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Thread: Double-Slit: Possible Reason for Disappearance of Interference

  1. #1 Double-Slit: Possible Reason for Disappearance of Interference 
    FAS
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    I want to propose a possible answer as to why an interference pattern disappears in a double-slit experiment when a detector is added. Here is my proposal:

    We know that the detector is an electrical device, correct? We also know that electrical devices in general produce magnetic frequency waves, right?

    A photon is an extremely tiny particle. So when it is subjected to an abnormal magnetic force from an electrical device, is it not possible for the photon to lose its ability to move in its normal movement pattern? When such a small particle is being subjected to a number of milligausses’ worth of magnetic frequency, is it not possible that it gets forced to move in a way that is different from its normal course of movement?

    So maybe the reason that the interference pattern stops is not because the particle is being detected or ‘watched’, but because it has been put in a different environment- one with abnormal levels of magnetic frequency, therefore losing its ability to move normally. I want to suggest this as a possibility.

    We might be able to test this idea by using a different device in the experiment. Instead of a detector, we can use some hair clippers. We can turn the device on and put it as close to the slits as the detector would be. If the interference pattern stops, then we might conclude that the reason was the magnetic frequency being emitted from the device.

    For more accuracy, the magnetic frequency being generated by the detector could be measured. Then an electric device generating approximately the same amount of frequency can be used for the experiment.


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    Quote Originally Posted by FAS View Post
    I want to propose a possible answer as to why an interference pattern disappears in a double-slit experiment when a detector is added.
    Can you explain what is wrong with the current theory (bearing in mind it is one of the most precisely tested theories in history)?

    We know that the detector is an electrical device, correct?
    No necessarily. You could use a passive device (photographic film, perhaps).

    We also know that electrical devices in general produce magnetic frequency waves, right?
    True. But that can be minimised through techniques such as circuit, screening, etc.

    Also, the size of any electromagnetic fields generated could be measured and their potential effects calculated.

    So when it is subjected to an abnormal magnetic force from an electrical device, is it not possible for the photon to lose its ability to move in its normal movement pattern?
    Apart from the fact that I'm not sure what that means, this could be easily eliminated by keeping the detector in the same place but turned off, keeping the detector turn on in (almost) the same place but out of the path of the photon, etc. Identifying and eliminating possible sources of error like this are a standard part of experimental design so I would be very surprised if every possible combination of detector present/not-present, turned-on/turned-off, etc is not included in the procedure.

    When such a small particle is being subjected to a number of milligausses’ worth of magnetic frequency, is it not possible that it gets forced to move in a way that is different from its normal course of movement?

    So maybe the reason that the interference pattern stops is not because the particle is being detected or ‘watched’, but because it has been put in a different environment- one with abnormal levels of magnetic frequency, therefore losing its ability to move normally.
    I don't know what "losing its ability to move normally" means (and I suspect you don't either) but how is interfering with the photon any different from detecting it?

    Instead of a detector, we can use some hair clippers.
    Have I just fallen for some sort of elaborate joke?


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    Quote Originally Posted by FAS View Post
    So maybe the reason that the interference pattern stops is not because the particle is being detected or ‘watched’, but because it has been put in a different environment- one with abnormal levels of magnetic frequency, therefore losing its ability to move normally. I want to suggest this as a possibility.
    You should look into two variants of the double slit experiment - The Quantum Eraser and the Delayed Choice Quantum Eraser.

    If the information exists as to which slit the photon passed through, we lose the interference pattern.

    If we erase that information, we can find the interference pattern again.

    We can even find the interference pattern again if we erase the "which slit" information from the system after the photons have hit the final detector screen.

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    Thanks for your reply, Strange. Here are my answers:

    1. I am not necessarily saying that there is anything wrong with the current theory. But I have seen that some sources mention that it is shocking for the interference to disappear when a detector attempts to detect the particle. So, it seems as though there is something still unclear about the issue. I have mentioned a possible reason.

    2. Regarding the information I mentioned about electrical devices emitting magnetic frequency waves, you said:

    "True. But that can be minimised through techniques such as circuit, screening, etc.

    Also, the size of any electromagnetic fields generated could be measured and their potential effects calculated."

    Considering the tiny size of photons and other particles used in the experiments, minimizing the magnetic force might be unhelpful. And the particles might be extremely sensitive due to their size.

    3. Yes, I knew what I meant when I said "losing its ability to move normally". I meant the disappearance of interference- without a detector, there is interference; with a detector, the interference is no longer present. Therefore, when a detector is present, the particle is no longer moving "normally".

    4. No, you did not fall for an elaborate joke in the issue with the clippers. I mentioned that as a suggestion to attempt to know if the reason behind the disappearance of interference is indeed the magnetic force emitted from an electrical device. Since electrical hair clippers produce magnetic frequency waves when turned on, we could put such a machine close to the slits during an experiment. If the interference disappears, then we might be able to say that it was due to the magnetic force from the clippers, or whatever other electrical equipment we use for the experiment.
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by FAS View Post
    So maybe the reason that the interference pattern stops is not because the particle is being detected or ‘watched’, but because it has been put in a different environment- one with abnormal levels of magnetic frequency, therefore losing its ability to move normally. I want to suggest this as a possibility.
    You should look into two variants of the double slit experiment - The Quantum Eraser and the Delayed Choice Quantum Eraser.

    If the information exists as to which slit the photon passed through, we lose the interference pattern.

    If we erase that information, we can find the interference pattern again.

    We can even find the interference pattern again if we erase the "which slit" information from the system after the photons have hit the final detector screen.

    Thanks for mentioning this information.

    In the situations you mentioned where we can find the interference pattern again, is it not true that some device was present in the experiment and doing some monitoring/recording? So assuming that this device is an electrical one and that it produces magnetic frequency, it might be irrelevant whether we try to know the 'which-slit' information before or after the experiment.

    My suggested possible idea was that the interference pattern is disrupted by the magnetic force emitted from the detector. Check out the following part of an article. The article could be found at: Disentangling the wave-particle duality in the double-slit experiment | Ars Technica. The quote is as follows:

    "The researchers used a second counter, called D2, to reveal the final position of the signal photon. First, D2 was placed right next to the slits, so it was able to tell which the signal photon went through. This was used to confirm that the entanglement measurements matched up with the ones from the detector. Then D2 was pulled far enough away from the slits for the photons to interfere. In this position, it measured the complete interference pattern produced by the single photons." (end of quote)

    Notice that last sentence where it says when D2 was pulled away from the slits, the complete interference was measured. So the device called D2 seems to be disrupting the interference. So this might be due to the magnetic force that is produced from the D2 device.


