Are any of nature’s fundamental parameters truly constant? If not, are they fixed by the vacuum state of the universe, or do they vary slowly in time even today? To fully answer those questions requires either an unambiguous experimental detection of a change in a fundamental quantity or a significantly deeper understanding of the underlying physics represented by those parameters.
At first glance, a long list of quantities usually assumed to be constant could potentially vary: Newton’s constant G N, Boltzmann’s constant k B, the charge of the electron e, the electric permittivity ∊0 and magnetic permeability µ 0, the speed of light c, Planck’s constant ℏ, Fermi’s constant G F, the fine-structure constant α = e 2/ℏc and other gauge coupling constants, Yukawa coupling constants that fix the masses of quarks and leptons, and so on. One must, however,...
