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Particle Entanglement and the Rarity-Tapster Experiment

  1. Nov 8, 2014 #1
    1. The problem statement, all variables and given/known data

    With respect to the Rarity-Tapster experiment which shows the interference pattern of photons as support for the idea of quantum entanglement...what would the graph look like if these photons behaved like ordinary Newtonian particles?

    2. Relevant equations

    There is a graph that shows a wave with several peaks and troughs as a function of y-x vs. number of 2-particle impacts...which I am having trouble uploading =(

    3. The attempt at a solution

    I am not sure if this is an experiment with which everyone in the physics community is familiar with; since I am myself new to physics but basically there is a source of 2 photons which are "entangled" (this concepts still eludes me a bit) and as each photon goes through a separate set of slits; it's impact is recorded on a screen. When this experiment is repeated numerous times and the impact points of photon 1 (x) and photon 2 (y) are graphed as the difference between y and x (y-x) then an interference pattern is apparent.

    So....if these were Newtonian particles I think that because the two photons move in opposite directions, they would have impacted at the same distances below the halfway of the first screen and above the halfway of the second screen.So, x=y which would make for a straight diagonal line with a slope of 1 and a y-intercept of 0...correct?

    Also, if it's not too much hassle, can someone just explain to me quantum entanglement in layman terms?

    Thanks as always for all the help, it is incredible appreciated!
  2. jcsd
  3. Nov 9, 2014 #2
    I think you would expect a smeared out distribution without the apparent oscillations. I would think the envelope would be the same, but you would not see any waves.
  4. Nov 10, 2014 #3


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    Objects in the quantum world can occupy many quantum states, but
    these are not fixed until they are actually observed - that is Schrodinger's
    cat can be both dead and alive at the same time. Some Physicists are
    even of the meaning that the entities are not even there until they are
    observed! Entangled objects have a common origin - they are created
    in close proximity and their quantum states become linked together.
    Entanglement have been observed on much larger scales - even
    with macromolecules. When these entangled objects separate -
    that is the photons travel off into different directions - we find that if one
    of them is observed the other immediately also falls into its corresponding
    quantum states. The problem comes with the term - observed. What does
    it mean "when the particle is observed" ? Here consciousness comes into
    play. It seems the objects are only there when they are observed. This is
    where Einstein objected "I believe the moon is there even if no one is looking."
    The quantum world is indeed strange! I entertain the idea that these objects
    exist on a "different plane" and we connect through our consciousness to them.
    It seems that your lecturer is expecting much more detailed knowledge from
    you though since such a specific experiment is mentioned.
    Last edited: Nov 10, 2014
  5. Nov 12, 2014 #4

    Thanks for the reply and the explanation. It makes a lot more sense to me now although it's still kind of "spooky". So, in terms of the appearance of the graph; would the distribution appear "smeared" or spread across and not show an interference pattern because the photons wouldn't be "entangled" from a Newtonian perspective...would they show an interference pattern if both photons were hitting the same screen?
  6. Nov 12, 2014 #5


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    Interference is a wave phenomena and cannot be explained by Newtonian
    type of particles. The Newtonian term is included to emphazise that just
    the particle aspect is present because today we know from a quantum
    mechanical perspective that even particles, like electrons, exhibit a wave
    nature as is evident from a double slit experiment.
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