So, before Lee made his discovery physicists believed (or assumed, or conjectured, or theorized) that “the laws of physics were identical whether observed direc

So, before Lee made his discovery physicists believed (or assumed, or conjectured, or theorized) that “the laws of physics were identical whether observed directly or as a mirror image." Lee and Yang proposed that this did not always hold. Their proposal was later confirmed by experiments. So, what physicists believed before Lee, was not a law of nature. Lee challenged what his colleagues believed to be true. But you are right all so called laws of physics are provisional.