Since light has no mass, Newton's equation predicts that it will not be attracted by gravity towards anything.既然光是没有质量的，牛顿的方程式便预言光不会受到引力作用。The earth gravitates to the sun.地球受到太阳的引力作用。Dark matter gives out no light and is detectable only because of its gravitational effect on visible matter.暗物质不发光，它之所以能被发现，只是因为它对可见物质产生引力作用。