Saturday, October 3, 2026

Classical vertex correction and Welton's vacuum fluctuations

In the previous blog post we found some heuristic reasons why the Feynman diagram might calculate the same numerical value for the Lamb shift as Theodore Welton's "zero-point fluctuations" do.

The idea is that the electron sends a random virtual photon to a random direction, which "smears" its probability distribution close to the proton.


The classic vertex correction is not random. That is a big difference from Welton. Why would the classical correction produce the same result? Does the classical correction displace the electron in such a way that δr² is roughly the same as for Welton?

The mass reduction fraction is:

       M(r)  = 1 / (4 π ε₀)¹⋅⁵ * e³ / (mₑ¹⋅⁵ c³) 
  
                      * sqrt(2) / r¹⋅⁵.

Let the electron move some distance Δr toward the proton. If it moves 1% faster, it will in the same time move 1.01 Δr. If the electron comes from a large distance close to the proton, we obtain the correction simply by integrating:

        ∞
       ∫   -1 / r¹⋅⁵  dr   *   constant
      r
            =  2 / sqrt(r)   *   constant.

A reasonable assumption is that we should calculate the displacement when

       r  =  λₑ  =  h / (mₑ c).

But the exponents for e and ε₀ will differ from the Welton formula. This is not going to work. The problem is that Welton's displacement is random, while the classical displacement is systematic?









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