Do we have to accept Quantum weirdness? De Broglie Bohm Pilot Wave Theory explained
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- Опубликовано: 7 июн 2024
- An explanation and the pros and cons of Pilot Wave Theory aka Bohmian mechanics.
Links to videos referenced:
Veritasium's video: • Is This What Quantum M...
My old Bohmian mechanics video: • Bohmian Mechanics- An ...
Contextuality: • A problem with Bohmian...
Entanglement and the EPR paradox: • Quantum Entanglement a...
Also see:
PBS spacetime's excellent video: • Pilot Wave Theory and ...
This amazing video about 'surreal paths' in Bohmian mechanics (this channel is also very worth checking out): • 14.What are the surrea... 
Наука
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.
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.
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
"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
I find your voice super relaxing. Love the content too. It's like educational asmr to me.
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..
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 :)
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!
Really nice video! It is of fundamental importance to understand the difference between reality and how we interpret it!
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.
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.
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!
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.
Searched RUclips and found this video immediately after watching Veritasium's video you mentioned. Both great videos!
I've missed these videos. Welcome back.
Thank you so much. I've genuinely really missed it too.
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.
Oh, I missed so much this almost-laugthing-cute voice that brings so much knowledge!
:) :)
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 :)
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.
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!)
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.
Thanks for the new video! I love your stuff.
Thank you very much!
Very good video! You made it all clear and you are good at explaining things!
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?
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.
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!
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!
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 :)
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?!
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.
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.
Hey can you do a collab with 3Blue1Brown
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 :)
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 ;)
I had to pinch myself to make sure i wasn't dreaming
Oh, me too...
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.
I had recommended Veritasiums video to Looking Glass universe
And now it's mentioned,
What an amazing feeling.
Came here from watching a documentary on David bohm. Good stuff! You explained it so clearly.
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.
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.
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.
You have brought me into the joy of wonderment.!!!
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 RUclips... 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
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".
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! 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.
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 ;)
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.
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!
Awesome video!
Ótimo vídeo!
Excellent work. Top notch
Thank you!
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!
Excellent video. Thanks a lot!
Thank you :)
This is a good beg/intermediate explanation. Good job
Thank you very much :)
Thanks for the Video! It was said that Bells Theorem suggests that a theory consistent with experimental results has to be non-local. I've read that the Copenhagen view is also non-local because of entanglement while Bohmian Mechanics gives up locality completely. So, is one of those more local than the other? Or am I mixing two different meanings of locality here?
I love this so much. Science storytelling through the roof.
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.
Great video. Congratulations
another amazing video!!
Thank you so much :D!
Love your work! A quick question from an armchair physicist, does the double slit eraser experiment pose an issue to decoherence within BM? the impression I get is that measuring instruments are causing the collapse, but the double slit eraser has particles/waves passing through certain detectors while ALSO scrambling their incoming paths, resulting in a wave pattern even though the waves creating them have passed through active detectors.
I've no doubt misunderstood most of what I typed above, just looking for some correction
This was awesome, thanks.
Great video as always!
Could you please make some videos on the main ideas in quantum information theory? Would love to know more about it :)
I'm doing my PhD in quantum info stuff now, so I really should! I will soon :)
What is your take on the Possiblist Transactional interpretation by Ruth Kastner?
Very well explained!
Thank you!
Thank's so much for this video! I was wondering how does look the relativist version of orthodox QM? is it in some points better? i heard that this theory wasn't satisfying because of some paradoxs, so the quantum field theory is used. Is there a bohmian equivalent?
Yes. Note that it can include special relativity, not general relativity, which requires much more theory.
Liked, subbed & commented off of this one video. GREAT WORK! :D
Thank you so much :)!!
Could the fact that some paths are longer than others come into it? Eg you can do the double slit one photon at a time, and from the 'stationary' reference frame some travel longer distances than others under Bohmian mechanics, in which case they should arrive at different times?
Very nicely explained with one exception in my opinion as a layman. How does the particle "feel" that the other slit is open?
Ah! It feels it through the 'pilot-wave' aka the wavefunction. I explained that a bit more in my old video on this.
Does Bell's Theorem really prove non-locality, or does it only prove correlation at any distance from a certain very particular starting point? Can we really disprove hidden variables or wave/field theories that make the same predictions?
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?
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?
Hi LGU, thanks for these videos they have been helpful. I'm trained in logic and philosophy not a physics and it's been nice listening to these videos and looking at the comments to see the response. I have an interesting interpretation of Quantum Mechanics that has a thought experiment that would lead to a real experiment - I appreciate that you in other videos encouraged people to share. Is it OK for me to share this here? It's relatively short in explanation, and the thought experiment is fairly simple too.
Do you ever talk about how measuring which door the particles go through causes two lumps on the back wall instead of the interference pattern?
