very, very fright'ning me
Bohemian Gravity
Easy come, easy go, will you let me go?
Bismillah! No, we will not let you go
(Let him go) Bismillah! We will not let you go
(Let him go) Bismillah! We will not let you go
(Let me go) Will not let you go
(Let me go) Will not let you go
(Let me go) Ah, no, no, no, no, no, no, no
(Oh mamma mia, mamma mia) Mama mia, let me go
Bohemian Uncertainty Principle
Nothing really matters, anyone can see
Nothing really matters
Nothing really matters to me
Any way the wind blows
HAHA! Thank you!
Did you smoke shrooms?
So... what does the wave function _actually_ represent in Pilot Wave Theory? I can't ever seem to find a good answer to this anywhere.
There is no good answer, in the same way this question isn't answered in other interpretations like many worlds. But it is the thing that causes the quantum force.
3 years later, a Science Asylum fan discovers this great channel! Feels wholesome and kinda funny. Best luck for you two!
I haven't seen a theory that puts it exactly this way, but what about some sort of fluctuations in a Dirac style aether? In his later conversations on the topic with Einstein they seem to have come to some sort of quantum mechanicalized alteration of the Lorentz aether that caused it to work well with general relativity as well. Fluctuations in a material like this could account for low level waves that push the particle, and it would have incredibly complex fluids dynamics because of its massless state.
In the undivided universe Bohm talks about active information. It's only the form of the wave which tells the particle what to do. The analogy he made is of a automatic pilot controlled by radiowaves
Background vibration of spacetime itself.
This channel is just awesome! I wish you can produce more great videos for physics enthusiasts like myself.
Thank you so much! I will try my best :)
Looking Glass Universe U r a genius..
Non-locality is explained with pilot wave. The pilot wave feels the effect of one particle and transmits that information to the other particle without the particles being local. The pilot wave spans all of existence. If you have 2 balls floating in a pool and one of the balls is pushed downwards such that it creates a ripple in the pool, that ripple will disturb/communicate with the other ball on the other side of the pool without the balls being near each other.
Yesss a video from LGU!! I learned so much from them, you are a great explainer of difficult stuff!
Thank you so much, I'm really glad you're back despite the fact that I upload so irregularly.
@@LookingGlassUniverse I do wish you would read my comments and let me know what you think.
@@david203you will never get a response because all of the LGU vids are total misinformation, just do a google search on any of these topics and you will discover this to be the case. I'm just waiting for the LGU vid that says dinosaur footprints can be found right beside human footprints!
I'm really glad you made a new video! Clearly there's a market for science explanations, clearly you have a niche people like, keep it up if you have the time!
Thank you very much- I will try :)
Really nice video! It is of fundamental importance to understand the difference between reality and how we interpret it!
The great thing about De Broglie Bohm Pilot Wave interpretation is that it accepts outside reality, agrees with
predictions of quantum formalism, and is not logically inconsistent (Copenhagen) and is not utter madness (many worlds)
Welcome back, we missed you.
Personally I'm glad that there are valid competing theories on how the universe works, because as soon as we "figure it out" we'll choose to stop learning.
Thank you so much :)
You're right- but luckily there is so so much we don't know that we'll need to keep learning for a long time yet!
Ehhh, not a big fan of the "science must have two sides" thing. It either fits reality or it doesn't. It's like when people pit evolution and creationism together -- it's not really a debate.
David Ralphsky
The problem with the 'evolution vs creationism' argument is that they aren't mutually exclusive. But the thing about 'Quantum vs Bohmian' is that they both have valid ideas about how the universe works and are exclusive. Only one can be right, but having multiple sides keeps us looking at the problem rather than just assuming that we understand it all.
A (new) video! Finally!
I know, I'm so sorry about the wait!
It's okay, I'm glad to see you've uploaded a new video :)
Me too. Although, I'm new to this channel.
no need to be sorry for these quality of videos I'd wait years between
(and de Broglie!)
my question is -- how is it that they came to the conclusion of superposition in the first place. it makes so much more sense that a guiding wave might be directing particles.
Detect those guiding waves then, interfere with them, predict how strong or far they are. Prove it!
The freaky thing about entanglement is that it doesn't care about Light Speed.
Perhaps it has to do with the double-slit experiment being accidental in the first place?
"Hey look at this. What the hell is going on? It almost seems like the particle is interfering with itself. That's odd man, like it seems like it's doing both at the same time."
"... What if it actually did that though?"
And then further experimentation only seemed to prove that idea.
(Perhaps because it is true)
LightSource Yes it doesn’t care about lightspeed but there is no additional information gained or transmitted once you collapse the wave function into that singular state.
It makes a lot of sense if you consider that it is impossible to put say a negative charge In the exact same place as another negative charge, They would just repel, something has got to give. And what “gives” When you force Two Electrons to be in the exact same place is that they have to occupy a new shared state (you have forced them to be one thing after all - When they are simply two things). When you do this they occupy a realm of existence where that particular property is undefined the property is called spin, And it’s an analog of angular momentum and clockwise and anticlockwise but off axis with an eccentricity each of them random, but each of them opposing. And this has nothing to do with gravity therefore space is a irrelevant.
Trying to apply the property of lightspeed to an electron spin is a meaningless statement to attempt to impose. Spin isn’t the same as angular momentum it is something entirely different it’s just the fourth quantum state. Along with quantum number which indicates energy. And the other two which you can look up. I think we should be teaching a periodic table that organises atoms into electronic spin states now because it is “more better” at grouping.
@Jon Do actually multiple universes and Copenaghen are two different interpretations.
Searched TH-cam and found this video immediately after watching Veritasium's video you mentioned. Both great videos!
Oh, I missed so much this almost-laugthing-cute voice that brings so much knowledge!
:) :)
Great fair video on QM and the merits & conundrums of Bohm-de Broglie theory. To resolve, it seems necessary to truly understand the "entanglement" theories.
11:22 "tradgectories"? Someone has clearly been to tired when editing that part of the video! :D
But hey! Great video! It reminds me to continue reading about mathematical physics in my free time.
