Nothing. At least not for any precise definition of "just as wrong" that would be useful. There is, today, not a single terrestrial observation in contradicti

Nothing. At least not for any precise definition of "just as wrong" that would be useful. There is, today, not a single terrestrial observation in contradiction to GR and QM. We have an incredibly good understanding of the fundamental nature of our reality. Our understanding is so good that it takes decades of work by brilliant scientists and engineers, to build machines that could show even the slightest evidence of something else going on. It's easy to overlook how stunning this situation is. It is utterly unprecedented in the history of science. This does not mean that there are no deeper truths to discover, but Newtonian mechanics does correctly describe how the apple falls, even if it is not the final word.