Physics for Everyone, Lecture 4. The Beating Heart of Modern Physics: The Dog Who Didn't Bark in the Night.

This lecture, recorded before lecture 5, which was released a month ago, actually more naturally follows it, which is why releasing it after lecture 5, while unintended, actually makes sense. In the last lecture I described the most important unification in all of physics, the unification of electricity and magnetism, a unification into electromagnetism by James Clerk Maxwell in the 19th century.…