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    Quote Originally Posted by FAS View Post
    Notice that last sentence where it says when D2 was pulled away from the slits, the complete interference was measured. So the device called D2 seems to be disrupting the interference. So this might be due to the magnetic force that is produced from the D2 device.
    That is a very poor description. Take a look here: Delayed choice quantum eraser - Wikipedia, the free encyclopedia

    (I have seen a better [easier to follow] description somewhere, I'll see if I can track it down.)
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    As I understand it with my very limited knowledge of physics; a photon does not travel as a particle but as a probability wave. IOW in transit a photon is smeared over an area much larger than the size of the particle itself. This is why we can see the interference pattern in the double slit experiment. Even when photons are fired in sequence they still exhibit the interference pattern which confirms the wavelike function while in transit. The photons (as particles) do not interfere with each other, it's their wavelike function.

    When we observe this function and determine the position of the photon the wavelike pattern collapses and the photon becomes fixed as a particle in a specific location. But as a result the interference pattern also disappears due to the collapsing of the probability wave function.

    Is this not also related to Heisenberg's uncertainty principle, where we can measure the speed but not the location or we can measure the location but not the speed of a fundamental particle?
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    I would also recommend finding Feynman's QED lectures on the web (or reading the book, if you are old skool).
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    Quote Originally Posted by FAS View Post
    In the situations you mentioned where we can find the interference pattern again, is it not true that some device was present in the experiment and doing some monitoring/recording? So assuming that this device is an electrical one and that it produces magnetic frequency, it might be irrelevant whether we try to know the 'which-slit' information before or after the experiment.
    The photons hit the detector screen where they hit the detector screen. If the detector screen was interfering with the experiment, we would not be able to find the interference pattern hidden in the data later on. The pattern is found when correlating the positions of the photons on the detector screen with the hits of their entangled partners on the other screen.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by FAS View Post
    Notice that last sentence where it says when D2 was pulled away from the slits, the complete interference was measured. So the device called D2 seems to be disrupting the interference. So this might be due to the magnetic force that is produced from the D2 device.
    That is a very poor description. Take a look here: Delayed choice quantum eraser - Wikipedia, the free encyclopedia

    (I have seen a better [easier to follow] description somewhere, I'll see if I can track it down.)
    It might sound like a poor description, but I think it might explain at least some of the issue. In terms of physics, what is the difference between having the D2 device close to the slits and having it far away?

    Regarding the double-slit experiment, the entry in Wikipedia says: "And in 2012, researchers finally succeeded in correctly identifying the path each particle had taken without any adverse effects at all on the interference pattern generated by the particles." It then points to the article that I quoted from above. Here is the link to the entry: Double-slit experiment - Wikipedia, the free encyclopedia

    Has any experiment attempted to move the detecting device far away from the slits before? If not, could this be the reason that this experiment succeeded? And I will check out the article that you mentioned regarding the delayed choice quantum eraser.

    Quote Originally Posted by Write4U View Post
    As I understand it with my very limited knowledge of physics; a photon does not travel as a particle but as a probability wave. IOW in transit a photon is smeared over an area much larger than the size of the particle itself. This is why we can see the interference pattern in the double slit experiment. Even when photons are fired in sequence they still exhibit the interference pattern which confirms the wavelike function while in transit. The photons (as particles) do not interfere with each other, it's their wavelike function.

    When we observe this function and determine the position of the photon the wavelike pattern collapses and the photon becomes fixed as a particle in a specific location. But as a result the interference pattern also disappears due to the collapsing of the probability wave function.

    Is this not also related to Heisenberg's uncertainty principle, where we can measure the speed but not the location or we can measure the location but not the speed of a fundamental particle?
    Thanks for trying to clarify some information. Now it seems that scientists still cannot fully explain the phenomenon of the disappearance of interference when a detector is added to the experiment. Any thoughts about a possible explanation for this?

    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by FAS View Post
    In the situations you mentioned where we can find the interference pattern again, is it not true that some device was present in the experiment and doing some monitoring/recording? So assuming that this device is an electrical one and that it produces magnetic frequency, it might be irrelevant whether we try to know the 'which-slit' information before or after the experiment.
    The photons hit the detector screen where they hit the detector screen. If the detector screen was interfering with the experiment, we would not be able to find the interference pattern hidden in the data later on. The pattern is found when correlating the positions of the photons on the detector screen with the hits of their entangled partners on the other screen.
    Good point. My proposed theory might apply in some versions of the experiment and not others.

    Thinking about it logically, what does a detector contribute to the experiment in terms of physics? If the readers know of other things besides the magnetic frequency emitted by the electrical device, let them post it here please. As I mentioned, my proposed hypothesis can be wrong in some versions of the experiment. But there still seems to be indicators that magnetic frequency has something to do with the issue, such as the experiment with the D2 device mentioned above.
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    Quote Originally Posted by FAS View Post
    Good point. My proposed theory might apply in some versions of the experiment and not others.
    Which would mean... ?
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    Quote Originally Posted by FAS View Post
    Notice that last sentence where it says when D2 was pulled away from the slits, the complete interference was measured. So the device called D2 seems to be disrupting the interference. So this might be due to the magnetic force that is produced from the D2 device.
    OK. I've just read this article more carefully. It is actually more interesting than I thought (thanks for that). But I should point out that it is D1 which determines which slit the photon passed through and D2 which registers the interference pattern.

    The only significance of putting D2 near the slits was to check that both detectors were seeing the "same" photon ("same" in that they are detecting two different but entangled "twin" photons). The "real" experiment begins when they move D2 away, where it can see the interference pattern while D1 sees which slit was taken. (I think that there is only a (high) probability of knowing which slit it went through but this is getting beyond my understanding. )

    Anyway, bottom line: putting the detector near the slits is irrelevant.
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by FAS View Post
    Good point. My proposed theory might apply in some versions of the experiment and not others.
    Which would mean... ?
    Let me change what I said. It is better if I say that my proposed theory might explain the issue partially. So there could be other factors besides magnetic frequency waves that cause the interference pattern to break.

    Quote Originally Posted by Strange View Post
    Quote Originally Posted by FAS View Post
    Notice that last sentence where it says when D2 was pulled away from the slits, the complete interference was measured. So the device called D2 seems to be disrupting the interference. So this might be due to the magnetic force that is produced from the D2 device.
    OK. I've just read this article more carefully. It is actually more interesting than I thought (thanks for that). But I should point out that it is D1 which determines which slit the photon passed through and D2 which registers the interference pattern.

    The only significance of putting D2 near the slits was to check that both detectors were seeing the "same" photon ("same" in that they are detecting two different but entangled "twin" photons). The "real" experiment begins when they move D2 away, where it can see the interference pattern while D1 sees which slit was taken. (I think that there is only a (high) probability of knowing which slit it went through but this is getting beyond my understanding. )

    Anyway, bottom line: putting the detector near the slits is irrelevant.
    I do not understand how putting the detector near the slits is irrelevant. If they move the D2 device away, the experiment is successful. If they keep it close, the experiment fails.

