7 ms·

The part I don't understand is the "spooky action at a distance." Isn't this just the same as if the qbits were already in whatever their final state was as soo

by bdamm 8y ago

The part I don't understand is the "spooky action at a distance." Isn't this just the same as if the qbits were already in whatever their final state was as soon as they were entangled? Or in other words, is there any experimental basis for determining that the "cat" stayed alive at all? It seems a lot less magical when we just determine that in fact the value is the same no matter when or where you measure it, although it may not be predictable. And since the "entangled" qbit always had the same value, no matter when you measured it, then there is no "spooky action at a distance". The action occurred when d=0, and what you actually have is two copies of the same ROM.

ahelwer 8y ago
The idea that the qbits choose which value they'll collapse to at time of entanglement is called local hidden variable theory, which John Bell disproved in 1964: https://en.wikipedia.org/wiki/Local_hidden_variable_theory https://en.wikipedia.org/wiki/Local_hidden_variable_theory In more practical terms, the theory also falls apart when you start doing more complicated things with entangled qbits than just measuring them, like quantum teleportation or error correction.
- madeuptempacct 8y ago
  So, it's kind of like closures in JavaScript? "A Bell test experiment or Bell's inequality experiment, also simply a Bell test, is a real-world physics experiment designed to test the theory of quantum mechanics in relation to two other concepts: the principle of locality and Einstein's concept of "local realism". The experiments test whether or not the real world satisfies local realism, which requires the presence of some additional local variables (called "hidden" because they are not a feature of quantum theory) to explain the behavior of particles like photons and electrons. According to Bell's theorem, if nature actually operates in accord with any theory of local hidden variables, then the results of a Bell test will be constrained in a particular, quantifiable way. If a Bell test is performed in a laboratory and the results are not thus constrained, then they are inconsistent with the hypothesis that local hidden variables exist." Spooky private method scope is spooky.
- donutte 8y ago
  It’s also worth noting that as of 2015[0], this has been experimentally verified. We’ve made real-world measurements here that correlate with measurements made at the exact same time over there in a way that mathematically cannot be accounted for without some species of intuition-violating spookiness. It’s all very real. 0: https://en.wikipedia.org/wiki/Bell_test_experiments#Hensen_et_al.,_Giustina_et_al.,_Shalm_et_al._(2015):_"loophole-free"_Bell_tests https://en.wikipedia.org/wiki/Bell_test_experiments#Hensen_e...
- deleted 8y ago
  [deleted]
- crumpington 8y ago
  Big deal. There's nothing shocking or spooky about two billiard balls being made to spin in arbitrarily opposing directions, selecting only one (omg! without discovering which way it spins, you guys), then separating them, and then noticing the spin of one, in order to reliably grasp that the other is the reversal. I have two guitars. I place the guitars facing one another, such that plucking the HIGH E string on one, also plucks the LOW E string on the other. We put ear plugs in our ears, such that I can separate the two guitars, without us ever hearing them. I pluck the guitars, give you one, and take the other one and travel far away. I then listen to my guitar. It is the HIGH E guitar. Now I know you have the LOW E guitar. Wow. Incredibly unspooky. Not teleportration.
  - ChrisClark 8y ago
    https://en.wikipedia.org/wiki/Local_hidden_variable_theory https://en.wikipedia.org/wiki/Local_hidden_variable_theory https://en.wikipedia.org/wiki/Bell_test_experiments#Hensen_et_al.,_Giustina_et_al.,_Shalm_et_al._(2015):_%22loophole-free%22_Bell_tests https://en.wikipedia.org/wiki/Bell_test_experiments#Hensen_e...
    - crumpington 8y ago
      These links are intended to suggest something contrary to what I've said, but they do not suggest any contradiction.
      - bazinga56 8y ago
        Im not an expert so from my outside viewpoint I think by taking the guitar far away you are implying possibility of faster than light communication, which is thought to be not possible, so his links address that? Hard for me to understand so I'm just saying my thoughts out loud to get clarified, thanks
        crumpington 8y ago
        The quantum state of interest is induced when plucking the conjoined "guitars". (analog for particles) That state is induced at the moment the guitars share "locality" because entanglement requires locality for initialization of polarization. So then, we say we are as yet unaware of the qualities of the polarization we, ourselves, induced. Very mysterious. So spooky, yes? We do not measure, because we choose not to, so we do not yet know. Even if we prevent ourselves from having the capacity to measure, the results hold true, but so what? And so what, if we ask others to do the same. Imagine that we ask two waiters to tape two coins together in the kitchen, flip the linked coins, peel the coins apart while preserving the outcome of the coin flip, then take one coin to your table, and one to mine. Now I know which side of the coin you are looking at, without walking over to your table. So what. Nothing about this claims transmit information superluminously. In reality, with instrumentation, carrier signals relay an electromagnetic transmission in such a way that one cannot peek or tamper (the waiters can't change the coin flip, we cannot hear the ringing guitar), but this does not invalidate the premise of the analog. For the purposes of the analogous guitar example, we say that our couriers (electromagnetism itself) are prevented from touching or listening to the ringing guitars, or disclosing what they might sense. With the guitars, we say the guitars move away from the place where they were entangled. We'll say that our instrumentation rang the guitars at the grand canyon. Our couriers then transported the guitars to you, at the top of the Empire State Building in New York, and me on the Golden Gate Bridge in San Francisco. I receive the guitar, and discover that the LOW E string is ringing, it can only mean that you guitar's HIGH E string in ringing in New York. There are no local hidden variables in this example. The premise of polarity as a corollary for guitar strings is modeled in the exact same manner. Six strings on a guitar maps to the same essential parameters of each of two directions for all three axes of spin.
