1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Do photons oscillate?

  1. Jun 14, 2012 #1
    OK I understand it’s a silly question but I have been thinking about this all day.

    Say you have an EM wave moving out from its source in a transverse wave formation. Where does the oscillation come from? And (another silly question) is the oscillation affected by mass?

    In my simplistic way I like to think about it like this:
    In the light source atoms are oscillating as they emit particles and energy. This means that some particles will be emitted at the top of the oscillation and othersat different points. This creates a steam with a wavelike formation of particles being emitted.
    I may be way off with that by the way?

    But what happens next?
    Does the oscillation continue until the photons bumps in to something? Are they affected by the rest of wave in a repulsive way (so forcing movement away from the centre)?

    So can anyone explain “why” the wave forms and "why" it doesn’t deteriorate over time as, sometimes, this is a VERY long time?

    Thank you
  2. jcsd
  3. Jun 14, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    First it may help to understand WHAT is oscillating. The electric and magnetic fields are oscillating from + to - and back. Did you know that?
    There is no "wavy motion" of light, it travels in straight lines.

    Edit: Just to be clear, light itself IS a wave. It is not little particles bouncing off of things. The photon is simply the result of the laws of the universe requiring the energy of an EM wave be absorbed or emitted in little packets or chunks that we call photons. In SOME cases it is possible to consider light in the particle sense, but not all.
  4. Jun 14, 2012 #3
    I was always taught that light moves in transvers waves - is this not correct. - and that the wave consisted of photons (packets of energy).

    Are you saying that em is just energising one photon twhich then passes this onto the next and so on (like an electric current down a cable). If this is case why do they teach that light moves in transverse wave.

    Sorry but a little lost with this - I have wiki'ed this no end
  5. Jun 14, 2012 #4
    The real ones oscillate. The virtual ones don't. The oscillation frequency is proportional to their energy.

    If you thought of them as semi classical balls or waves you'd conclude that their physical (longitudinal) extent is given by the narrowness of their energy spectrum. But this can't really be the case for the typical photon unless it's part of an infinite plane wave.

    If you connect a highly directed antenna to an RF generator that pushes out a single broadband RF quantum, the probability of finding it at a certain place far away will exactly obey the antenna pattern as measured with many quanta.

    Such a photon cannot be localized either in space or time (it's not a ball or point particle until and unless its measured by a receiver and you can't say it left the antenna at this instant and not that instant unless the energy is sufficiently indefinite), it interferes with itself especially around the antenna.

    Balls and point particles don't help visualize this much.
  6. Jun 14, 2012 #5
    OK thanks.

    I have not been in a class room for over 35 years and am simply trying to understand things as a hobby. So I really do appreciate and answer you have time to give.

    Back to my thoughts. Looking your answer it seems you are saying that at a quantum level there is no oscillations but it helps to visualize it as such.

    I am along the right lines here?
  7. Jun 14, 2012 #6


    User Avatar
    Staff Emeritus
    Science Advisor

    No, that is true. The electric and magnetic fields have a vector and these are oriented at 90 degrees to each other and to the direction of propagation, so it is a transverse wave. What I am saying is that the light does not travel in a wavy path. If you drop a pebble into a pond the wavefront of the expanding wave cannot be said to be wavy in the direction it travels. (Because it travels out while the oscillations of the water go up and down.) This is just an analogy, but it is similar to an EM wave. From a point source, the wavefront propagates out in a spherical shape, just like the water wave propagates outward in a circular shape on the surface of the water.

    No, the EM wave is literally a wave, a disturbance in the EM field. It merely interacts in packets called photons. By this I mean that pretty much all the rules we use to describe how an EM wave propagates follow wave rules, but when we go to detect the EM wave we find that in certain experiments we are only able to explain how it works if we think of the wave as being composed of little particles. Hence the wave-particle duality in quantum mechanics.
  8. Jun 14, 2012 #7
    Hi Drakkith

    Thank you that makes sense.

    I will do some more reading and than come back with some more silly questions :redface:

    Thank you for helping (it's really quite fun all this)

  9. Jun 14, 2012 #8
    if I connect an alternate current source or RF generator to an antenna how does the electromagnetic field "exit" from the antenna? is that field mainteined by photons and how can they move from the + to - in the air?

    thank you!
    Last edited: Jun 14, 2012
  10. Jun 14, 2012 #9


    User Avatar
    Staff Emeritus
    Science Advisor

    The electrons in the antenna move back and forth, which generates a disturbance in the EM field that propagates outward from the source. It is the acceleration of charges that generates disturbances in the EM field. Once the wave has been generated it "self generates" by the alternating fields. The changing magnetic field induces a changing electric field, which itself induces a changing magnetic field. (I think at least. This discussion is quickly reaching the limit of my knowledge of EM theory)
  11. Jun 14, 2012 #10
    I like Drakkith's water wave analogy....

    If you want to see some nuts and bolts of photons discussed try this on for size:

    How big are photons:

    To get you started:
    don't have the source:
    And one step further is the emission or absorption of a photon from an orbital electron:
    I think I posted this previously:

    It's emits a purer and purer 'photon' the longer it has existed!!!
  12. Jun 14, 2012 #11
    when an alternate current flow in a coil, will it generate a magnetic or electromagnetic field?
  13. Jun 14, 2012 #12


    User Avatar
    Staff Emeritus
    Science Advisor

    The magnetic and electric fields are different aspects of the Electromagnetic field. Generally if you are talking solely about one aspect of the EM field you would just say magnetic or electric.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook