PHYSICS. — From the Greek φύσις (nature). Thus is designated the science that studies the genetic properties of matter and the elementary particles that constitute it, as well as the manifestations and transformations of energy in all bodies insofar as they are material.
Other mathematical, physical, and natural sciences also concern themselves with material bodies. However, 1) mathematics studies them from a most general standpoint (number, quantity, form, dimensions); 2) chemistry studies their specific properties and substantial transformations; 3) the natural sciences (astronomy, geology, biology) concern themselves with both generic properties (as in physics) and specific ones (as in chemistry), but only in certain categories of bodies and from a particular aspect proper to each (as a celestial body, as a living being, etc.), neglecting more or less what pertains to mathematics, physics, and chemistry.
I. HISTORICAL DEVELOPMENT
The first attempts at scientific study arose in the schools of Greek philosophy, scattered along the shores of the entire eastern Mediterranean basin. Anaximander and Anaximenes of Miletus (6th century B.C.) interpreted creation as due to the Nōus (mind), the ordering principle. Leucippus of Miletus and Democritus of Abdera (6th century B.C.) formulated theories clearly derived from the preceding ones. Democritus, in particular, developed concepts of atoms, motion, and their interaction that seem to anticipate modern conceptions.The word “physics” is first encountered in the works of Aristotle of Stagira (4th century B.C.), where it denotes the observation and study of sensible things, distinct from insensible things, which are designated as metaphysics. In the vast corpus of Aristotle’s works, the only physical question considered is motion. While in other fields, such as logic, his arguments are so precisely formulated that they remain the foundation of that discipline, and in natural history, his descriptions and classifications of animals and plants demonstrate an accurate spirit of observation, the question of motion is treated with a purely deductive method, deriving laws from principles of a general character. Nevertheless, due to the great value of Aristotle’s works in other fields and because Scholasticism, the dominant philosophy of the Middle Ages, was predominantly metaphysical in tendency, Aristotle’s works exercised an unchallenged influence in the field of physics for at least fifteen centuries.
To Archimedes of Syracuse (3rd century B.C.) is owed the discovery of the law of buoyancy for a body immersed in a fluid and that of the lever, the only exact laws transmitted by Greek civilization.
Aristotelian physics was subjected to criticism beginning in the thirteenth century by Roger Bacon and later by Nicholas of Cusa, Leonardo da Vinci, William Gilbert, and others, who called for a more realistic conception of facts based on observation. To Galileo Galilei (1546–1642) is owed the precise formulation of the laws of motion and mechanics, and as such he is recognized as the founder of the experimental method. These laws were later confirmed and linked with the heliocentric system advocated by Nicolaus Copernicus and with the laws of planetary motion discovered by Johannes Kepler by Isaac Newton (1642–1727), who demonstrated, with the aid of calculus, their dependence upon the single law of universal gravitation.
Evangelista Torricelli, in the mid-seventeenth century, carried out the experiment of the mercury barometer. From this arose new conceptions regarding the gaseous state, for which Robert Boyle and Daniel Bernoulli, in the eighteenth century, formulated laws of the free motion of molecules (kinetic theory of gases).
Robert Mayer, in the nineteenth century, determined the fixed ratio between work and heat when one is transformed into the other, enunciating the first principle of thermodynamics, the beginning of the more general law of the conservation of energy. Shortly afterward, Sadi Carnot and Rudolf Clausius enunciated the second principle of thermodynamics regarding the incomplete reversibility of transformations between heat and work.
Optical phenomena attracted interest after the invention of lenses and telescopes by artisans (Florentines, Venetians, Dutch) from the seventeenth to the eighteenth centuries. The law of reflection was known from ancient times; those of refraction date to the 1600s.
Some electrical and magnetic phenomena were already known in antiquity. It appears that the Chinese knew of the compass as early as 2000 B.C., and Amalfitan navigators used it in the twelfth century. In the eighteenth century, the first electrostatic machines were built, as well as the Leyden jar, and the lightning rod was invented (Benjamin Franklin). At the end of the same century, Charles-Augustin de Coulomb extended to electric charges the law of attraction previously determined by Newton for matter.
Electrodynamic phenomena were first observed by Luigi Galvani at the end of the eighteenth century and by Alessandro Volta, who first constructed an apparatus capable of producing electric currents (the pile). In the first two decades of the nineteenth century, Biot, Savart, and Ampère established laws of the interdependence between electric currents and magnetic fields.
The study of physics has greatly benefited from the application of mathematics, especially infinitesimal calculus, due to Gottfried Wilhelm Leibniz in the eighteenth century. With this method (theoretical physics), nearly all topics have been treated in an effort to unify them into ever more general theories, sometimes even predicting new phenomena. Jean-Baptiste Fourier treated heat; Carl Friedrich Gauss and Augustin-Louis Cauchy, elasticity; Heinrich Hertz and James Clerk Maxwell, electricity and magnetism, with reference also to light. More recently, Hendrik Lorentz, Albert Einstein, and Max Planck, through a revision of the basic concepts of physics, have developed more general theories that encompass and influence all its fields.
II. METHOD
Methods are distinguished into two types: inductive and deductive. The first method is followed when, through the observation of a certain number of phenomena—necessarily limited—and with regard also to other concomitant phenomena as well as the conditions under which such phenomena occur, a general judgment (law of causal relations) is reached. The second method follows an opposite path. From postulates (which are therefore assumed and not demonstrated), facts are deduced that must, however, be in agreement with experiment to verify the assumed postulate.The discipline pursued by the first method is called experimental; that by the second, theoretical, also mathematical due to the prevalent means employed.