Trying to solve quantum gravity is frustrating. We have made tremendous progress in quantum theory, but it seems that every time we find a new quantum technique, there's a reason it doesn't quite work with gravity. Take, for example, the case of quantum fluctuations and renormalization. There are many ways to calculate quantum interactions, but one of them involves quantum fluctuations. Suppose you wanted to determine the odds of an electron at point A being later observed at point B. It's possible that the electron could just travel from A to B. But because of quantum uncertainty, it's also possible that a virtual electron-positron pair appears, interacts with your electron, and shifts the odds. Less likely, but not impossible, you might have two virtual pairs, or three, or fifteen. If you want to calculate the odds of your electron going from A to B, you have to calculate the odds of all possible paths and interactions. You may have seen these represented as Feynman diagrams.…