- lisper 8y ago
  Something else worth noting: an entangled state is itself a superposition of two non-entangled states. This is obvious when you look at the math: the entangled state |10> + |01> is the superposition of the factorizable (non-entangled) states |10> and |01>. But physically what this means is that entanglement is intimately related to interference. Interference happens when a photon "goes both ways". Entanglement happens when a pair of photons go in such a way that you can't tell which photon went which way. (There's more to it than that, but the point is that entanglement and interference are closely related phenomena. This fact is often overlooked, particularly when it comes to explanations of entanglement directed at lay audiences.) Also, the idea that collapse is a physical phenomenon that propagates faster than light is not universally accepted. There are other ways to interpret these results. None of them take a toll on your intuition, but personally I like this one: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf (There's a video too: https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc)
- moosinho 8y ago
  Can someone tell me if I understand this correctly. So Bell famously proved that it is not the case that the correlation we see between 2 entangled particles A and B is because of some common cause C. Therefore we concluded that it must be that A => B or B => A and we called it a spooky action at a distance. But aren't we forgetting that there's a one more way to get a correlation between A and B without resorting to spooky action at a distance - conditioning on a common effect, aka collider: http://www.the100.ci/2017/03/14/that-one-weird-third-variable-problem-nobody-ever-mentions-conditioning-on-a-collider/ http://www.the100.ci/2017/03/14/that-one-weird-third-variabl... Has anyone proven that this is not the case?
  - abecedarius 8y ago
    What you're proposing is essentially what Bell's inequalities contradict. That's why they're surprising. I think the many-worlds picture is a clearer way to think about this than "spooky action at a distance".
  - avip 8y ago
    Bell inequality proves (or is used to show) that the shared/correlated state of "entangled" particles cannot be fixed before the act of measurement. It has nothing to say about "A => B" or the likes. If there exists a third "C" it'll still have to set the state of A and B, at the moment of measurement, regardless of distance.
  - mundo 8y ago
    Yes, this is more or less what Bell's theorem disproves, although it's kind of a poor metaphor, because entanglement deals with indeterminate states, not just unknown ones.
stouset 8y ago
The explanation you're supposing for the "spooky action at a distance" is called a hidden variable theory, and as others have said, this explanation has been disproven. You might be wondering how, and I'll tell you the scenario (adapted from The Elegant Universe) that helped me understand. Imagine you and I each have a device: a small box with one openable window on the top, one on the front, and one on the back. When one of these windows is opened, it shows either white or black. Further, I tell you that these boxes are entangled: if we both open the same window, the same color will be displayed on both boxes. This only works for the first window opened and only if we both open the same window: if a second window is opened or if we open two different windows, the colors shown will no longer be correlated in any way. I actually have many of these pairs of boxes, each pair numbered uniquely to identify its matching twin, and we run the experiment for an arbitrarily large number of them until you're satisfied that my claim holds true. You see nothing special about these boxes and argue that they're simply preprogrammed from the factory to display a set of colors the first time a window is opened (for example, BWB or WWB). I counter that entanglement is special and the boxes are not preprogrammed from the factory. In fact, they decide at random which color to show right at the moment one of the boxes' windows is opened! My claim seems crazy and at first glance possibly even unprovable! But it turns out with a bit of cleverness we can test this. We take an arbitrarily large number of boxes and begin independently opening their windows at random (without consulting or coordinating with each other when deciding which window to open), recording box numbers, window choices, and the resulting colors. When finished, we compare notes. Sure enough, when we both open the same window on entangled boxes, the colors match as expected. Upon a closer look at the data, we discover something surprising. Ignoring which window we opened, each pair of entangled boxes showed the same color exactly 50% of the time. How is this surprising? A little bit of probabilistic analysis conclusively demonstrates that such a result is fundamentally incompatible with any hidden variable theory. Assume for the sake of argument that the boxes are preprogrammed. The only possible programming for each box is some form of XXX or XXY. Consider: if both boxes are programmed WWW (or BBB) and we both open a window at random, it will show the same color 100% of the time. If both are programmed WWB (or BWB, or BWW, or any equivalent variant), 2/3 of the time there's a 2/3 chance of displaying the same color when choosing windows at random and 1/3rd of the time there's a 1/3 chance. Combined, whenever the colors are in an XXY configuration, there's a 5/9 chance of showing the same color when windows are chosen at random. Note that in both scenarios the odds of seeing the same color from randomly-chosen windows are greater than 50%! Assuming the preprogrammed colors are chosen at random, some form of XXX will be chosen 2/8 of the time and XXY will be chosen 6/8 of the time, we see that the total odds of seeing the same color if the boxes were preprogrammed should be 2/8 * 100% + 6/8 * 5/9 = 2/3. In theory, our data should have shown a 66% agreement in color, but our experiment consistently shows colors matching 50% of the time. A hidden variable theory—any hidden variable theory—runs into this probabilistic hurdle.

