Few words about relativity

        In November 1915, Albert Einstein published a series of papers that laid out the ideas, equations, and some astronomical applications of the general theory of relativity. While Isaac Newton described gravity as a force between two massive bodies, Einstein's general relativity re-interprets gravity as a geometric distortion of space and time. One example cited in those papers was that general relativity can explain the extra precession of Mercury's orbit that Newton's formulation does not explain. Another prediction, the bending of light as it passes a massive object, was tested and shown accurate less than four years later. This effect, called gravitational lensing, has been shown in tremendous detail by the Hubble Space Telescope, and is one of the prime motivations behind the Frontier Fields project. Last year, scientists celebrated the centennial of general relativity, which has been a resounding success in diverse astronomical situations. However, there was one major prediction that had not yet been tested: gravitational waves. General relativity predicts that mass not only can create distortions in space-time, but also can create waves of those distortions propagating across space-time. In cosmology, the global expansion of space over time is a familiar concept. For a gravitational wave, space also stretches/shrinks, but that localized distortion moves across space at the speed of light.