‘The Discovery that the Universe is Expanding’

In this lecture, Professor Peebles explains how people hit on the idea that the universe is expanding, and the major discoveries that led from the idea to the now persuasive evidence for expansion. The evidence includes a fossil sea of thermal radiation, left from when the universe was dense, hot and expanding far more rapidly than now. This fossil radiation is marked by the early growth of the structures we see now as galaxies of stars surrounded by planets. As in other branches of natural science, the remarkable advances in understanding of the evolution of the universe has led us to new questions, the most immediate being the nature of the dark matter that the established theory requires. In natural science we explore the wonders of nature in successive approximations.