Physics is the fundamental science. It explains how the universe behaves at every scale, from the subatomic to the extragalactic. It describes the most basic objects and forces and how they interact. Its laws tell us how the planets move, where light comes from, what keeps birds aloft, why a magnet attracts and also repels, and when a falling object will hit the ground, and it gives answers to countless other questions about how the world works. Physics also gives us extraordinary power over the world, paving the way for devices from radios to GPS satellites, from steam engines to nanomaterials. It’s no exaggeration to say that every invention ever conceived makes use of the principles of physics. Moreover, physics not only underlies all of the natural sciences and engineering, but also its discoveries touch on the deepest philosophical questions about the nature of reality.