QM alone fails to account for certain facts. QFT does this by using somewhat “weird” methods in order to bring Special Relativity and QM together. It has been w

QM alone fails to account for certain facts. QFT does this by using somewhat “weird” methods in order to bring Special Relativity and QM together. It has been working pretty well so far, and it is indeed the best we have. String Theory, on the other hand, while being a consistent theory of quantum gravity, uses a model (or models) that we may never be able to verify experimentally.