Hahaha, I'm also dyslexic so I usually spell check everything I write- but I forgot to do this one clearly :P
Yay! I'm really happy to hear that :)
Wow, I am so excited about this video right now. It's so incredibly well put together, amazing work! Favorited instantly. You are truly one of a kind, such a clear thinker, not to mention beautiful. Now I just really have to study entanglement and pilot wave nonlocality. It's the only bit I am still confused about.
I really like the classical pilot wave theory that Derek from Veritassium showed in his video, and I really dislike the Copenhagen interpretation of quantum mechanics, but still I have a fundamental problem with QM pilot wave theory: if there really is a medium upon which there are waves that the particles interact with, shouldn't we be able to somehow detect and measure that? I guess my basic question is, what is this medium and via which forces do particles interact? I just think that Bohmian mechanics leaves more questions open than what it solves (not that Coppenhagen interpretation doesn't).
TravelerInTime The medium for PWT would be Spacetime itself. All fields are contained within Spacetime and contains Spacetime. Both GR and QFT treats Spacetime as a physical entity.
I dont think it implies its detectable, it implies ut is hidden and the observations we have already seen are evidence for it. Whatever "it" is.
A field? Informational?
I like something about the informational approach but its got so many flaws. Therein each particle contains knowledge of the process of the wave. The wave is just knowledge and doesnt necessarily have to exist.
Thats weird, but then so are nonlocal particles. In fact yes its nonlocal, near "omnipresent" information but if we observe that in other situations, then why not? At least then we may say there is "one less type" of quantum strangeness and take nonlocal information as an axiom of fundamental particle behaviour. Each electron contains some knowledge of all electrons and i thought that was well accepted so why not "contains information on how it should move based on surrounding particles"?
Of course, it may just be a hidden variable again...a hidden field...a hidden force...it doesnt say anything about what it is, only that it predicts well, but we dont need to know until we found it?!
The answer to that question depends upon what type of “Pilot Wave Theory” is being referred to. A reasonable place to start is “Pilot Wave Theory in the Twenty-First Century” which is freely available online in its entirety. That very topic is a focal point of what differentiates various types of “Pilot Wave Theories”. And generally that “something” is a foundational “thing”!
From “Pilot Wave Theory in the Twenty-First Century”:
“Pilot wave theory vindicates an ontological belief about the nature of quantum phenomena, wherein corpuscles and waves are two very real physical entities, coexisting and interacting at all times. The wave guides or pilots the quantum corpuscle, and in turn, the corpuscle reenforces the wave, acting as a moving oscillator. This physical picture of the quantum world is very different from that put forward by the Bohrian complementarity view, according to which the undulatory and corpuscular aspects always present themselves in a mutually exclusive way. Louis de Broglie ontology is also distinct from that put forward by David Bohm; specifically, Bohmian mechanics does not posit the physical existence of a particle-generated quantum wave: the pilot-wave is the wave function of standard quantum theory and only in de Broglie's ontology would it make sense to discuss the possibility of a quantum wave detection. Something that is addressed in this volume (Croca, ch. 17) and that has also been recently treated in another publication (Croca et al.)”
.
Great video! One critique: the bohmian particle is not "affected by all the other possible places it could be". That is simply wrong for pilot wave theory. The particle does not have any other "possible" places because its a deterministic theory. You're placing standard QM rhetoric where it doesn't belong. What the bohmian particle is affected by is not any "possibilities" but a concrete field that pushes it around in space. That field in QM is called the "wave function".
Sounds good, except that the wave function doesn't exist in standard quantum mechanics. It's a purely abstract, mathematical construct that can not be measured. Bohm didn't understand that and he mistook it for something real. The result is complete intellectual nonsense that nobody uses because it doesn't work.
I had to pinch myself to make sure i wasn't dreaming
Oh, me too...
One of the reasons I *LOVE* pilot wave theory is that it beautifully unites QM with the findings of chaos theory - another area where randomness and order are weirdly intertwined. The more we learn about complex systems, the more we understand how fields are a macroscopic description of quanta the same way that temperature is a macroscopic description of molecular motion. It's all layers of emergence. It explains why the gestalt of seemingly random individual events can be predicted statistically with a wave function - because the wave function describes a literal feature of spacetime. A literal ripple of spacetime quanta, much like a ripple in water is a macroscopic description of the motion of water molecules in response to a disturbance. It all makes sense in a very Einsteinian way: matter telling spacetime how to ripple, and spacetime telling matter how to move.
Also, nonlocality is just causality reflecting backward in time.
I'm a huge proponent of Bohmian mechanics.
Look into Unified Physics
@@jacobglassmeyer5961 Also Super Fluid Vacuum Theory. It seems to work very well with Pilot wave theory and Bohmian Mechanics.
This is different. I like it. Perfectly balanced on more than one dimension. Almost like a conversation rather than imperative. Thanks for sharing!
Oh thank you so much! Do you think it's different from my other videos or from other people's videos?
Looking Glass Universe other people's. This is the first video I see of yours. Looking forward to the next one!
Hey can you do a collab with 3Blue1Brown
FANTASTIC VIDEO! Thank you. It's good to bring these wild concepts back to reality a bit. What can we prove. We shouldn't assume things we can't actually directly measure or properly infer. The fact that measuring the particle will affect it is super important. It's like trying to measure a runners location by standing blindfolded in his path so you can tell when he goes by, of course you will affect his path!
Also, while we are theorizing...what about simulation theory? The program is playing out all possible paths (within its processing power for each plank frame that is being rendered), and then collapsing into the chosen outcome. Are we playing this game?, is it in control of the possibilities or are we? Dream on you dreamers ;)
For the question why a partical "gets shy": It makes perfect sense if you look at it from a design perspective. As a coder myself this is the kind of optimization i would do if i would design a simulation. I wouldnt calculate every interaction but only interactions that actualy matter (get measured). So you can see superposition and uncertainty as a optimization process which cuts out unnecessary calculations. Only if a measurement is taken the calculations are done and the final position is determined.
This is a very good thought- but I think I disagree.
I do quantum computing and in particular looking at why a classical computers can't simulate classical computers. And from that you see that superposition is actually incredibly hard to keep track of!
