Godel, Escher, Bach - Douglas R Hofstadter

Godel's theorem showed that provability is a weaker notion than truth, and that no fixed system could represent the complexity of whole numbers.

Gödel showed that for any formal axiomatic system, there is always a statement about natural numbers which is true, but which cannot be proven in the system. In other words, mathematics will always have a little fuzziness around the edges: it will never be the rigorous unshakable system that mathematicians dreamed of for millennia.

We are going to see that particles are - in a certain sense which can only be defined rigorously in relativistic quantum mechanics - nested inside each other in a way which can be described recursively, perhaps even by some sort of grammar.... These real particles are said to be renormalized - an ugly but intriguing term. What happens is that no particle can even be defined without referring to all other particles, whose definitions in turn depend on the first particles, etc. Round and round, in a never-ending loop.

Every real particle's existence therefore involves the existence of infinitely many other particles, contained in a virtual "cloud" which surrounds it as it propagates. And each of the virtual particles in the cloud, of course, also drags along its own virtual cloud, and so on ad infinitum.