The research here is based on the interesting premise that "the masses of electrons and protons were smaller" in the early universe, leading to different emissi

The research here is based on the interesting premise that "the masses of electrons and protons were smaller" in the early universe, leading to different emission spectra that we have thus far interpreted as an expanding universe. I have not read the original research article in detail, but it is my impression that all masses would have to scale at the same rate in order to avoid changes in fundamental physical behaviors. (This seems consistent with the article's premise that the effect comes from some sort of field redefinition in the Lagrangian.) As a particle physicist, I see this as highly unlikely. The first big obstacle that I see for such a theory to overcome is that electrons and protons get their mass from entirely different sources. As far as we know, electrons are fundamental particles: their mass is a fundamental parameter of the theory (presumably encoded as the electron coupling to the Higgs boson). But although protons are composed of three fundamental particles (two up quarks and a down quark), the quarks' fundamental masses are only a tiny fraction of the total proton mass. Instead, the vast majority of a proton's mass results from complicated non-linear QCD (strong nuclear force) self-interactions that draw on both the fundamental masses and things like the QCD interaction strength. We've had some success at simulating those QCD interactions in recent years, but there's no known way of just reading off the proton mass from a fundamental equation. So for the idea behind this proposal to work, it seems to me that both the fundamental particle masses and these complicated QCD effective masses would have to scale completely in parallel. I'm not at all clear on whether a field redefinition (as proposed here) would work that way. Maybe it would be more natural than it seems, but that's my first big concern with the proposal.