It's hard to keep track of from a classical stand point. I just wanted to point out the analogy. As classical logic is build on top of "weird" quantum behavior there is enough reason to consider the possibility that for the mechanism of the universe it could be easier to keep track of waves and do the actual mechanics backwards from the point of measurement to the previous point of measurement.
I agree because it gives the system flexibility to fix internal contradictions. Both keeping track of the precise positions of every particle in the universe and maintaining the consistency of that system when it is also chaotic and doing all of this in real time is a bafflingly difficult task. If, on the other hand, you have the flexibility to back-calculate and fudge your numbers a little bit, you don't have to keep track of every real position at all times and instead you can just calculate the outcome. With entanglement, it's even easier because one property covers more than one particle.
Thorium CatBit - Big problem:
You now have to keep track of the whole universe at all times - doesn't make any sense as a programmer to do that rather than having mostly local influences.
ABaumstumpf You dont have to keep track of everything. Thats why there is uncertainty. Because you dont keep track and just assume its everywere.
Thanks for the video. I love seeing the interpretations that challenge QM being represented so well, and in general I love your channel and found your videos very instructive.
I have noticed something when thinking hard about the interpretations of the double slit experiment, something that I can't shake off my head but that I haven't been able to find out if someone already talked about, or, if it doesn't make sense, why it doesn't.
The Copenhagen interpretation of QM says that the wavefunction is not a "real thing". That the fact that the particle goes through all the possible paths at the same time is something that only happens "virtually", and that until measurement occurs, there is no interaction.
This has always struck me as an incomplete explanation.
1. Given that the double slit experiment can be reproduced even with a device that sends one photon at a time, that means that the wavefunction of that photon needs to be aware of the slits to interfere with itself and change the likelihood of the photon hitting one particular spot. That awareness means that, on some level, the wavefunction and the particles on the barrier interact. Not only that: if we are proposing that the wavefunction's shape is influenced by the particles in the surroundings, and we are also saying that the wavefunction is a description of all the possible paths the particle could take, then it implies that, at some level, there is interaction between the wavefunction and the entire universe, only with weaker and weaker force in bigger distances. Does it makes sense so far?
2. If 1 is correct, then that means that even QM implies that the wavefunction has reality, and this "subliminal" (not-measurable) interactions exist. Again, if they wouldn't, the wavefunction would not be affected by the particles in space. It follows that the wavefunction could potentially be interacting with other wavefunctions that are also happening in the same space, since those also have reality. Why wouldn't it? If we know some "invisible aspects" of the photon are affected by the shape of the surrounding objects, both in QM and Bohmian M, then what is stopping us from thinking that invisible aspects of other particles are also interacting with the wavefunction?
3. If 2 makes sense, and the wavefunctions can potentially interact, wouldn't that interaction be a potential source of hidden variables that explain the apparent randomness? Isn't it reasonable to think that the same aspects of the photon that we can't see directly but that are clearly affected by the shape of the slits are also interacting with other things that we can't see, because their energy levels are not enough to be measured directly?
4. And finally: isn't it possible that a measurement just happens to be the point where a continuous wave surpasses a certain threshold that makes it change the state of the other particles in a degree that we can actually measure? Isn't it possible that there is no such thing as an individual photon, but rather what we called a "photon" being emitted is the electromagnetic field being perturbed to the point that we can measure it? Do we need to assume that the electromagnetic field is, when we are not emitting a photon, at rest? What if the electromagnetic (and other quantum fields) are more like an ocean which always have waves, and a photon is more like a tsunami? The waves would affect the tsunami in a way that would seem random to us, and ripples of the tsunami that we can't measure would affect other tsunamis in ways that would, again, seem random to us. Could the apparent randomness of QM be a side effect of such ripples coming from everywhere, a kind of "white noise" of the field?
This to me seems to be neither Bohmian Mechanics (which if I understand correctly, postulates that the particle is being driven by a wave, but really exists as something being carried by the wave, and not just as an artifact of measurement) and certainly different than QM, since QM (at least Copenhagen) dismisses the physical reality of the wavefunction. Is there a theory around Quantum Mechanics that approaches it in this way? It seems to be hidden variables approach, but I don't know which one.
Thanks a lot for reading :)
Thanks for articulating your thoughts! Even I, an undergrad understand your point. 😃
What are tradgetories?
A tradgetory is the path a pottycle must take.
love, love, love this. Understood double split when I was younger but always curious... "spooky" maybe not as it turns out... this gives glimpses of a possible new understanding for me. Thanks.
now im left wanting to know why relativity isn't solved with this model
Mahasiddhic Sceptic the Pronoid Vegan Because QM doesn't work with special relativity. In this case the "wave" giving the Quantum force transmits information faster than light. This gets you into trouble because simultaneous events in one frame are not in another, so you could do things like: entangling two particle, separating them, changing the quantum state of the wave function and making a sort of code language and sending todays lottery ticket numbers to the other experimenter, but then in some other reference frame the event of receiving the message will actually happen before you send the signal!
Adolfo Holguin But QM can be relativized with Quantum Field Theory, which is the single most accurate theory of all time. My limited understanding of the subject is that to relativize Bohmian mechanics, which Bell did, you have to give up the determinism that was at the heart of the motivation behind the theory. I'm hoping she makes a video on that, as I really don't understand that and I'm not totally sure I'm right about it.
Adolfo Holguin You're a bit off. QM is perfectly consistent with relativity (special relativity, at least). Entanglement doesn't break the rules of relativity - it doesn't permit any signals to be transmitted faster than light, only correlations between measurements which can't be directly observed.
Bohmian mechanics' problem with relativity stems from the fact that BM posits a single universal wave function whose shape is determined by the instantaneous positions and momenta of all the particles within the universe. I.e., it requires an absolute reference frame where one can definitively state the relative distances and speeds of every particle in the universe at a given moment. Special relativity doesn't allow that - like, it REALLY doesn't allow that. Not that it's necessarily impossible to marry BM and relativity - but it would probably make the theory even weirder and more needlessly complex than it already is.
