joigus

Sorry, "break coherence." I mix up these opposites from time to time. Yes, I prefer Swansont's answer too. He's as brief as surgically precise. There are many instances in which you learn something about a quantum particle long before you do anything else with it. That's my understanding of filtering, for example. Measurement is not necessarily interaction. But some interaction is necessary at some point, of course, as Studiot just pointed out. Otherwise, as he said, how are you to tell anything about it? Sorry for not having addressed your specific concerns about entanglement. I've been talking about entanglement for like a month. I also have a feeling that some people see in entanglement something that's not involved in the principles of QM themselves, some new law, some extra magic. There isn't. All the mystery is already in the double-slit experiment already, or the "paradox" of partial reflection, etc. I also totally concur with MigL's comments:

What you're suggesting is measuring without interaction or measuring counterfactuals. It's better to deal with it for one particle in the double-slit experiment. You place a detector intercepting particles only in one of the branching paths. You fire your particles one by one and observe where they land in a faraway screen. You gather only the results that didn't do "click" at the detector. You do the statistics of all of those that didn't make the detector click. What's observed is that decoherence is broken. Counterfactual measurements, or interaction-free measurements --as they're also called-- break decoherence. This effect is so real that there is a bomb tester to know if a bomb would go off without actually making it go off: https://en.wikipedia.org/wiki/Elitzur–Vaidman_bomb_tester Sorry for re-directing your question, but I think the essential aspect that you want to understand is contained here more simply than considering entanglement. I hope that has to do with your question at least. Look up for "interaction-free measurement," or perhaps, "counterfactual measurement." Also: https://en.wikipedia.org/wiki/Renninger_negative-result_experiment

OK, @bangstrom. Enough is enough. Take a code "0" and "1." Describe a protocol that sends either "0" or "1" to a distant observer by using an entangled state. Describe it clearly. It could even be, "0" = "I have performed a measurement" and, "1" = "I have not performed a measurement" So that the distant observer knows immediately it's either "0" or "1" Or, it could be, "0" = "Spin is up along the x-direction" and, "1" = "Spin is down along the x-direction" Or, it could be, "0" = "I have performed a measurement along the x-direction" and, "1" = "I have performed a measurement along a direction other than the x-direction" Describe a protocol that does this without infinitely many data having to be gathered after long hours of painstaking readings, and thereby inferring decoherence has been lost when the STL waiting time has long, long been exceeded. Of course, most of us here understand: (1) That's not possible (2) If it were, SR would be violated But you don't, you don't understand it. You're still clueless after all that's been said. So, please, stop blowing smoke once and for all and give an answer to everybody. Your last paragraphs were some more smoke-blowing and quoting news you don't understand, so I'm not even gonna bother to answer them.

No need to apologise. I haven't found you at fault at any point. We respectfully disagree, that's all. I'm very passionate about interpretations of QM. I'm very emphatic about points I've thought about, and read about, for many years. Sometimes, when I see what I perceive as a fundamental misunderstanding of both the facts and the theory, I take issue with it, but in no way it should be understood as hostility. I've seen people's careers destroyed for valiently going down this particular rabbit hole, never to be seen again. It's no joke to me.

The state of a particle does not correspond to one wave function. Rather, it is an equivalence class of infinitely many wave functions, all differing in a global relative phase. Further, when you include gauge ambiguity, it's no longer just a global-phase ambiguity, but an infinite collection of local prescriptions for the phase that constitutes the ambiguity. This means that you can attach whatever time-position dependent factor to the wave function, add a counterterm to the gauge field, and the equations of motion are exactly the same. How are you so sure, how is anybody, that factors of this incommensurably infinite group are not relevant to a more complete description of the quantum state? On the other hand, saying that the history of the entire universe is somehow involved in the deflection of, eg, a paramagnetic particle by a Stern-Gerlach magnet is only evidence of how misleading the ongoing blabber about non-locality has been for all these years. Research in beables is a serious branch of theoretical physics, however much making the models falsifiable remains a challenge. Vague assumptions about omniscient agents is not.

