Physics is at the heart of our understanding of physical reality. Principles of physics apply universally—from the behavior of the infinitesimally tiny quarks that comprise the protons and neutrons of the atomic nucleus to the ordering of matter into galaxies, galaxy clusters, and superclusters at the largest scales imaginable. Physics also lays the groundwork for the other sciences, especially chemistry and biology. Nevertheless, emergent properties in complex systems mean that physics alone cannot provide a complete and comprehensible description of chemical and biological phenomena.