How Does QED Explain the Electromagnetic Force

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Discussion Overview

The discussion centers on how Quantum Electrodynamics (QED) explains the electromagnetic force, particularly the interactions between charged particles such as electrons and protons. Participants explore conceptual questions about photon exchange, energy transfer, and the implications of these interactions in various scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how electrons "know" when to exchange photons and how this process differs between like and unlike charges.
  • Another participant suggests that the concept of virtual photons is a linguistic tool that does not fully address the underlying mechanics of QED, implying a need for mathematical understanding.
  • A different participant notes that calculations in QED can yield the Rutherford formula for electron interactions, indicating a repulsive force, while similar calculations for opposite charges yield an attractive potential.
  • Another participant seeks a simplified explanation of how free electrons oscillate in response to a plane wave, asking for an intuitive understanding from a QED perspective.

Areas of Agreement / Disagreement

Participants express differing views on the conceptual understanding of photon exchange and its implications. There is no consensus on how to intuitively explain these phenomena or the role of virtual photons in QED.

Contextual Notes

Participants highlight limitations in understanding the intuitive aspects of QED and the necessity of mathematical formulations to fully grasp the interactions described.

Who May Find This Useful

This discussion may be of interest to those studying quantum mechanics, particularly in the context of electromagnetic interactions, as well as individuals seeking to deepen their understanding of QED concepts.

Physicist97
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From a conceptual point of view, how is it that Quantum Electrodynamics explains the interaction between two charged particles, (let's say two electrons)? I've heard people say that the electrons exchange photons, but how is it that an electron would know when to send off a photon and that it will be absorbed by another charged particle? And how is it that an exchange of photons would be different for two electrons (which repel) and an electron and, say, proton (which attract)? Also, by exchanging photons, would the photons not carry away a little bit of energy, thus causing the electron to lose energy? Thank you for any explanation :)
 
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Physicist97 said:
I've heard people say that the electrons exchange photons
Virtual photons are an attempt to describe the theory in words, that attempt works well in some setups but it cannot answer questions like those you asked. The actual theory (the formulas) can, but then you have to understand the calculations.
 
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Basically, if you calculate the differential cross-section for a process like you have described (an electron exchange a virtual photon with another electron) in QED, in the non relativistic limit you will find the Rutherford formula, which is calculated assuming the repulsive Coulomb force. If you do the same with opposite charged particle, you will find an attractive potential.
 
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Is there a simple way to explain the following fact, at the level of a reader who has just made his way through "QED The Strange Theory..."

When a plane wave reaches a cloud of free electrons, they oscillate at right angles to the direction of propagation.

How does this emerge from QED, (intuitive picture if such is possible)?
 

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