by bdamm 8y ago

ahelwer 8y ago

The idea that the qbits choose which value they'll collapse to at time of entanglement is called local hidden variable theory, which John Bell disproved in 1964: https://en.wikipedia.org/wiki/Local_hidden_variable_theory https://en.wikipedia.org/wiki/Local_hidden_variable_theory In more practical terms, the theory also falls apart when you start doing more complicated things with entangled qbits than just measuring them, like quantum teleportation or error correction.

madeuptempacct 8y ago
So, it's kind of like closures in JavaScript? "A Bell test experiment or Bell's inequality experiment, also simply a Bell test, is a real-world physics experiment designed to test the theory of quantum mechanics in relation to two other concepts: the principle of locality and Einstein's concept of "local realism". The experiments test whether or not the real world satisfies local realism, which requires the presence of some additional local variables (called "hidden" because they are not a feature of quantum theory) to explain the behavior of particles like photons and electrons. According to Bell's theorem, if nature actually operates in accord with any theory of local hidden variables, then the results of a Bell test will be constrained in a particular, quantifiable way. If a Bell test is performed in a laboratory and the results are not thus constrained, then they are inconsistent with the hypothesis that local hidden variables exist." Spooky private method scope is spooky.
donutte 8y ago
It’s also worth noting that as of 2015[0], this has been experimentally verified. We’ve made real-world measurements here that correlate with measurements made at the exact same time over there in a way that mathematically cannot be accounted for without some species of intuition-violating spookiness. It’s all very real. 0: https://en.wikipedia.org/wiki/Bell_test_experiments#Hensen_et_al.,_Giustina_et_al.,_Shalm_et_al._(2015):_"loophole-free"_Bell_tests https://en.wikipedia.org/wiki/Bell_test_experiments#Hensen_e...
deleted 8y ago
[deleted]
crumpington 8y ago
Big deal. There's nothing shocking or spooky about two billiard balls being made to spin in arbitrarily opposing directions, selecting only one (omg! without discovering which way it spins, you guys), then separating them, and then noticing the spin of one, in order to reliably grasp that the other is the reversal. I have two guitars. I place the guitars facing one another, such that plucking the HIGH E string on one, also plucks the LOW E string on the other. We put ear plugs in our ears, such that I can separate the two guitars, without us ever hearing them. I pluck the guitars, give you one, and take the other one and travel far away. I then listen to my guitar. It is the HIGH E guitar. Now I know you have the LOW E guitar. Wow. Incredibly unspooky. Not teleportration.
- ChrisClark 8y ago
  https://en.wikipedia.org/wiki/Local_hidden_variable_theory https://en.wikipedia.org/wiki/Local_hidden_variable_theory https://en.wikipedia.org/wiki/Bell_test_experiments#Hensen_et_al.,_Giustina_et_al.,_Shalm_et_al._(2015):_%22loophole-free%22_Bell_tests https://en.wikipedia.org/wiki/Bell_test_experiments#Hensen_e...
  - crumpington 8y ago
    These links are intended to suggest something contrary to what I've said, but they do not suggest any contradiction.
    - bazinga56 8y ago
      Im not an expert so from my outside viewpoint I think by taking the guitar far away you are implying possibility of faster than light communication, which is thought to be not possible, so his links address that? Hard for me to understand so I'm just saying my thoughts out loud to get clarified, thanks
      - crumpington 8y ago
