In the 19th century, ether (not to be confused with the once-popular anesthetic diethyl ether) was the medium that scientists believed filled space. It might be considered the first “dark matter,” an undetectable something theory said should be out there, the explanation for a number of problems having to do with electricity, the movement of light, even the whole concept of “nothing.” It was, according to one early-20th-century physicist, “accepted as a necessity by all modern physicists.” But as Einstein’s theory noted, there was no experimental confirmation for the substance. There was no proof it existed, other than that the scientific establishment had accepted the concept. As Stanley Goldberg reminds us, British physicists had a “theoretical commitment to the ether.” For instance, Lord Kelvin argued in 1907 that ether must be an “elastic, compressible, non-gravitational solid.” However, in the end it didn’t conceptually work well enough.

Still, when Einstein published his work contradicting ether, the only place he seems to have been understood was in Germany, where his theory was “discussed, criticized, elaborated upon, and defended,” writes Goldberg. For the next six years, virtually all the literature on Einstein’s paper came from Germany and three other countries. In France, Einstein was largely ignored until he visited in 1910. In the U.S., a few understood it, but, in general, relativity was ridiculed as “totally impractical and absurd.” In Britain, his theories met with resistance, because relativity was seen as a direct challenge to the widely accepted theory of ether.