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What substance makes up E and B fields in EM wave

  1. Apr 16, 2005 #1
    Please link me to threads that may already discuss this because i do not really know what to search for when i use the word substance.

    I neglect to use the word matter because matter in physics world means mass
    and i neglect to use the word particles because in physics world they usualy pertain to our standard model.

    Im not keen on the idea of modelling light through its wave ppts and have decided to attempt to model Young Slit Results by code, trying to simulate through particle model (idea came from jezzball)

    Sorry the keyboards messed so i dont have question or quotation marks.

    (0) What ^substance^ makes up E and B fieldsin EM waves and what allows them to propogate in the cross direction(is it because of the discharge from the last reaction it came from).

    (1)And what exactly is a charge. It is my belief that an interaction requires the transferance of substances over space, which also applies to attraction and repulsion. So what exactly is a charge that causes these two reactions.

    (2) If i remember correctly from physics ...an electron can cause and Electric Field around it. What is in this field.
  2. jcsd
  3. Apr 17, 2005 #2

    Claude Bile

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    I think the correct term your looking for is 'medium' (or media pl.).

    (0) EM waves propagate in a vacuum, they do not require a medium. They are transverse waves because Maxwell's equations say this is so.

    (1) Charge is just charge, it is a fundamental property of particles. Force between charged particles is transmitted via virtual photons (This is not my area of expertise, perhaps others can elaborate).

    (2) There are electric fields everywhere, at every point in space. Again, no medium is required for these fields to exist.

  4. Apr 17, 2005 #3
    Thx for replying claude
    (0)they are waves..but do they contain substance? To put it into perspective...if i was to computer model a photon...would the 3D graphical representation truly be a wave(this was suggested by a friend of mine). So i'd just draw a sine wave at the location.

    (1)"charge is just charge"? so your saying there exists "virtual photons" inbetween two particles that communicate teh attraction/repulsion force between the two if they are charged. Lets just call them FCP(force carrying particles). Would this be the correct notion?

    (2) So Efields come from particles? but what substance is in these Efields? I use the term substance because you already used the term medium to describe something i think is different(ie your term medium would be the ether that was thought to exist for light). If there need not exist substance in these "Efields" I find it hard to believe that there is a magical # representing the weight of the field floating in space...IMO there would have to exist some substance to maintain that field...Especially in the E&Bfields that exist in the photon.

  5. Apr 18, 2005 #4

    Claude Bile

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    (0) Photons exist in 3D space and so cannot be described by a 1D function such as a sine wave. As far as I know, nobody has experimentally determined the E/M profile of a single photon.

    (1) Virtual particles (or Force-carrying particles) are a nice way to describe the transferance of momentum over a distance.

    (2) The magical number is an artificial (man-made) representation. The whole concept of electric fields is a convenient way for us to describe how charges and their fields interact with one another. When we say the E fields is # at a particular point, we are really saying that if a +1 C charge was placed at this point, it would feel a force equal to #.

    P.S. Unless this 'substance' you refer to has some measurable consequence in our world, you will have to post in the Philospohy forum!

  6. Apr 18, 2005 #5
    Totally agree....
  7. Apr 18, 2005 #6


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    I vote for skepticism & debunking...:uhh:

  8. Apr 19, 2005 #7
    so fields/energy are philosophical tersm that have no substance?
  9. Apr 19, 2005 #8
    Are you asking what is substance? Because that is philosophical.

    An electric field is only what it is defined to be. An electric field E is defined by F=qE, where q is a small "test charge" (in that it doesn't affect the field distribution) and F is the force it feels. There is no need for this field to be made out of anything at all.

    In fact, all matter is the "invisible organisation of energy" (I quote Pagels, I think). You can go on to ask, what is energy? That is indeed a philosophical question. All physicists can do is tell you how the energy behaves. At the moment there is some behaviour that we do not understand -- our aim is to be able to describe all the possible behaviours in a (hopefully) neat mathematical framework.
  10. Apr 19, 2005 #9
    Hello neurocomp2003,

    maybe you got the impression that electromagnetic waves need a medium because of the analogy between water waves and electromagnetic waves, for example interference.
    At first, it was only logical because of that analogy, that that electromagnetic waves propagate through a medium, that they called "ether".
    But an experiment, called "Michelson-Morley experiment" showed that such an "ether" doesn't exist.
    You may want to read more about that interesting experiment.
  11. Apr 19, 2005 #10
    no i know the medium/ether stuff...i'm asking when one says a "EM wave propogates" what is propogating...substance that we have yet to detect or is it a mathematical model(numbers), because we cannot comprehend or detect what is in teh EM itself. That is to say that it is similar to sound...where substance isn't really propogating but the motion of the system of substance(ie air) that causes the phenomenon

    masudr: so your saying its only a mathematical model? and that there needs to be a 2nd particle to cause the field to occur whereby transfering FCPs.
    Last edited: Apr 19, 2005
  12. Apr 19, 2005 #11


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    Ok, I hesitate to say it, because I'm working on a publication on it, so I'm affraid my idea might be stolen, but I have serious indications to believe that the substance that propagates EM waves is chocolate pudding.


  13. Apr 19, 2005 #12
    Firstly, in any kind of a material classical wave, there is no propagation, only motion with respect to some equilbirium.

    And yes, an electric field is only a mathematical model. Even the term force is not physical nor is particle. All the words and the equations do is describe reality -- it is all a model. And besides just because we need two particles for there to be a force, doesn't mean that one particle cannot creat a field. Furthermore, don't mix a discussion about classical electromagnetism with quantum field theory -- the two are very different!
  14. Apr 19, 2005 #13
    oh so the discussion of what makes up light belongs in EM not QM? my mistake...i only took senior level astrophysics so the QM side of things is abit iffy.
    and i never said the a single particle couldn't make a field...because i was taught that it could. I'm just trying to differentiate between what is a model and what people deem 3D reality..so i can attempt ot model it
  15. Apr 19, 2005 #14

    "i'm asking when one says a "EM wave propogates" what is propogating"

    Suppose that instead of a continuous wave, a single EM pulse propagates. Do you have any problem with what is propagating in that case? If so, it's an electromagnetic field. It's here right now, and one second later it's 186,000 miles away. It propagated from here to there.
  16. Apr 19, 2005 #15


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    Really? I would think Jell-O would propagate transvese waves better! :confused:
  17. Apr 19, 2005 #16


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    "If a tree falls in a forest, and nobody is present to hear it, does it make a sound?"
  18. Apr 19, 2005 #17

    James R

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    Actually, what propagates is a disturbance in the E/M field. That disturbance carries energy from one place to another.
  19. Apr 19, 2005 #18
    ok so we're using a new term "disturbance" plz describe...remember i'm trying to model this in a computer simulation.
  20. Apr 19, 2005 #19
    James R,

    "Actually, what propagates is a disturbance in the E/M field."

    What does that mean? What field is being disturbed?

    If I take two equal but opposite charges, both located at the origin, pull them apart and then let them go back together, I get a little field near the origin for a brief time, then it disappears and one second later a field appears briefly at about 186,000 from the origin, and then it disappears at that location.

    Isn't that a field propagating?
  21. Apr 19, 2005 #20

    Claude Bile

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    That's a technical issue and depends what you refer to by a field. Any field is technically just some mathematical function that assigns a vector to each point in space, so the field itself does not propagate, it just takes different values at different points in space.

    Most physicists though just say that the field is propagating.

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