        The quantum state of interest is induced when plucking the conjoined "guitars". (analog for particles) That state is induced at the moment the guitars share "locality" because entanglement requires locality for initialization of polarization. So then, we say we are as yet unaware of the qualities of the polarization we, ourselves, induced. Very mysterious. So spooky, yes? We do not measure, because we choose not to, so we do not yet know. Even if we prevent ourselves from having the capacity to measure, the results hold true, but so what? And so what, if we ask others to do the same. Imagine that we ask two waiters to tape two coins together in the kitchen, flip the linked coins, peel the coins apart while preserving the outcome of the coin flip, then take one coin to your table, and one to mine. Now I know which side of the coin you are looking at, without walking over to your table. So what. Nothing about this claims transmit information superluminously. In reality, with instrumentation, carrier signals relay an electromagnetic transmission in such a way that one cannot peek or tamper (the waiters can't change the coin flip, we cannot hear the ringing guitar), but this does not invalidate the premise of the analog. For the purposes of the analogous guitar example, we say that our couriers (electromagnetism itself) are prevented from touching or listening to the ringing guitars, or disclosing what they might sense. With the guitars, we say the guitars move away from the place where they were entangled. We'll say that our instrumentation rang the guitars at the grand canyon. Our couriers then transported the guitars to you, at the top of the Empire State Building in New York, and me on the Golden Gate Bridge in San Francisco. I receive the guitar, and discover that the LOW E string is ringing, it can only mean that you guitar's HIGH E string in ringing in New York. There are no local hidden variables in this example. The premise of polarity as a corollary for guitar strings is modeled in the exact same manner. Six strings on a guitar maps to the same essential parameters of each of two directions for all three axes of spin.
lisper 8y ago
Something else worth noting: an entangled state is itself a superposition of two non-entangled states. This is obvious when you look at the math: the entangled state |10> + |01> is the superposition of the factorizable (non-entangled) states |10> and |01>. But physically what this means is that entanglement is intimately related to interference. Interference happens when a photon "goes both ways". Entanglement happens when a pair of photons go in such a way that you can't tell which photon went which way. (There's more to it than that, but the point is that entanglement and interference are closely related phenomena. This fact is often overlooked, particularly when it comes to explanations of entanglement directed at lay audiences.) Also, the idea that collapse is a physical phenomenon that propagates faster than light is not universally accepted. There are other ways to interpret these results. None of them take a toll on your intuition, but personally I like this one: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf (There's a video too: https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc)
moosinho 8y ago
Can someone tell me if I understand this correctly. So Bell famously proved that it is not the case that the correlation we see between 2 entangled particles A and B is because of some common cause C. Therefore we concluded that it must be that A => B or B => A and we called it a spooky action at a distance. But aren't we forgetting that there's a one more way to get a correlation between A and B without resorting to spooky action at a distance - conditioning on a common effect, aka collider: http://www.the100.ci/2017/03/14/that-one-weird-third-variable-problem-nobody-ever-mentions-conditioning-on-a-collider/ http://www.the100.ci/2017/03/14/that-one-weird-third-variabl... Has anyone proven that this is not the case?
- abecedarius 8y ago
  What you're proposing is essentially what Bell's inequalities contradict. That's why they're surprising. I think the many-worlds picture is a clearer way to think about this than "spooky action at a distance".
- avip 8y ago
  Bell inequality proves (or is used to show) that the shared/correlated state of "entangled" particles cannot be fixed before the act of measurement. It has nothing to say about "A => B" or the likes. If there exists a third "C" it'll still have to set the state of A and B, at the moment of measurement, regardless of distance.
- mundo 8y ago
  Yes, this is more or less what Bell's theorem disproves, although it's kind of a poor metaphor, because entanglement deals with indeterminate states, not just unknown ones.

