A century ago this year, a young Swiss physicist, who had already revolutionized physics with discoveries about the relationship between space and time, developed a radical new understanding of gravity.
In 1915, Albert Einstein published his general theory of relativity, which described gravity as a fundamental property of space-time. He came up with a set of equations that relate the curvature of space-time to the energy and momentum of the matter and radiation that are present in a particular region.
Today, 100 years later, Einstein's theory of gravitation remains a pillar of modern understanding, and has withstood all the tests that scientists could throw at it. But until recently, it wasn't possible to do experiments to probe the theory under extreme conditions to see whether it breaks down. [6 Weird Facts About Gravity]