If the fundamental constants of physics change, they do so too slowly for us to detect.

Case in point: Researchers at the National Institute of Standards and Technology in Boulder, Colorado, have ruled out any change in the fine-structure constant (alpha) greater than between 7×10^-15 and 7×10^-16 per year.

Alpha is a measure of how strongly light interacts with matter. If it has a different value today than billions of years ago, the speed of light has changed too and Einstein was wrong.