PHYSICS

Physics is a systematic, organized, and ordered knowledge about the physical world. Concepts, theories, and laws of physics are obtained by experimental and mathematical reasoning.

Physics around 1914 was different from natural philosophy (as the study of the physical world was then known) around 1789. First, the community of physicists by 1914 was self-conscious and international, and consisted of trained professional physicists, whereas in 1789 natural philosophy was local and its community consisted of both professionals and amateurs. Second, the education of physicists in universities was systematic, whereas there was no such systematic education in natural philosophy. Third, research in physics was performed in university and national laboratories, whereas natural philosophy was practiced in private laboratories, theaters, salons, and even coffeehouses. Fourth, the tight linkage between mathematics and experimental data was emphasized in physics, whereas natural philosophy was largely experimental. Finally, research in physics was performed for its own sake or for the sake of technology and industries, whereas natural philosophy was more tig'htly coupled with religion and social philosophy.

emergence of physics

In the mid-nineteenth century, scientists noticed the emergence of a scientific discipline that is now called physics. Around this same time, some physicists appeared who began to teach physics at physics departments in universities. Before then, mathematical physics, such as Newtonian mechanics, belonged to mathematics, and experimental fields, such as the study of electricity, magnetism, and heat, belonged to natural philosophy. These two different traditions—mathematics and experimental (Baconian) physics—had developed along different paths. Mathematical physics, such as mechanics, had existed since ancient times, and it underwent a radical, conceptual transformation during the scientific revolution of the seventeenth century. On the other hand, experimental physics, such as the study of electricity, magnetism, and heat, was born during the scientific revolution with Francis Bacon's emphasis on experiments, and these fields used such new instruments as the barometer, air pump, and microscope. These two different fields, that is, mathematical mechanics and the experimental sciences, merged into a single discipline called physics in the mid-nineteenth century.

The gap between the mathematical sciences and the Baconian sciences was wide during the eighteenth century. One can see this in the case of French physique. Throughout the eighteenth century in France, physique had consisted of two separate disciplines: physique générale (general physics) and physique particulière (particular physics). The former meant Newtonian mechanics, while the latter connoted experimental science in general, but sometimes meant specific studies in heat, light, sound, electricity, and magnetism. They were not considered to form a unified discipline.

factors contributing to physics's formation

One factor that contributed to the formation of the single discipline of physics was the mathematization of experimental fields. Since the last quarter of the eighteenth century, experimental fields were rapidly mathematized mainly by French physicists such as Charles-Augustin de Coulomb, Pierre-Simon de Laplace, Siméon-Denis Poisson, Augustin-Jean Fresnel, and Jean-Baptiste Biot. Because of this mathematization, several branches of physics now use the same mathematics and the same mathematical equations. The second factor was the principle of the conservation of energy. In the first half of the nineteenth century, scientists discovered that various forms of forces were converted into other forms. The Danish physicist Hans Christian Ørsted and the English chemist and physicist Michael Faraday discovered the mutual relation between electricity and magnetism; Faraday also discovered the connection between magnetism and light; and the English physicist James Joule discovered the conversion of mechanical motion into heat. Mechanical motions, heat, electricity, and magnetism could be converted into one other, which meant that something in the universe was being conserved. This something was then named energy, which became a common element among various studies that eventually merged into physics.

The germ of this unifying concept can be found in the Scottish natural philosopher John Robison. He had divided mechanical philosophy into four subdisciplines: astronomy, studies on the force of cohesion (involving the theory of machines, hydrostatics, hydraulics, and pneumatics), electricity and magnetism, and optics. Robison saw two links between these four subdisciplines. First, all concentrated on "forces" existing in nature: gravitation, cohesion, electrical and magnetic forces, as well as forces between light and material particles. Second, all concerned motions of bodies in one fashion or another. Newtonian mechanics and electricity and magnetism were classified into a single discipline. During the 1850s, the second law of thermo-dynamics, which states that the entropy of the universe is always increased, was established.

Laplace's Celestial Mechanics (1799–1825) provided a conceptual basis for mathematization. In it, Laplace examined two phenomena—capillary action and the refraction of light in air—by employing the assumption of short-range forces that act between material particles, and between material particles and imponderables. These forces took the form of mathematical equations. His work influenced such followers as Biot, Étienne-Louis Malus, and Poisson. Biot extensively studied voltaic electricity, the propagation of sound, and chromatic polarization; Malus worked on double refraction and polarization; and Poisson devised mathematical formula on electricity and magnetism by using Laplace's method. Their work comprises what is now called "Laplacian physics."

