How and when did the universe begin? How has it evolved? What will be its fate? Albert Einstein and others pondered those questions in the early part of the century. But not until 1929, when Edwin Hubble observed that galaxies were moving away from ours in every direction, did solid empirical evidence begin to support any postulated answers. And not until the second half of the century did cosmology transition from a highly abstract discipline to a field in which accepted theories had to conform to measurements.
After World War II, cosmology discussions revolved around two competing theories. Relativistic evolution, which became known as Big Bang theory, postulated that the universe is expanding from an ultra-dense point that contained all the matter in today’s universe. The alternative steady-state theory rejected the concept of a moment of creation and postulated that although the universe is expanding, matter is continuously created so...
