> One of the key challenges with quantizing gravity is in how the terms in the expressions resulting from analyzing the Feynman diagram interactions behave [4]

> One of the key challenges with quantizing gravity is in how the terms in the expressions resulting from analyzing the Feynman diagram interactions behave [4] which prevent them being renormalized. Not being renormalizable actually isn't a problem in itself if you view the theory as an effective theory, valid only up to some energy scale, not beyond that. You can still use the theory to make some predictions, as long as you're careful. But that does mean that the QFT of a massless spin-2 field can't be a fundamental theory of gravity; it can only be an effective theory, that approximates something deeper.