Spooky or not spooky, that is the question.

Discussion in 'Physics & Math' started by quantum_wave, Jan 27, 2016.

  1. Cheezle Hab SoSlI' Quch! Registered Senior Member

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    Interesting. I pulled that statement ("So the system is B*NOT*B = I and no real world classical B has this property") directly (I thought) from the David Deutsch video. What he said was actually a little more narrowly defined. Here is a better quote:
    Perhaps his quote has built in the assumption that hidden variables are not allowed. Or that using hidden variables require more computations. Do you have an example where a classical B fits this pattern, or how to modify the pattern with hidden variables to make it classically workable? I am not saying you are wrong, but I would be interested in an example. I had assumed that a person like Deutsch would be a good source. But I realize that he is a quantum computing advocate and it would seem that if hidden variables were the explanation, then quantum computers as I understand them would be impossible because everything would really just be classical computation and therefore not the super fast and powerful devices that many expect to be possible.

    It seems that hidden variable interpretation (DeBroglie-Bohm) is not very popular among physicists. The most popular interpretation is the Copenhagen one, followed by Information-based interpretation, and then Many Worlds (Everett). In the informal study I am referring to, hidden variables has 0% supporters. Of course its not a popularity contest but it is an interesting result. I thought maybe others would find this interesting.

    A Snapshot of Foundational Attitudes Toward Quantum Mechanics [http://arxiv.org/pdf/1301.1069v1.pdf]
     
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  3. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    That last post of mine is what I call a "falling on your own sword" post. I acknowledge that I may be wrong in one or several respects as the thread developed, as pointed out by fellow members. Fortunately you don't bleed to death when you fall on your sword in cyberspace.

    You don't always know the direction that a thread will go, and I went with Cheezle's link, and then got off my intended topic. Please feel free to continue ongoing thoughts, but for my part, when I started the thread, I was referring to the article linked in the OP, and saw something interesting in how Alice could choose to always set her filter to allow vertically polarized particles to pass. Using those particles that passed her vertical filter, I imagined that would define a set of particle pairs where Alice's were all vertical, and Bob's would be all horizontal. That assumption is based on the knowledge that their pair emission was designed to produce one each, vertical (V) and horizontal (H).

    At that point, I said I couldn't understand the statement that: "The photon does not have an orientation until Alice detects it. Same for Bob’s."

    So let's evaluate that declaration. It is known that there is a pair of photons emitted, one vertically (V) and one horizontally (H) polarized. Isn't it safe to say that if Alice found a vertical photon, then Bob's would be horizontal? Going on ...

    How do we come up with the conclusion that the particle does not have an orientation until Alice detects it. Is it because we don't know which particular one is V and which was H? Is it because the pair is thought no be entangled with a superposition of the V and H state until one is measured?

    Please help me understand the declaration that the photon doesn't have an orientation until Alice detects it, so I can go on through the experiment asking questions from there.
     
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  5. Fednis48 Registered Senior Member

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    That's fair. I may have been overstating things when I said the fundamental building blocks would have to be too exotic to qualify as real properties. I just wanted to convey that in order to be local, such properties would have to be really weird - much more so than simply obeying physical laws we don't know about yet. In particular, the statement "a particle's state can only depend on things that have causal influence on it" would not hold.

    A good question! I agree that when people embrace the intrinsic uncertainty of quantum mechanics, they're kind of just invoking the naturalistic equivalent of a "God of the gaps". On the other hand, I haven't heard any explanation of quantum mechanics that's especially satisfying, so maybe I shouldn't criticize. If I had to guess what's really going on, I'd lean toward some type of FTL signalling. A lattice of entanglement-strands binding distant parts of the universe together would be pretty trippy, but I can at least wrap my mind around the idea. For the other two postulates, I can't even come up with a sci-fi-tier explanation, except maybe that some great cosmic architect is having a big laugh at our expense.