Copydot Old Fashioned QM is NOT Lorentz covariant (It treats time and space on different footings). What I wanted to say was that QM breaks causality (the wave function will be non zero outside your light cone so you can design experiments to send information back and forward in time depending on the frame of reference). And you seem to misunderstand Special Relativity. It doesn't state that the universe doesn't have an absolute frame of reference, but rather that physics is the same in all frames (physics doesn't prefer a frame, but the universe might!) In fact there is a very special frame of reference, the CMB rest frame (where the CMB looks uniform) which can be thought as the rest frame of universe. The problem with Pilot Wave theory is that it pretty much requires you to throw away Lorentz covariance and build a theory where physics is different in different places.
+Adolfo Holguin Dude I never thought of it that way. But I think it can still be reasoned via the uncertainty principle. I mean, the particle is still bound by its light cone but since you can't really know where the particle is, you can't know where the light cone is either. And thus the light cone too is spread out throughout the universe. That doesn't necessarily imply the probability of finding the particle outside the light cone is nonzero. Just a thought.
Glad to see you continue, and happy to see you do something on brogly/bohm ! +1 for a vid on decoherence !
Ahaha thank you! It has been a while since a bohmian mech video! Thank you, I'll get onto the decoherence video soon :)
If Bohemian mechanics is true, doesn't this say some fundamentally different things about our universe? Things like atomic randomness wouldn't be a thing. I also don't think quantum computing would work like they want it to. It would mean that the world is not inherently probabilistic?
I am no exepert but i think the uncertainty princeple still works in this theory so particals do have a position but we cant know exectly where they are soo there is still randomnos kinda
Pilot wave theory is deterministic, meaning there are no probabilities involved. If you know the current state you know all future states. However, since we are physically limited to never know the current state of the universe, we can only use approximations and assign probabilities to events - meaning experimentally we can't do any better than conventional quantum mechanics.
(as i understand it) quantum computing works by setting up quantum circuits in a way that causes the wave form to cancel out any wrong answers and output only the answer to the desired query. and pilot wave still has the wave form. so i think it would still work
Check out the "heligone" channel / user on TH-cam... He has some amazing walking droplet experiments that mimic radioactive decay and quantum tunneling... in vibrating silicon anyway :)
Halberdier I think having weird rules is mor intuitive than having weird particles. A knight in a game of chess moves unintuitive but it appears more natural transforming it into a wave or multyplying. Well, that's how I feel anyway.
I had recommended Veritasiums video to Looking Glass universe
And now it's mentioned,
What an amazing feeling.
While PWT is 'weird' due to non locality and the 'hidden' variable of the theory, it is 'weird' in an entirely different manner than the Copenhagen Interpretation (QM). The Copenhagen Interpretation is 'weird' because it is illogical (Ontological Probability is a logically incoherent and untenable notion) and contradicts everything we know about nature through Science, which tells us that everything that happens has causes and is causally determined. PWT is only 'weird' because people are unfamiliar with it. It ISN'T weird insofar as it is illogical nor is it weird as in it contradicts causal determinism. PWT actually explains the weirdness it proposes. The Copenhagen Interpretation doesn't explain the weirdness it proposes. These are SIGNIFICANT differences between the 'weirdness' of both interpretations. I know which of the two I am a proponent of..the one that is logically coherent.
(Keep in mind PWT is an actual and full fleged Scientific Theory, while the Copengagen Interpretation can't even be considered a proper Scientific Hypothesis, because it doesn't explain what it proposes.)
Looking Glass Universe
thatchinaboi Copenhagen is fine. It doesn't rely on any incoherent ontology. It posits epistemic propositions about observables, not ontic ones.
I beg to differ. The Shrodinger's Cat Thought Experiment clearly shows the ABSURDITY of the notion of ontological probability that underpins the Copenhagen Interpretation.
+thatchinaboi I thought PWT couldn't explain the delayed choice quantum eraser and that is why it was discarded.
All the reasons for why some scientists rejected PWT have been proven to be misunderstandings.
You're mostly correct, except that something doesn't have to explain what it proposes to be a proper scientific hypothesis, but it does have to be falsifiable... if your hypothesis asserts "there can exist no reason for a coin flip to land heads rather than tales or tales rather than heads, it is random" then the whole theory is falsified upon demonstration that actually, explanations that are perfectly consistent with our really existing universe are really existing... which, duh, as if people could really believe "if the universe doesn't tell me, it must be because it doesn't know".
Lovely Looking Glass Universe thank you for all the great content on quantum mechanics! I am sure you have your reasons on why pause on making more of these amazing videos but if I may ask: a video on decoherence would be most appreciated :)
Bohmian is the way to go!
Ahaha!
Looking Glass Universe : Thanks for introducing me to pilot wave... before it was cool 😊
You're very welcome ;)
Perfect timing, I'm just about caught up on my rewatch of LGU. Love the videos, keep making great content!
Oh thank you so much! Wow, you want to watch my videos more than once..
Absolutely. Re-watching them helps me understand the concepts better, too, since I've never studied physics at the university level... I just find it fascinating.
This video was incredibly easy to understand!! I really love your videos although i tend to scratch my head a fair bit, and i agree with you saying that bohmian mechanics made it look like superposition isnt the only interpretation, i grew to really dislike superposition
I really really appreciate that you found this easier to understand- I really tried!
Thank you!
Hadn't heard about Pilot wave theory before, I thought that quantum theory is the only widely accepted theory for the particles. Thanks for introducing it. Well explained and very interesting. I loved it :)
Came here from watching a documentary on David bohm. Good stuff! You explained it so clearly.
Great video and I'm glad this interpretation is alive and coming into mainstream.
P.S. Veritasium did a great video on this interpretation a few months back, too!
Do you mean the video that she mentions at 9:35?
Yeah, and PBS spacetime did one as well- very exciting that people care suddenly!
You have brought me into the joy of wonderment.!!!
Great video! Very logical and clear to understand - just like a Pilot Wave Theory ;)
I find just once small detail missing - the actual pilot-wave wasn't shown in the diagrams like at 3:59.
For newcomers to quantum mechanics (and wave theories) it can help clarify the main concept.
The Pilot Wave is imaginary. What is real is the deterministic paths of particles from source through one slit to the screen. These paths are based on the Schrödinger equation plus the initial positions of each particle.
I've missed these videos. Welcome back.
Thank you so much. I've genuinely really missed it too.
