In Oklo, Gabon there was a natural nuclear fission reactor about 1.7 billion years ago. The concentration of uranium and groundwater was just right that nuclear fission occurred naturally.

We can measure the elements left behind and we have determined that the fine structure constant was the same then as it is now.

If the laws of physics have remained constant for that long then most scientists think they will remain constant in the future.

https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...