MigL Posted August 17, 2016 Posted August 17, 2016 I believe I may have used the coin example of entangled particles a long time ago... Take a coin and slice it in half, such that one half has heads showing and the other has tails showing. Seal each half in an envelope and then give one to DrP and the other to DrmDoc ( the two doctors ). Neither one knows the state of the coin in his envelope, it could be either heads or tails. But as soon as either one opens his envelope ( and collapses the wave function ), he immediately knows the state of the other coin held by the other doctor. Even though one is in the US and the other is in the UK. And no actual information has been transmitted.
StringJunky Posted August 17, 2016 Posted August 17, 2016 (edited) I believe I may have used the coin example of entangled particles a long time ago... Take a coin and slice it in half, such that one half has heads showing and the other has tails showing. Seal each half in an envelope and then give one to DrP and the other to DrmDoc ( the two doctors ). Neither one knows the state of the coin in his envelope, it could be either heads or tails. But as soon as either one opens his envelope ( and collapses the wave function ), he immediately knows the state of the other coin held by the other doctor. Even though one is in the US and the other is in the UK. And no actual information has been transmitted. If you split a quantum coin the same way, entangling the two halves, and knew which half you'd sent each to, the probability that it is the same coin/state that you sent to each is 50%, not 100%, when one envelope is opened, isn't it? Edited August 17, 2016 by StringJunky
swansont Posted August 17, 2016 Posted August 17, 2016 If you split a quantum coin the same way, entangling the two halves, and knew which half you'd sent each to, the probability that it is the same coin/state that you sent to each is 50%, not 100%, when one envelope is opened, isn't it? If one is heads, the other is tails. But other quantum measurements don't give the observed results if the particle is in a known state before the measurement, so there is no point in using the analogy for that. It fails. It's only a demonstration of a "conserved" quantity, if spin or polarization is too abstract.
StringJunky Posted August 17, 2016 Posted August 17, 2016 (edited) ....if the particle is in a known state before the measurement, so there is no point in using the analogy for that. It fails. ... I glossed over that bit... I knew it would be pushing the analogy too far and, as you say, wrong. I just intended it to show that, when the envelopes were sealed, the two halves went into superposition. Oh well.. Edited August 17, 2016 by StringJunky
DrmDoc Posted August 17, 2016 Author Posted August 17, 2016 (edited) I believe I may have used the coin example of entangled particles a long time ago... Take a coin and slice it in half, such that one half has heads showing and the other has tails showing. Seal each half in an envelope and then give one to DrP and the other to DrmDoc ( the two doctors ). Neither one knows the state of the coin in his envelope, it could be either heads or tails. But as soon as either one opens his envelope ( and collapses the wave function ), he immediately knows the state of the other coin held by the other doctor. Even though one is in the US and the other is in the UK. And no actual information has been transmitted. I see; therefore, in particle terms, if my envelope revealed heads, DrP's would reveal tails. So, this is not entanglement in the sense that what happens to one particle affects another, correct? Essentially, separating superposition particles is merely separating entangled polar particle into their separate or opposite polar state, correct? Edited August 17, 2016 by DrmDoc
StringJunky Posted August 17, 2016 Posted August 17, 2016 (edited) I see; therefore, in particle terms, if my envelope revealed heads, DrP's would reveal tails. So, this is not entanglement in the sense that what happens to one particle affects another, correct? Essentially, separating superposition particles is merely separating entangled polar particle into their separate or opposite polar state, correct? Yes, they are entangled but, as swansont pointed out, you don't know the initial states; you only know the state when you collapse the wave function/open the envelope. Edited August 17, 2016 by StringJunky
Strange Posted August 18, 2016 Posted August 18, 2016 (edited) oh man - now I'm confused again - from what you said SJ it sounds like the left shoe right shoe argument.... which I thought was proven wrong experimentally. If one is spin up when you test it does this mean the other is ALWAYS going to measure spin down? If so then how is this not just the pair of gloves argument? The difference is that the shoe (glove) is right or left from the moment it is made. So this is just a problem of lack of information. In the quantum case, the state of either photon is not just unknown but is indeterminate until measured. You can tell the difference from the probabilities of various outcomes. There is a good video on this that has been posted here a few times. There is also a good series of articles by someone going by the name of "Dr Chinese" which explain it very well - with and without math. Edited August 18, 2016 by Strange
DrP Posted August 18, 2016 Posted August 18, 2016 (edited) Do you have time to track the vid down Strange? I said I'd look for it for DrmDoc but forgot last night when I got home. I was quite good at explaining why it is not just like a pair of gloves, which it is easy to confuse with. (PS-I think the vid I am on about had a very small bit of math - but it was just simple probability) I think that the confusion (for me anyway) lies with the thinking that just because we haven't measured them yet they must still be one spin up one down (left or right gloves)... when we measure them we know what state they are in, but how do we know they aren't just in that state anyway before we measure them... like the gloves - before we open the package to see if we have a right or left one - if we have the right hand one then, with the gloves, we would have always had the right one........ with the photons though they are constantly changing and only when you pin it down to a measurement do they commit to being up or down - at that moment the other commits to being the opposite. Is that right? Edited August 18, 2016 by DrP
swansont Posted August 18, 2016 Posted August 18, 2016 Here's a discussion of entanglement and why hidden variables don't work, with a video link, explaining the difference between QM and having that particle have a definite state (like the glove) http://www.scienceforums.net/topic/87347-why-hidden-variables-dont-work/ 1
Strange Posted August 18, 2016 Posted August 18, 2016 Here: http://www.scienceforums.net/topic/87347-why-hidden-variables-dont-work/ with the photons though they are constantly changing and only when you pin it down to a measurement do they commit to being up or down - at that moment the other commits to being the opposite. Is that right? Not so much that they are constantly changing. They just don't have a well-defined state. 1
DrP Posted August 18, 2016 Posted August 18, 2016 that video is pretty good and outlines the Bell experiment. The one I was on about was pretty much the same - but that was it - the Bell experiment.
swansont Posted August 18, 2016 Posted August 18, 2016 Somewhat better article, in that it cautions you about the goals of the mission http://motherboard.vice.com/read/so-china-just-launched-a-quantum-satellite Still not a lot of technical detail, but at least they don't botch the entanglement explanation.
DrmDoc Posted August 18, 2016 Author Posted August 18, 2016 Here's a discussion of entanglement and why hidden variables don't work, with a video link, explaining the difference between QM and having that particle have a definite state (like the glove) http://www.scienceforums.net/topic/87347-why-hidden-variables-dont-work/ Illuminating, thanks for the link.
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