    Maybe you are saying this since D1 is near the slits anyway, and therefore putting a device near the particle would not affect it. Well, two electrical devices produce more frequency than one device. So the particle might have been doing fine with just D1 next to it, but when D2's magnetic waves were added, it was a different case. Whatever is behind the issue, it seems clear that the position of the D2 device played a critical role in the experiment. And I think that would be potential evidence for the theory I proposed.
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    Quote Originally Posted by FAS View Post
    I do not understand how putting the detector near the slits is irrelevant. If they move the D2 device away, the experiment is successful. If they keep it close, the experiment fails.
    You seem to think that the way you work out which slit a photon went through, you put a detector next to the slit and watch it go past. That is not how it works. There is no need for either detector to be near the slits when the experiment is performed.

    Firstly, D2 has to be a sufficient distance away for an interference pattern to develop; i.e. if it is too close, it will only receive light from one slit and therefore an interference pattern cannot form. This is true of the classical optics version, a quantum version where you don't care which slit the light went through, the "quantum erasure" version, delayed quantum erasure, this one, or any other.

    D2 must be distant when the experiment is performed (we'll come back to why they moved it later).

    D1 does not have to be near the slits either. The reason is the way you detect which slit the photon went through. This starts by splitting the photon into two entangled photons. Entangled simply means they have some properties in common so when you detect one of the pair, it tells you something about the other. Because the "which slit" detector (D1) is just detecting a photon (the "idler" photon) it can be any distance away. In fact, in the delayed quantum erasure experiment D1 must be further away than D2 (because that's the whole point of the experiment) - take a look here: File:Kim EtAl Quantum Eraser.svg - Wikipedia, the free encyclopedia for example.

    Furthermore, the sketch of the experimental set up in the actual paper, shows that the photons get to the detectors via fibre optic cables. So the two detectors are actually next to each other in a fixed location (which makes sense as they need to be connected to the same coincidence counter).

    Back to moving D2 (or at least, moving he fibre optic cable). This is just part of the double-checking of the set up that any experiment performs. In this case, they are using a novel variation on how to detect which slit the photon went through. In order to check that this gives the correct results, they temporarily use D2 to check that D1 is giving the correct results; i.e. stick D2 in front of slit A and check that it detects a photon when D1 says the photon went through slit A. And ditto for slit B.

    Having checked that D1 is detecting what they expect, they move D2 back to the location where it can detect the interference pattern and run the experiment proper.

    Does that make sense?

    [Edit: Having just skimmed through the paper again, that description may not be completely accurate. I'll try and find time to read it properly.]
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    Quote Originally Posted by FAS View Post
    Now it seems that scientists still cannot fully explain the phenomenon of the disappearance of interference when a detector is added to the experiment. Any thoughts about a possible explanation for this?
    Thoughts? Yes, it's not true.

    The result was exactly as predicted by theory. The whole experiment was developed based on an understanding of quantum theory. As they say in the paper:
    This interpretation arises from our theoretical
    analysis within quantum theory.
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    Thanks for all this information, Strange. I will say that there are some things that I still do not understand clearly about the procedures in the experiments. So I need to do more reading and analyzing. But still, I do not want to rule out the issue of magnetic frequency having some effect. Maybe I can propose this theory in a better way when I get a more clear understanding of the experiments and their details.
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    The full paper describing the experiment is here: http://www.pnas.org/content/109/24/9314.full.pdf
    It gets pretty technical though.

    I mentioned the Feynman lectures earlier. These give a good description of what we know (and what we cannot know) about photon interactions. This is aimed at a relatively non-technical audience.
    The Vega Science Trust - Richard Feynman - Science Videos
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    Cool. I will check these out.
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    Ow guys you make me so happy to see that you are all into the Delayed choice experiment
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    I have never seen a publication about the standerd double slit with detectors on the slits, with a description of the slit-detector. If this detector disturbs the coherence of the wave, the disappearing of the inteference pattern is a logical result.
    Does someone know a publication?
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    The detection of which slit the photon goes through doesn't have to be done at the slit; it can be done in such a way that it doesn't disturb the photons going through the slits at all. In fact, the 'which-slit' detection can be done after the interference pattern is formed. There is a description here: Delayed choice quantum eraser - Wikipedia, the free encyclopedia.
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    The point of the quantum eraser experiments is that the measured photon is a different photon to the photon that does or doesn't form an interference pattern. This rules out explanations that involve tampering with the photon.

    I don't think magnetism can actually affect the path of a photon due to the linearity of electrodynamics (the superposition principle).

    Quantum mechanics actually explains in mathematical terms why measuring the which-slit information destroys the interference pattern. This explanation says that irrespective of how the which-slit information is determined, the interference pattern will be destroyed. This rules out explanations involving specific detection mechanisms or the specific nature of the particle passing through the double-slits. While quantum mechanics still continues to be experimentally tested, the mathematical explanation lies at the core of how quantum mechanics operates, so it is unlikely that there will be any experiment that produces a result that is contrary to this particular aspect of quantum mechanics.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    I just noticed that this thread is 18 months old.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    It's a software bug in the laws of Physics of the Universe. Somebody didn't finish beta testing before the Big Bang.
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    Quote Originally Posted by Daecon View Post
    It's a software bug in the laws of Physics of the Universe. Somebody didn't finish beta testing before the Big Bang.
    On the contrary... quantum mechanics is a very elegant solution indeed.

    It's a bit like friction... a bugbear to the efficiency of machines, but we wouldn't be able to do anything without it.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by Strange View Post
    The detection of which slit the photon goes through doesn't have to be done at the slit; it can be done in such a way that it doesn't disturb the photons going through the slits at all. In fact, the 'which-slit' detection can be done <em>after</em> the interference pattern is formed.
    Indeed, but everybody is using the detector-before-each-slit but never refers to an actual publiced measurement. Such a publication should first show that it is not the tcehnical behaviour of the detector which caused disappearence (and I never seen such a detector)

    The delayed choice quantum eraser is a more complicated measurement which has its own problems in explanition (at one photon level). I want to address that later. First I want to be sure about the basic measurement.
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    Quote Originally Posted by DParlevliet View Post
    Indeed, but everybody is using the detector-before-each-slit but never refers to an actual publiced measurement.
    Who is "everybody"? Obviously a detector before or both slits will destroy the interference pattern because it will stop any photons passing through the slit(s).

