in 1945. He was the archetypal theoretical physicist: it was said of him that even his presence in the same town would make experiments go wrong! PauliΓÇÖs exclusion principle says that two similar particles cannot exist in the same state, that is, they cannot have both the same position and the same velocity, within the limits given by the uncertainty principle. The exclusion principle is crucial because it explains why matter particles do not collapse to a state of very high density under the influence of the forces produced by the particles of spin 0, 1, and 2: if the matter particles have very nearly the same positions, they must have different velocities, which means that they will not stay in the same position for long. If the world had been created without the exclusion principle, quarks would not form separate, well-defined protons and neutrons. Nor would these, together with electrons,
