Xkcd: Popper

With a lot of simplifications, the main idea of Popper epistemology is that even if you drop 100 stones you can not prove that the acceleration of gravity is 9.8m/s^2 (32ft/s^2) because you will never be sure that the next stone will follow the same physics law.

You can only refute "all" the alternatives: That g=10m/s^2. That g=7m/s^2. That g=-1m/s^2. That the stone falls with a constant vertical velocity of 2m/s. That the fall is a cubic with h=7.3 m/s^3 * t^3. That ... Well, there are too many alternatives and you never can refute "all" of them, you can only refute many of them.

So, there are laws of physics are not "proven", it's just that the main alternatives are "refuted". You can find the details and a correct explanation in https://en.wikipedia.org/wiki/Karl_Popper [1]

The joke is that while technically true, it's too difficult to talk in this way, so most people just talk as if the laws of physics were "proven".

As a general rule, you can get a good explanation of the xkcd comics in the explainxkcd site. In this case https://explainxkcd.com/wiki/index.php/2078 But I don't like the current version of the explanation there too much, it will get better in a few days.

[1] No one has proven that you can't find the details and a correct explanation in https://en.wikipedia.org/wiki/Karl_Popper