3 Low-Energy Quantum Gravity

According to the approach just described, non-renormalizable theories are not fundamentally different from renormalizable ones. They simply differ in their sensitivity to more microscopic scales which have been integrated out. It is instructive to see what this implies for the non-renormalizable theories which sometimes are required to successfully describe experiments. This is particularly true for the most famous such case, Einstein’s theory of gravity. (See [57] for another pedagogical review of gravity as an effective theory.)