There are some phenomena which allow good remote assessments of properties, based on various interactions. Cephid variable brightness, for example, serving to validate the expanding universe theory. The stellar Main Sequence gives a good sense of stellar masses. Spectroscopy works pretty well across a wide span of the Universe (several billions of light years). Etc.

Since these operate in concert across the observable universe, and themselves involve various other interactions (elements, strong and week nuclear forces, gravity, speed of light, rates of hydrogen fusion, etc.), we can conclude that either there is no appreciable change in any of the underlying fundamental constants or that change occurs in a compensated fashion such that no net change is detectable.

The second fails Occam's Razor. The conclusion that the laws of physics appear to be similar throughout observable space seems robust.