The Early Days of the Big Bang Theory

In honor of the World Year of Physics, Physical Review is republishing archive papers related to Einstein's 1905 accomplishments. By the 1940's, Hubble's measurements of the receding velocities of distant galaxies had established that the Universe was expanding and had existed in a more dense state in the past. In 1948, Alpher, Bethe, and Gamow (the two collaborators allegedly chosen by Gamow because their collective names sounded like the three first letters of the Greek alphabet alpha, beta, and gamma) proposed that the Universe began in the form of a neutron fluid, which would decay into protons and electrons as it expanded, allowing elements like deuterium, helium, and lithium to form. Although the picture of the early Universe was to change considerably over the following decades, the Alpher, Bethe, and Gamow paper continued to have considerable historical influence over future work in the area.