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What are electromagnetic waves made of?

  1. Jul 7, 2011 #1
    Electromagnetic waves, aka light and such. What is it?. I know that it is a wave of energy, magnetic and electric forces traveling in wave forms but when struck turning into a particle. But what exactly are they made of? Is it just a pure wave of energy and nothing else to it?

    Do physicists even know what it is in itself?. I know what it does, but not what it is.. I am confused.
     
    Last edited by a moderator: Jul 7, 2011
  2. jcsd
  3. Jul 7, 2011 #2

    Drakkith

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    I wouldn't use the term "energy" like that personally. Energy isn't a thing or a property like mass or charge. A photon is made up of an oscillating electric and magnetic field. That IS what photons are made of.
     
  4. Jul 7, 2011 #3

    Good kind of clears it up, but dont the electromagnetic forces travel instantly or infinently fast, and since photons are these forces, shouldnt they travel instantly?
     
  5. Jul 7, 2011 #4
    Oh or maybe it's just an oscillating source of magnetic field not A magnetic field.
     
  6. Jul 7, 2011 #5

    Drakkith

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    No, the maximum speed that anything can move or propagate at is c, the speed of light. If you were to move a charge towards another charge, the effect would travel at c to the other charge. There would be a delay between moving one charge and it affecting the other one.

    There is no "source" that travels with the photon. It is only the fields that exist.
     
  7. Jul 7, 2011 #6
    I think I got it now, it is a particle that produces electromagnetic forces, but it moves in wave form, and turns into a particle if disturbed.

    Am I right?
     
  8. Jul 7, 2011 #7

    Drakkith

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    Nope! This is where things get a little confusing in QM. A photon IS composed of two fields and acts just like a wave. But it also acts like a particle. When you do experiments to determine which one it acts like, if you look for a particle effect you will get that. If you look for a wave effect you will see that one instead. It never "turns into a particle". The energy of a photon is quantized, which means that the photon doesn't dissipate and when it interacts, such as when being detected by a detector or your eye, all of the energy is absorbed, not half or part or anything.

    See here: http://en.wikipedia.org/wiki/Photon
     
  9. Jul 8, 2011 #8
    Umm I seem to have misunderstood the world. I know that quantum entanglements travels infinently fast but I tought Electromagnetism was the only force that travels infinently fast I must have confused entanglement with electromagnetism, so if you would create a charged particle, people lightyears away would immideatly know. So does not Electromagnetism travel infinetly fast?:O Is that true?
     
  10. Jul 8, 2011 #9
    electromagnetic field is a wave that consist a magnetic field and electric field that simultaneously spread .
    it once only the prediction of maxwell that predicted there was a relation between magnetic and electric field from the fact that each of them can create the other with the unconsistent dimention of time. then its become reality when hertz prove it with his experiments.
    CMIIW
     
  11. Jul 8, 2011 #10

    Dotini

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    So magnetic and electric fields can propagate through empty space, and do not require charge carrier particles?

    Respectfully submitted,
    Steve
     
  12. Jul 8, 2011 #11

    HallsofIvy

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    Magnetic and electric fields exist in empty space. I wouldn't use the word "propogate"- they just "sit there". It is "ripples" in the electromagnetic fields that permeates space that are light.
     
  13. Jul 8, 2011 #12

    WannabeNewton

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    As Drakkith pointed out, electromagnetism is not instantaneous just like gravity is not instantaneous. Changes in an electromagnetic field propagate at c.
     
  14. Jul 8, 2011 #13

    Drakkith

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    Any change will propagate at c. So if you create a particle with an electric charge of -1, then it will take finite time for another particle at a distance to feel any force from it. If you then move the new particle back and forth the effects again propagate at c to the other particle.

    Changes in the fields propegate. Two particles at a distance from each other always feel each others field, but if you move one closer to or further away from the other, then the other particle doesn't feel any decrease or increase in force until the change reaches it, which moves at c. A photon is an oscillating electric and magnetic field, and moves at c. It does not require a particle to travel with it.
     
  15. Jul 8, 2011 #14
    Wow, mind blown. I have been thinking that electromagnetism travels infinetly fast for months. Pretty funny actually.
     
  16. Jul 9, 2011 #15

    Dotini

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    HallsofIvy, thank you very much for your answer - it's just what I wanted to hear. However, this morning I was perusing the wiki on Maxwell's equations, and ran across the entry on "Maxwell's macroscopic equations", also known as Maxwell's equations in matter, and I wondered if we might be in some trouble, since molecules and surfaces of materials seem to be implied, and therefore particles ARE involved. http://en.wikipedia.org/wiki/Maxwell's_equations

    Of course I'm a complete amateur with no real insight on this subject, so I'd like some more help and clarification, please. First I'd like to clarify that my own original question about "empty space" meant "empty outer space".

    Am I badly misunderstanding what I'm reading in wiki?
    Is Maxwell in error here, and can be safely dismissed?
    Or?

    Thanks again for your help.

    Respectfully yours,
    Steve
     
    Last edited: Jul 9, 2011
  17. Jul 9, 2011 #16
    Dotini,
    There is nothing wrong with electromagnetic fields in matter, this is exactly what causes electric current in wires and antennas for example. When EM fields travel in matter they slow down because the two constants responsible for the velocity of light (ε0 and μ0) change. These fields cause disturbances in the charge distribution in the solid, causing losses, but the molecules aren't required for them to propagate (just like copper wires aren't required for electrons to move). Also note that while the waves will travel less than c, the photons do not. They are moving at c, get absorbed by an atom, and then re-emitted a short time later traveling again at speed c. This means a photon traveling through a medium will take longer to go a given distance than it would in a vacuum, but it is not moving any slower (it just makes a lot of "stops" along the way)
     
  18. Jul 9, 2011 #17

    Drakkith

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    I have been told and have read here on PF that the absorb-re-emitted view is incorrect. But I don't know the details Omega.
     
  19. Jul 9, 2011 #18

    Nabeshin

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    One way to think about it is that Maxwell's microscopic equations are what is REALLY going on. They perfectly describe the behavior of electromagnetic fields, end of story.

    However, when you want to investigate some material, you have to think about what you're really doing. A solid, for example, is nothing more than a lattice of atoms. Therefore, it's really just empty space punctuated by the occasional atom. Maxwell's microscopic equations still hold, but would be impossible to write down if one had to consider the contribution from every single atom. So what you do is you average over a characteristic length for the lattice structure, and what comes out are Maxwell's macroscopic equations. They are approximations to the true Maxwell's equations, and represent a sort of 'smoothed out' version of the spikey normal Maxwell's equations.

    What I mean by smoothed out and spikey is that at the nucleus of every atom, the electric field increases without bound (assuming an infinitely small nucleus). So if you imagine the electric field as a function of distance inside the material, it looks rather like the teeth of a comb. Not terribly useful, so you can smooth over all this spikiness and get an average electric field -- this is the macroscopic interpretation.
     
  20. Jul 9, 2011 #19
    Thanks for your insight Drakkith, I searched archived posts and must admit, I never heard this disputed before but there are compelling arguments that it is not a correct argument. There was a lot of debate but it never seemed to reach resolution: If photons must travel at speed c and they aren't absorbed, what is the QM/QED explanation for the slowing of EM in media?
     
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