Physics is the most basic science, its laws describing force and motion, electricity, magnetism, light, heat, waves, the quantum world, and the nature of time, space, and gravity. In describing the fundamental principles of the world around us, physics has provided the keys to some of the world's most widely used technological developments. Fiber-optical communications, global positioning systems, compact discs, computers, and special polymers used in clothing for extreme conditions are among the advances fostered by physics research. Physicists have helped drive medical advances in technologies such as magnetic resonance imaging and ultrasound. Physicists play a special role in developing alternate energy sources, such as solar, wind, and nuclear power, and in developing energy-efficient technologies.