This question relates to the physicality of force exchange. I'm comfortable with QM as far as it relates to chemistry, (BO approximation, Hartree-Fock method, most particle interactions basics, etc) but am interested in understanding the physical nature of force exchange. Let's take for example, intermolecular long-range electrostatic interactions (coulomb force).

  1. In Scenario 1, let's say we have a point-like molecule/atom (let's not integrate please) with a formal charge of +1, called P1. It is at a fixed distance from another like object, P2.

  2. In Scenario 2, we have P1 at the same fixed distance from another point-like that has a formal charge of -1, called N1.

The attractive force and repulsive force between the interactions in Scenario 1 and 2 are the same, just the sign is flipped in all thermodynamic or energetic descriptions of the relationship.

To my knowledge, force carriers mediate these interactions. So my question is, how does that work, physically? To put it simply, if I pull or push on a solid rod, that to me makes intuitive sense as to its symmetry. How does force exchange work physically at the subatomic level to mediate "pull" and "push" forces to be symmetrical? Can someone provide an example of how force carriers would mediate Scenario 1 and 2?

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    $\begingroup$ Are you asking what is the fundamental origin of the electrostatic force i.e. how does quantum field theory explain electrostatic forces (attractive and repulsive)? $\endgroup$ Sep 6 '19 at 4:56
  • $\begingroup$ No, I am asking why and how force carriers like virtual photons actually physically mediates electrostatic forces, and if particle exchange is how it all works, why is it symmetrical? As in, why would particle exchange be able to "pull" and "push" symmetrically when it is discontinuous? I'm looking for a detailed, physical description of force carriers, and provided virtual photons and the electrostatic force as an example. $\endgroup$ Sep 6 '19 at 9:52
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    $\begingroup$ That's because the electrostatic force is not mediated by virtual photons. It is mediated by a quantum field, and the virtual photons are just a computational device that we use to do the calculation of the force. Virtual photons do not exist. They are a convenient fiction. This applies to all forces. $\endgroup$ Sep 6 '19 at 10:25
  • $\begingroup$ Sort of related: physics.stackexchange.com/q/217126/123208 $\endgroup$
    – PM 2Ring
    Sep 6 '19 at 12:27
  • $\begingroup$ John - that doesn't appear to be what is canonically believed by the field in physics, as virtual photons are considered more than just a device. Also, even if they are "mediated by a quantum field" that is a very vague unphysical description and doesn't answer my question at all. Thanks for your attempt at an answer, but I am looking for a higher level response. $\endgroup$ Sep 6 '19 at 20:23

Historically, Newton has "invented" the word "force". He was some kind of person who liked myths and witchcraft and lived in a time of alchemy. Asking Wikipedia, for him force was something quite magic.

Next vision of forces came from Faraday. He described electro-magnetic force-fields as a kind of surrounding fluid. A positive charge is a source of this fluid, pressing this fluid away. A negative charge is quite the same, but it is a drain for this fluid. A drain and a source move closer together, while two sources push each other away. Also two drains push each other away, because they can suck less of this fluid from the space in between them. To me, that is the most intuitive vision.

The next level is quantum-field-theory with its photons. The idea of particles comes from the quantized energy transfer. I think this view is less intuitive and lead to the vision of solid particles that would bump like real particles in the classical world. Here a lot of confusion starts, because that analogy is often wrong.

You should also note, that forces are not always as symmetric. In chemistry basically all occuring forces are Coulomb forces, thus you might get this feeling. However, for example in gravity, there is no repulsive counterpart like in electro-magnetic farces by changing the charge.

  • $\begingroup$ Interesting typo: "electro-magnetic farces" ! Some of my students would agree with this descriptor. :) $\endgroup$
    – Bill N
    Sep 6 '19 at 17:15
  • $\begingroup$ Gravity is the only force that is not symmetric. I really didn't think your answer was very helpful, it was extremely simplistic, like middle school physics level. $\endgroup$ Sep 6 '19 at 20:24

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