    If you just stick with H and V polarizations, there's nothing especially spooky about Alice's and Bob's measurements. Things only get weird when you let them measure along multiple, non-orthogonal axes. Say the initial state of our photon pair is maximally entangled but rotationally invariant; that is, we know the photons have orthogonal polarizations but we have no idea along what axis. If Alice sets her polarizer along the vertical or horizontal axes, the situation will behave exactly as you described. But what if Alice decides to set her polarizer to 45 degrees, and she detects a photon? We instantly know Bob's photon is polarized at minus 45 degrees. If Alice sets her polarizer to 45 degrees and doesn't detect a photon, then we know Bob's photon is at plus 45 degrees. Note that either way, Bob's photon ends up diagonally polarized; Alice's measurement just tells us along which diagonal. Meanwhile, recall that if Alice was using a vertical polarizer, Bob's photon will be either horizonally or vertically polarized. If we're treating polarization as a realistic hidden variable, we might ask the question: for a given run of the experiment, does Bob have a horizontal/vertical polarization or some diagonal polarization? The answer to that question depends only on how Alice decided to align her polarizer! Alice's measurement isn't just telling her what Bob's polarization is - it's defining the set of polarizations that Bob's photon could possibly have.
     
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  7. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    I can just give that a "maybe", though my imagination is at work, but it works best out in the Fringe, lol.
    I will say that in my model everything is connected at the speed of light and gravity, so no FTL in my book. My version is more like your lattice of entanglement-strands, but I don't go for "strings". I won't be a complete bore by giving you a Fringe post on my version, but it has to do with a foundational background in space where there is continual wave action at the local speed of light, and that causes an oscillation at every point in space between tiny expanding spherical waves and their subsequent wave intersections/overlaps. The intersections inflict a brief time delay on the advance of the spherical waves and momentarily convert wave energy to mass in the tiniest increments, in what I call a momentary high energy density spot at the point of every convergence. Because the HDS is surrounded by the lower energy density of the expanding "parent" waves, there is nothing to contain the high energy in the overlap space, and so the HDSs "burst" into new expanding spherical waves, perpetuating the oscillation at all points in the foundational background. That background then serves as a mechanism to advance more meaningful waves like light waves and gravity waves at the local finite speed of light and gravity. It is akin the Christiaan Huygens version of how a light wave advances at a finite velocity through space.
    I agree that it is a whole new ball game if we don't know the polarity directions of the pair of photons, but only know that A and B are orthogonal. And I agree that using a 45 degree setting between A and B detectors will allow a different set of photons than when using the 90 degree settings at A and B. What I don't yet embrace is that the source of the orthogonal pairs entangles the states of each particle. Why wouldn't the interaction of the two photons at the source mean that the particles individually have one or the other polarization, H or V relative to each other, but we just don't know which is H and which is V?
     
  8. Fednis48 Registered Senior Member

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    Because if the interaction at the source is rotationally symmetric, the photons have no reason to prefer H/V polarizations as opposed to +/- 45 degree polarizations, or any other pair of orthogonal polarizations. If you're working from classical intuition, it might make sense to assume that the photons must pick some axis, and we just don't know what it is. But these maximally entangled, rotationally invariant states aren't that hard to make in the lab (at least not by QM experiment standards), and we've seen the behavior predicted by quantum mechanics: no matter what polarization one measures for the first photon, the second photon ends up polarized orthogonal to it. Your intuition isn't bad, it just doesn't square with the (surprising) experimental observations.
     
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  9. PhysBang Valued Senior Member

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    What Deutsch is doing is kinda like excluding hidden variables.

    One of the key theorems of quantum computing is that one cannot get a result from a quantum computer that one cannot get from a classical computer. It may be that there are speed advantages with quantum computers, but this too has not been proven, only shown to be the case relative to currently known algorithms.

    I'm not Deutsch's biggest fan: he tends to want to have his cake and eat it too, tends to blur the proper distinction between concepts, and tends to ignore that not everyone accepts the assumptions that he makes---implicitly or otherwise. I feel that too often he misrepresents the conclusions of the field, so I urge caution when citing him. I don't think that anything you've cited is far off the mark, though.

    Here's one issue: is the quantum computing that Deutsch is talking about really just one bit or is it using multiple bits? It could be that we are just making use of some of the mathematical features of QM to deal with more than one bit at once using one photon/particle/whatever. Just because we are using one particle does not mean that we are limited to one bit of information in what we are processing. (It does mean that we are restricted to one bit in the result of our processing. I find that Deutsch is not usually clear on this difference and that it sometimes is crucial to the argument that he is trying to make, but that is an aside.)
     