Wow! Just the other day I was wondering if you had stopped creating videos! Nice!
Haha! No, I've just spent 3 months thinking about the next one!
(No, real life just got a bit hectic- sorry about that!)
Just finished the video, it's awesome! One question though, if they both produce the same results in all possible experiments, will we ever know if either of these is correct? Is either of these correct at all?
Don't be sorry. It's not your fault. But thanks for another interesting video! You really inspire me to think more critically about Physics in general.
+Quim Last Hi. No theory is ever correct. Every theory is just that: a theory. The schooling process gives illusion we know exactly. We don't. There is no such thing as the exact knowledge. There are just interpretations. Interpretations, also known as theories. There's actually one extremely important theorem in mathematics, called Goedel's theorem. There are two of them, actually. In rather vague words, it says that every theory is incomplete or inconsistent. There's a problem that cannot be solved within any given theory, or there's a problem that has two solutions, such as "yes" and "no". There are Nobel prizes being awarded for theories that were vastly expanded just a year after awards being given out. There is no exact theory. Oh, by the way, the Goedel theorems come from -- logic. The Goedel statements are larger than mathematics. They concern logic. Stop using logic, it's incomplete or inconsistent :D Cheers :D
I know that theories can't be correct, when I said "correct" I meant, better models of reality.
I love this so much. Science storytelling through the roof.
Really nice presentation.
QM is a very interesting field PRECISELY because there are numerous possibles interpretations for what is observed during experiments. The more experiments conducted, the more interpretations/theories spring out.
The quantum world isn't weird we just have to accept it. its our inability to comprehend it that makes us call it strange and weird
YES! We are too limited by our commonsense physics, which does not apply in other regimes.
"Let's close one door and see which way it will go now...” Theoretical physicists must have access to some really good shit.
Dual slit experiment possible explanation:
Via QED, basically anything shot out of the gun would have it's magnetic field interact with the magnetic fields especially of the electrons in the atoms and molecules of the gun itself, the medium the projectile is traveling though, and/or from around the slits themselves. Any newly generated photons would possibly set up hills and valleys of energy. In the case of protons or electrons being shot out of the gun, the newly generated EMR wave would travel faster than the projectile of which the projectile would then follow whatever valley it entered. Even shooting only one electron or proton at a time would still possibly have the interference pattern show up.
Finally, got to see valuable videos again...and hope to see more often as well... 😊😋
Thank you very much! Sorry, I will try my best.
Brilliant, balanced analysis, even if you didn't approach explaining Bohm's pilot waves per se and how it attempts to mechanistically a count for delocalization. Next video? Still, I still get stuck on whether mathematical solutions (like Bohm's) need intrinsically to reflect basic processes. I see Schroedinger wave formulation as descriptive, and yielding beautiful results (in computationally tractable contexts) BUT dancing around the fact the computed probability densities are only descriptive and predictive. "Piss off, Bohr", my prejudices scream, and I thank you for taking a shot into this philosophical mine field!
One particle surrounded by a wave. The wave goes through both slits first and creates its pattern of interference which the particle follows at random. The device they used to see through which slit the particle went through actually disrupted the wave and its interference pattern, the particle then made a normal 2 slits pattern.
yay another vid!! Good luck on your studies
Thank you so much! I really need it- I've skipped like a week of work to do this.
In the diagram at 5:00, suppose the particle is an electron. From Gauss's Law and Ampere's Law, we can model the moving electron as a moving spherically radial electric field with an associated disk-shaped magnetic field. When both doors are open, the center of the Gaussian Sphere might pass through one door, but a portion of the associated magnetic field passes through the adjacent open door. This unbalances the geometric symmetries of the electric and magnetic fields of the moving electron. According to Maxwell's Equations, this sideways imbalance in the magnetic field causes the resultant trajectory to veer to one side. This is how the E-M fields of one electron interferes with itself. The electric permittivity and magnetic permeability of the material forming the double slit barrier depart from their values in free space.
Here is another way to think about it.
Suppose you shoot an electron through the hole of a donut. Let the donut be made out of a material with a magnetic permeability larger than that of free space. As the moving electron approaches the hole, the magnetic field inside the donut builds up, and this changing magnetic field creates a back EMF that slows down the electron. To the extent that the magnetic field collapses after the moving electron passes through the donut hole, the collapsing magnetic field will then accelerate the moving electron.
Now comes the fun part. Instead of a complete donut, take a bite out of one side, so that the donut is now more like the capital letter 'C'. As the electron passes through the center of the semi-donut, the forces that created the back EMF that previously slowed down the electron are now circularly asymmetric. The electron won't just slow down on approach and speed up after, it will also be deflected sideways.
Opening and closing the door in the double slit is like using a full donut vs one with a bite taken out.
Has anyone tested this effect experimentally, replacing the double slit with a donut with a bite taken out of it, to demonstrate how Maxwell's Equations predict the sideways deflection?
Beautifully made! I am a huge fan of bohmian mechanics, his book "Quantum theory" is must read !
A great video. To further clarify - both the Copenhagen interpretation and the pilot wave theory both have unappealing aspects as theories in physical science.
In the Copenhagen interpretation, the idea of collapsing wave function has much to do with modeling probabilistic phenomena (i.e., a trial, experiment such as a coin toss). Once an experiment is over, there is no longer a probability distribution. This view introduces a subtle bias - a subjective perspective (that of an observer performing the experiment), and thus leads to the unsettling prospect of "consciousness" or the question of "who is observing."
The Pilot wave theory is clearly a version of QM that works. By (1) interpreting the probability distributions of the particles as results of their initial conditions; and (2) with the idea that measuring a minute system disturbs the system, the Pilot wave theory does away with the "collapsing of the wave function," or the measurement problem.
But to me, the Pilot Wave theory is a bit annoying. The probability distributions of particles, although reflecting the initial conditions and the pilot waves, are still probabilities that indicate the presence or the absence of each particles. This comes across as a feature that does not stem from some fundamental-ness of the theory but from its attempt to deal specifically with the measurement problem. It smells of contrivance.