    Here are a few references to get you started:
    Stochastic and deterministic absorption in neutron-interference experiments
    Updating the wave-particle duality - PhilSci-Archive
    Unsharp particle-wave duality in a photon split-beam experiment

    The delayed choice quantum eraser is a more complicated measurement which has its own problems in explanition (at one photon level).
    What problems does it have? Are you sure it is not a problem with your understanding?
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    Quote Originally Posted by Strange View Post
    Who is "everybody"?
    Feynman
    Brian Greene
    Wikipedia and problaby the 5 citations mentioned there

    I agree with what you say, but that is not what I read in books and articals.
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    Quote Originally Posted by DParlevliet View Post
    Quote Originally Posted by Strange View Post
    Who is "everybody"?
    Feynman
    Brian Greene
    Wikipedia and problaby the 5 citations mentioned there

    I agree with what you say, but that is not what I read in books and articals.
    Maybe you need to find some peer reviewed science that says what you claim.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by DParlevliet View Post
    The delayed choice quantum eraser is a more complicated measurement which has its own problems in explanition (at one photon level).
    What problems does it have? Are you sure it is not a problem with your understanding?
    See a simplified diagram of the measurement of Kim et al:

    This is not a real two-slit measurement. The red and blue area of the BBO emit a double photon now and then, not at the same time and not coherent. They act as two independent sources. When you look at the one photon level: suppose the red part emits a double photon. Then in general there will be no blue photon emitted. So with what does this red photon interfere on D0?
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    Quote Originally Posted by DParlevliet View Post
    This is not a real two-slit measurement.
    It is equivalent, using two sources instead of two slits.

    The red and blue area of the BBO emit a double photon now and then, not at the same time and not coherent.
    They always emit two (entangled) photons: one to create the interference pattern (or not) and the other to detect the source (or not).

    When you look at the one photon level: suppose the red part emits a double photon. Then in general there will be no blue photon emitted. So with what does this red photon interfere on D0?
    That is the whole point of the single-photon two slit experiment: there is only one photon at a time and the question "what does it interfere with" has no intuitive answer. However, it is (of course) fully explained by quantum theory.
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    The photon goes through one slit, but its wave goes through both slits. It is the two waves which interfere at the detector and determines the probability of detecting the photon. So the waves through both slits must be coherent, having the same phase (shift). Two sources do not produce coherent waves at the same time.

    If the red part emits a double photon, generally the blue part does not emit a photon. One red photon goes to D0 but there is no double slit in between, so no phase shift so no interference pattern

    The same as if you switch off the blue part: the red photons alone will not cause an interference pattern.
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    Quote Originally Posted by DParlevliet View Post
    The photon goes through one slit, but its wave goes through both slits.
    That is one interpretation. However, the Kim setup would appear to make it a rather poor one.

    Two sources do not produce coherent waves at the same time.
    And yet they still produce an interference pattern.
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    Yes, so therefore it has is own difficulties. Interference pattern is explained with one wave which is split in two paths with different length, so different phase, so interference. The double-slit can be explained in that way on single photon level. Kim e.a. cannot be explained with a single photon with wave theory.

    The problem with Kim e.a. is that they do not describe the measurement in detail. Not the lengths, the number of counts, the timing procedure. So the article cannot be checked by readers. They do not explain it in wave theory (what interferes with what), not on single photon level, don't make variations, don't argue to rule out other explanations.
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    Quote Originally Posted by DParlevliet View Post
    Yes, so therefore it has is own difficulties. Interference pattern is explained with one wave which is split in two paths with different length, so different phase, so interference. The double-slit can be explained in that way on single photon level. Kim e.a. cannot be explained with a single photon with wave theory.

    The problem with Kim e.a. is that they do not describe the measurement in detail. Not the lengths, the number of counts, the timing procedure. So the article cannot be checked by readers. They do not explain it in wave theory (what interferes with what), not on single photon level, don't make variations, don't argue to rule out other explanations.
    Looking for a loophole to rescue your explanation?

    Why not consider that reality might just be counterfactually indefinite, and that the photon actually does pass through both slits when it has not been determined to have passed through only one?
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by KJW View Post
    Looking for a loophole to rescue your explanation?<br>
    <br>
    Why not consider that reality might just be counterfactually indefinite, and that the photon actually does pass through both slits when it has not been determined to have passed through only one?
    Which explantion? I told I have no explanation of the measured interference in Kim e.a.
    The photon generated in the BBO going to D0 does not go through slits.
    The double slit is explained with wave properties but Kim e.a. cannot be explained that way. That is a weak point which they should have considered.
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    Quote Originally Posted by DParlevliet View Post
    Yes, so therefore it has is own difficulties.
    Nope.

    Interference pattern is explained with one wave which is split in two paths with different length, so different phase, so interference.
    That is one interpretation. But, obviously, not a very good one.

    The double-slit can be explained in that way on single photon level. Kim e.a. cannot be explained with a single photon with wave theory.
    Which is why that interpretation is a bit rubbish.

    Note that interpretations are just analogies to try and explain what the theory says. They have no real meaning. So the fact that your preferred interpretation doesn't work is irrelevant.

    The problem with Kim e.a. is that they do not describe the measurement in detail.
    Really?
    Quote Originally Posted by Kim et al.
    In this experiment, the 351.1nm Argon ion pump laser beam is divided by a double-slit and incident onto a type-II phase matching [7] nonlinear optical crystal BBO (β−BaB2O4) at two regions A and B. A pair of 702.2nm orthogonally polarized signal-idler photon is generated either from A or B region. The width of the SPDC region is about 0.3mm and the distance between the center of A and B is about 0.7mm. A Glen-Thompson prism is used to split the orthogonally polarized signal and idler. The signal photon (photon 1, either from A or B) passes a lens LS to meet detector D0, which is placed on the Fourier transform plane (focal plane for collimated light beam) of the lens. The use of lens LS is to achieve the “far field” condition, but still keep a short distance between the slit and the detector D0. Detector D0 can be scanned along its x-axis by a step motor. The idler photon (photon 2) is sent to an interferometer with equal-path optical arms. The interferometer includes a prism PS, two 50-50 beamsplitters BSA, BSB, two reflecting mirrors MA, MB, and a 50-50 beamsplitter BS. Detectors D1 and D2 are placed at the two output ports of the BS, respectively, for erasing the which-path information. The triggering of detectors D3 and D4 provide which-path information of the idler (photon 2) and in turn provide which-path information of the signal (photon 1). The electronic output pulses of detectors D1, D2, D3, and D4 are sent to coincidence circuits with the out- put pulse of detector D0, respectively, for the counting of “joint detection” rates R01 , R02 , R03 , and R04 . In this experiment the optical delay (Li − L0) is chosen to be ≃ 2.5m, where L0 is the optical distance between the output surface of BBO and detector D0, and Li is the optical distance between the output surface of the BBO and detectors D1, D2, D3, and D4, respectively. This means that any information one can learn from photon 2 must be at least 8ns later than what one has learned from the registration of photon 1. Compared to the 1ns response time of the detectors, 2.5m delay is good enough for a “delayed erasure”.
    And so on and so on.

