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Wave-particle duality and electromagnetic waves

  1. Jan 8, 2009 #1
    I have three points:

    1. According to wave-particle duality, even regular matter can be classified as a wave instead of a particle, for example, an electron or a neutron. My question is, what is this a wave of? A photon is a wave of oscillating electric and magnetic fields. Are electrons, say, also waves of oscillating electric and magnetic fields, or something else? If so, then why are they not constantly moving at the speed of light?

    2. When people draw an electromagnetic wave on paper or a screen, to for example display frequency, all they draw is one wave. If I am not mistaken, though, EM waves are composed of an electric and magnetic component. Thus, how can they be drawn as a single waveform?

    3. Also, when they do draw these waves, does a positive amplitude for the electric component mean a positive electric field, and a negative amplitude mean a negative electric field, or is this related to direction not charge? Same goes for the magnetic component.

    Thank you for answering any of these!
  2. jcsd
  3. Jan 8, 2009 #2


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    Welcome to PhysicsForums! I'll get things started...

    1. Matter and light share wave-particle elements. Electrons, and even entire atoms, can be diffracted through a double-slit setup and will exhibit self-interference (as waves do). Both are subject to the Heisenberg Uncertainty Principle. They can all also be observed as point particles (except for protons & neutrons, which exhibit a defined size).

    2. I think this is more for simplicity of representation that anything else. Photons are also polarized, which is essentially describes the relationship of the oscillating components.
  4. Jan 8, 2009 #3
    too many questions all at once, some with no simple answers.
    (1) try Wikipedia: http://en.wikipedia.org/wiki/Wave_particle_duality
    Photons might be considered bumps/concentrations in EM fields; electrons have rest mass.

    (2) EM can be described different ways....what you observe (electric vs magnetic) depends on your frame of reference relative to the EM source...
    try wikipedia http://en.wikipedia.org/wiki/Electromagnetic_radiation
    According to Maxwell's equations, a time-varying electric field generates a magnetic field and vice versa....EM radiation exhibits both wave properties and particle properties at the same time....

    (3) You can represent an EM wave as a transverse wave with varying amplitude...the electric and magnetic portions are othonogal to the direction of propagation and to each other....(unlike a sound wave which is longitudional) the Em wave doesn't know where you set you set a zero axis so plus and minus is purely at the formulators discretion....notice some of the reference diagramsn in (2) have an x axis others don't...

    Having said all that, keep in mind that most of physics describes what happens...that is we model mathematics to represent experimental observations, sometimes vice versa, but often we do not understand fundamental physicality...for example you use the term "regular matter" yet you don't know what it is..nor where it came from nor why....neither does anybody else, but because you can see and touch it we all think it "makes sense"...QM says its made mostly of space, just a small portion is physical atomic "cloud like" constituents; the standard model suggests point particles make a good analogy; string theory posits its all vibrating bits of energy...and on and on

    So there is plenty of opprtunity for more Nobel Prizes!!!

    "we know a lot; we understand little"
  5. Jan 8, 2009 #4
    I might be mistaken on this, but I don't think a photon is a wave of oscillating electromagnetic fields... A photon, and an electromagnetic wave, are two different models of electromagnetic radiation, and both happen to be needed to explain different things.
  6. Jan 8, 2009 #5
    Hey everybody thanks for answering my questions. I have a few comments to make:

    So if I am getting this straight, then according to wave-particle duality, matter has properties of particles and of waves. My confusion is in the fact of what the wave components are made of? If we can think of photons as the particle versions of electromagnetic radiation, and EM waves as the wave versions of EM radiation, then what is, say an electron? The particle version of electron radiation? And its wave version is what?

    I have read the Wikipedia article on wave-particle duality many times and all it says is that particles exhibit wave-like properties. Nowhere does it say how these waves are propagated and what they are.

    Let me explain my problem in other words: Now if I am getting this correctly, an electron has about 0.5 MeV at rest. So, it has about the same amount of energy as a gamma ray. If it has the same energy, then it must have the same wavelength and frequency. So if the gamma ray is 300 EHZ say, then the electron must also have that frequency. See http://en.wikipedia.org/wiki/EM_spectrum

    My problem is defining the frequency which is how many oscillations per second. In an electron, these are oscillations of what? Oscillations of a magnetic field, oscillation of pure energy, oscillation of what?
  7. Jan 8, 2009 #6
    Look at the Wikipedia article on Electromagnetic Radiation.
  8. Jan 9, 2009 #7
    But you see, I understand EM radiation. The problem I have is with the definition of other matter as waves. Scientists have created diffraction on electrons and neutrons, so I'll use those as an example. For example, what defines the "frequency" of the electron? Same goes for neutrons. What is the "matter wave" composed of? Is it the same as EM radiation or what?
  9. Jan 10, 2009 #8
    This was the leap de Broglie made. If photons can be described by waves, why can't elctrons? or protons?..
  10. Jan 10, 2009 #9


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    No, it is not the same as electromagnetic waves that we use in classical electrodynamics. With electromagnetic waves, we can observe the electric and magnetic fields that they are composed of, by ovserving the motion of charged particles as a wave passes by. For example, the oscillating electric field in a radio or TV signal causes electrons in an antenna to oscillate back and forth.

    The QM wave function [itex]\Psi[/itex] manifests itself only in calculating probabilities for values of physical quantities, and does not have any direct observable effect itself.

    The question of what [itex]\Psi[/itex] "really means" in an ontological sense is the subject of interpretations of QM, of which there are several. There is no general consensus as to which interpretation is "best" and people argue about it a lot, especially on forums like this one. :rolleyes:
  11. Jan 10, 2009 #10
    I always pictured the wave nature as the "main" feature of EM radiation (since it is just propagating fields, it seems much more like a wave), and the particle nature as the "main" feature of particles with rest mass.

    Am I just asking unanswered questions? Am I correct in thinking that they came up with wave-particle duality, got evidence for it, but never made an explanation?
  12. Jan 10, 2009 #11
    I think you might need to work through the mathematics to get the wave equation because I think you are still wondering about whether it is a wave or a particle.

    Also my take is: a matter wave is a probability wave not like an EM wave or water wave. It looks wavey but is in fact defining probabilities. So for example, an electron has a probability of being at A, B or C. Similarly for wavelength (relates to momemtum) and spin.

    Maybe thats not your problem though and you are asking something deeper?
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