If we only look at the "standing wave" solutions, knowing which slit a "particle" goes through becomes equivalent to imposing a boundary condition: That is knowing that a particle goes through slit A is equivalent to closing slit B. Standing wave solutions may also address entanglement and "quantum eraser."
I think both are wrong, like when Galileu started looking at planets like Saturno and it's moons with telescope he thought the moons were moving in harmonical moviments because of his perspective and ALL the formulas of harmonical moviments(HM) could predict what he observed, same way that quantum mecanics works, but then we realise that what was happening wasn't an HM( lateral perspective) but a circular moviment of the moon.What I'm saying is that even quantum mecanics works, it's explanations could be wrong because of the way we're looking at it.( I love your videos....keep making them)
Great vid 👏 highlighting some misunderstandings about Pilot Wave Þeory (PWÞ)! PWÞ is not a mere interpretation of QM; it's a framework ðat can explain a broader range of phenomena. If and only if particles are distributed according to ðe Born Rule (quantum equilibrium) does PWÞ foretell ðe same results as QM. However, wið quantum unequilibrium, a range of awesome phenomena becomes possible, like sending a signal in an eyeblink and violating ðe Uncertainty Principle. Doesn't ðat cause time paradoxes? No, because in PWÞ, Lorentz invariance is an illusion and holds only macroscopically due to quantum equilibrium. If we find matter in quantum unequilibrium or a way to make it, we can refute QM while keeping PWÞ... and do a lot of awesome stuff, as Antony Valentini talks about in Subquantum Information and Computation. So, PWÞ is 1. *testable against QM* and 2. *offers mind-boggling practical applications* to boot. What more can we ask for?
Bohm doesn't do anything to explain the measurement process. Copenhagen does. ;-)
@@lepidoptera9337 Please elaborate, for when last I looked, it was ðe oðer way round. 😉
@@TristanLaguz You didn't look carefully enough. In Copenhagen the measurement process is a trivial irreversible energy transfer and the Born rule links the absorption spectrum of the measurement device directly to the possible measurement outcomes. You have nothing of this sort in Bohm. What you do have is an unphysical ghost field that nobody has ever seen, a hard ball that nobody has ever seen, either and a complicated non-linear differential equation that returns absolutely nothing new in comparison to the old linear one. Bohm is total bullshit. ;-)
@lepidoptera9337 In Copenhagen, ðe term "measurement" is not defined. In Copenhagen, ðere are no particles and waves. Raðer, waves and particles are taken to be mere ways of talking about measurement outcomes ... which concept is, as said, not defined. But on ðe oðer hand, ðe very measuring appatatus itself and ðe physicist's brain are made up of ðe very quantum objects ðat are supposed to be mere figures of speech. What a wagonload of circular and illogical literal nonsense 😂! (Yes, not wrong, but nonsense, just like "dgtwp jkjdhhd ddcn".) I quote from ðe Wikipedia article on ðe Measurement Problem in ðe part about Copenhagen: "Exactly how to understand this process remains a topic of dispute."
Beautiful Bohmian Mechanics, by contrast, has no MP. I quote from ðe Wiki article on BM: "The theory does not have a "measurement problem", due to the fact that the particles have a definite configuration at all times. The Born rule in de Broglie-Bohm theory is not a basic law."
In BM, particles interact wið each oðer þrough ðe wave function. Because our 🧠 are made up of particles, which always have definite positions, we observe definite outcomes in experiments. Oh, right, measurements: What are ðey in BM? Plain old physical processes obeying ðe laws of ðe þeory like any oðers.
In short, BM is a well-defined, self-consistent þeory in which we know exactly what we're talking about: particles in well-defined states interacting wið each oðer þrough a field in an equally well-defined state. And most importantly, it foretells precisely what we see. We infer ðe existence of ψ from ðe way particles which we behold directly behave.
By contrast, what is Copenhagen even about? What kinds of entities does it posit? What is measurement in Copenhagen?
Unlikely BM, Copenhagen is clearly BS. And by extension, any claim ðat Copenhagen explain ðe MP and BM be wrong or nonsense is itself BS. 😉
@@TristanLaguz Yes, that was bullshit, just like Bohm. ;-)
Thanks for the new video! I love your stuff.
Thank you very much!
I'm commeting it here because it's your latest video:
I have very troublesome doubts about the quantum eraser, which you covered in previous videos:
Take the nomenclature you used, M1 and M2 as measuring devices:
1) What would happen if you place M1 far enough away so that you can first know whether you are having an interference pattern or not? If you saw the interference, then you could turn the device on and know which slit the photons went through, and you have already seen the interference pattern so it's very unlikely that it magically changes itself into two clumps. If you don't see the interference pattern, you could keep your device off, and that would mean that the mere threat of measurement collapsed the state. Either way, it's very unsettling, so I'd like to know the experimental results.
2) Is this not allowing faster-than-light communication? The observer of the double-slit experiment can know whether M1 is turned on or off, because we get interference if it's off and two clumps if it's on. That would in theory allow to send messages faster than light.
If anyone know the answer to these two, I'd be very glad, I've been trying to wrap my mind about it for too much.
This is a good beg/intermediate explanation. Good job
Thank you very much :)
What happens when the slits are moved further apart?
What if it was a matter that each electron created a field of probability with a given radius which when the slits are smaller than the given radius you get an interference pattern but when the slits are moved further apart, larger than than the radius of probability, the interference pattern doesn't develop?
Yes you're right. If it's far apart, in QM you'd say that the particle goes through both but the weight of the second one is much less. In BM you'd say the particle is less effected by the other slit now.
Why doesn't edge diffraction explain the behavior?
The detectors would have an energy field that is one way when on and a different way when off. The interaction of this energy field, or lack thereof, with whatever is passing through it would possibly give the indication observed.
In the double slit experiment you get the interference pattern, I understand how the pilot wave theory can explain the resulting pattern. But when doing the double slit experiment and using a sensor to observe which slit the particle passes through, the interference pattern disappears (and there's the more complex quantum entanglement experiments) . How does observing which slit the particle passes through, eliminate the pilot wave / particle interaction in Bohmian mechanics? How would Bohmian mechanics explain the results we see when sending through quantum entangled pairs and using quantum erasers to observe the results?
Very good video! You made it all clear and you are good at explaining things!
