Scientific Revolution is a social policy in Civilization V. It is part of the Rationalism tree and requires Sovereignty. After your society has been prepared by the careful introduction of progressive policies, it starts what's known as the "scientific revolution." Of course, no guns or swords are involved here, but the revolutionary concepts and ideas which develop as a result of questioning centuries-old assumptions, such as that the Sun rotates around the (flat) Earth. After a number of these ridiculous concepts are conclusively disproved, people feel so enlightened that they are encouraged to seriously delve into science, along with other nations' scientists - which greatly benefits the nation's technological progress, of course.