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What is the mechanism that transmits force?

  1. Oct 12, 2012 #1
    Hello all,

    New to this forum. Have had an interest in physics for a long time and studied it for a while at undergraduate level.

    Anyway, my question is this:

    What is the mechanism which actually transmits force? I'm thinking about electric or magnetic force. When two objects are physically separate, how is the force actually transmitted from one object to another?

    I'm aware of electromagnetic fields, and how the force is proportional to the distance between the objects, but this doesn't explain how the force is actually transmitted through space between the objects.

  2. jcsd
  3. Oct 13, 2012 #2


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    Staff: Mentor

    Well, in quantum theories forces are transmitted by virtual particles.

    However I think you may be disappointed in that answer. Unfortunately all I can really say is that we don't know. We can watch one particle interact with another, and do math about how the interaction works, but that's it.
  4. Oct 13, 2012 #3
    The question itself is a bit flawed..I mean when you ask why, you are asking for an explanation in terms of axioms, it just so happens that the principle "the charge creates a field, the field pushes the other charges" is the axiom here.
  5. Oct 13, 2012 #4
    Sometimes people (included me, many years ago) ask themselves this, the first time, because they are used to think in terms of "contact" between bodies, because of our sensorial experience. Of course, if you can't give up to such an explanation, you will never be satisfied (I'm not talking about you specifically, of course). Physics however is not interested in what it should be to satisfy an inner need of us, but in what it actually happens.
    Of course this doesn't absolutely imply that we won't in the future find another description of what happens in the transmission of forces, that uses the concept of contact between some kinds of (really existing) bodies; at the moment however there isn't.
  6. Oct 13, 2012 #5
    Yes you're right, I was hoping for a more revealing answer into the actual physical method as you probably guessed.

    I have read up on the current theories (wikipedia is useful), but the whole gauge boson / virtual particle idea just doesn't cut it for me I'm afraid. It feels like its a mathematical construct which describes the behaviour but unfortunately doesn't reveal the actual mechanism.

    Are there any theories out there as to what the actual mechanism might be in reality? May be more of a philosophical question than a physics one.
    Last edited: Oct 13, 2012
  7. Oct 13, 2012 #6
    In classical theory, fields transmit forces; as already noted, in quantum mechanics virtual particles. These are convenient mathematical constructs that so far are pretty good at describing observations.

    Here are excerpts from several different explanations of 'particles'......

    From a CArlo Rovelli's Introduction:

    "..uniquely-defined particle states do not exist in general in QFT on a curved spacetime. .... in general, particle states are difficult to define in a background-independent quantum theory of gravity.."

    As you can probably tell from the above descriptions, we have a lot more to learn!!
  8. Oct 13, 2012 #7


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    Science Advisor

    Disclaimer - I don't know much about quantum field theories. However, I don't think you are going to get a better answer.

    Try a simpler question: Imagine a pool table (a purely classical one). Viewed from the white ball, a red ball is just to the left of the pocket. Where do you aim the white ball to sink the red one? Left of the center, of course. It's easy enough to calculate your aim point. But what is the actual physical mechanism at work?

    Conservation of energy and conservation of momentum would be the stock answer. But what is energy and what is momentum? You can't hold a chunk of energy in your hand, or a slice of momentum. You can calculate the kinetic energy of something, but you cannot separate the energy and the momentum from the ball. They are, ultimately, just book-keeping tools that are handy for figuring out what happens on a pool table. They turn out to be much more powerful than that, of course, which is the beauty of science.

    What I'm getting at is that there never is an "actual physical mechanism" in the sense that you mean. When I talk about conservation of energy and momentum, I am just talking mathematical constructs. The same is true of quantum field theory - it's just that the concepts are weird enough that you are questioning more.

    Does that make sense?
  9. Oct 14, 2012 #8
    Furthermore, even if it could be all reduced to the contact between balls, what is a ball made of? Atoms separated in space but held together by forces which acts at a distance. And what are atoms made of? Particles separated in space held by forces at distance.....
    Fields nested in other fields, there never is a real "contact".
  10. Oct 14, 2012 #9
    Absolutely. I'm well aware that there are fundamental questions underpinning everything we see and do. I chose the force example for the reason below:

    I was leaning up against a wall the other day and I thought to myself, my atoms are not actually in physical contact with the atoms of the wall. That's what started the question off.

    These four fundamental forces are key to unraveling the whole universe.
  11. Oct 14, 2012 #10


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    Staff: Mentor

    It's the best we've got so far.

    Yes, there is a serious philosophical question lurking here: How will we know it's the "actual mechanism" rather than just another "mathematical construct?"
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