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Magnetic fields

  1. Jul 15, 2004 #1

    mee

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    Is a magnetic field carried by a particle? If two north ends of a magnet are brought together they push apart as if they were two rivers meeting head on and if a north pole and a south pole are brought together it is like two rivers flowing together in the same direction. What are these "rivers" made of? Are they a property of space like gravity may be or are they slowly evaporating as the particles making up the field slowly change the material they emanate from. Sorry if this seems silly but I really don't know what a magnetic field consists of or how it works.
     
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  3. Jul 16, 2004 #2

    Clausius2

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    Your question is not silly at all. Well, I'm not a physicist, but I have spent good times reading some Hawkins books. As far as I know, there is some fundamental particles that transport this interaction, one of the four fundamentals ones (gravity, electromagnetic, weak and strong interaction). There is a set of particles that transpor each of them, or so it was said when quantum mechanics was surged. In particular, the electromagnetic transport particles are the virtual photons.

    I usally imagine this interaction as two charges exchanging virtual particles. I mean, one particle is emited by one charge, arrives at the other and turns back transportating the fundamental information that says: hey, the other charge is there!. This virtual particles acts like messengers or something like that, it is not proved their existence. As you could imagine, it comes to a contradiction when we employ this theory with gravitational interactions. Space-time curving and photons exchanging does not seem a good combination. One might think about a black hole. It emmites radiation (Hawkins radiation), and nearby bodys such as planets feel that inmmense atraction force. The question is how this gravitational force may be transported if any mass particle (photons inclusive) is swallowed by the black hole itself. Some forum-ers that I have requested that answered me that gravitational interaction is transported via space-time curved. But I think I heard that quantum mechanics and general relativity comes into a contradiction just at this point.

    Hoping that an engineering student can be answered to this physically complex question.... don't be hard with your replys.
     
  4. Jul 16, 2004 #3
    your right about the electromagnetic foce and virtualt photons, but gravity CAN be explained using quantum theory. The force carying particle is a graviton, and this graviton is what tells objects that there is gravity pulling on them. Gravitons are the virtual photons of gravity. And about the black hole. Anything within the event horizon is swallowed back in, any particle outside this event horizon can pass by with little or no effect.
     
  5. Jul 16, 2004 #4
    The graviton is only a theoretical particle. It has yet to be discovered.
     
  6. Jul 16, 2004 #5
    I cannot really answer your question , I have another if a particle exchange is required to mitigate a force how do they know where to go , dont tell me another force guides them ??????????????
     
  7. Jul 17, 2004 #6

    Clausius2

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    I'm happy seeing all of you have not been too hard with an opinion of a non-physicist man. :biggrin:

    Nenad,
    I've founded a contradiction because it has to be a virtual particle exchanging between the body and blackhole in order both of them can feel gravity force. But the question is, if no mass body can escape out of the hole, then it is impossible such exchanging, isn't it?

    All of you knows that photons have no mass at rest, but gravity acts over its dynamic relativistic mass, as a light ray curves its path when passing near a black hole or any mass body. So that virtual particles rays ejected by the black hole must have cero radio of curvature, turning back inside him, isn't it?.
     
  8. Jul 17, 2004 #7

    Integral

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    Electric and Magnetic fields are really the same thing, so photons are the energy exchange particle between magnets. This is true for every electromagnetic interaction.
     
  9. Jul 20, 2004 #8

    mee

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    So why dont the magnets run out of photons? What wavelenth are these photons? Does this mean that by sticking a light collector near a magnet we can get free energy ad infinitum? Please explain.
     
  10. Jul 20, 2004 #9

    Njorl

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    Magnetic fields do decay. The fields are due to ordering of the spins of charged particles within the magnet. Over time, disorder sets in, and the fields reduce. You will never get more enrgy out of a magnet than you put into making it.

    Njorl
     
  11. Jul 20, 2004 #10

    turin

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    If the magnets sends a virtual photon out into space and "no one is around to catch it," then the magnet yanks the virtual photon back to itself, and thus has lost nothing. The magnet recoils when it sends out the virtual photon and then recoils when it yanks the virtual photon back, for an overall net recoil of zero. The magnet (or, rather, the "magnetons") does this periodically, kind of like probing space. Sometimes it sends out large virtual photons that don't get very far; sometimes small virtual photons that can go real far. The limit to how far these virtual photons can go is governed by the limit to how little energy they can have. Since photons can have arbitrarily small amounts of energy, they can go arbitrarily far from the magnet. However, the magnet basically randomly selects an energy for each virtual photon, so that most don't travel extremely large distances.

    If there is something to catch the virtual photon, like another magnet, then the magnet that sent it out has lost it (the one that catches it does not directly return it). Both magnets suffer a recoil. The magnet that sent the virtual photon out will recoil away, and the magnet that catches the virtual photon also recoils (assume a N-N or S-S interaction). For the electromagnetic interaction, there can actually be negative recoils (which is the particle exchange mechanism for attraction). I will leave that issue to someone who can explain it better than I. It basically gets into the momentum-position uncertainty relationship thereby allowing the opposite part of the momentum of the virtual photon to interact with the other particle.
     
  12. Jul 21, 2004 #11

    mee

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    photons

    If photons in a magnet are strong enough to push another magnet away, wouldn't it take a phenominal amount of light to do this? Also, if photons are being emitted at such a high rate, why is no heat felt from the magnet? If photons carry the magnetic charge, why is light from the sun and stars not bent like the solar wind and would only reach the earth mostly at the poles? Not trying to cause trouble, just ignorant and confused. :)
     
  13. Jul 21, 2004 #12

    turin

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    It's really a fundamentally different kind of photon than light. Light photons are "legitimate." Virtual photons are "borrowed without asking." What this amounts to in terms of the physics is that light photons are directly detectable (as photons) whereas virtual photons are not. AFAIK, the only reason why we say that they exist is because of this issue of attraction and repulsion. But, at least part of your question may hold some significance. Indeed, it takes a large amount of energy in the form of a virtual photon, or a whole crap-load of smaller energy photons, in order to push macroscopic objects around in the way we see magnets push each other around.




    Magnets do emit heat. Anything above absolute zero emits heat according to current theory. One of the ways in which an object emits heat is through electromagnetic radiation. However, this is fundamentally a different kind of electromagnetic phenomenon than the emission of virtual photons. The virtual photons are strictly told to be very sneeky so that they don't raise a lot of suspicion. They are secret spies on a mission to find other magnetons to deliver the message of each others' existence. The magnetons that send out these secret spies do not want them to be intercepted by any other kind of matter. So the virtual photon spies are told to return within some certain amount of time if they don't find any other magneton. It is kind of a strange physical process, but, there isn't any net emission of virtual photons if they are not interacting with another magneton.




     
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