By the same token, you can jump from a rooftop a zillion times. That does not *prove* the LUG! The difference between Pythagoras theorem and the LUG, however, is that there are no postulates for the latter from which to prove the law! Pythagoras theorem *is eternal*, in that as long as you accept the postulates, it is valid. The theorem is as valid today as it was 2500 years ago. LUG in not eternal, in that it is possible that the law breaks down when new circumstances arise for which the law was not designed. And that’s precisely what happened in the early parts of the 20th century.

After Einstein discovered the special theory of relativity (STR) in 1905, he wanted to apply it to the second of the only two forces known at the time, gravity. STR was a *consequence* of the electromagnetic force, in the sense that it was created to account for the predictions of electromagnetism. So STR fitted nicely in the electromagnetic framework.

Gravity was another story. Newtonian LUG did not fit in with STR. After 11 years of struggle and trial and error, Einstein succeeded in reconciling gravity with STR by completely abandoning the Newtonian gravity and introducing a geometry of the four-dimensional spacetime whose curvature was identified as gravity. It is called the general theory of relativity (GTR). The word “theory” is used, not “law.” Does that mean that GTR is inferior to Newtonian gravitational “law?” On the contrary!

All the situations in which LUG works so does GTR. However, there are situations in which GTR gives the right answer, but LUG does not! For example, LUG does not know what happens to a star when its hydrogen fuel is depleted to the extent that gravity becomes a dominant force. GTR, on the other hand, predicts an explosion of the star that ends up in a white dwarf, a neutron star, or a black hole.