had been proposed on theoretical grounds earlier in the decade. Protons and neutrons, it now appeared, are not elementary like photons and electrons, but composed of quarks. Here at last was reason for hope that a fundamental theory, as compelling as Quantum Electrodynamics, might one day be constructed for nuclear physics. On the face of it, the discoveries of the cosmic background and of quarks seemed to take place at opposite ends of the scale of distances. Indeed, the size of the observable universe is about forty-five powers of ten larger than that of a quark. Nevertheless, the two realms turn out to be closely related. The cosmic background radiation provides evidence of the universe the way it was about 1010 years ago, before it had expanded to its present size. A fraction of a second after the Big Bang, its particles were packed tighter than they are in an atom, so it was ruled by quantum mechanics. At one time, furthermore, the universe consisted not of atoms but of quarks. in this way cosmology brings the physics of the immensely large back to join the physics of the immeasurably small. The scope of modern physics may be symbolized by a circle that extends from quarks, past atoms, molecules, and boulders, past planets, stars, and galaxies, out to the universe and, via the Big Bang back to its elementary building blocks. Cosmology also relates how the universe has evolved in time. When this story is combined with stellar evolution and the geological history of the planet, with biological and cultural evolution, and finally with recorded history, a coherent narrative of truly epic proportions emerges. To be sure, the story is riddled with gaps and puzzles -- including the mystery of the origin of life -- but its broad outlines are firmly in place. In the nineteen sixties, physicists first began to draft the opening chapters of this story. Future generations may well look back on this ambitious undertaking as the p...
