Gravitational waves—ripples in the geometry of space-time—are analogous to electromagnetic waves. The challenge in trying to observe these waves directly is that they are extremely weak. To make waves large enough to be detectable, the most voilent events in the universe are required: supernova explosions, the formation of black holes, or the collision of stars. Even so, the effects are minuscule. The geometry changes so little that a distance of several kilometers changes by less than the diameter of a proton.

请问老师这里的by的是什么用法，还有类似的例句吗？ 谢谢！