Issues at small scale (the charge self-force problem, the uniqueness of photons in the Standard-Model as free particles), at large scale (the undetected dark constituents compose 96% of the universe when sticking to Einstein and Maxwell theories), the linearity of Maxwell’s theory as opposed to the non-linearity of Einstein’s framework, are among the motivations that induce thinking whether the equations underlying all electromagnetic phenomena are the well-known Maxwell equations or whether we have to accommodate modifications.
Referring to massive theories – started by de Broglie-Proca but now surfacing in the SM Extension (SME) - or non-linear, by Euler-Heisenberg and Born-Infeld, surprising options emerge for reading the universe.
A collaboration (including CERN, London, Napoli, Rio de Janeiro) has found an effective mass for the photon, a group velocity differing from c and birefringence within the SM Extension (SME). Further, it determined three experimental- observational upper limits on photon mass. In the SME, a frequency shift appears for a photon propagating in vacuo to be added to the expansion redshift, and it might explain the discrepancy between the red shift and luminosity distances for Supernovae without recurring to an accelerated expansion. We also obtain frequency shifts in the case of generalized non-linear electromagnetism.
Time permitting, we examine how the Heisenberg principle in the energy-time form and applied to cosmological scales lead to a reinterpretation of the so-called Hubble tension and to a reconsideration of what is measurable.