Like the Planck–Einstein relation E = ℏω, de Broglie’s $$ {\mathbf{p}} = \hbar {\mathbf{k}} $$p=ħk is another fundamental equation but the universal momentum formulation should be $$ {\mathbf{p}} = \hbar {\varvec{\upbeta}} $$p=ħβ. We propose the compelling evidence (vacuum Cherenkov radiation) and a new consequence which could lead to experimental checks is also worked out.