PHYSICS. – From the Greek φύσις (nature). This is the name given to the science that studies the general properties of matter and of the elementary particles that constitute it, as well as the manifestations and transformations of energy in all bodies, insofar as they are material.
The other mathematical-physical-natural sciences also concern themselves with material bodies. But 1) mathematics studies them from an entirely general standpoint (number, quantity, form, dimensions); 2) chemistry studies their specific properties and substantial transformations; 3) the natural sciences (astronomy, geology, biology) do indeed concern themselves with general properties (as does physics) and specific properties (as does chemistry), but only of certain categories of bodies and from a standpoint particular to each of them (as a heavenly body, as a living being, etc.), more or less disregarding what already falls within the domain of mathematics, physics, and chemistry.
I. HISTORICAL DEVELOPMENT
The first attempts at study date back to the schools of Greek philosophy scattered along the shores of the entire eastern Mediterranean basin. Anassimandro and Anassimone of Mileto (6th century B.C.) interpret the created world as due to the Νοῦς (mind), the ordering element. Leucippo of Mileto and Democrito of Abdera (5th–4th centuries B.C.) formulate theories clearly derived from the preceding ones. Democrito in particular develops concepts of atoms, movements, and interactions among them that seem to foreshadow modern conceptions.The word “physics” is encountered for the first time in the works of Aristotele of Stagira (4th century B.C.), where it indicates the observation and study of sensible things, as distinct from non-sensible things, designated as metaphysics. In the great body of Aristotele’s works, the only question of physics considered is motion. Whereas in other fields, such as logic, the arguments are formulated and developed so accurately as to remain the basis of that discipline even today, and, in natural history, the description and classification of animals and plants demonstrate a careful spirit of observation, the question of motion is treated by a purely deductive method, with laws derived from principles of a general character. Nevertheless, because of their great value in other fields and because scholasticism, the dominant philosophy in the Middle Ages, was predominantly metaphysical in tendency, Aristotele’s works exercised undisputed influence also in the field of physics for at least 15 centuries.
To Archimede of Siracusa (3rd century B.C.) are due the discovery of the law governing the thrust received by a body immersed in a liquid and that of the lever, the only exact laws handed down by Greek civilization.
Aristotele’s physics was subjected to criticism from as early as the thirteenth century by Ruggero Bacone and subsequently by Nicola of Cusa, Leonardo da Vinci, Guglielmo Gilberto, and others, as a call for a more realistic conception of facts based on observation. To Galileo Galilei (1564–1642) is due the exact formulation of the laws of motion and mechanics, and he is therefore recognized as the founder of the experimental method. These laws were subsequently confirmed and connected with the heliocentric system advocated by Nicola Copernico and with the laws of planetary motion discovered by Giovanni Keplero, through the work of Isacco Newton (1642–1727), who showed, with the aid of calculus, their dependence upon the single law of universal gravitation.
In the middle of the seventeenth century, Evangelista Torricelli carried out the experiment involving the mercury barometer. New conceptions of the gaseous state resulted from it, for which Roberto Boyle and Daniele Bernoulli in the eighteenth century subsequently formulated laws concerning the free movement of molecules (the kinetic theory of gases).
In the nineteenth century, Roberto Mayer determined the fixed ratio between work and heat when one was 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 Rodolfo Cissius enunciated the second principle of thermodynamics, concerning the incomplete reversibility of transformations between heat and work.
Luminous phenomena attracted interest following the invention of lenses and telescopes by craftsmen (Florentine, Venetian, and Dutch, from the seventeenth to the eighteenth century). The law of reflection had been known since ancient times; those of refraction and diffraction date from 1600.
Some electrical and magnetic phenomena had already been known since ancient times. It appears that the Chinese knew the compass as early as 2000 B.C., and the navigators of Amalfi were using it by the twelfth century. In the eighteenth century the first electrostatic machines and the Leyden jar were constructed, and the lightning conductor was invented (Benjamino Franklin). At the end of that century, Coulomb extended to electric charges the law of attraction 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 was the first to construct an apparatus capable of producing electric currents (pile). In the first twenty years of the nineteenth century, Biot, Sestert, and Ampère established laws of interdependence between electric currents and magnetic fields.
The study of physics received considerable assistance from the application of mathematics, especially infinitesimal calculus, due to Guglielmo Leibnik in the eighteenth century. By this method (theoretical physics), almost all subjects have been treated, with the aim of unifying them in increasingly general theories and occasionally succeeding in predicting new phenomena. Giovanni Fourier treated heat; Carlo Gauss and Luigi Cauchy, elasticity; Enrico Hertz and Clerk Maxwell, electricity and magnetism, also in relation to light. More recently, Antonio Lorentz, Alberto Einstein, and Max Planck, by revising the basic concepts of physics, developed more general theories that concern and encompass all its fields.
II. METHOD OF STUDY
The methods are divided into two: inductive and deductive. The first method is followed when, through observation of a certain number of phenomena—necessarily limited, and with regard also to other concomitant phenomena and to the conditions under which such phenomena occur—a judgment of a general character is formulated (a law governing the relations between causes and effects). The second method follows the opposite course. From postulates (which are therefore accepted rather than demonstrated), facts are deduced; these, however, must accord with experiment, which serves to verify the postulate accepted.Physics treated by the first method is called experimental; when treated by the second, it is called theoretical, or also mathematical, because of the means predominantly employed.