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Is the action instantaneous? How is momentum/energy conserved? Is the action non-local?

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- Thread starter Gerenuk
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- #1

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Is the action instantaneous? How is momentum/energy conserved? Is the action non-local?

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RUTA

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Is the action instantaneous? How is momentum/energy conserved? Is the action non-local?

See Zee, A.: Quantum Field Theory in a Nutshell. Princeton University Press, Princeton (2003), Chap I.4, From Field to Particle to Force, pp 24-27.

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jtbell

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According to QFT, how do two masses attract?

Since you said "masses", are you asking specifically about gravity? There is no generally accepted QFT for gravity yet, as far as I know, so this is still an open question.

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Yes, I did ask about gravity. But it would also be interesting to know how the Coulomb force acts through photons. At some point I will dive into QFT, but for know I was hoping to get a rough answer about what happens when two charges interaction. I mean where/when are there photons? How is momentum conserved?Since you said "masses", are you asking specifically about gravity? There is no generally accepted QFT for gravity yet, as far as I know, so this is still an open question.

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Look at the Hamiltonian of QED. It has three terms, one for the electron, one for the EM field, and an interaction term that is like [itex]\mathbf{A} \cdot \mathbf{J}[/itex]. The virtual photons that exchange energy between the field and the matter live in the interaction term.... now I was hoping to get a rough answer about what happens when two charges interaction. I mean where/when are there photons? How is momentum conserved?

I don't know if this helps with the forces...

- #7

RUTA

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Since you said "masses", are you asking specifically about gravity? There is no generally accepted QFT for gravity yet, as far as I know, so this is still an open question.

See Zee, A.: Quantum Field Theory in a Nutshell. Princeton University Press, Princeton (2003), Chap I.5, Coulomb & Newtown: Repulsion and Attraction, pp 30-34. Quote from bottom of p 33, "We are now ready to understand one of the fundamental mysteries of the universe: Why masses attract."

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Yes, I did ask about gravity. But it would also be interesting to know how the Coulomb force acts through photons. At some point I will dive into QFT, but for know I was hoping to get a rough answer about what happens when two charges interaction. I mean where/when are there photons? How is momentum conserved?

In the Coulomb gauge where only physical (photon) variables are present, there is an instant Coulomb interaction term. But even in non-relativistic case the Coulomb interaction occurs bewteen de Broglie waves, not between point-like charges.

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