Welcome to the ‘anthropic principle’, a kind of Goldilocks phenomenon or ‘intelligent design’ for the whole Universe. It’s easy to describe, but difficult to categorise: it might be a scientific question, a philosophical concept, a religious argument — or some combination. The anthropic principle holds that if such phenomena as the gravitational constant, the exact electric charge on the proton, the mass of electrons and neutrons, and a number of other deep characteristics of the Universe differed at all, human life would be impossible. According to its proponents, the Universe is fine-tuned for human life.