Einstein ushers in modern cosmology

On this day in 1917, Albert Einstein presented the paper “Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie” (“Cosmological considerations in the general theory of relativity”) at the weekly meeting of the Prussian Academy of Sciences in Berlin. The pivotal research, often overlooked amid Einstein’s many accomplishments, applied his newly minted general theory of relativity to the universe as a whole. The study of cosmology would never be the same again. Einstein posited that the cosmos is unbounded spatially yet finite in content. To keep his model universe static, he introduced the constant λ into his general relativity field equations. Known as the cosmological constant, Einstein later allegedly called λ his “biggest blunder” once astronomer Edwin Hubble’s measurements established that the universe is expanding. Despite the shortcomings of Einstein’s model universe, the paper (which was published on 15 February 1917) was a major advance considering that at the time the Milky Way was thought to constitute the entire universe. And some of Einstein’s ideas are making a comeback: The cosmological constant is used to account for dark energy, and some theorists are exploring the possibility that the universe was initially static. For a detailed explanation of the “Cosmological considerations” paper, read the Physics Today article by Cormac O’Raifeartaigh. (Photo credit: Ferdinand Schmutzer)

Date in History: 8 February 1917