Relativity doesn’t seem to fit at all in any reasonable way into quantum mechanics, and yet relativity is quite useful and accurate for problems at the atomic level and above.
General relativity doesn’t seem to fit at all in any reasonable way into quantum mechanics, and it is way overkill for problems at the atomic level (and for a sizeable fraction of problems at the planetary level, too), where special relativity (which does fit with quantum mechanics, save for a few theoretical loose ends that few non-mathematicians have reasons to care about) suffices.
Good_Burning_Plastic comments on Open thread, December 7-13, 2015