Because guessing operators more general than Hermitian being relevant to QM is a natural mathematical extrapolation of the postulates of QM, while talking about gods, demigods, and leprechauns is a mythological idiocy with no basis on, relation to, or even suggestions of QM in it. I should think that's next-to-obvious.

Emphasis-answered. Seems like I violated causality, because I answered your question before you asked it. @Lorentz Jr, I know it's a lot to ask of anybody to read carefully what came before, but I already mentioned: "weaken the criterion of reality." I'll give you a pointer, if you're interested. The theoretical environment in which similar ideas grow is "loopholes to the impossibility theorems." Keep in mind that impossibility theorems always have premises. If you weaken the premises, you find doors to unexpected landscapes. It's happened before.

Every entanglement is different and depends partly upon the conditions of the entanglement. Ghideon's example is classical. But with the wife, socks, gloves and so on you need at least the information that they are married, there is a pair of socks of gloves. Otherwise when the box of gloves is opened the discovery that it contains a right hand glove is of no extra meaning. Yes. Thank you. Very interesting comments. +1 To me the big "mystery" is how the quantum state --or perhaps an appropriate extension of it, or more detailed understanding of it-- manages to pack in it what we perceive as classical data (the results of experiments, or how the quantum systems "decide.") It is my feeling that there are enough clues in the formalism, to the extent that it's been developed today, for these classical data to be carried by the wave function. But the lesson from the impossibility theorems is, perhaps, that we cannot make this connection naively. That the demand that the eigenvalues are defined inside the quantum state is too strong a requirement. This information could be stored in the quantum state through "beables," rather than "observables." Quantities that can never be observed, essentially complex in nature --more general complex operators, rather than Hermitian--, and essentially "internal" to the quantum state. Very much like John Bell once suggested, if I understood his ideas correctly. When you look closely at the quantum formalism, you find that there is an extraordinary freedom that seems to point to a fundamentally unobservable domain: global phase, local phase (gauge ambiguity), indefinition of the measure in the Feynman path integral... The problem is, of course, how do we formulate this "internal domain of the wave function" in terms that can be made into a falsifiable theory? What's clearly not the path to follow, IMO, is denouncing the principles of locality and relativistic causality, as @bangstrom --deeply involved in an internal monologue, AFAICT at this point-- keeps parrotting, rather than making a case for. And the reasons are (1) There's no experimental evidence for it, and (2) There's no suggestion from the formalism that this should be the case. Or/and also perhaps how the information is packed in the quantum state, like eg, in thermodynamics of state variables, cyclically: Sx(Sy,Sz), Sy(Sz,Sx), Sz(Sx,Sy); in such a way that there are no three fundamental variables of spin, but only two complex variables. I've always found fascinating how the mathematics of spin resembles the mathematics of thermodynamic variables.

I think it's interesting to try and find analogies that reproduce some of the peculiarities of QM. What I usually feel is that some analogies manage to reproduce one aspect of it, while others are good at reproducing another. But all of them generally fail at reproducing all features completely. Incompatible questions are questions you can't ask at the same time (impossibility of simultaneous interacting measurements) and for which you cannot prepare states perfectly defined in both answers (impossibility of filtering measurements that produce definite values for both.) After you introduced your husband and wife analogy, I started thinking of a similar extension for the analogy corresponding to another, incompatible observable. I was thinking along the terms of: When both of them got married they signed a pre-nup contract, and one of them owns a house. But for some reason the contract was ambiguous as to the ownership of real estate. So until the question is legally settled, it is not defined whether the house belongs to the family of the deceased, or to the surviving one. Something like that. I will take more than one look at your version of the analogy, but for the time being I'll tell you that I was thinking in similar terms. Only with the undefined property being ownership over one object --or the right to use it, if you prefer. I think it gets close to the idea somehow, although the analogy becomes more and more complicated as you try to fit more aspects of actual QM.