It is worth noting that Laplace's followers were all graduates from the École Polytechnique, which was a new educational institution established during the French Revolution. It opened its doors to all classes of people, not just to the upper class. Though it was a military engineering institution, it trained students not only in military and civil engineering but also in mathematics and physics, including experimental fields such as heat, optics, electricity, and magnetism. Biot and Malus, two full-fledged Laplacians, were among the first polytechniciens. Poisson and François Arago studied there, as did Fresnel, who was, however, not a Laplacian physicist. Fresnel suggested the wave theory of light in the mid-1810s, and with this he successfully refuted the most important part of the Laplacian program in optics. After Fresnel's success, the Laplacian program rapidly declined. Although it was short-lived, Laplacian physics has historical significance, because it provided a model for research in experimental physics. The Laplacian physicists devised mathematical formulas for electricity, light, heat, and magnetism, and combined these mathematical formulas with precise experimental data.

discoveries in electromagnetism

During the nineteenth century, classical electro-magnetism was fully developed. The Italian physicist Alessandro Volta invented the voltaic pile to generate continuous electrical currents in 1800. Twenty years after Volta's invention, Ørsted discovered that a small magnetic needle was affected by a current-carrying wire near it, which showed that a magnetic force exists in a circular way around a current-carrying wire. This phenomenon was theoretically explained by a French physicist and mathematician, André-Marie Ampère. He conjectured that there were many tiny atomic electrical currents in a magnetic needle, and explained the interaction that Ørsted noticed in terms of the interaction between macrocurrent and atomic currents. Based on this idea, he established a mathematical formula of this force, following the Newtonian tradition. Ampère's achievement was developed further by some German scientists of the nineteenth century.

Faraday, however, suggested a radically different approach to electrical phenomena. In the early 1830s he discovered that a moving magnetic field (or a moving conductor that cuts the magnetic field lines) will generate electric currents on a nearby conductor. Faraday suggested a unique theory to understand electrical and magnetic phenomena. His theory had several distinct features, one of which was that electric and magnetic actions occurred along the curved line of actions. He later called these curves "the lines of electric and magnetic force" and gradually believed that these lines exist as a physical reality in the medium. His idea of the lines of force was taken up by two eminent British physicists, William Thomson and James Clerk Maxwell, and was developed in mathematical terms into the field theory.

In particular, Maxwell's field theory predicted the existence of electromagnetic waves that propagate in the medium at the velocity of light. In other words, light became a special form of electromagnetic waves. Around 1888, German physicist, Heinrich Hertz, first succeeded in generating and detecting the electromagnetic waves that Maxwell had predicted. The Italian physicist Guglielmo Marconi soon transformed Hertz's laboratory experiment into commercial wireless telegraphy, which opened a new era of radio communication and eventually radio and television broadcasting in the twentieth century.

the new physics

At the end of the nineteenth century, physicists began to feel that classical electromagnetism and thermodynamics did not fully or satisfactorily explain questions related to the microscopic world, such as blackbody radiation, the evasive ether, and the atomic structure. During the early twentieth century, new theories, such as Albert Einstein's special theory of relativity and quantum mechanics, began to replace the old physics. With this substitution, people gradually realized that there is a mysterious source of enormous energy inside the atom. Some scientists and writers dreamed about using this power for military or industrial purposes. Later, this dream came true with the discovery of atomic fission and chain reaction. The atomic bomb was the ultimate result of the power residing inside the atom.

See alsoChemistry; Einstein, Albert; Helmholtz, Hermann von; Hertz, Heinrich; Marconi, Guglielmo; Maxwell, James Clerk.

bibliography

Buchwald, Jed Z., and Sungook Hong. "Physics." In From Natural Philosophy to the Sciences: Writing the History of Nineteenth-Century Science, edited by David Cahan, 163–195. Chicago, 2003.

Harman, P. M. Energy, Force, and Matter: The Conceptual Development of Nineteenth-Century Physics. Cambridge, U.K., 1982.

Purrington, Robert D. Physics in the Nineteenth Century. New Brunswick, N.J., 1997.

Warwick, Andrew. Masters of Theory: Cambridge and the Rise of Mathematical Physics. Chicago, 2003.

Sungook Hong