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Photon Characteristics

  1. Jan 14, 2007 #1
    What are the characteristics of a photon that cause it's parts to behave similarly when split in two and then to reform later ?
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  3. Jan 14, 2007 #2


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    Welcome to PF RayDartist. Your question has been asked many times here. You might want to use the search function.
  4. Jan 14, 2007 #3
    A photon does not "split in two". You need to be very careful with the language that you use to describe physics to avoid any confusion.

  5. Jan 14, 2007 #4
  6. Jan 14, 2007 #5


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    I've not read the article thoroughly, but since the second paragraph begins with "the twin-photon experiment" I don't think that one photon splits into two.

    P.S. Listen to Marlon; he knows his stuff! :tongue2:
  7. Jan 14, 2007 #6


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    You need to be very careful when reading such a thing. The photon wasn't split, but rather two correlated photons were sent in opposite direction as part of a EPR-type experiment.

    When you typed your original post, everyone, I'm sure (including me), thought you were asking about the 2-slit experiment. It is imperative that you give the clearest and fullest possible scenario that you're asking, or else we will be answering based on one context, while you're asking based on another.

    I suggest, if you are not sure what was involved in the photo source that you cited, that you look for parametric down conversion photon source.

  8. Jan 14, 2007 #7
    Don't understand

    This is a quote from the site.


    "One way to create a pair of entangled twins is to start with a single photon of ultraviolet radiation and pass it through a peculiar artificial mineral called a "down-conversion crystal." In the Swiss experiment, the crystal consisted of potassium niobate. The crystal splits the photon in two, producing two new photons that continue on in somewhat different directions, and whose combined energy equals the energy of their parent photon."

    Am I reading this incorrectly ?
  9. Jan 14, 2007 #8


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    You read it correctly, but not in terms of the physics. That's why I said that you really should read up on what is meant by a parametric down conversion. Naively, the incoming photon actually causes a atomic transition, but the decay of that transition undergoes two separate energy levels, which produces the two photons. These two photons will have the total spin orientation of the original photon.

  10. Jan 14, 2007 #9


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    Unfortunately, stuff written for media consumption tends to use sloppy language. Instead of "The crystal splits the photon in two, producing two new photons," it would have been better to write "The crystal absorbs the photon and uses its energy to produce two new photons..."
  11. Jan 14, 2007 #10
    Thanks ZapperZ and JTbell

    Actually these are some of the photon characteristics I was seeking in my original question, although maybe I didn't phrase the question clearly and implied a condition that doesn't exist.

    Even though more clearly explained by the Spontaneous parametric down conversion than the site, in any event two photons are the result with the combined energy of the parent photon. But more, the photon pair make the same decisions with regard to possibly 10 different pathways to select in an interferometer even when they are separated by significant distances. It seems to me , this may imply additional characteristics that may be related to atomic transition and spin orientation when separation occurs. But, also possibly with properties not yet fully explored such as a connection or awareness not affected by distance. There seems to be something here not fully explained.

    What do you think ?
  12. Jan 15, 2007 #11


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    I think you may need to do a lot of background reading on a lot of "water that has passed under the bridge", so to speak. You might want to look around PF for discussions (there have been a lot of threads on these) on (i) superposition and (ii) entanglement, EPR-type experiments, non-locality, etc.

  13. Jan 15, 2007 #12
    Just a few more comments on Photon Characteristics

    A few more ideas, then I will look around PF. Thanks for your advice.

    Please check my understanding of the parametric down conversion;

    As incoming photons enter a non-linear crystal, only those who's spin axis is parallel to the direction of travel pass through the crystal unabsorbed . This permits conservation of both energy and momentum. However, an energy transition does takes place changing the one photon into a photon pair who's total combined energy is equal to the parent photon. Reference; http://en.wikipedia.org/wiki/Spontaneous_parametric_down_conversion

    According to Gauge symmetry, it appears both Global and Local symmetries are maintained for both these photons because they behave similarly regardless of distance, implying a connection. Reference;

    http://www.cebaf.gov/news/internet/1997/spooky.html conversion without absorption

    But what are the physical properties that retain a connection independent of space ? These may be internal properties of waves in a vacuum or a non light -absorbing medium. But, could it be, under these conditions the connection maybe the wave itself and energy has a dimension of it's own ? i.e. the energy is never divided.
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