Exactly. If you measure a particle's spin along a particular direction, that spin is no longer entangled to any other spin in the universe. You have just set up a qubit to 0 or 1, as people in quantum computing say. Well, sure, of course. You could also send electrons and positrons, one after the other. Or whatever other code, or use the frequencies and positions, like we do for a TV set. But then it's not information contained in the spin. It's in other variables. And they would be subject to subluminal speed limits and causality. Like anything else. Is that helpful?

If you sit at one place and take spin measurements on a particle (say a photon,) being completely clueless about whether that particle comes from an entangled pair, or triplet, etc., you wouldn't know. There's hardly anything you would be able to say about other parts of the universe it's just disentangled from. One particle is... well, one particle. You measure its spin --after that, it becomes disentangled from whatever it was entangled with before --as @MigL said. Suppose it gives +1 in the direction you set your polariser at. What can you say from that? Practically nothing. +1: That's all your information. Just one piece of data from a measurement doesn't tell you anything much about where it came from. If you take care not to do anything that changes the spin, it will produce +1 again and again. So, sure, you can say something about this photon now. If, OTOH, you measure spins for a stream of particles all identically prepared in the same entangled state, you would see a sequence now. It could go like: +1, +1, -1, +1, -1, +1, -1, -1, -1, +1, +1, -1, +1, +1... So what? What can you tell from that? You can call upon Zeilinger himself, if you wish, to interpret your data. You can tell nothing from that. Not yet. It's just a random sequence of binary code. But, if you can arrange to communicate --by the usual, sub-luminal channels-- with someone far away in the Andromeda galaxy measuring the partner particles making up the identically-entangled pairs, now, and not before, you would be able to tell something, if you're lucky. If you both have chosen the same polarisation direction for your respective polarisers, you would find something funny: They're exactly anti-correlated each and every time. When your particle reads "+1", the other one reads "-1", and viceversa. But if you set your polarisers in a non-parallel way, there's not even the slightest amount of correlation. That's a big wow! on my part. It's strange, weird, seems magic --if you don't understand QM. But still doesn't allow you to send any signals in and of itself. As I said in the other thread, concerning quantum teleportation: https://en.wikipedia.org/wiki/Quantum_teleportation However, and most importantly, even if, after having gone through all that trouble, you find the perfect anti-correlation, your local stream of data (the sequence of +1, +1, -1, +1, -1, +1, -1, -1, -1, +1, +1, -1, +1, +1..., etc.) is still a random, nonsense, totally-garbage noise of +1's and -1's. What do you wanna do with that for the purposes of communication? See my point? Do you want to communicate with the Andromeda galaxy with photon spins somehow coding a message? Fine. Here's one particular way you could go about doing that. You take a sufficient power of 2, eg, 27=128 You can code 128 characters with this. More than enough for all to represent the different characters in the English language, lower case and capitals, plus Arabic numerals, spaces, punctuation, and a bunch of special symbols. It could go like, Space -> 0000000 Dot -> 0000001 a -> 0000010 etc. Now you can prepare your photons to "mean something." It would --it would have to-- look like a pre-determined, precise sequence of zeros and ones. Importantly, you have to filter the sequence so that each photon is +1 (stand-in for 1) or -1 (stand-in for 0) to be precisely at the place it has to be to constitute your message. I think the idea is clear enough at this point. You can't do that with the output of an entangled state. A random string of 0's and 1's is not a message. And it's not, no matter what direction you set your polarisers in. Sending a random sequence is not a message, no matter how non-classically structured these strings of noise are. Even though they are. All my previous comments go without even starting to consider the problem of keeping quantum coherence through interstellar space all the way from here to the Andromeda galaxy, with interstellar dust, asteroid rings, cosmic rays knocking off my photons, etc. I don't envy the engineer whose task was to guarantee something like that.

