wikipedia has a high level review of current constraints: https://en.wikipedia.org/wiki/Time-variation_of_fundamental_constants https://en.wikipedia.org/wiki/Ti

wikipedia has a high level review of current constraints: https://en.wikipedia.org/wiki/Time-variation_of_fundamental_constants https://en.wikipedia.org/wiki/Time-variation_of_fundamental_... fine-structure constant: less than 10^−17 per year gravitational constant: less than 10^−10 per year proton-electron mass ratio: less than 10^−16 per year