How we know physical laws are constant over time

From EvoWiki

Creationists often assert that real scientists have no justification for assuming that physical laws are constant over time, and therefore, any work which is based upon this assumption (such as radiometric dating) is invalid. In reality, this Creationist assertion is not just wrong twice over, but if it were valid, it would necessarily render all science (including the Creationist version) a perfect and utter waste of time.

This Creationist assertion is wrong in the first place, because real scientists don't actually presume that physical laws are constant; rather, they presume that if physical laws really did change, that change would leave traces of itself which could be detected by an appropriate experiment or observation.

Second, this Creationist assertion is wrong because real scientists can and do look for evidence that physical laws have changed. Empirical observations have, in fact, established that the greatest possible change which could have occured in physical laws is on the order of 1 part in several billion over the gigayears-long lifetime of the Universe.

Finally, if physical laws do change in an indetectable manner, how can you trust that anything is reliable? Perhaps gravity might become a repulsive force tomorrow morning. Perhaps the molecules of your Bible might have rearranged themselves, transforming it into a copy of the Bhagavad-Gita or Moby Dick, when you weren't looking. Perhaps the molecules in your brain rearranged themselves, rendering your thought processes useless. Perhaps the chemical reactions of your body's metabolism might change to the point where you can gain nourishment from eating silicon crystals and drinking liquid helium.