This week’s 100th anniversary of Albert Einstein’s general theory of relativity is a geeky cause for celebration, but what’s arguably the concept’s toughest test has just gotten under way.
General relativity was a follow-up to special relativity, Einstein’s big idea from a decade earlier. Back in 1905, he worked out a way to explain why the speed of light is constant, regardless of an observer’s point of view: It’s because space and time are not inflexible metrics, but interrelated dimensions that are measured differently depending on your perspective.
Special relativity explained a lot of the weirdness that physicists were puzzling over at the time, but the theory applied only to “special” conditions that didn’t involve acceleration – for example, how things fall in a gravitational field. On Nov. 25, 1915, Einstein laid out how the interplay of space and time gives rise to gravity and the fabric of the cosmos.
The theory passed its first big test in 1919, when observations during a total solar eclipse were found to be more consistent with Einstein’s view of gravity than with Isaac Newton’s. General relativity has been passing tests ever since. For example, if we didn’t take relativistic effects into account, our GPS readings would seem out of whack.
This week is prime time for centennial retrospectives on the theory and its implications. Here are a few to keep you entertained.