Motus Mentis

It’s a big day in physics: researchers using the Laser Interferometer Gravitational-Wave Observatory (LIGO) have confirmed the existence and propagation of ripples in spacetime caused by the movement of massive objects.

The observation of such waves is a posthumous triumph for Albert Einstein, who first predicted their existence a century ago this year. While I’m sure he would have been happy, I doubt he’d have been surprised. In 1919, Arthur Eddington’s observations of a solar eclipse confirmed Einstein’s prediction of the warping of spacetime by large masses (in this case, the Sun). When a report of this reached Einstein, he received the news without much excitement, saying he knew that he had to be right. A graduate student, Ilse Schneider, asked what his reaction would have been had the experiment violated his prediction. He replied, “Then I would have been sorry for the dear Lord; the theory is correct.”

Also worth noting here is that the LIGO apparatus, which very sensitively compared the length of two perpendicular axes to detect expansions and contractions, is almost perfectly analogous to the famous (and shocking!) Michelson-Morley experiment of 1887, which also used perpendicular-axis interferometry to refute the idea of the “luminiferous aether”, which until then was assumed by nearly all physical scientists to be a rarefied medium, filling all of space, that acted as a substrate for the propagation of light waves. Despite an all-but unanimous consensus, the MM experiment showed the science not to be “settled” at all, and threw theorists into a bit of a panic. Into this breach stepped the young genius Einstein, who, in 1905 (his annus mirabilis), began a new era of physics with his paper On The Electrodynamics of Moving Bodies, which introduced the idea that came to be known as “Special Relativity”. (It took Einstein another 11 years of difficult work to generalize the theory to include gravitation.)

Learn more about today’s historic result here.