In a paper from 1961 (Gauge Theories of Vector Particles, Glashow and Gell-Mann), the authors describe quantum electrodynamics thusly:

"It is of universal strength and form..."

What exactly does it mean to say that it's of "universal" strength? Is there some special meaning to that? Universal in what sense, exactly?

Source Reference

  • $\begingroup$ that it couples the same to anything (that is charged under it)? who knows... $\endgroup$ – AccidentalFourierTransform Jun 28 at 22:51
  • $\begingroup$ @Physics_Et_Al As a general rule on Physics SE we discourage answering questions in comments. Suggest you convert your comment to an answer and that will allow the OP to accept it if they think it's a good answer. $\endgroup$ – StephenG Jun 29 at 11:01
  • $\begingroup$ I am guessing something along the following lines but I am not sure: There is only one coupling constant with which the gauge boson for U(1) EM couples to objects charged under U(1) EM because the symmetry is unbroken. Contrast this to the broken SU(2) of the LSM where the W and Z bosons couple to different particles with different coupling constants because the SU(2) symmetry is broken. $\endgroup$ – Dvij Mankad Jun 29 at 17:48
  • $\begingroup$ Also, can you link to the Journal webpage for this paper? $\endgroup$ – Dvij Mankad Jun 29 at 17:50
  • $\begingroup$ This is more appropriate for the history of science SE. Universal form meant EM couples vector-like to all charged particles, with integral charges (form). This is in contrast to strong or weak couplings, (remember Fermi vs Gamow-Teller transitions?) and varying Cabbibo and L-R complications, as yet unentangled. $\endgroup$ – Cosmas Zachos Jun 30 at 14:22

The following is the comment I made in or around June 28th 2019 and have now converted to my answer:

``Reading down the paragraph at the source it seems to me that a partial answer refers to the fact that the force is independent of the type of elementary particle in question and depends only on the charge of the elementary particles involved."


The answer seems to be the one suggested by Physics_Et_Al (you should really post an answer as an answer; not as a comment. That's the way this is supposed to work).

Here's a quote from Invitation to Contemporary Physics (Ho-Kim, Kumar, Lam):

"By universality, we mean that the coupling to matter is proportional to Q [electric charge], whatever the other quantum numbers are."

This implies that there are interactions in which universality is not the case. Which I think is what W and Z are up to, according to Feynmans Out for Grumpy Cat.

  • $\begingroup$ Something tells me that had you properly posted this to HSMSE, as suggested, you'd get a better picture of what was poorly understood in 1961 and how the universality of of the strong and weak interactions recognized today in the SM was out of sight in 1961. Both the strong and the weak interactions are recognized today to obey universality in Murray's sense, of course! $\endgroup$ – Cosmas Zachos Jul 2 at 0:13

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