Section 10.1 Introduction
If the universe is like a movie, then the elementary particles that we discussed in the previous chapter are like the cast for this movie. But what if actors in a movie didn't interact at all with each other or with anything else in the movie? Imagine that you went to see Star Wars: The Rise of Skywalker. The movie started and you saw Daisy Ridley, John Boyega, Adam Driver, a CGI version of Carrie Fisher and a cute, beach-ball-like android on the screen, but they didn't do anything. They didn't interact at all with each other. They didn't talk with each other. They didn't fly cool spaceships from one planet to another or engage in long fight scenes with conveniently-colored light sabers. They didn't fight against an evil Emperor who supposedly had died in a previous trilogy and for some ridiculous reason was back again. And they didn't inexplicably kiss each other at the end of the movie. Nothing at all happened — they just sat there. An interesting movie it would not be. 1
That's what the universe would be like without any forces or interactions. Only worse. A lot worse. The universe would be a really boring place without any interactions. Nothing of any interest would happen. In fact, it would be so boring that there wouldn't even be anyone to realize just how bored they were.
Forces probably rank #1 on the list of things that we most take for granted. Particles are all very nice, but if they don't interact with anything else, then for all intents and purposes they might as well not even exist. 2 We would never be able to detect the effects of any particle that didn't experience at least some kind of force/interaction.
In this chapter, we discuss our current understanding of the fundamental forces of the universe. We describe the four fundamental forces — strong, electromagnetic, weak, and gravitational — and discuss efforts being made by physicists to describe all of these forces under the framework of a single, unified theory. We then discuss Richard Feynman's quantum field theory that describes how forces might actually work, and apply these approach to the electromagnetic and strong forces. (We will extend the approach to the weak force in the next chapter.)