Physics is the most basic and general science of natural phenomena, both historically and conceptually. As such, its concepts, theories and methods underpin those of all other special disciplines concerned with all aspects and levels of organization in nature − from chemistry to neurophysiology. For this reason the study of physical subjects is not only the province of physicists, but is often pursued by practitioners of many other scientific disciplines. Taking account of this fact this guide addresses the needs of persons with different backgrounds and levels of expertise in this science.
The historical origins of modern physics are coextensive with those of the creation of modern science in the “scientific revolution” (the creation of a mathematical and experimental account of natural phenomena). The new science of nature emerged in the seventeenth century through the work of such eminent researchers as Galileo, Kepler and Newton. Astronomy, an ancient discipline, was intimately linked to these investigations because of the then current need to explain and justify the adoption of the Copernican conception of a sun-centered planetary system. Since then progress in astronomy and developments in general physics have been continuously linked through a sequence of reciprocally stimulating discoveries. These gave rise to astrophysics in the nineteenth century and to scientific cosmology in the early decades of the past century.
The main division of the field of physics is the partition into theoretical and applied physics, which cuts across the remaining classifications. Another usual classification discriminates between theoretical, applied and experimental physics, but these research fields frequently overlap.