The aim of physics is to understand how nature works. Developing this understanding begins with careful observation and experimentation, followed by tentative hypotheses and eventually formal theories to explain the phenomena. Predictions made by the theories are in turn tested against new experiments, which may lead to refinements in the theories, and so on in an ever-tightening spiral.

Historically, the first successful theory of universal scope was Newtonian mechanics, which explained how forces cause objects to change their motion. Later physicists developed equally successful theories of electromagnetism, light (optics), and heat (thermodynamics).

Early in the 20th century, refined experiments forced physicists to extend Newtonian mechanics in two ways. To describe objects moving near the speed of light or in strong gravitational fields, Einstein developed his famous theories of relativity. Even more radical was quantum mechanics, a theory that explained the behavior of particles at the atomic scale.

Today, the scope of physics extends from the smallest subatomic particles to the entire observable universe. In between, physicists study nuclear reactions, the interactions of atoms with light, properties of solids, chaotic dynamics of fluids, atmospheric processes, pulsations of stars, and the evolution of galaxies. One of the fascinating aspects of all these seemingly disparate fields is that they are so closely related to each other. For example, the mathematics that describes electrons in a metal can also be used to predict the size of a neutron star. On a grander scale, our understanding of the earliest history of the universe depends entirely on our knowledge of the forces that act between elementary particles.

Any person with a curiosity about the physical universe can benefit from studying physics. One needs not have aspirations to be a professional physicist, although that is certainly a career option. In general, everyone needs an understanding of physics because of the bearing it has on the wide range of issues facing us in today's world such as energy resources, the environment, space exploration, communication, medicine and arms control.