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Photons Are 'Wave-like' in What Way Exactly?

  1. Feb 17, 2013 #1
    Exactly in what way are photons wave-like? With respect to what property or metric? For example, we often hear the wave-like nature of photons compared to waves in water. Well, wave behavior in water can be measured or observed in respect to mechanical displacement - crests and troughs which can be seen in the Z and other axes. Water waves can be quickly recognized to oscillate the observed/measured height of the water. What property exactly is being oscillated by the wave-like behavior of photons? What most obvious physical property would I look at first to immediately identify that the photon is in fact wave-like?

    We often use the example of the slit diffraction experiment to show that light is wave-like, as exhibited by the interference pattern. But so that interference pattern is identifiable by its variations in brightness, where brightness at any particular point is the result of number of photons landing there. So since photons arriving at a particular point is due to motion or trajectory, are we saying that it's specifically in their motion or trajectory that photons are wave-like?
  2. jcsd
  3. Feb 17, 2013 #2


    Staff: Mentor

    They have a frequency and a wavelength, also they diffract and interfere.
  4. Feb 17, 2013 #3
    Photons are not wave-like, because photons are particles.
  5. Feb 17, 2013 #4
    Last edited by a moderator: Sep 25, 2014
  6. Feb 17, 2013 #5


    Staff: Mentor

    And particles have a frequencies and wavelengths, and they diffract and interfere. Just like waves.
  7. Feb 17, 2013 #6
    which is why e=hc/λ ?.......cough cough they have a frequency.
  8. Feb 17, 2013 #7
    I've never done it but there is also the marshmallow microwave experiment, your supposed to see the wavelength as bumps in the surface. What does that represent?

    Last edited: Feb 17, 2013
  9. Feb 17, 2013 #8
    "The activity requires a microwave oven, a microwave-safe casserole dish, a bag of marshmallows, and a ruler. (The oven must be of the type that has no mechanical motion-no turntable or rotating mirror. If there is a turn-table, remove it first.) First, open the marshmallows and place them in the casserole dish, completely covering it with a layer one marshmallow thick. Next, put the dish of marshmallows in the microwave and cook on low heat. Microwaves do not cook evenly and the marshmallows will begin to melt at the hottest spots in the microwave. (I leaned this from our Food Science teacher Anita Cornwall.) Heat the marshmallows until they begin to melt in four or five different spots. Remove the dish from the microwave and observe the melted spots. Take the ruler and measure the distance between the melted spots. You will find that one distance repeats over and over. This distance will correspond to half the wavelength of the microwave, about 6 cm. Now turn the oven around and look for a small sign that gives you the frequency of the microwave. Most commercial microwaves operate at 2450 MHz." - taken from http://www.physics.umd.edu/icpe/newsletters/n34/marshmal.htm
    although, I wont vouch for the accuracy of this article
  10. Feb 17, 2013 #9
    Does it heat more at troughs or peaks or zero crossings? What about the wave does this represent?
  11. Feb 18, 2013 #10
    So are we saying that photons oscillate in all of their properties? Is there no property of the photon which does not oscillate, but instead stays constant?

    I just feel a little frustrated with the "LIKE" part of "wave-like"

    When we say 2+2=4 then we know exactly what that means.
    But if we say that "2 plus 2 is 4-like" then what the hell does that even mean??
  12. Feb 18, 2013 #11


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    Staff Emeritus
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    This thread is very confusing.

    Are you asking what properties of light that gives us indications that it is wave-like? Or are you asking about ONE photon in particular? The former is a bit puzzling since one only has to solve for the wave equation from Maxwell equation and, viola, it falls right onto your lap!

    If it is the latter, then is there a reason why it is ONLY on a photon, and not any quantum particle in general? Do you have no issues with electrons, protons, neutrons, buckyball, etc. that also show the same wavelike properties?

    I'm trying to figure out what exactly is the problem here...

  13. Feb 18, 2013 #12
    Zapper: I am asking the first question, and I would appreciate a more illustrative answer than merely citing the Maxwell equation.
  14. Feb 18, 2013 #13
    Well, Maxwell came before Einstein, and his description of light was purely as electromagnetic oscillations, which actually explains most everyday phenomena; the photon was described only later as an explanation for the photoelectric effect. It seems the more proper question would be to ask how light can be particle-like. Also, as ZapperZ has mentioned, the wave-particle duality exhibited by light is by no means unique to it; all particles exhibit this behavior. I don't mean to dodge the question, but can you clarify whether you're wondering about something specific to photons, or about wave-particle duality in general?
  15. Feb 18, 2013 #14
    From Maxwell's equations, one can derive a wave equation for the electric and magnetic fields. These are what oscillate. That is classical EM. The oscillations are in the electric and magnetic field. Illustrations of this come from Young's double slit experiment, and pretty much every optics experiment up until the late 19th century.

    Your comment about 2+2=4 is a good example. This is a common idea that has been around for probably 6000+ years, so we have simple language to explain it as well as the formula. For quantum optics, the simple language has not been devised. Wave-like is a way of relating something you can see to the facts of the formulae. If you want to know exactly, you need to study for a long time.
  16. Feb 18, 2013 #15


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    Staff: Mentor

    That's fine that the brightness in general can be described in terms of waves and particles, but interference itself, including what the brightness actually is is only explainable as a wavelike property: Saying that X brightness corresponds to Y photons hitting a certain spot doesn't tell you why you got Y photons to hit that spot.
  17. Feb 18, 2013 #16


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    I think Feynman explains it best (as usual):

    Last edited by a moderator: Sep 25, 2014
  18. Feb 18, 2013 #17


    Staff: Mentor

    It has all of the properties associated with waves: diffraction, reflection, refraction, wavelength, frequency. It also shows polarization, which is characteristic of transverse waves.
  19. Feb 18, 2013 #18


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    Staff: Mentor

    Spin, charge, and a few others I'm sure.

    That's because a photon also behaves in a "particle-like" manner. If it was only a wave then you wouldn't have "wave-like" being thrown around. Actually if it was only a wave you wouldn't even have a photon at all since it's the quantized interaction of the EM wave.

    It's important to understand that the theory that describes photons NEVER says "wave-like". It explains it in perfectly clear mathematical language that is subsequently garbled beyond all recognition when you try to explain it in everyday language. This isn't a problem just with photons, but with many things in science that are very clear when you are working with the theory itself but are almost impossible to adequately describe when you have to reword it for someone who isn't familiar with the theory.
  20. Feb 18, 2013 #19
    sanman posts:
    What you really mean is that a photon " is both wave like and particle like'. The most obvious physical property is what you choose to detect it.....Different circumstances tease out one property or the other.

    You simply have to read accepted experimental evidence which reveals current understanding.
    None is better than the double slit experiment [wave particle duality] and the photoelectric [particle] effect explanations. Wikipedia has the necessary insights regarding each.

    These are not necessarily intuitive and arrived at via some suddenly "EUREKA" moment...but are observational, empirical results. It's the way stuff works and that's why quantum mechanic models are the way they are...to mimic what is observed experimentally.
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