    Note that, contrary to your claim, they do use a single laser and a double-slit to perform the experiment.

    They do not explain it in wave theory (what interferes with what), not on single photon level, don't make variations, don't argue to rule out other explanations.
    They explain it using quantum mechanics. What "other explanations" should they consider?
    Quote Originally Posted by Kim et al.
    To explain the experimental results, a standard quantum mechanical calculation is presented in the following. The “joint detection” counting rate, R0i, of detector D0 and detector Dj, on the time interval T, is given by the Glauber formula …
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    Quote Originally Posted by DParlevliet View Post
    The double slit is explained with wave properties but Kim e.a. cannot be explained that way.
    That is a purely classical explanation. No one explains the single-photon double slit experiment that way.
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    Quote Originally Posted by Strange View Post
    That is a purely classical explanation. No one explains the single-photon double slit experiment that way.
    Feynman: his paths are a representation of (propability) waves.
    Brian Greene
    Wikipedia
    They all describe the behaviour of single photons (giving a classical wave shaped interference pattern when added) with their wave properties.
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    Quote Originally Posted by DParlevliet View Post
    Quote Originally Posted by Strange View Post
    That is a purely classical explanation. No one explains the single-photon double slit experiment that way.
    Feynman: his paths are a representation of (propability) waves.
    Brian Greene
    Wikipedia
    They all describe the behaviour of single photons (giving a classical wave shaped interference pattern when added) with their wave properties.
    I don't mean popular science explanations, I mean the quantum mechanical explanation.
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    Now a different measurement:



    It is a well know interference measurement, but now asymmetrical.
    Suppose the red path is 1 m and the blue path 10 m. If you measure the time between detector 1 and 2 I expect you will find two times: 3.3 ns and 33 ns. Then you know which path the photon took.
    But between BBO source and detector 2 the photons are not disturbed, so according Feynman rules there will be interference.
    Right?
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    Nobody knows what is wrong here? So this experiment would show both interference and path?

    Then let me go back to Kim e.a.:
    Quote Originally Posted by Strange View Post
    That is a purely classical explanation. No one explains the single-photon double slit experiment that way.
    How does QM explain interference with the single-photon?
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    Quote Originally Posted by DParlevliet View Post
    Quote Originally Posted by DParlevliet View Post
    Nobody knows what is wrong here? So this experiment would show both interference and path?
    Looking at the experiment, I can't see where the interference comes into it. If you distinguish the two paths by any means, there will be no interference.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    When you measure any observable, the quantum states corresponding to each possible value of that observable are orthogonal. Orthogonal states do not interfere with each other, and only one such state is observed.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    It this one, does that interfere?



    It is a asymmetrical version of the Mach-Zehnder interferometer
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    Quote Originally Posted by DParlevliet View Post
    It this one, does that interfere?



    It is a asymmetrical version of the Mach-Zehnder interferometer
    Ok, I can see how one would distinguish between interference and no interference by a suitable choice of path-lengths (in both diagrams). In the diagram quoted in this post, there would be interference because the which-path information is not determined, but in the diagram quoted in my previous post, there would be no interference because the timing would determine the which-path information.

    EDIT: You seem to be suggesting that just because you have set up an interferometer, that there will be interference.
    Last edited by KJW; January 1st, 2014 at 05:19 AM.
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    Quote Originally Posted by KJW View Post
    You seem to be suggesting that just because you have set up an interferometer, that there will be interference.
    If you compare both measurements with Feynman paths, how does it differ? So if you calculate the first measurement with Feynman rules, why does it not interfere?.
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    Quote Originally Posted by DParlevliet View Post
    Quote Originally Posted by KJW View Post
    You seem to be suggesting that just because you have set up an interferometer, that there will be interference.
    If you compare both measurements with Feynman paths, how does it differ? So if you calculate the first measurement with Feynman rules, why does it not interfere?.
    Because the timing has determined which path the photon has travelled. If the photon travels one path, it doesn't travel the other path, and there is nothing for the photon travelling one definite path to interfere with.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    But according Feynman every path is valid and should be added. He makes no exception from what happens outside the measurement and there is nothing between source (BBO) and detector 2 which disturbs the path/history/photon/wave.
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    Quote Originally Posted by DParlevliet View Post
    But according Feynman every path is valid and should be added. He makes no exception from what happens outside the measurement and there is nothing between source (BBO) and detector 2 which disturbs the path/history/photon/wave.
    Every path is valid provided it hasn't been excluded by measurement. The measurement of the photon travelling one path excludes the other path. It doesn't matter that there is nothing between BBO and detector 2 because the measurement of the other photon at detector 1 has determined the path of the photon. This is what I meant in an earlier post when I said: "This rules out explanations that involve tampering with the photon". The explanation is that you've created an entangled two-photon state and by measuring one photon, you've also measured the other photon even though you've not interacted with it in any way (the measurement has been performed on the two-photon state).
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Note that you've explicitly designed the experiment so that measuring the photon at detector 1 does measure the path the photon at detector 2 travelled, so you can't even ask how measuring the photon at detector 1 measures the other photon, because the design of the experiment answers that.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Of course I understand that this measurement challenges the QM principle that you cannot have position and interference at the same time. Therefore I did place it here. If you think this challenge is not allowed, then there is no discussion.
    But is also a principle that a photon has both particle and wave properties with which you can calculate its behaviour. The double-slit can be fully explained with classical waves, even with single photons, as long as it is used as probability. That is also what Feynman predicts. It interferes when both waves are coherent (phase, polarisation etc.). My question was which property of the wave becomes non-coherent in this measurement. If one say: I don't know, it's just non-coherent, that is an answer, but I did hope for a more detailed suggestion.
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    Quote Originally Posted by DParlevliet View Post
    Of course I understand that this measurement challenges the QM principle that you cannot have position and interference at the same time. Therefore I did place it here. If you think this challenge is not allowed, then there is no discussion.
    But is also a principle that a photon has both particle and wave properties with which you can calculate its behaviour. The double-slit can be fully explained with classical waves, even with single photons, as long as it is used as probability. That is also what Feynman predicts. It interferes when both waves are coherent (phase, polarisation etc.). My question was which property of the wave becomes non-coherent in this measurement. If one say: I don't know, it's just non-coherent, that is an answer, but I did hope for a more detailed suggestion.
    I never suggested that the challenge is "not allowed". What I'm saying is what the result according to QM would be and why. Actually, I thought further about the experiment and realised that one should consider the photon travelling both paths. However, in this case, considering both photons (because the measurement involves both photons), the two possibilities are orthogonal in the Hilbert space (being eigenvectors of the observable being measured) and therefore their sum will correspond to no interference (orthogonal components of a wavefunctions do not exhibit interference).

