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If light is a wave, what is waving?

  1. Jun 29, 2011 #1
    We are all familiar with the description of a wave as being the ripples on a pond with water being the displacement medium for the wave. I understand that light is a electromagnetic/magnetic wave but in reality there has to be a displacement medium for the wave to transmit, what is it?
     
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  3. Jun 29, 2011 #2

    Doc Al

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    Why do you think that?
     
  4. Jun 29, 2011 #3
    Any mathematical model used to describe waves, is just that, a model, and is not reality. I see, therefore I am receiving information, how is it possible to receive information ie light without there being a transfer of information from the subject to the receiver? There has to be a disturbance in some form along the path between the two? What is the displacement or disturbed medium?
     
  5. Jun 29, 2011 #4

    Doc Al

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    The information is carried by the E&M field itself. It's not a disturbance of some medium (as is the case with sound, for example).
     
  6. Jun 29, 2011 #5

    HallsofIvy

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    Yes, light is a wave (or ripple) in the electro-magnetic field. That is the "displacement medium".
     
  7. Jun 29, 2011 #6
    If light is transmitted via E&M fields, then how does the field manifest itself in reality, if information is "carried" there has to be a transmittance through the field as you state so what is the mechanism for the transmittance?
     
  8. Jun 29, 2011 #7

    Borek

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  9. Jun 29, 2011 #8

    ZapperZ

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    Haven't we gone through this already at the beginning of the 20th Century?

    Zz.
     
  10. Jun 29, 2011 #9
    I would say, light is a disturbance of the E&M field.

    By the light that you see. Or by the cellphone you are using. Or the lightning that burns down your house.

    The mechanism is waves.
     
  11. Jun 29, 2011 #10
    The explanation of "a field" or "wave" is a mathematical description of a disturbance of a physical something. Light travels through a vacuum so by your definition so does the field, so if you prefer the question could be, what in reality is a field and what is being disturbed to transmit the information through that field? There has to be a physical reality and not just a mathematical concept of a field or wave? So what is it?
     
  12. Jun 29, 2011 #11
    But wasn't answered adequately then, nor is it now
     
  13. Jun 29, 2011 #12

    Doc Al

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    Sounds like you don't think that the E&M field is 'real'.
     
  14. Jun 29, 2011 #13
    Are we talking about mathematics or physics? In physics, the physical something you talk about IS the field. That physical something is modelled using the mathematical concept of a field. So a field can be real or imaginary in a sense. But it's all just semantics of the language we use.

    We could maybe just say that a field is real. Like a corn field or an E&M field. We then invent an abstract mathematical concept that we call the fieldotronicoid and use that to model real fields.... It just happens that the word field is overloaded. That's all.

    First of all the field doesnt travel. It's just there, everywhere, including the vacuum. In reality the field is made up of quantized harmonic oscilators. Does that help? We know the field is there because we can measure it. That's all. What more do you want?
     
  15. Jun 29, 2011 #14

    ZapperZ

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    Actually, it has, per Special Relativity!

    The problem here is that you have made an a priori assumption that ANY wave needs a medium of transmission. So now you're asking for what that medium is for EM radiation. That's like asking someone "when was the last time you bashed your wife?". The question can't be answered within the framework that it was asked!

    We have seen, in physics, where our "prejudice" needs to be revised in light of (i) experimental evidence and (ii) new formalism to describe something. So far, your question is based on a matter of "taste" ("there has to be some disturbance of something") without pointing out experiments in which such a thing is supported. On the other hand, a whole zoo of experiments have indicated that our current understanding of EM radiation is valid, that light requires NO medium for transmission.

    Zz.
     
  16. Jun 29, 2011 #15
    I am talking about the physical reality, in Schrodingers equation for quantum harmonic oscillation the wave form is a function of kinetics and angular frequency which may describe reality but is in truth a mathematical interpretation of a reality. If we interpret a measurement, or series thereof, as being the evidence of a force or field as reality, surely we have only supplied a plausible interpretation of that measurement. For example Newton "discovered gravity" (I assume we all floated round before he did so (joke)) anyway he saw the apple fall and offered an interpretation to the best of his knowledge and dutifully quantified that experience and numerically was able to predict the behaviour of or movement of objects. Many years later along came other thinking and we now visualise gravity in terms of space time.

    The reality of field theory seems to be at the same stage as Newton. If a field is "just there" or "real" because we have measured something the question remains through what physical medium, in reality does it function?
     
  17. Jun 29, 2011 #16

    Dale

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    This is a pretty common complaint of crackpots everywhere. Unfortunately, it doesn't hold water in the context of science. This is not just an arbitrary mathematical model, it has been experimentally validated to incredible precision. So although math is a construct of human logic, in this case it is a model which does in fact accurately describe reality.
     
  18. Jun 29, 2011 #17
    So, you just want a non mathematical explanation. Fine, but that's not physics.

    How do you think that happened? I suppose you think that someone just had a better idea and was able to convince the others that he was right?

    What happened was that MEASUREMENTS at some point started to conflict with existing theory and assumptions. So, some people thought long about how that could be. those person ended by proposing a refinement of the existing theory which encompassed both. Since then no experiment has been able to falsify that. In fact it keeps coinciding with reality to an absurd level of precision, everyday.

    Your question is one of philosophy. In which language do you expect the answer to be?
     
  19. Jun 29, 2011 #18
    I assume the term crackpot was not to be taken personally, even though you may have been a little exasperated when you wrote it. If questioning interpretation of experimental evidence is crackpot then you would have to add Galileo and Einstein to your collection. I can accept the existence of waves and all the experimental evidence for them, but in every graphical representation of those waves amplitude is shown as well as a wave length. I believe my original question was asked of Einstein who coined the term photon after Hertz demonstrated with his plate experiment that waves were inadequate explanation of light. It is also known that waves are transmitted through vacuum yet there is no obvious explanation offered other than “a field”. So assuming EM wave or field is a widely accepted term for a light field what in reality is the amplitude of the wave (other than brilliance), something physical must change in the field so what is it? I really hope I am not exasperating you over this but my searching question is genuine.
     
  20. Jun 29, 2011 #19
    The question is one of reality which is neither mathematical or philosophical
     
  21. Jun 29, 2011 #20
    I think http://www.physicsclub.net/images/wave_anim.gif" [Broken] is a decent animation of the physical interpretation of an electromagnetic wave in classical electromagnetism. One of the colors represents the electric field and the other color represents the magnetic field. You probably understand electric and magnetic fields as being fields of vectors, well in that picture the arrows are electric and magnetic vectors. That wave can be created from an accelerating charge. In order to conserve energy the charge radiates away some of it's energy in the form of that oscillating electric and magnetic field shown in the link. That oscillating electric and magnetic field is an electromagnetic wave. The wave continues to propagate in order to satisfy Maxwell's equations.
     
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