stouset 8y ago

The explanation you're supposing for the "spooky action at a distance" is called a hidden variable theory, and as others have said, this explanation has been disproven. You might be wondering how, and I'll tell you the scenario (adapted from The Elegant Universe) that helped me understand. Imagine you and I each have a device: a small box with one openable window on the top, one on the front, and one on the back. When one of these windows is opened, it shows either white or black. Further, I tell you that these boxes are entangled: if we both open the same window, the same color will be displayed on both boxes. This only works for the first window opened and only if we both open the same window: if a second window is opened or if we open two different windows, the colors shown will no longer be correlated in any way. I actually have many of these pairs of boxes, each pair numbered uniquely to identify its matching twin, and we run the experiment for an arbitrarily large number of them until you're satisfied that my claim holds true. You see nothing special about these boxes and argue that they're simply preprogrammed from the factory to display a set of colors the first time a window is opened (for example, BWB or WWB). I counter that entanglement is special and the boxes are not preprogrammed from the factory. In fact, they decide at random which color to show right at the moment one of the boxes' windows is opened! My claim seems crazy and at first glance possibly even unprovable! But it turns out with a bit of cleverness we can test this. We take an arbitrarily large number of boxes and begin independently opening their windows at random (without consulting or coordinating with each other when deciding which window to open), recording box numbers, window choices, and the resulting colors. When finished, we compare notes. Sure enough, when we both open the same window on entangled boxes, the colors match as expected. Upon a closer look at the data, we discover something surprising. Ignoring which window we opened, each pair of entangled boxes showed the same color exactly 50% of the time. How is this surprising? A little bit of probabilistic analysis conclusively demonstrates that such a result is fundamentally incompatible with any hidden variable theory. Assume for the sake of argument that the boxes are preprogrammed. The only possible programming for each box is some form of XXX or XXY. Consider: if both boxes are programmed WWW (or BBB) and we both open a window at random, it will show the same color 100% of the time. If both are programmed WWB (or BWB, or BWW, or any equivalent variant), 2/3 of the time there's a 2/3 chance of displaying the same color when choosing windows at random and 1/3rd of the time there's a 1/3 chance. Combined, whenever the colors are in an XXY configuration, there's a 5/9 chance of showing the same color when windows are chosen at random. Note that in both scenarios the odds of seeing the same color from randomly-chosen windows are greater than 50%! Assuming the preprogrammed colors are chosen at random, some form of XXX will be chosen 2/8 of the time and XXY will be chosen 6/8 of the time, we see that the total odds of seeing the same color if the boxes were preprogrammed should be 2/8 * 100% + 6/8 * 5/9 = 2/3. In theory, our data should have shown a 66% agreement in color, but our experiment consistently shows colors matching 50% of the time. A hidden variable theory—any hidden variable theory—runs into this probabilistic hurdle.