    Note that in the double-slit experiment, simply rotating the polarisation plane at one of the slits by 90° will prevent the interference pattern, even if the polarisation of the photons is never measured (thus no actual measurement of which slit the photons passed through), simply because the quantum states corresponding to each slit are orthogonal.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by KJW View Post
    Actually, I thought further about the experiment and realised that one should consider the photon travelling both paths. However, in this case, considering both photons (because the measurement involves both photons)
    I am no sure what you mean. It sounds as Feynman who calculate all possible paths, but not as actually photon traveling but propabilities paths the photon could follow. It the measurement I use a single photon. If I would use a coincident circuit which selects only the 3 ns photons (or only 30 ns photons), it would form a interference pattern too. What interferes are not the photons but two split parts of the wave of a single photon. For the photon which travelled the short 3 ns path, its split wave through the long path does not need to travel 30 ns to reach the detector. It is there at the moment the single photon exist.
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    Quote Originally Posted by DParlevliet View Post
    What interferes are not the photons but two split parts of the wave of a single photon. For the photon which travelled the short 3 ns path, its split wave through the long path does not need to travel 30 ns to reach the detector. It is there at the moment the single photon exist.
    For the experiment where entangled photons are being detected at detector 1, the photon reaches the beam-splitter at a definite time relative to the detection of its entangled partner at detector 1. The probability wave then travels through both paths at the speed of light, so that by the time the wave travelling the long path has reached the detector, the wave travelling the short path had already reached the detector earlier and is now gone... no interference.

    By contrast, for the experiment where there are no entangled photons being detected, the time at which the photon reaches the bean-splitter is indefinite. Therefore, the wave can travel the long path and still overlap with the wave travelling the short path... interference.

    Thus, the difference between detecting entangled photons and not detecting entangled photons is the shape of the wave travelling the two paths, being narrow in the case of detecting entangled photons, and broad in the case of not detecting entangled photons.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by DParlevliet View Post
    I am no sure what you mean. It sounds as Feynman who calculate all possible paths, but not as actually photon traveling but propabilities paths the photon could follow.
    And by making different measurements, you change the probabilities of all paths. Which leads to the destruction of the interference pattern.
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    Quote Originally Posted by KJW View Post
    By contrast, for the experiment where there are no entangled photons being detected, the time at which the photon reaches the bean-splitter is indefinite. Therefore, the wave can travel the long path and still overlap with the wave travelling the short path... interference.
    So this measurement will show an interference pattern if the source does not produce entangled photons, also with (single) photons at low rate?

    Last edited by DParlevliet; January 3rd, 2014 at 03:20 AM.
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    Quote Originally Posted by DParlevliet View Post
    Of course I understand that this measurement challenges the QM principle that you cannot have position and interference at the same time. Therefore I did place it here. If you think this challenge is not allowed, then there is no discussion.
    But is also a principle that a photon has both particle and wave properties with which you can calculate its behaviour. The double-slit can be fully explained with classical waves, even with single photons, as long as it is used as probability. That is also what Feynman predicts. It interferes when both waves are coherent (phase, polarisation etc.). My question was which property of the wave becomes non-coherent in this measurement. If one say: I don't know, it's just non-coherent, that is an answer, but I did hope for a more detailed suggestion.
    Another explanation is energy forming a packet of energy (photon) is one thing and mode of travel is another displaying time itself comes in waves. Changing when viewed has to do with an approaching mass and or special relativity showing time and gravity are related.
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    Quote Originally Posted by YangYin View Post
    Another explanation is energy forming a packet of energy (photon) is one thing and mode of travel is another displaying time itself comes in waves. Changing when viewed has to do with an approaching mass and or special relativity showing time and gravity are related. [/COLOR][/FONT]
    [/SIZE]
    Utterly incomprehensible. Perhaps you could explain what is wrong with the current explanation which makes highly accurate predictions which can be ested in the lab and used to make technology such as your computer. That sounds much more useful than some vague waffle about "approaching mass" - especially as photons don't have mass and and gravity is irrelevant to the interference of light.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by YangYin View Post
    Another explanation is energy forming a packet of energy (photon) is one thing and mode of travel is another displaying time itself comes in waves. Changing when viewed has to do with an approaching mass and or special relativity showing time and gravity are related. [/COLOR][/FONT]
    [/SIZE]
    Utterly incomprehensible. Perhaps you could explain what is wrong with the current explanation which makes highly accurate predictions which can be ested in the lab and used to make technology such as your computer. That sounds much more useful than some vague waffle about "approaching mass" - especially as photons don't have mass and and gravity is irrelevant to the interference of light.
    So gravity cannot bend light and does not have the ability to pull in light faster than light can travel?
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    Please keep your nonsense to pseudoscience or trash where it belongs.
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    Quote Originally Posted by YangYin View Post
    So gravity cannot bend light
    Of course it does.

    and does not have the ability to pull in light faster than light can travel?
    Of course not.

    None of which has anything to do with double-slit interferometry.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by YangYin View Post
    So gravity cannot bend light
    Of course it does.

    and does not have the ability to pull in light faster than light can travel?
    Of course not.

    None of which has anything to do with double-slit interferometry.
    How does a black hole affect light?
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    Quote Originally Posted by YangYin View Post
    How does a black hole affect light?[/COLOR][/FONT]
    [/SIZE]
    Gravity. Of course.

    Which has nothing to do with double-slit interferometry. So please shut up.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by YangYin View Post
    How does a black hole affect light?[/COLOR][/FONT]
    [/SIZE]
    Gravity. Of course.

    Which has nothing to do with double-slit interferometry. So please shut up.
    So that was Strange.
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    Quote Originally Posted by YangYin View Post
    So that was Strange.[/SIZE]
    Not really.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by YangYin View Post
    So that was Strange.[/SIZE]
    Not really.
    Oh good, what about gravitational time dilation and its effect on light? I only ask because you stated gravity does not affect wavelengths.
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    Quote Originally Posted by YangYin View Post
    [SIZE=3][FONT=Times New Roman][COLOR=#000000]Oh good, what about gravitational time dilation and its effect on light? I only ask because you stated gravity does not affect wavelengths. [/COLOR][/FONT]
    [/SIZE]
    No I didn't. I agreed that gravity affects light but pointed out that, obviously, it cannot "pull in light faster than light can travel".

    Again, this has NOTHING to do with interferometry.
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    Quote Originally Posted by YangYin View Post
    Quote Originally Posted by Strange View Post
    Quote Originally Posted by YangYin View Post
    So that was Strange.[/SIZE]
    Not really.
    Oh good, what about gravitational time dilation and its effect on light? I only ask because you stated gravity does not affect wavelengths.
    It is bad manners to hijack a thread started by someone else on a different topic. Please confine yourself to the topic of the thread, if you have something to contribute.
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    It's doubtful he has yet to contribute anything to any thread except nonsense.
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    Quote Originally Posted by PhDemon View Post
    It's doubtful he has yet to contribute anything to any thread except nonsense.
    You might think that. I couldn't possibly comment.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by YangYin View Post
    [SIZE=3][FONT=Times New Roman][COLOR=#000000]Oh good, what about gravitational time dilation and its effect on light? I only ask because you stated gravity does not affect wavelengths. [/COLOR][/FONT]
    [/SIZE]
    No I didn't. I agreed that gravity affects light but pointed out that, obviously, it cannot "pull in light faster than light can travel".

