Are Feynman's Equations on Superconductivity Valid?

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Discussion Overview

The discussion centers on the validity of Feynman's equations related to superconductivity as presented in the "Feynman Lectures on Physics." Participants explore the context, implications, and experimental evidence surrounding these equations, particularly in relation to quantum mechanics and the historical development of superconductivity theory.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses interest in the experimental evidence supporting the validity of Feynman's equations (21.19, 21.31, and 21.38) related to superconductivity.
  • Another participant suggests that understanding the context of the equations is crucial and recommends reading the entire section of the book for clarity.
  • A participant describes the equations as relating to the velocity and acceleration of electrons in a superconductor, highlighting the influence of the wave function and external electromagnetic fields.
  • One participant claims that the equations represent a "classical" understanding of superconductivity and asserts that their validity has been established historically, particularly in deriving the Meissner effect.
  • There is a challenge regarding the applicability of equation (21.19) in non-constant electric fields, and a question is raised about the testing of equation (21.38).

Areas of Agreement / Disagreement

Participants express differing views on the validity and applicability of Feynman's equations. While some assert that the equations have been historically verified, others question their relevance in certain conditions, indicating that the discussion remains unresolved.

Contextual Notes

Participants note the importance of the context in which the equations were derived and the limitations of the classical approach to superconductivity, suggesting a dependence on specific definitions and assumptions.

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In the last chapter of "Feynman Lectures on Physics" part III, Feynman discusses superconductivity. I am particularly intrigued by his equations (21.19) and (21.31), and even more by (21.38). Is there any experimental evidence for validity of these equations?

The question of validity of these equations is particularly important for foundations of quantum mechanics:
https://www.physicsforums.com/showthread.php?t=448366
 
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Maybe you could write down the formulas for our convenience? Thank you.
 
Well, it is important to understand the whole context in which the equations are derived. Therefore, it would be better to read the whole section in the book. The book itself is well known, so I assume that most serious physicists have it.

Let me just say that the equations describe the velocity (describing the electron current in a superconductor) and acceleration of electrons as a function of the wave function and the external electromagnetic field. In particular, the velocity has one term proportional to the electromagnetic potential and another term proportional to the divergence of the phase of the wave function. The acceleration has a classical term and a quantum correction that strongly depends on the wave function.
 
Last edited:
These equations (as well as the rest of the chapter) are just what I guess you could call "classical" (pre-BCS) supeconductivity, so yes their validity were verified ages ago (21.19 is what you use to derive the Meissner effect).
However, thyey do not give a correct microscopic description of superconductivity, I am too tired to read the whole chapter now; but Feymann is -as far as I remember-mainly just using the two-fluid model.
You can find more information in one of the standard texts about superonductivity (e.g. Tinkham)
 
f95toli said:
so yes their validity were verified ages ago (21.19 is what you use to derive the Meissner effect).
(21.19) is relatively trivial when the electric field is constant. But is (21.19) tested for the case of a non-constant (either in space or time) field? And what about a test of (21.38)?
 

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