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  10. Cheezle Hab SoSlI' Quch! Registered Senior Member

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    Thanks, that makes a lot of sense. From my own experience, when confronted with problem where no solution seems to exist, it invariably comes down to an wrong assumption on my part. So this explanation resonates with me. Been there, done that.

    The reason that I believed the 'no classical solution is possible' idea is that I had read it so many times from people that are supposedly experts. However, many also said that hidden variable theory is a possibly correct solution. I am still skeptical, but the balance has shifted somewhat between the problematic 'hidden variables we can't see,' and unsettling 'things we can never understand.' Interesting stuff.
     
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  11. CptBork Valued Senior Member

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    That's what I'm saying. They forbid spacelike causation, but not spacelike correlation, and as you probably know yourself but other might not be aware, quantum field theory complies with this restriction, as proven by the CPT Theorem (charge-parity-time).

    https://en.wikipedia.org/wiki/CPT_symmetry
     
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  12. CptBork Valued Senior Member

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    "Hidden variables" is a vague term without context. Physicists are virtually unanimous that there's more to the picture than what the Standard Model reveals, but there's also virtually no dispute that theories requiring determinism and local reality can't account for existing experimental results, regardless of the details one might postulate in such theories.
     
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  13. Cheezle Hab SoSlI' Quch! Registered Senior Member

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    745
    As I said, I am skeptical. That is my nature. Proposing undetectable non-local hidden variables seems to me to be as much of a kludge as the spooky physics we can never understand. But there has to be some idea there, call it a kludge, that bridges the gaps. I would say that a theory that says that we don't or can't really understand it, is more satisfactory and prudent to me than one that proposes possibly fictional extra parts. But whatever the case, it is what it is.

    I was just listening to an interview with Sean Carroll and here is what he said about hidden variable theories, "they [hidden variable proponents] say that the wave function is not all the information there is and that you can only make statements and predictions about probabilities, because you don't have all the information there is to have, [they say] there are sneaky variables that you don't know about. People recoil at the idea but it is a theory that makes sense. It makes unambiguous predictions." Sean Carroll is a Many World proponent, but was discussing some of the other theories. He was somewhat disparaging of the Copenhagen interpretation and said that it is is very popular because that is what is in the textbooks and taught in Universities. I have read some quotes from other well know prominent scientists who also do not completely dismiss hidden variable theories, but they do not support it either. They seem to leave that door open. Perhaps they are just being polite to pro-hidden variable colleagues.
     
  14. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Good, we are talking about the source of the pairs of photons. There are various reactions and particle decays that will produce two photons at a time, and in this case the "box" emits pairs that are orthogonally polarized. At the moment the photons are emitted, individually there is no preferred polarization, i.e., they will be orthogonally polarized, but as that polarization is applied to the pair, there is no way to say that the one that goes out of the box in one direction is going to be H or V on a given axis, and we don't know what the orientation of the axis is relative to 0 degrees, if I understand correctly.

    A "box" that contains the pair emitting capability or apparatus, will send out two photons at a time, one in direction A which goes to Alice, and one in direction B which goes to Bob.

    If we could measure all of the photons going in one direction, say to Alice, there is a 50% chance that they will be H, and a 50% chance they will be V, for example. But because we don't know the orientation of the polarization relative to 0 degrees, only a fraction of the photons will pass a vertical filter setting relative to the 0 degree orientation. Do we know what percentage will pass her vertical filter if she always sets it vertical 90 degrees to the right?

    Am I right that photons that are polarized on an axis between 45 degrees and 135 degrees will pass through the vertical filter set at 90 degree, meaning that 1 in 4 will pass? Or will photons polarized at 45 to 135 degrees, as well as photons polarized at 195 to 285 degrees, also pass the vertical filter, meaning that 1 in 2 will pass the vertical filter?

    This post is basically to test my understanding to this point, and I would appreciate being corrected on any point I have in error or incomplete.
     