    Again, this has NOTHING to do with interferometry.
    OK nothing strange going on in the double slit experiment we can just file in the cold case library in the aisle marked fundamental laws, no, no in the aisle marked quantum physics where everything can and cannot be explained.
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    Quote Originally Posted by YangYin View Post
    OK nothing strange going on in the double slit experiment we can just file in the cold case library in the aisle marked fundamental laws, no, no in the aisle marked quantum physics where everything can and cannot be explained. [/COLOR][/FONT]
    [/SIZE]
    Is that your way of conceding that your mention of gravity was utterly irrelevant (and wrong in some details)?

    You have failed to show any problem with current theory. Nothing you have said has any relevance to double slit interferometry. As someone else has said, this sort of hijacking and pollution of someone else's thread is very bad manners.
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    Quote Originally Posted by DParlevliet View Post
    So this measurement will show an interference pattern if the source does not produce entangled photons, also with (single) photons at low rate?

    Sorry KJW , I was repeating myself. I looked back and saw you did already agree that this measurement gives interference.
    Anyway I understand your arguments. But then I come into timing problems. When the wave travels the red or blue path in the above measurement, how does it looks like, in time? If it would be an electron a solution of the Schrödinger equation looks like several periods around the average position of the electron (according Wikipedia). For photons that cannot be used, but how does it look there?
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    Quote Originally Posted by DParlevliet View Post


    Anyway I understand your arguments. But then I come into timing problems. When the wave travels the red or blue path in the above measurement, how does it looks like, in time?
    Ok, the photon source is coherent, so the photon number at any given time is indeterminate. In this case, the wavefunction describing the probability of detecting a single photon can be described as . When this reaches the beam-splitter, the two waves follow the two paths at a phase (or group) velocity of (assuming the paths can be treated as a vacuum). The two waves meet at the detector with a phase difference and add to produce the interference. This is pretty much the same as the classical picture except the detector is statistically detecting individual photons.

    In the case of the experiment with the entangled photons, the detection of the entangled partner photon guarantees that there is a photon at the beam-splitter at a definite time relative to the detection of its partner. Therefore, the wavefunction of this photon is a narrow pulse (ideally, a Dirac delta function). The two narrow pulses travel the two paths at and arrive at the detector at two different times, corresponding to the two possible times at which the photon would be detected. There is no interference because the two narrow pulses do not overlap at the detector.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by YangYin View Post
    OK nothing strange going on in the double slit experiment we can just file in the cold case library in the aisle marked fundamental laws, no, no in the aisle marked quantum physics where everything can and cannot be explained. [/COLOR][/FONT]
    [/SIZE]
    Is that your way of conceding that your mention of gravity was utterly irrelevant (and wrong in some details)?

    You have failed to show any problem with current theory. Nothing you have said has any relevance to double slit interferometry. As someone else has said, this sort of hijacking and pollution of someone else's thread is very bad manners.
    You contradict yourself so much and make big waves out of nothing and see nothing what’s the point.
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    What is the point of any of your posts? All they do is show your ignorance and comprehension issues.
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    Note that simply expecting the photon to be detected at one of two definite times, indicating which path the photon travelled, implies that the wavefunction at the detector is two narrow pulses. Given that the wavefunction determines the probability of detecting a photon, the wavefunction would be zero at other times, otherwise the photon could be detected at other times. Thus, it becomes clearer why determining which path the photon travelled by any means destroys the interference.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by YangYin View Post
    You contradict yourself so much and make big waves out of nothing and see nothing what’s the point. [/COLOR][/FONT]
    [/SIZE]
    Please show me where I have contradicted myself, because I am not aware of doing so. (I have contradicted you, for obvious reasons (*), but that is not quite the same thing.)

    (*) In case it isn't obvious: because much of what your write is simply wrong.
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    Quote Originally Posted by KJW View Post
    For the experiment where entangled photons are being detected at detector 1, the photon reaches the beam-splitter at a definite time relative to the detection of its entangled partner at detector 1. The probability wave then travels through both paths at the speed of light, so that by the time the wave travelling the long path has reached the detector, the wave travelling the short path had already reached the detector earlier and is now gone... no interference.
    Now I place the detector 1 at 15 meter, so at greater distance then the blue path. Now the photons are first detected in detector 2. Until that time the photon reaches the bean-splitter is indefinite. the wave can travel the long path and still overlap with the wave travelling the short path... interference., as you described with no entangled photons?
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    Quote Originally Posted by DParlevliet View Post
    Quote Originally Posted by KJW View Post
    For the experiment where entangled photons are being detected at detector 1, the photon reaches the beam-splitter at a definite time relative to the detection of its entangled partner at detector 1. The probability wave then travels through both paths at the speed of light, so that by the time the wave travelling the long path has reached the detector, the wave travelling the short path had already reached the detector earlier and is now gone... no interference.
    Now I place the detector 1 at 15 meter, so at greater distance then the blue path. Now the photons are first detected in detector 2. Until that time the photon reaches the bean-splitter is indefinite. the wave can travel the long path and still overlap with the wave travelling the short path... interference., as you described with no entangled photons?
    The delayed choice quantum eraser experiment deals with the case where the decision to erase or not to erase occurs after the other photon has reached the detector to form or not form an interference pattern, and has shown that it doesn't matter when the decision to erase or not to erase has occurred. Similarly, it doesn't matter when the photons are detected at detector 1. Detection of photons at detector 1 will guarantee that there will be a photon at the beam-splitter at a definite time even if this time is before the detection of the photon at detector 1... no interference.

    Also, from what I said in post #78, even if there is interference, this would mean that one would be unable to determine the path the photon travelled.
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    I know, but still: the earlier argument of detecting in detector 2 does not fit anymore... and other detailed explanation.

    But going back to the original argument, what is the exact definition of "knowing-which-path"? The general principle is that when you know the which-path (particle property) there cannot interference (wave property). But look to a simple one-slit measurement:



    You know which path, but still the photon can be detected sideways from the slit because of diffraction. And diffraction is also a wave property, also based on interference (Huygens principle, calculated on waves travelling in a medium). So do we have here a knowing-which-path together with wave property?

    But back to the first question. We know which-path in the macro world, but in the quantum world the slit is very wide. There are numeroes paths the small photon can go though the slit, and we don't know which. So perhaps still a situation of not knowing the path?

