A Contemporary Case In Point
Physicists have total faith in the hypothesis that G, the Newtonian gravitational coupling factor, is exactly the same on all scales of the hierarchical cosmos, from the Planck scale to the scale of the entire observable cosmos. For them this is not a debatable matter; G is treated as an absolute constant. Case closed.
Has this ever been tested within atoms, or for the interactions between bound galaxies. No, it has definitely not been subjected to rigorous testing. We can measure G for unbound particles down to very small distances, but we cannot measure G within atoms or within subatomic particles.
In the case of atoms, such a test is currently impossible. In the case of galaxies, we can only estimate the combination GM, where M is the mass of the galactic entities. We cannot measure G in isolation for galactic scale objects.
Is this important? You probably have no idea how important this may be! So here is a brief piece that tells you why assuming that G is an absolute constant on all scales may be one of the greatest mistakes in modern physics history.