  15. Fednis48 Registered Senior Member

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    725
    You've got the right idea, with one correction: when we talk about photons that are neither completely parallel nor completely perpendicular to the polarizer, they pass through with some probability greater than zero but less than one. Specifically, if the photon comes in at an angle \(\theta\) to the polarizer, it will pass through with probability \(\cos(\theta)^2\). So your second intuition is correct: 1 in 2 randomly polarized photons will pass a vertical filter, or any filter for that matter. Similarly, Bob will see 50% of photons pass his polarizer, regardless of its orientation. If we treat the photon polarization as a classical variable, though, we would expect to see some cases where Alice's and Bob's measurements don't give orthogonal results. For example, if Alice and Bob are both using vertical filters and the photons come in at +/- 45 degrees, each photon should have a 50% chance to pass its respective filter, meaning both parties should detect a photon 25% of the time. Instead, we find that exactly one photon is always detected: half the time by Alice and half the time by Bob, but never both at once. It's as if Alice's measurement "snaps" the photons into her chosen basis, allowing Bob to predict the results of subsequent measurements in the same basis with certainty.
     
  16. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Fednis48, you are a trooper to go through this. I'm sure it is agonizingly basic, but necessary to specify the point where there is no physics to describe the results, i.e., what exactly is the spooky thing we are saying is inexplicable, such that my mind knows what a lot of you already know.

    So I have to go one step at a time to get there, but I want to know what is making these experiments Spooky and inexplicable. Then I want to use that to establish the basis against which any "incompleteness" in QM will have to corrected or completed, if in fact the inexplicability is to every go away. That is said from the perspective of the Hidden Variables Interpretation of QM, which I take to mean QM may be incomplete.

    The experiments use the circumstance that a particle can have different properties, and we call the two properties in this experiment, color (black or white) and hardness (hard or soft). If you have a stream of particles that are 100 % of one or the other colors, and you measure them for hardness, they will turn out to be 50% hard and 50% soft, and that is a repeatable fact. That says that the properties are persistent, in that the color measurement can be repeated, and uncorrelated, meaning that color and hardness are two independent properties. Knowing that about the properties, we can make various predictions.

    To say that spin up or down on one axis reveals the color property, and to show that subsequent measurements of all of the "up" (black) particles, subsequently measured on the same axis, will be "up" (black), is not very spooky to me. What we have demonstrated is that if you can keep the particle on the same axis from the first measurement to the subsequent measurement, "color" will be repeatable and persistent.

    Let's call that a characteristic of all electrons, i.e., it has measurable spin on a given axis and the spin on that axis remains the same in subsequent measurements, as long as the axis of spin is preserved, and as long as future measurements are made on the same axis, (and as long as you don't insert another angle of measurement in between).

    I'll post this much, just to break a longer discussion into several bite sized chunks. My question at this point is, do I have it right that the orientation of the axis of the electron particle after the first measurement (box) has to be faithfully preserved in order to be sure that when we put it through an identical box with an identical orientation for a second measurement, we can confirm color repeatability.

    This recognizes that you lose the 100 % repeatability of the color "property" ("up") as soon as you measure the "up" particle on another axis.
     
    Last edited: Feb 8, 2016
  17. Cheezle Hab SoSlI' Quch! Registered Senior Member

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    745
    Here is a simple experiment that illustrates this feature. [3 minutes]

     
  18. iceaura Valued Senior Member

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    I know this is far below the level of the thread discussion, and I've posted this link before, but it sounds as if the questioner here wants to nail down what is disconcerting about the fact that QED agrees fully with experiment. This is the clearest description of the confrontation between QED and ordinary human intuition, as illustrated by Bell's Theorem, I have found: http://webpages.charter.net/sn9/science/bellstheorem.html

    I've found when going through this with others that a Venn diagram illustrating Bell's Theorem can clarify. It's easy to draw from the notation in that link. It confronts one with the experimental result that an area of the Venn diagram that is inside another area is being measured as bigger than the area surrounding and including it.
     
    Last edited: Feb 8, 2016
  19. Fednis48 Registered Senior Member

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    725

    Not a problem! It's not actually that basic; I learned some of this stuff in Quantum Mechanics, but I didn't really understand it until I actually did the experiment in Modern Physics my last term of college.