It's always a pleasure to see a new video from you. I hope everything is well with you.
Regarding Bohmian mechanics, or whatever you want to call it, I'm afraid that I still just don's see the point. Sure, QM is weird, but so what? Why would one expect humans to intuitively understand things on such a small scale that we could not detect them until recently (meaning that evolution could not have given our brains such intuition)? Why would one expect things on that scale to be just like things on human scales?
I also think that BM raises its own questions. What exactly is waving in the pilot wave? How does it interact with the "real" particles it is piloting?
I have a counter to your question: why would we *not* expect things on a small scale to behave (roughly) like they do on bigger scales? In particular, why would we *not* expect things to be in 1 place at 1 time, and *not* expect that every effect has a cause?
Partly because in the real world we can easily see things that are different at different scales, even when those scales are close to human scale. For example, have you ever seen a movie that used model ships? You can easily tell that they are models, because water behaves differently at different scales. Fractals would not be as surprising as they are if scale invariance were common.
More generally, though, your questions get things backwards. We should not make assumptions about how things are without evidence. The default position should be neutral with regard to scale. We should not assume that things are the same on every scale, nor should we assume that things are different. We should not assume at all.
Hey Michael, good to hear from you!
I have to agree with Ahsim on this one though, why would you presuppose weirdness? Also, as I tried to explain in this video, I don't support one theory or the other. I just want people to understand that both theories work and have the same experimental evidence. I don't see why then people choose to believe QM (rather than accepting either could be true) while making it sound like the other people are the dogmatic ones.
@@LookingGlassUniverse This would be more due to Philosophical issues concerning Science than ofc rather than Science issues. As Adam Becker points out in his book "What is Real?" “And Philosophers of Physics today almost unanimously reject the Copenhagen Interpretation (Logical Empiricism of a sort has made a comeback since 1980, but scientific realism is still the standard position among philosophers of physics - and even the most staunch defenders of empiricism today agree that the sort of positivism deployed in standard defenses of Copenhagen doesn't work). How have many physicists failed to get the memo from philosophers after all this time? Part of the problem is that physicists generally don't know much about philosophy.”
Nice to pick out pilot wave theory as a more than plausible alternative. I liked the hidden variables introduction, the double slit and bell experiments have numerous potential hidden variables which are so often just cast aside as an inconvenience. The strength of pilot wave is the wave part - everything moving creates a forward wave, the bow wave of a boat, the invisible pressure wave in front of a bullet etc etc. Pilot wave theory is saying that this front wave is independent of the particle and will spread out and pass through both slits and create a pattern of interference waves on the other side of the two slits. It is this wave pattern that is altering the direction of particles fired through the slits in rapid succession even if they are alternating between the slits. Most particles don’t pass through the slits remember, they hit the barrier either side of the slits and likely cause oscillating waves, another “hidden variable” made even more important when firing electrons at conductive materials like copper or gold, commonly used for the experiments, probably because insulators don’t produce the same results I’d imagine.
Almost. The pilot wave is not created by the particle as a bow wave, moving faster than the particle is moving to explore the experimental geometry. The physics of the very tiny is stranger than that!
Yeah! I've been looking forward to your take on this. I'm among those who believes that the relevant portion of Bohmian Mechanics has been discredited, but my expertise is not sufficient to be sure I'm right and I'm excited for you to let me know.
I've been talking up your channel on other channels whose audience I think would appreciate you, like PBS Spacetime.
Oh thank you so much :) :) I really appreciate that. I'm glad you liked the topic of this video!
One experiment differed with the Bohmian prediction, but it was done incorrectly. Two other experiments have confirmed the quantum potential.
It's not a different theory, it's just a different interpretation. Entanglement, or superposition is a fundamental part of the universe and it's up to us to make sense of it.
what i believe is important to expand upon is how exactly a conscious observer affects the physical state in the pilot wave model.
I got to hear about the theory when it was really really uncool in 2011 When Brian Hiley who collaborated with David Bohm visited us from Birbeck University which was just over the road. I bought his book which was published just before bohm’s death in 1993 called the undivided universe & I’ve tried to understand it many a time without any success but the talk made a lot of sense! Brian believed he was on the verge of a breakthrough looking at the fourth degree stress energy and momentum tensor.. (Something like that) he was combining it with general relativity and was still full of vitality well into his 80s to find these answers!
Am I right in assuming that the titular pilot wave is in the field the particle is in - e.g. the photon is the peak of an excitation of the EM field and the pilot wave is 'the rest of' the excitation we don't see because it doesn't rise to the level we can measure? If so this presumably also explains the Elitzur-Vaidman bomb tester experiment, because the excitation is actually and (semi-)classically filling the whole array and we are only detecting the portion that rises to the level of 'one photon', the location of which will vary depending on the setup of the tester.
An important detail that everybody forget when they believe that a photon is a particle is that it still keep it's frequency/wavelength no matter how we imagine the model. That mean, if the photon is a point particle, it still radiate an energy at a distance equal to its wavelength.
Another detail is that the matter used for the slit absorb photons everywhere except in the space where are the slits. Similar to iron exposed to magnetic force, an opaque object which absorb photons remain "magnetized" for some time. A normal magnet exercise a macroscopic force with iron when the magnetic domain are large enough. These magnet don't interact with visible light because of these domain are many order of magnitude too large.
However, visible light photon can be deviated by two slits because of these self generated tiny magnetic domains. The photons follow the guide of magnetic loops which, by coincidence, look exactly like interference pattern from wave.
Great video. I believe that the non-local aspects of PWT can be explained best by considering other dimensions (than our traditional 3D universe - I don’t really consider time as an extra dimension as the units of xy&z are in units of spacetime anyway). You can think of this as some dimension (s) smaller than Planck’s Constant (which by definition is the smallest thing we can resolve as it is limited to the wavelength of light). Those dimensions could easily exist and we would have no other wave to measure them but it is quite possible that the non-local aspects in our dimensions are “local” there so it may be too early to say that PWT can’t be classical.
Their have been a few experiments in the last few years that have been promising for Bohmian mechanics in the last few years.
Think not in terms of "single particles" being sourced, but single detections amidst noise being sinked. We're confusing detections with particles.
