In 1929 Hubble published evidence that the universe is expanding, refuting the idea that the universe is static. This discovery irritated Einstein. It tore down the conceptual wall Einstein had built to keep God out. A year or so later, Lemaître showed that the general relativity equations had a solution for an expanding universe and thereby gained a hearing with Einstein. Over a period of several days in private meetings Lemaître persuaded Einstein to change his mind and let his equations speak for themselves. Eventually Einstein visited Mount Wilson in California and looked through the 100-inch Hale telescope that Hubble had used to gather his data. Einstein then and there repudiated the special value of the cosmological constant. Later, in private communications with his friend Gamow, Einstein admitted that his choice for the value of the cosmological constant was “the biggest blunder” of his scientific career.