    So far so good.
    There's nothing spooky about the fact that a measurement on the same particle will give the same result over and over. What's spooky is that once you've measured one particle, you can predict the result of a measurement on the other particle with 100% certainty. Since this works regardless of the measurement axes, we know the solution isn't so simple as the photons being aligned with the measurements when they are produced. Bell's theorem generalizes this result to show that no hidden variable theory, no matter how clever, can produce the correct statistics without giving up basic assumptions about locality or realism.
    This is all correct.
    Thanks for the link! There are a lot of explanations of Bell's inequality out there, and they all have their strengths and weaknesses. I'm not sure where this one fits in terms of quality, but at first glance it seems very readable at least..
     
  20. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Thanks, that is a great demonstration of the fact that we can polarize a photon beam, and measure polarization, and repeat the measurement as long as we can keep the photon stream on that angle of polarization, it will all pass through again and again. If we rotate the angle of measurement, we affect the amount of light that passes, and we can make the two polarized filters perpendicular and eliminate all of the light.

    Polarized photon beams vs. single photons present other questions in regard to how much photon energy you have to have in order to detect the single photon, but I'm not going in that direction at this point.

    So the answer to my question about electrons would be "Yes, you do have to be careful to preserve the particle's spin orientation in order to get 100% repeatability, and as the angle of the spin of the physical particle is allowed to change a little between the first and second measurement, some of the particles that originally passed will not pass; to get the original 100% pass rate, their angle of spin must be faithfully maintained. That applies to photons as well as electrons", right? And that is what I get also from what Fednis48 has said.

    I know it is a tiny point, and it does lead to other questions about how the physical orientation of the particle is faithfully maintained when sending them one at a time across distances, like the link about the 1.3 km experiment that the OP article refers to (in an embedded hyperlink). But I want to go step by step, and address the introduction of the mirrors and blocks in the lecture on Superposition, so bear with me.
    Thank you for posting that link. I will look it over, and the step by step way I am going will give me time to review and respond.
    Thanks for all of that, and it does lead to other questions like I mentioned to Cheezle's, about how the physical orientation of the particle is faithfully maintained when sending them one at a time across distances, like the link about the 1.3 km experiment that the OP article refers to (in an embedded hyperlink). But as I posted to Cheezle's, I want to go step by step, and address the introduction of the mirrors, combined paths, and blocks discussed in the lecture on Superposition, so bear with me. I will post next as soon as I get my thoughts together :0, but your point is taken, that there is more to it than the particles being aligned when they are produced.
     
  21. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    In regard to the Superposition video from Cheezle, in the first set of simple experiments with the color and hardness "boxes", once color is established on the first measurement, it is persistent/repeatable and can be remeasured and found to remain the same. Then if they measure the same electron of either color, on the orthogonal axis, they get a 50/50 result for hardness. Color and hardness are not correlated. Then, once hardness is established, if they measure the hard or soft electrons again for color, they get a 50/50 result for color again.

    I'm wondering if it is right to say that an electron that has spin "up" or "down" on one axis, and then measures spin "left" or "right" on an axis orthogonal to that, has two independent properties? Isn't it a characteristic of an electron to respond to a magnetic field in one of two directions of deflection, regardless of the axis or orientation of the measurement?

    If so, then wouldn't "up or down" on a vertical axis be the same characteristic of an electron as "left or right" on its horizontal axis, instead of two independent properties. Maybe they just call that two independent properties to make the point in class that the spin can be measured on any axis with two results relative to the magnetic field?
     
  22. Waiter_2001 Registered Senior Member

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    459
    Hi there. The wave must measure the same regardless though:

    Xroot(1^(X))=X

    It EQUALS X!
     
  23. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Thanks again for that link. I got a chance to read it over, and it does cover the territory, nicely, and makes a good quick reference source. My conclusion is that we live in a world, a universe, that has micro and macro complexity, and they work together in ways that we don't yet understand. That makes my view quite philosophical I guess. Add to that that my interest has been cosmology first, and that invariably leads to acknowledgement and contemplation of the quantum realm, the quantum nature of particles and gravity. All of my thinking has been done before by many who follow the path to gain a personal understanding of the universe; no one gets it all right. I still say I am wrong, and so is everyone else, and I base that belief on the premise that there are many "as yet" unknowns". My world view though, is that there is a set of invariant natural laws the govern the mechanics of how things work together at all levels, macro and micro and in between. Thanks for the post, and accept my regards.
     

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