+Looking Glass Universe
I have an idea for a test, I'm not sure about all the implications of the results and would like to see what you think.
The basics of it would be a stacked double slit experiment, where the second test only gets electrons when the first part of the test results in an interference field. The first test would have no measurement happening to the particle except for where it lands when passing through both slits. The second test would measure the particle only as it passed through the second slit and where it lands. The expected results for the first set of tests would be to see interference evidence when landing after passing through each slit. The second test should result in interference for the first part and no interference for the second... or it could result in no interference at all.
Scientific method is based on rationality. Einstein reasoned that the laws of the universe should be the same for all observers and that was how he was able to discover relativity. For the laws of the universe to be the same for all observers then there can not be anything that is innately random. Therefore we can conclude that everything has a cause even if things can be so complex to appear random. This is why De Broglie Bohm Pilot Wave theory is on the right track. If we are to have a theory of everything it has to be deterministic.
I'm questioning Bohmian mechanics because of the quantum eraser. It would be too much to explain it in a youtube comment, but PBS Spacetime makes a great video on it
Needs an in-depth examination by a Bohmian expert.
Thanks for putting this so well. I was trying to derive the fundamentals of QM when reading up about it. Turns out I was just finding my way to Bohmian mechanics. :)
I hope something like consistent histories might help to fix relativity in Bohmian mechanics?
LGU: Great video. Loved it. On another note, there is one aspect of gravity that no one explains. I understand Einstein's theory about gravity being a warping of space-time. And it makes perfect sense that the moon is orbiting the earth because it thinks it is following a straight line, except it is following a straight line in a warped space-time. But what about a stationary object? Why does a weight on the end of a spring pull toward the earth? How can a warped space-time cause a stationary object to have a force on it? Where does the force come from? Some say the earth is accelerating towards the weight. If that were the case, then a weight on the opposite side of the earth would fly off the earth, not be pulled towards it. I would love to see a video which explains gravity for stationary objects. Full disclosure: I ran this by Science Asylum and he is showing some interest in this. But interests can change over time. No reason why you could not look at the problem also if it interests you. I'd love to see your perspective.
Nick would do a great video of this I'm sure! I'm not good at GR stuff. It's an excellent question though!
You should read "Quantum mechanics: Historical contingency and the Copenhagen interpretation" of Cushing. And Mara Beller's work about Quantum mechanic. She explains what were the strategies used to impose Copenhague Orthodoxy
Hi, im just getting started on qm and am a complete novice but i was hoping you could help with a conundrum. By assuming a particle has a definite speed and position, doesnt bohm contradict Heisenberg's uncertainty principle? Or am i understanding it incorrectly in thinking that Heisenberg said both cannot be MEASURED to high accuracy but the particle can possess well defined speed n position, and we are just restricted by our ability to measure? Thanks in advance for your reply. Cheers!
Can someone explain and define what do we mean when we're saying " superposition happens when we're not observing it"?
There are different states. A dust particle can be here and there and everywhere. Similarly, a dust particle can be standing still, or moving, or moving even faster, or moving in reverse even. These positions and velocities are called states. When we look at a dust particle, it's in one single state: it's exactly here and it moves at the very precise velocity. It is not both here and there, and it is not both still and moving. This is classical. But what if a dust particle was both here and there and over there too, and both standing still as well as moving? Then the dust particle would not be in a single state, it would be in many states at the same time. it would be in not just a single position: it would be in a superposition. Superposition actually means "a sum, an addition". But one can see it as a super-position as well :D So... is a dust particle here and there being still while moving? Yup. If you're not watching it, that is :D Once we turn our eyes towards it, the dust particle collapses to only one state: only one position and only one velocity. How does the collapsing into just one state happen? No one knows!!!!!!!!!!!!! It's the biggest mystery of quantum theory. However, it's not a mystery for de Broglie theory. However, there is the mystery in the pilot wave theory. It's: the pilot wave. What's the pilot wave? No one knows. But there is one thing quantum theory has that is extremely similar to the pilot wave: the quantum vacuum. So, the quantum vacuum could be the pilot wave. So, the pilot wave theory has one mystery less than the quantum theory. And it answers the question: how does the collapse into just one state happen? The collapse doesn't happen, because a particle was never in a superposition. A particle is always at one place with only one velocity. This is the beauty of it. Cheers :D
Anything we do to detect, determine or even deduce, however indirectly, which path the particle will take / is taking / took, causes it to take a classical path. It isn't enough that the particle is free to choose either path. Interference only happens when the setup is such that it is impossible, even in principle, to know which path it took. Something about "measurement," itself, no matter how tricky or indirect, destroys superposition. Google "quantum eraser" for more of a taste of just how puzzling this can be.
ramkrishan charan the observation cannot be passive. So when they say "observe" they don't mean simply looking at it. These systems are so small that they have to be interacted with to make any type of measurement.
Cosmic Atrophy, true it's like firing a canon with a hill that blocks your view and calculating the the speed and trajectory depending on from where the ball would land. At the same time the ball has 8 possible ways to exist in between and you'll never actually "see,verify" it with current technology. Fluiddynamics without the knowlegde of atoms from about 200 years ago is perhaps An example of this.
The thing is, we are talking about things so small that even bouncing light or electrons of them will have an effect.
But if one considers the photon particles are moving in a HELICAL motion - it would depend on which part of each loop the particle happened to be as it reached the slits. Some would pass through one slit and others the other slit - but many would hit the surrounding wall. Once through the slits the particle can create the interference patterns.
Link to video on contextuality? It's referenced in the above video but no link is given. Thanks!
Oh, it's because these new TH-cam Cards thing is very annoying.... I'll put the link into the description as well then.
th-cam.com/video/Qz4CHI_W-TA/w-d-xo.html
I always thought in quantum mecanics a particle isn't even a particle but a wave, but when two waves interact, not interfer, they interact as if they were particles.
That is kind of the nonsense that the Copenhagen Interpretation insists on.
If every possible quantum mechanics result is also explained by Bohmian mechanics, does that mean no experiment can tell the difference, and, consequently, we'll never know which interpretation is correct?
Nice, clear, intelligent.