Modern Cosmology

Modern cosmologists base their theories on astronomical observations, physical concepts such as quantum mechanics, and an element of imagination and philosophy. Cosmologists have moved beyond trying to find Earth’s place in the universe to explaining the origins, nature, and fate of the universe.







The current “standard model” of the origin of the universe, called the big bang theory, proposes that a major event, not unlike a huge explosion, set free all the matter and energy in the universe and started its expansion. Theories of the evolution and fate of the universe go on to describe a universe that has been expanding and cooling since the big bang. Early versions of the theory held that the universe would keep expanding forever or eventually collapse back to its initial state, an extremely dense object that contains all of the matter in the universe. When the big bang theory was developed in the mid-20th century, some cosmologists found the idea of a sudden beginning of the universe philosophically unacceptable. They proposed the steady-state theory, which said that the universe has always looked more-or-less the same as it does now and that it does not change over time. The steady-state theory could not explain the background radiation, though, and essentially all cosmologists have abandoned it.