Yes. He really needs to read --with utmost attention-- Einstein's Gedanken on how two distant observers synchronise their clocks. SR is not a nagging theoretical preconception that can be brushed aside for the purposes of doing your thing. It's the theory of how one attaches times and positions to events, and does it consistently. That's why we're beeing such "sticklers" about this. Let's see if he finally understands this, because last time I looked he qualified it as "bickering."

Eise also told you how the Clauser experiment is not, while the Aspect experiment is an Alice & Bob SR situation. You really should get your "stuff" together, Bangstrom. I can't say a 100% you're just trolling around, because I must confess I've also considered --like Eise-- possible language barrier, circumstances I may not be aware of, etc. But this is getting ridiculous, and it does sound like you're just trolling around.

1+1=0. Easy peasy. Only problem is that's not true. If a person can't handle addition, any silly mistake they see as easy-peasy. It's easy for you because you've got the wrong picture. An observer moving away from your "first" measurement at high-enough speed would see it happen later. I took pains to make a drawing to explain it to you, but to no avail. Sure. "Madam, your husband died in an accident. You're a widow now, but don't worry. That's just a name we're giving you." This person's life changes abruptly from there on, but she's none the wiser until the news come. The problem is you don't even understand the dumbed-down example. And that's because you think you understand it and try to explain it to everybody else. I leave you with Bertrand Russell: We're all here probably fools and fanatics ganging up on a wiser, enlightened mind. This is the whole question of non-commutativity. Dirac introduced this interesting concept of q-numbers, as opposed to c-numbers, to highlight this idea, I think. C-numbers are the ordinary quantities of our classical, well-defined world. Q-numbers, on the contrary, are more like matrices. They do not commute. So they cannot be defined (diagonalised, perceived, spelled out, as numbers) at the same time = in the same basis of reference states. If you want to define one thing, you must un-define, or blur out, the other. This concept takes quite a bit of getting used to, but I can assure you --if I understand QM at all, and I think I do to some extent--, it's the actuall crux of the matter. The idea that, when something is "defined," other things, other attributes, must become "undefined" or a superposition of possibilities.

I love pasta.

No. That's one good reason, and a pretty important one, but not the only reason. Any initial-condition wave function of any shape you like --not necessarily a function for which Ax+By+Cz=K (plane) is a surface of constant phase, and let it propagate freely. Eventually, it will get close to a plane wave if you leave it alone, but it never reaches that profile. It's curved and contorted for a long, long while, ever so slightly less so as time goes by, but never totally plane. It takes infinite time to do so, and then the multiplicative constant must become zero. "Plane" is what they tend to be, given enough time, but not what they are. Plane waves are extreme simplifications. Their localisation probabilities produce an infinity, so they're not the actual representation of a physical state. They're toy models. Plane waves are, eg, what the amplitude looks like in some region when you prepare the state having it go through infinitely many collimating screens, and then let it "relax" until it reaches this situation in some region of interest. OTOH, there has been extensive study of states which propagate in one direction, but package orbital angular momentum in the directions perpendicular to the propagation direction, so they're not plane waves. Look up for Bessel and Airy packets. They're very interesting, and quite a surprise when you're used to this simplifying idea that free waves are plane waves. Many people say it, but it's very old, sloppy, non-rigorous QM. We understand it better now. Another more realistic approach to a free Schrödinger wave is a Gaussian wave packet. Another one is the wave function of a particle coming out of a slit. It's never plane, although once it's got out of the slit, it's totally free. So V=0. But even more simply. Take the free Schrödinger equation: \[ i\hbar\frac{\partial\psi}{\partial t}=-\frac{\hbar^{2}}{2m}\nabla^{2}\psi \] Now suppose you know, for some reason, that the momentum is in the z-direction. So you can do the separation \( \psi\left(x,y,z,t\right)=e^{-iEt/\hbar}e^{ip_{z}z/\hbar}\varphi\left(x,y\right) \). Now plug it into the time-independent Schrödinger equation: \[ -\frac{\hbar^{2}}{2m}\left(\frac{\partial^{2}}{\partial x^{2}}+\frac{\partial^{2}}{\partial y^{2}}+\frac{\partial^{2}}{\partial z^{2}}\right)\psi=\frac{p_{z}^{2}}{2m}\psi \] So your Schrödinger equation splits into, \[ \frac{\hbar}{i}\frac{\partial}{\partial z}\psi=p_{z}\psi \] and, \[ \left(\frac{\partial^{2}}{\partial x^{2}}+\frac{\partial^{2}}{\partial y^{2}}\right)\varphi=0 \] The second one is the Laplace equation, so any harmonic function in the variables perpendicular to the selected momentum will do as a perfectly valid --and actually much more realistic-- solution to the Schrödinger equation. This is why people have been studying for some time now these very interesting states with orbital angular momentum packaged in them that I like to call --privately-- fusilli or tagliatelle electrons. They are free particles, and they are not plane waves.

