Scenario : I understand that if I push a boulder the mechanical structure of my body is being used. Cells, molecules, atoms and ultimately the electromagnetic force of my electrons are being used to push that boulder. Providing I have a footing between this rock and a harder place :-) and that I have the "strength" I can move that boulder.

Question : If photons are responsible for exchanging the EM force, are photons interacting between my atoms and the rock and the hard place ( All the atoms ) to allow my energy to be applied to the boulder, thus overcoming gravity for a moment ( no pun intended ) and allowing the boulder to move?

I'm very curious to understand what happens in such a case at the electromagnetic level. I get the Newtonian view, but really wonder what happens at the EM level.

  • $\begingroup$ When you push on the boulder, even if it doesn't move, your tissue compresses. At the molecular level, that involves electrostatic forces. But electrostatic forces are not electromagnetic radiation (EM waves or photons). So I don't think photons enter into this at all, though perhaps I could be wrong. $\endgroup$
    – Bob D
    Feb 15 at 13:21
  • $\begingroup$ @BobD I think what is meant here is that the electrostatic forces are understood as exchange by virtual photons. $\endgroup$ Feb 15 at 13:34
  • $\begingroup$ @Vadim Like I said, I could be wrong. Particle physics is not my forte. $\endgroup$
    – Bob D
    Feb 15 at 13:43
  • $\begingroup$ @nialloc: In your question you are asking explicitly about the EM interaction. So, if you are solely interested in the EM contribution, my answer misses the point. Please let me know, if this is the case. $\endgroup$
    – Semoi
    Feb 15 at 18:32

When your shoulder pushes against a boulder, the electron clouds surrounding the molecules that form the skin on your shoulder are pressed up into proximity to the electron clouds surrounding the molecules that make up the surface of the boulder. Those electron clouds repel one another electrostatically, so you are using electrostatics (that is, the electromagnetic force) to move the boulder.

Those electrons exert forces on one another via the exchange of (virtual) force-carrying particles which for the electromagnetic force are photons.

  • $\begingroup$ Nice answer. +1 from me. So are these photons virtual? $\endgroup$
    – Gert
    Feb 15 at 16:55
  • $\begingroup$ you mean the ones with which you and I are pushing text back and forth at this instant? physics joke there, to which the standard physics laugh is r dr dr d(theta). actually, the photons exchanged during electrostatic repulsion are virtual. $\endgroup$ Feb 15 at 17:01
  • $\begingroup$ I marvel at the thought that pressing keys for typing this comment involves virtual photons! $\endgroup$
    – Gert
    Feb 15 at 17:08
  • $\begingroup$ the virtual photon explanation is due to Feynman, who presented it in one of his books for nonphysicists. this means nonphysicists can experience this fun too! $\endgroup$ Feb 15 at 17:13
  • $\begingroup$ As a chemist I qualify! $\endgroup$
    – Gert
    Feb 15 at 17:33

No, it's not the electro-magnetic force, which is responsible for the interaction between the two bodies. Instead, it's the so called Pauli's principle (or Pauli's exclusion principle), which in fact is not a force, but a concept of symmetry. Pauli's principle states that two electrons (Fermions) are not allowed to occupy the same quantum state -- a state where all their quantum numbers are identical. In fancy: Their wave function must be anti-symmetric.

Here is what happens: Each body consists of atoms. Within the atoms we have the "localised" electrons -- for an electric conductor, these are the electrons which are not in the conductor band and thus are not free to move across the solid. If we bring the two bodies close to each another, the "localised" electron, which belong to atoms at the surfaces of the bodies, start to overlap. However, at a certain proximity the electrons from the two bodies become indistinguishable, and Pauli's principle demands that two electrons are not allowed to occupy the same quantum state. As a result the electrons stay apart and we experienced the symmetry constrain as a "repulsion" between the two body. So clap your hands is in fact a demonstration of a quantum mechanics effect.

  • $\begingroup$ Thank you. That makes sense. The rules for those quanta must be respected. Wow so the wave function, from a perspective, is what stops all matter passing between itsself. With out the randomness at the hart of quamtum mechanics, wave functions would not be able to operate the way they do and give us the universe. In credible :-) $\endgroup$
    – nialloc
    Feb 17 at 12:30

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