Does the geometry of the Projection Screen influence the distribution of the lumps? Say I have a concave/convex shape. To formulate this more rigorously: if I have some function f which describes the distribution of particles on the flat screen and apply a transformation g to f which bends the flat surface into the concave/convex shape, will this produce the same result distribution as in an experiment with concave/convex screen? (or any other surface)
It wouldn't give the right answer. Think of the double slit experiment with actual waves, and what would happen if you had a warped screen in that case. The answer is the same in QM for the intensity distribution.
Wonderful video!
Thank you so much!
Tks, I love the ideas and the video.
Thank you for coming back :) I really appreciate it.
Great vid. Thanks.
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.
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!
Do you have a video on the bell experiment?
Yes, a couple :) ruclips.net/video/z-s3q9wlLag/видео.html
Really enjoy your videos! Am curious if you had any exposure to Representation Theory? Would love to see some videos on the topic!
Me too. I'd like to see some proof that RT is not meaningless pseudoscience.
Can u explain about virtual photons?
And force carrying particles
Great video!
Thank you!
Great video
Looking Glass Universe -
Can't seem to find a way to contact you directly with this question, but I'm very interested in your response.
You referenced Veritasium's video with the walking droplets, mentioning that it can emulate three peculiar quantum effects but not entanglement.
Is it possible that entanglement is the occupation of the same trough of a pilot wave? Could we replace instantaneous transmission with the velocity of sound on the surface of the water? Say that nonlocal effects are the conservation of some symmetry between two entangled particles. Then the transmission of entangled momentum in our experiment is confined by refraction within that trough, and we might demonstrate that two droplets will perfectly offset each the other's momentum. Ignoring losses to surface tension and other classical effects, I'm asking whether you agree this might effectively demonstrate entanglement by classical analogy.
Really anticipating your response! (Also, if you know any youtubers who would try this on video, please let me know and let's reach out!)
In the modified double-slit experiment (discussed around 7:11), what would happen if only one detector was placed on one "door"? Do PWT and regular QM make the same prediction?
Yes :) I think I know where your question is coming from though- I explained decoherence very badly here. Let me make it up in my video about it later.
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.
Can you make a video explaining the guiding equation? I find the online resources to have too little information or having too much unnecessary information with no in-between
Why don't you read the original papers? It's not like they are not on the internet. In any case, no matter how much you read about bullshit, it still stays bullshit. Bohm has absolutely no scientific value.
Great video :)
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.
Nice, clear, intelligent.
Link to video on contextuality? It's referenced in the above video but no link is given. Thanks!
Oh, it's because these new RUclips Cards thing is very annoying.... I'll put the link into the description as well then.
ruclips.net/video/Qz4CHI_W-TA/видео.html
*chef hand kiss gesture* mmmwah! your videos are a treat to watch, thank you so much! :)
AHAHA! Yay thank you!!
If in the double slit experiment one door being open effects the particle in a way to change its path doesn’t this seem pretty similar to general theory of relativity where on small change can in one part can change things in an other part? So does general theory of relativity support bohemian mechanics??
Mithuna, Has anyone thought about what are the implications of changing the distance between the double slits and the detection plates in the back? How does the positions of the electrons change as a function of the distance, and what does this say about the theory?
Thank you for the explanation. I was getting so confused why people were still talking about Pilot wave theory after Bells theorem ruled out hidden variable.
She addressed this misconception. Bell showed that LOCAL hidden variable interpretations had to be wrong. Bohm is not local.
Thank you for this video, i really learned something new, but i have a question. Would't Bohmian mechanics cause slightly different "speed" for the patticle? If in both cases particle moves with the speed of light, but Bohmian path is more curved, so the particle should take slightly more time to get to the screen than Quantum mechanics would predict. Please correct me if I'm wrong.
Great question!! It doesn't change that overall time (it can't or it's predictions would contradict QM), so it must be that the particle (if it's a photon) moves faster than light some times. Of course that's no good in SR. So it must have a different answer in the relativistic version of BM. Unfortunately that's not a theory I know much about!
BM doesn't predict a particle's "speed", it's not like a classical particle with a trajectory. As with all other interpretations compatible with QM, Bohmian Mechanics uses the quantum wavefunction to calculate a probability density function for each particle. It is this function that exhibits interference patterns when both slits are open.
In BM a particle need not move at all. Indeed this was a charge Einstein made against it to which David Bohm replied that it doesn't contradict any experimental fact and thus Einstein's charge was arbitrary. Its speed can depend on contexuality. As Travis Norsen says: “Turning off the confining potential energy changes the subsequent time-evolution of the electron's wave function, which in turn causes the particle to acquire a non-zero momentum!” Travis Norsen, Foundations of Quantum Mechanics: An Exploration of the Physical Meaning of Quantum Theory (Springer, 2017), pp. 195, 196
Wonderful video and explanation of Bohmian mechanics .. shared on G+
Thanks a lot :) Really glad you liked it!