[metmom]

When has the law of gravity not held true?

[Dimensio]

When has the law of gravity not held true?

It doesn't work at a subatomic level or across different relativistic frames. There's also the problem of it assuming that the force of gravity is instantaneous, when Einstein's theory of relativity suggests that gravity is limited to the speed of light.

[elmer fudd]

When has the law of gravity not held true?

In astronomical calculations of orbits.

http://theory.uwinnipeg.ca/mod_tech/node60.html

[Virginia-American]

When has the law of gravity not held true?

One of the biggest problems in cosmology and astrophysics is whether it does in fact hold true in galaxies and clusters. If it does, you need to hypothesize "dark matter" to account for the observations. If it doesn't, we need a new Einstein to revise General Relativity.