Theoretical physics began at least 2,300 years ago, under the
pre-Socratic philosophy, and continued by
Plato and
Aristotle, whose views held sway for a millennium. During the rise of
medieval universities, the only
acknowledged intellectual disciplines were the seven
liberal arts of the
Trivium like
grammar,
logic, and
rhetoric and of the
Quadrivium like
arithmetic,
geometry,
music and
astronomy. During the
Middle Ages and
Renaissance, the concept of
experimental science, the
counterpoint to theory, began with scholars such as
Ibn al-Haytham and
Francis Bacon. As the
Scientific Revolution gathered pace, the concepts of
matter, energy, space, time and
causality slowly began to acquire the form we know today, and other sciences spun off from the rubric of
natural philosophy. Thus began the modern era of theory with the
Copernican paradigm shift in astronomy, soon followed by
Johannes Kepler's expressions for planetary orbits, which summarized the meticulous observations of
Tycho Brahe; the works of these men (alongside Galileo's) can perhaps be considered to constitute the Scientific Revolution. The great push toward the modern concept of explanation started with
Galileo Galilei, one of the few
physicists who was both a consummate theoretician and a great
experimentalist. The
analytic geometry and mechanics of
René Descartes were incorporated into the
calculus and
mechanics of
Isaac Newton, another theoretician/experimentalist of the highest order, writing
Principia Mathematica. In it contained a
grand synthesis of the work of Copernicus, Galileo and Kepler; as well as Newton's theories of mechanics and gravitation, which held sway as worldviews until the early 20th century. Simultaneously, progress was also made in optics (in particular colour theory and the ancient science of
geometrical optics), courtesy of Newton, Descartes and the Dutchmen
Willebrord Snell and
Christiaan Huygens. In the 18th and 19th centuries
Joseph-Louis Lagrange,
Leonhard Euler and
William Rowan Hamilton would extend the theory of classical mechanics considerably. They picked up the interactive intertwining of
mathematics and
physics begun two millennia earlier by Pythagoras. Among the great conceptual achievements of the 19th and 20th centuries were the consolidation of the idea of
energy (as well as its global conservation) by the inclusion of
heat,
electricity and magnetism, and then
light.
Lord Kelvin and
Walther Nernst's discoveries of the
laws of thermodynamics, and more importantly
Rudolf Clausius's introduction of the singular concept of
entropy, began to provide a macroscopic explanation for the properties of matter.
Statistical mechanics (followed by
statistical physics and
quantum statistical mechanics) emerged as an offshoot of thermodynamics late in the 19th century. Another important event in the 19th century was
James Clerk Maxwell's discovery of
electromagnetic theory,
unifying the previously separate phenomena of electricity, magnetism and light. The pillars of
modern physics, and perhaps the most revolutionary theories in the history of physics, have been
relativity theory, devised by
Albert Einstein, and
quantum mechanics, founded by
Werner Heisenberg,
Max Born,
Pascual Jordan, and
Erwin Schrödinger. Newtonian mechanics was subsumed under special relativity and Newton's
gravity was given a
kinematic explanation by
general relativity. Quantum mechanics led to an understanding of
blackbody radiation (which indeed, was an original motivation for the theory) and of anomalies in the
specific heats of
solids — and finally to an understanding of the internal structures of
atoms and
molecules. Quantum mechanics soon gave way to the formulation of
quantum field theory (QFT), begun in the late 1920s. In the aftermath of
World War II, more progress brought much renewed interest in QFT, which had since the early efforts, stagnated. The same period also saw fresh attacks on the problems of
superconductivity and
phase transitions, as well as the first applications of QFT in the area of theoretical condensed matter. The 1960s and 70s saw the formulation of the
Standard Model of particle physics using QFT and progress in
condensed matter physics (theoretical
foundations of superconductivity and
critical phenomena,
among others), in parallel to the applications of relativity to
problems in astronomy and
cosmology respectively. All of these achievements depended on the theoretical physics as a moving force both to suggest experiments and to consolidate results — often by ingenious application of existing mathematics, or, as in the case of Descartes and Newton (with
Leibniz), by inventing new mathematics.
Fourier's studies of heat conduction led to a new branch of mathematics:
infinite, orthogonal series. Modern theoretical physics attempts to unify theories and explain phenomena in further attempts to understand the
Universe, from the
cosmological to the
elementary particle scale. Where experimentation cannot be done, theoretical physics still tries to advance through the use of mathematical models. ==See also==