This is incorrect. It's what some/many freshman or sophomore "introduction to quantum mechanics" books suggest say, and it's badly, badly wrong. Wanna know why?

Eigenstates of what? Position eigenstates could not be farther from being oscillatory. Waves do not have to be oscillatory. But the question actually all depends on how you define a wave, and what you wish to include in the definition. Perhaps you should actually read what I posted, as I provided a somewhat restrictive one, although by no means necessarily unique: You could, of course, weaken this definition and therefore expand the concept to include non-linear phenomena, like solitons or gravitational waves. In that case, it would be just any solution to a field equation that admits particular solutions that propagate as a travelling disturbance, \[ u\left( x-vt \right) \] Being "oscillatory" --most certainly-- is not a requisite in any definition I know. You are confusing the particular case with the general one. You are confusing the pieces into which we analyse waves with what is is an analysis of --the waves themselves. In fact, no realistic interesting solution of a wave equation is "oscillatory." Most waves suffer dispersion. What you are referring to is a monochromatic wave. The classical wave equation, the equation for the vibrating string, for example, has infinitely many oscillatory Fourier components, while the overall solution doesn't have to be oscillatory in any sense --even though every one of the pieces oscillate with its particular frequency. Welcome to the forums. I don't think chemists are mere. Not anymore than isomers are mere "isos." I think in Chemistry you're mainly concerned with electrons being comfortably set in stationary states. Either atomic or molecular wave functions with a given energy. This dispersion is still going on, but due to the peculiarities of the function being complex, and the "diffusion coefficient" being imaginary, the stationary situation, when it's spatially confined, allows for states going back and forth withing a small volume. Like --another Wikipedia image--,

You're absolutely right. +1. An image is worth a thousand words: The image is not mine, of course. It's from Wikipedia, and it represents the time evolution of a free quantum-mechanical wave packet. You can actually see how dispersive the non-relativistic regime is. The low-down is: Even empty space somehow operates as a dispersive medium for Schrödinger waves. Although you can get a similar behaviour for waves that are actually waves --same order in time and space derivatives-- by having them propagate through a dispersive material. The diffusion equation is, \[ \frac{\partial n}{\partial t}=-D\nabla^{2}n \] with D being what we call the diffusion coefficient. The Schrödinger equation, OTOH, is, \[ i\hbar\frac{\partial\psi}{\partial t}=-\frac{\hbar^{2}}{2m}\nabla^{2}\psi \] So it's exactly mathematically equivalent to the evolution of a complex space-time valued function with complex values and purely imaginary diffusion coefficient, \[ D\rightarrow\frac{i\hbar}{2m} \] Whether something is a wave or not is, of course, a matter of definition. I would be happy enough with an equation that's linear in the field variable and admits travelling solutions being in some sense a wave. Travelling solutions meaning, \[ \psi\left(x,t\right)=u\left(\omega t-kx\right) \] If the equation is linear, we can do a Fourier analysis of the wave, and an arbitrary solution is a linear superposition of infinitely many travelling solutions like these. But the problem of whether our equation is dispersive or not is coded in the relation, \[ \omega\left(k\right) \] That's why it's called dispersion relation. Fourier components with different frequencies have different velocities. The velocity of propagation for each component of wave number k depends on that particular value of k. That's why the wave spreads out as it evolves. In the case of the Schrödinger equation, the dispersion relation is, \[ \hbar\omega=\frac{\left(\hbar k\right)^{2}}{2m}\Rightarrow \] so that, \[ \omega\left(k\right)=\frac{\hbar k^{2}}{2m} \] The phase velocity for Schrödinger waves being, \[ v_{p}=\frac{\omega}{k}=\frac{\hbar k}{2m} \] And their group velocity being, \[ v_{g}=\frac{d\omega}{dk}=\frac{\hbar k}{m} \] For light in a vacuum, there's no dispersion, or the dispersion relation is linear, so group velocity and phase velocity coincide. If we enter a medium, then we have dispersion. For relativistic (massive, matter) waves, the dispersion relation is very interesting, giving a group velocity that's subluminal, and a phase velocity that's superluminal, the product of both giving exactly c2. The problem with relativistic equations is that they cannot be consistently interpreted in terms of one particle. They are multi-particle systems from the get go.

