Theory of the creation of the universe. The big bang theory, as proposed by the late Belgian astrophysicist Georges Lemaitre (1894-1966), states that the universe came into being in a huge explosion sometime between 10 and 20 billion years ago. In the beginning, all the matter that currently exists or has ever existed was contained in a state called a singularity, a spot of tremendous density and tiny volume. When the singularity exploded, it threw out all the matter that makes up stars, galaxies, and planets and their inhabitants. Scientists theorize that the new universe was so hot that the first simple atoms of hydrogen did not form until one million years after the initial event. Stars and galaxies followed about one billion years later, and the solar system in which we live did not form until the universe was about 10 billion years old.
Albert Einstein’s theory of general relativity, published in 1915, provided the impetus for the big bang theory. After Lemaitre proposed it, the big bang theory was itself rejected as pseudoscience by some researchers. Scientists in the 19th and early 20th centuries believed that the universe was both infinitely large and infinitely old. They believed that, although individual stars and planets moved, the universe as a whole was motionless. Einsteins theory overturned this model, suggesting instead that the universe is expanding constantly, presumably from some initial event. Astronomical observations of distant galaxies have since proven him correct. The American astrophysicists Arno Penzias and Robert Wilson began measuring universal background radiation in 1965, looking for evidence of the intensely hot period of the initial explosion. Penzias and Wilson found that this radiation was almost completely uniform across the entire sky, and realized that it was the remnant of the initial big bang. They were awarded the Nobel Prize in 1978 for their work.