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When does the photon splits in 2 on the Two Slit Experiment?

  1. Feb 9, 2015 #1
    Hello!

    I have questions in regards to the Two Slit Experiment. If the photon splits in two and passes through both slits at the same time and interferes with itself on the other side of the screen and then it hits on the second screen thereby creating the interference pattern. At what point does the photon splits in two before it hits the two slits? After it leaves the laser or a few nanometers before hitting the slits? If the distance of the laser is 5 inches, or 6 inches from the two slits, can it be calculated when it will split in two before hitting the two slits? Is it possible that the photon is already split in two way before the photon is release from the laser? Or immediately just after it is release from the laser? Or is it that we just don't know?


    Would you please be so kind to tell me your insights of this Quantum Physics behavior referring to the questions above?


    Very appreciatively,

    Arthur Hernandez
     
  2. jcsd
  3. Feb 9, 2015 #2

    Borg

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    The photon doesn't "split in two" and an interference pattern isn't created by a single photon. In the classic two slit experiment, the photon has an equal chance of passing through either slit. The interference pattern is the result of many photons passing through the slits. The odds of the photon landing in any one place describes the pattern that is seen when many photons pass through the slits.

    Note that I only explained this with regards to the particle nature of photons that you were asking about. Photons exhibit a wave-particle duality that I didn't explain.
     
    Last edited: Feb 9, 2015
  4. Feb 9, 2015 #3

    bhobba

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    Nice answer - but the so called wave-particle duality is a left over from the early days of QM and isn't really part of modern quantum physics:
    https://www.physicsforums.com/threads/is-light-a-wave-or-a-particle.511178/

    At the risk of getting into controversy because some have issues with it the following gives a fully quantum explanation of the double slit not involving the wave-particle duality:
    http://arxiv.org/ftp/quant-ph/papers/0703/0703126.pdf

    Thanks
    Bill
     
    Last edited: Feb 9, 2015
  5. Feb 9, 2015 #4

    Borg

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  6. Feb 9, 2015 #5
    Out of shear curiosity: what would you define as modern quantum physics out of curiosity (since quantum physics is just defined broadly as the study of phenomenon of things as small or smaller than atoms)? Simply things currently researched today (or within some time frame?) or some other way?
     
  7. Feb 9, 2015 #6

    bhobba

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    What Dirac came up with in 1926 called the transformation theory, which is basically what we call QM today.

    Here is the history:
    http://www.lajpe.org/may08/09_Carlos_Madrid.pdf

    It consigned to the dustbin of history old ideas like De-Broglie's matter waves etc.

    I would call modern QM that branch of science based on the following two axioms (or equivalent ones) found in Ballentine - QM - A Modern development:

    Axiom 1
    Associated with an observation we can find a Hermitian operator O, called the observations observable, such that the possible outcomes of the observation are its eigenvalues.

    Axiom 2 - called the Born Rule
    Associated with any system is a positive operator of unit trace, P, called the state of the system, such that expected the value of the outcomes of the observation is Trace (PO).

    We are having an interesting discussion in another thread about if they are the only axioms because a strange, beautiful, baffling and very interesting thing is the dynamics is determined by symmetry considerations ie Scrodingers equation follows from the invariance of probabilities between inertial frames as required by the POR and assuming the Galilean transformations. But are such symmetries separate axioms or do they in fact define our region of applicability? See the thread if such interests you:
    https://www.physicsforums.com/threads/the-original-postulates-of-quantum-mechanics.796784/

    Thanks
    Bill
     
    Last edited: Feb 13, 2015
  8. Feb 10, 2015 #7
    Thank You!
     
  9. Feb 11, 2015 #8
    The photon doesn't split in two, in fact the statement is meaningless. A photon is an excitation of the electromagnetic field which by definition cannot be split as it's already the fundamental quanta of the field. Instead it's wave function is scattered through the slits which adds up as an interference pattern on the receiver. In terms of electrons this means that a single electron will interfere with itself just like a photon will.
     
  10. Feb 11, 2015 #9
    I like Feynman's take. The photon takes all paths each with a probability weighted by the exp of the delta of the action from the min action. So no need to answer your question it always takes all paths.
     
  11. Feb 11, 2015 #10

    bhobba

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    Indeed looking at it through the lens of Quantum Field Theory removes many misconceptions.

    If you are just starting out in QM check out:
    https://www.amazon.com/Fields-Color-theory-escaped-Einstein/dp/0473179768

    Thanks
    Bill
     
  12. Feb 12, 2015 #11

    Nugatory

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    And after that, for a sense of just how different the quantum field theory picture of a photon is from what you're imagining, give Feynman's "QED: The strange theory of light and matter" a try... no hard math required.
     
  13. Feb 12, 2015 #12
    Thank you!
     
  14. Feb 12, 2015 #13
    Thank you!
     
  15. Feb 12, 2015 #14
    Thank you!
     
  16. Feb 12, 2015 #15
    Thank you!
     
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