There you go again. There is no "first." None of them comes first, and then the other. It'd better not. That's why those people in Taiwan that you mentioned earlier are just measuring the speed of nothing. It is a non-speed. That's why Ghideon's analogy is so brilliant. There's no speed at which the woman becomes a widow. Or it's infinite, whatever way you want to say it. It's a logical fitting between both ends. Nothing travels. No Cramer, I'm sorry. It's the "speed" at which infinitely many propositions are anticorrelated, and infinitely many other propositions are totally non-correlated. I am. Let me give it a try. Let's introduce another Ghideon-observable: If I destroy their house while they're away, they "instantly" become homeless. In the classical world, It's possible to know whether a person is "widowed" and "homeless" at the same time. In QM those could be incompatible observables. What's interesting in your analogy is that you've introduced a world of potentialities: Legal bindings, conditions, attachments, etc. This is, in the analogical space, playing the part of the wave function.

You guys are forgetting that sometimes we are surprised with a gem by other members. I personally find @Ghideon's analogy of the widow/widower very illuminating. I've been trying for years to find an analogy that illustrates this particularly difficult point that you can instantly obtain information about a remote thing without physically affecting it, and there you are --and the example not being quantum mechanical. To me, it's worth all the effort spent. Here it is again:

A Zen master once said, Light is what allows you to see the elephants. Light is not the elephants. Dark is not light. Light is not dark. Light is light. And there's nothing lighter than light.

Our goal is to have goals. Our purpose, to have purpose. May I also point out that there is such a thing as too much reproduction... 🤷‍♂️

Cosmology is of no relevance here. Experimenters doing quantum interferometry, quantum teleportation, and the like, do not refer anything to the CMB. That would be silly. The CMBR is distinguished from a cosmological POV, not from a POV of local quantum mechanics. Seems trivial to you only because you do not understand, and looks now as if you will never do. The experimenters decide who does the measurement: One of them, the other, or both. And they also decide when that happens, in their respective local reference frame. OTOH, observers moving with respect to them, see the measurements happen in different temporal order, depending on their state of motion. Will you at some point understand this? You have a flair for getting everything backwards like I've never seen before. Everything is together --non-separable, that's why I say it's "hardwired," and it comes apart after we do the measurement --the particles become disentangled, and the density matrix goes from pure state to strict mixture state. Nothing is observed until it is observed. There is no signal. Filtering measurements carry no signal either. In this way, it's similar to a non-interaction measurement, like counterfactuals --Elitzer-Vaidman bomb tester-- or filterings.

Seems to me that this is an insurmountable objection. It is what I would call a zero-order problem with the OP's idea. IOW: The hypothesis is not even designed to do the job it's intended to do.