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SINGLE e-/photon diffraction patterns.

  1. Jul 25, 2005 #1
    Is it true that firing SINGLE electrons or photons at a double slit over a time interval will create diffraction patterns?
    And does anyone know of articles where particles can create diffraction patterns.
     
  2. jcsd
  3. Jul 25, 2005 #2

    robphy

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  4. Jul 25, 2005 #3
    heh not gonna give me the simple answer...its coo thx for the ref.
     
  5. Jul 25, 2005 #4

    DrChinese

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  6. May 21, 2008 #5

    taylaron

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    are alternate universes and defraction patterns related?

    Is there any law of physics that says waves or particles in alternate universes can influence the path of waves or particles in this universe?

    i recently viewed a video where scientists were puzzled by the results of
    taking a single slit diffraction pattern setup; but instead of shining a whole barrage of photons in multiple streams; they let only 1 photon through at a time.
    the results were 1 stream of photon coming out of a hole and creating a diffraction pattern on the screen a distance away from the hole.
    how can this make sense? i thought diffraction patterns are due to the constructive and deconstructive interference of other photons.

    the conclusion that they came to puzzled me most... 'because no other particle or wave was interfering with this single stream of photons (making a diffraction pattern) they came to the conclusion that photons or particles in alternate universes are interacting with this single stream of photons to create the interference patterns.'

    is this true or is it a bunch of garbage?
    im a junior in high school taking AP physics B and i was just introduced to this phenomenon.
    i would appreciate it if you could explain it at a high schooler's level of understanding.
    thanks.
     
  7. May 22, 2008 #6
    No there is no law that says so, because there is no other universes thats proven.
    It's not even a theory, It's a highly speculative hypothesis
     
  8. May 22, 2008 #7

    DrChinese

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    The facts are correct, the conclusion is not generally accepted. This phenomenon has been known for a long time, it is not new. It is generally considered that a photon takes all possible paths, and that these paths interfere with each other. No additional universes are required. On the other hand, this makes the possible potential paths "real" in some sense, which is probably just as confusing.

    Good luck in your studies!
     
  9. May 22, 2008 #8

    taylaron

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    outside forces

    "It is generally considered that a photon takes all possible paths, and that these paths interfere with each other"

    i agree that it could take any path randomly;
    but how can electrons or photons in single file interfere with each other's path in the opposite axis?
    wouldn't there have to be intersecting particles/ waves that would either repel, attract or cause constructive/ de-constructive interference with each other.
    i don't see how interference would happen without an outside force.
     
  10. May 23, 2008 #9

    ZapperZ

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    Until you are able to show the evidence of this "outside force" and its fingerprint in influencing the interference pattern, then this is highly speculative.

    Note that the interference pattern in a 2-slit experiment is merely ONE example of the superposition principle in QM. It means that you will need to account for this "outside force" in phenomena as wide-ranging as the Bragg-diffraction pattern of crystals, the bonding-antibonding state of molecules such as NH3, and the coherence gap in the SQUID experiments of Delft/Stony Brook.

    Zz.
     
  11. May 23, 2008 #10

    DrChinese

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    Richard Feynman developed the path integral formulation of QM. In this view, each of the possible paths of a particle cause just sufficient constructive/destructive interference that the resulting path is the "normal" one. For a double slit setup, that leads to an interference pattern. You can also deduce the same interference pattern using the Heisenberg Uncertainty Principle (HUP), as ZapperZ has pointed out a number of times previously.

    The issue ultimately is that the Quantum Theory uses mathematical constructs to explain the particle behavior we observe; and those constructs appear to have no obvious physical explanation. Yet they work, and have led to predictions about particle behavior that would not otherwise be possible (such as entanglement - see Bell's Theorem or EPR - to name just one).
     
  12. May 23, 2008 #11
    Photons, electrons, protons, atoms, etc. can in some cases appear to behave as particles, and in other cases as waves (some argue that there are circumstances where they can behave as both particles and waves at the same time, but I don't find this argument persuasive)

    When a photon (or electron, proton, atom, or whatever) behaves like a wave, it doesn't just move in a straight line. Think instead of circular water waves. It ends up looking like this:

    http://upload.wikimedia.org/wikipedia/commons/9/9e/Doubleslitdiffraction.png

    Then the probability waves interact with each other like any other waves (such as water waves).

    It only appears to move "in single file" when it behaves like a particle.

    The big mystery is why it can switch between particle and wave depending on what you're trying to observe (and even weirder, depending on what you actually observe).

    I highly recommend the book In Search of Schrodinger's Cat by John Gribben - it explains it nicely.
     
  13. May 23, 2008 #12

    taylaron

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    Hey Thanks everybody;
    This strange conversion of particles to waves is rather fascinating.
    It is now clear to me that it is only speculation which led to deduction about the influence of alternate universes.
    Its for sure that I need to learn a lot more about QM to fully understand this concept; this should be interesting.

    on the side:
    Is there any suggestion in the mathematics involved in QM that alternate universes can influence particles/ waves this world? -sorry this question is so broad.
     
  14. May 23, 2008 #13

    DrChinese

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    No, not at all. The idea is that there is a missing "something" that is contributed by the alternate universe. Significant effort has been put into this question, and there does not appear to be ANYTHING missing that is contributed by an outside agency or similar. As best as can be determined, the HUP covers pretty much everything (although there is still no explanation for the perfect randomness of the distribution of results). This question is not entirely settled, and certainly not to everyone's satisfaction.
     
  15. May 24, 2008 #14
    There's an unfortunate tendency in popular science to confuse what we *know* about quantum mechanics (which is that the outcome of experiments is intrinsically probabilistic in nature, that what we tend to consider as hard solid particles behave like waves when we aren't looking, and that if you look hard enough at waves you see localised particles) with some of the various proposed "interpretations" of it. The orthodox way of looking at things is that the universe does what it says on its mathematical tin- that if you understand how the maths of QM relates to what we see in the world, there's no deeper level to be understood.
    However, some people consider the idea of "wavefunction collapse" central to this orthodox interpretation to be philosophically problematic, and try and re-frame the maths in a different physical picture. The particular idea about "multiple universes interfering with our own" is a corruption of what's commonly known as the "many-worlds" interpretation. If you'd like to know more (and I'm doing a whole degree because I did) I'd strongly suggest getting to grips with the basic ideas of QM before trying to fit it to any particuar interpretation. Wikpedia's not a terrible start:
    http://en.wikipedia.org/wiki/Quantum_mechanics
    http://en.wikipedia.org/wiki/Interpretations_of_Quantum_Mechanics
    (in that order!). If you want to know more about the philosophical aspects of it all, try http://plato.standford.edu and search for quantum mechanics. You'll get detailed expositions of particular interpretations and how they measure up to each other there. One caveat though: the articles are written by proponents of a particular interpretation, or even of a particular variant of an interpretation; so don't expect any degree of neutrality in any of the articles.
     
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