Growing up in Missouri, they would kind of take us out into the woods, and they would give you a map, and they would give you a compass, and you had to find your way home. And without the compass, you can't even read the map. That's what I'm here to tell you. The compass is the key. [Small thing.] [Big idea.] A compass is most simply a piece of metal that has been magnetized, so that it will turn towards the Earth's magnetic pole. The one that we all think of is the pocket compass. It looks like a watch, right? You can hold it in your hand and watch the little needle bounce around until you find north. Magnetism is still a pretty mysterious force to physicists, but what we do know for sure is that a compass works because the Earth is this giant magnet. And when you use a compass, you are in touch with the very center of our planet, where this kind of roiling ball of molten iron is spinning around and creating a magnetic field. Just like a magnet you can play with on your tabletop, it has a north pole and a south pole, and we use compasses to find our way north because of that fact. The earliest known compass comes from about 200 BC in China. They figured out that some of the metal coming out of the ground was naturally magnetic, and so they fashioned this magnetized metal into this kind of ladle-looking thing, put it on a brass plate and then it would point north. It seems to have been primarily used to improve feng shui, so they could figure out what was the best way for energy to flow through their living spaces. Sailors were probably the early adopters of the more portable versions of it, because no matter where the sun was, no matter what the condition of the stars were, they would always be able to find north. Now, much later, the Europeans are the ones who innovate and come up with the compass rose. It essentially laid out what north, south, east and west looked like, and it also enabled you to kind of create new directions, like northwest, southeast, what have you. And for the first time, they knew where they were going. That's kind of a big deal. But also, I think it was part of this general reinvigoration of European science. You might know it as the Renaissance. Lots of new tools were invented, from the telescope to the microscope. Maps got better because of compasses, right? Because then you start to understand which direction is which, you get a lot more detail, and that just kind of changes the human relationship to the world. The compass with a map is like a superpower. Everything that we think of as world history would not have taken place without the compass: the age of exploration, Magellan circumnavigating the globe, even the fact that we know it is a globe. The compass ends up getting embedded in all these other tools, because it is such a functional object. So you might have it embedded in your multi-tool, you might have it embedded in your phone. The compass is everywhere, because it's literally how we find our way across the face of the Earth. So you can go off and explore, and find out what is over that next hill or that next horizon, but you can also reliably find your way home.