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. In the 1960s physicists first began to draft the opening chapters of this story. Future generations may well look back on this ambitious undertaking as the principal accomplishment of physics in the twentieth century. Each poster covers about a decade and is introduced by a thumbnail essay to provide a glimpse of the historical and scientific context of the time. A Century of Physics will be on display at the Atlanta Centennial Meeting in March.