    So what is the exact defination of "knowing the path"?
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    Quote Originally Posted by DParlevliet View Post
    I know, but still: the earlier argument of detecting in detector 2 does not fit anymore... and other detailed explanation.

    But going back to the original argument, what is the exact definition of "knowing-which-path"? The general principle is that when you know the which-path (particle property) there cannot interference (wave property). But look to a simple one-slit measurement:



    You know which path, but still the photon can be detected sideways from the slit because of diffraction. And diffraction is also a wave property, also based on interference (Huygens principle, calculated on waves travelling in a medium). So do we have here a knowing-which-path together with wave property?

    But back to the first question. We know which-path in the macro world, but in the quantum world the slit is very wide. There are numeroes paths the small photon can go though the slit, and we don't know which. So perhaps still a situation of not knowing the path?

    So what is the exact defination of "knowing the path"?
    Personally, I regard the "wave-particle duality" as an oversimplification. The way I see it, it's never "particles", just waveforms of various shapes, including very narrow pulses, which could be considered as "particles". So for the single-slit diffraction, it's not a particle, but a waveform that is as wide as the slit, and this produces a single-slit interference pattern. For the double-slit experiment, the waveform is a pair of slit-shaped pulses, and measuring which slit the photon passed through means eliminating one of the slit-shape pulses.

    The crucial aspect of quantum mechanics is that when one performs a measurement, any measurement, of all the possible classically distinct results (with probabilities given by the wavefunction), only one is realised. This is the true meaning of a "particle" in quantum mechanics. Thus, the true nature of a particle depends entirely on the property that is actually being measured, noting that it is in the classical realm that the different possible results distinguish themselves. That is, a measuring device is a macroscopic object and it is the possible distinct states of that macroscopic object that constitute the possible measured results, and it is this that represents the measured quantum state.

    As for what it means to "know the path", it is important to note that it is not actually the knowledge of the path that destroys the interference. Strictly speaking, it is orthogonalising the quantum states corresponding to each of the paths that destroys the interference. Typically, this means making each of the paths classically distinguishable, even if this is not the result of an explicit measurement. This means that destroying interference is rather easy, and maintaining interference is rather difficult.
    Last edited by KJW; January 5th, 2014 at 08:48 PM.
    Strange and Implicate Order like this.
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    It is great to see KJW in action when he de-cloaks....*sniggers* :-))
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    Quote Originally Posted by KJW View Post
    Quote Originally Posted by DParlevliet View Post
    I know, but still: the earlier argument of detecting in detector 2 does not fit anymore... and other detailed explanation.

    But going back to the original argument, what is the exact definition of "knowing-which-path"? The general principle is that when you know the which-path (particle property) there cannot interference (wave property). But look to a simple one-slit measurement:



    You know which path, but still the photon can be detected sideways from the slit because of diffraction. And diffraction is also a wave property, also based on interference (Huygens principle, calculated on waves travelling in a medium). So do we have here a knowing-which-path together with wave property?

    But back to the first question. We know which-path in the macro world, but in the quantum world the slit is very wide. There are numeroes paths the small photon can go though the slit, and we don't know which. So perhaps still a situation of not knowing the path?

    So what is the exact defination of "knowing the path"?
    Personally, I regard the "wave-particle duality" as an oversimplification. The way I see it, it's never "particles", just waveforms of various shapes, including very narrow pulses, which could be considered as "particles". So for the single-slit diffraction, it's not a particle, but a waveform that is as wide as the slit, and this produces a single-slit interference pattern. For the double-slit experiment, the waveform is a pair of slit-shaped pulses, and measuring which slit the photon passed through means eliminating one of the slit-shape pulses.

    The crucial aspect of quantum mechanics is that when one performs a measurement, any measurement, of all the possible classically distinct results (with probabilities given by the wavefunction), only one is realised. This is the true meaning of a "particle" in quantum mechanics. Thus, the true nature of a particle depends entirely on the property that is actually being measured, noting that it is in the classical realm that the different possible results distinguish themselves. That is, a measuring device is a macroscopic object and it is the possible distinct states of that macroscopic object that constitute the possible measured results, and it is this that represents the measured quantum state.

    As for what it means to "know the path", it is important to note that it is not actually the knowledge of the path that destroys the interference. Strictly speaking, it is orthogonalising the quantum states corresponding to each of the paths that destroys the interference. Typically, this means making each of the paths classically distinguishable, even if this is not the result of an explicit measurement. This means that destroying interference is rather easy, and maintaining interference is rather difficult.
    I also believe "wave-particleduality" is an over simplification. All entities in this universe are in a process of collapse and expansion unless acted upon by another force including time, the same process that created this universe. A wavelength has created a balance between these two actions in one moment of time. A wavelength collapses and expands out with the expansion of the universe. It acts more like an eccentric orbit around itself and is able to self-perpetuatelike an ice skater pulling in their arms continuously in a spin only it is the environment that is expanding. This creates the pulse,the wave-particle duality. Destroying interference is easy and hard to maintain because to exist in this universe a balancing act must be made between collapse and expansion.
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    Errr... what?!
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    Quote Originally Posted by YangYin View Post
    I also believe "wave-particleduality" is an over simplification. All entities in this universe are in a process of collapse and expansion unless acted upon by another force including time, the same process that created this universe.


    Time is not a force, and there is no supported scientific theory of creation, so your declaration that this is "the same process that created this universe" is just the musings of another RGOTI.

    Yawn.

    A wavelength has created a balance between these two actions in one moment of time. A wavelength collapses and expands out with the expansion of the universe. It acts more like an eccentric orbit around itself and is able to self-perpetuatelike an ice skater pulling in their arms continuously in a spin only it is the environment that is expanding. This creates the pulse,the wave-particle duality.
    No.

    Destroying interference is easy and hard to maintain because to exist in this universe a balancing act must be made between collapse and expansion.


    No. And you mangled KJW's notes. You should have written that interference is hard to maintain and thus easy to destroy. The rest of what you wrote is meaningless.
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    I'm pretty sure I warned Yangyin about posting his nonsense in the hard science areas. I'm giving him 3 days off.
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    A layman's observation.

    When listening to people addressing the particle/wave duality, I never hear the word "potential energy" as part of an explanation of the phenomenon.

    Question,

    Could we equate the "probability wave function of a non massive particle in transit" as a "potential field of a certain wavelength"?

    If we speak of quantum mechanics, the concept of potential (a latent ability) and potential fields (causal ability) should become ever more prominent as a fundamantal consideration.

    Potential is the metaphysical causal force between quantum events. It is exempt from SOL limitation, because potential represents a field of information (the Implicate) rather than individual bits (the Explicate).

    If these intuitive musings are completely off base or simplistic, have a good laugh and tell me. I can only learn.
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