The second major revolution in theoretical physics (after the theory of relativity) was the birth of quantum mechanics. We understand a lot about relativity, and by contrast we understand very little about the quantum side of physics. ‘A theory of everything?’ considers the impact quantum physics has had on cosmology and ponders how near we are now to explaining the Universe. There are many areas in which particle physicists and cosmologists have attempted to weld together their theories. Can the laws of physics change? Is nature mathematical? The search for a theory of everything raises interesting philosophical questions. It remains to be seen whether cosmology can explain why the Universe is the way it is.