History of physics

History of Physics

At the moment, this article is almost the same as the "Ridiculously Brief History of Physics" on the main Physics page. However, it is intended that this article should grow to be a more detailed history of physics, whilst the one on the Physics page should remain as a summary only.

This article is a work in progress: please add more material here

Antiquity

Since antiquity, people have tried to understand the behavior of matter: why unsupported objects drop to the ground, why different materials have different properties, and so forth. Also a mystery was the character of the universe, such as the form of the Earth and the behavior of celestial objects such as the Sun and the Moon. Several theories were proposed, most of them were wrong, but this is part of the nature of the scientific enterprise, and even modern theories of quantum mechanics and relativity are considered merely as "theories that haven't broken yet". Physical theories in antiquity were largely couched in philosophical terms, and rarely verified by systematic experimental testing.

Typically the behaviour and nature of the world were explained by invoking the actions of gods. Around 200 BC, many Greek philosophers began to propose that the world could be understod as the result of natural processes. Many also challenged traditional ideas presented in mythology, such as the origin of humans, although this falls into the history of biology, not physics.

Due to the absence of advanced experimental equipment such as telescopes and accurate time-keeping devices, experimental testing testing of many such ideas was impossible or impractical. There were exceptions: for example, the Greek thinker Archimedes derived many correct quantitative descriptions of mechanics and also hydrostatics when, so the story goes, he noticed that his own body displaced a volume of water while he was getting into a bath one day. Another remarkable example was that of Eratosthenes, who deduced that the Earth was a sphere, and accurately calculated its circumference using the shadows of sticks to measure the angle between two widely separated points on the Earth's surface. Greek mathematicians also proposed calculating the volume of objects like spheres and cones by dividing them into very thin disks and adding up the volume of each disk - anticipating the invention of integral calculus by almost two millennia.

Modern knowledge of these early ideas in physics, and the extent to which they were experimentally tested, is sketchy. Almost all direct record of these ideas was lost when the Library at Alexandria was destroyed, around 400 AD. Perhaps the most remarkable idea we know of from this era was the deduction by Aristarchus of Samos that the Earth was a planet that travelled around the Sun once a year, and rotated on its axis once a day (accounting for the seasons and the cycle of day and night), and that the stars were other, very distant suns which also had their own accompanying planets (and possibly, lifeforms upon those planets).

Regrettably, this period of inquiry into the nature of the world was eventually stifled by a tendency to accept the ideas of eminent philosophers, rather than to question and test those ideas. For the following one thousand years, Ptolemy's (not to be confused with the Egyptian Ptolemies) model of an Earth-centred universe with planets moving in perfect circular orbits was accepted as absolute truth.

16th century

In the 16th century Kepler formulated a model of the solar system based upon the five Platonic solids. His access to extremely accurate astronomical observations by Tycho Brahe enabled him to determine that his model was inconsistent with the observed facts. His attempt to more accurately model the motion of the planet Mars led him to the conclusion that the planets follow not circular orbits, but elliptical orbits with the Sun at one focus of the ellipse. This breakthrough overturned a millennium of dogma based on Ptolmey's idea of "perfect" circular orbits for the "perfect" heavenly bodies. Kepler then went on to formulate his three laws of planetary motion.

During the late 16th century, Galileo pioneered the use of experiment to validate physical theories, which is the key idea in the scientific method. Galileo's use of experiment, and Kepler's insistence that observational results must always take precedence over theoretical results brushed away the acceptance of dogma, and gave birth to an era where scientific ideas were openly discussed and rigorously tested. Galileo formulated and successfully tested several results in dynamics, in particular the Law of Inertia.

17th century

In 1687, Isaac Newton published the Principia Mathematica, detailing two comprehensive and successful physical theories: Newton's laws of motion, from which arise classical mechanics; and Newton's Law of Gravitation, which describes the fundamental force of gravity. Both theories agreed well with experiment. Classical mechanics would be exhaustively extended by Lagrange, Hamilton, and others, who produced new formulations, principles, and results. The Law of Gravitation initiated the field of astrophysics, which describes astronomical phenomena using physical theories.

18th century

From the 18th century onwards, thermodynamics was developed by Boyle, Young, and many others. In 1733, Daniel Bernoulli used statistical arguments with classical mechanics to derive thermodynamic results, initiating the field of statistical mechanics. In 1798, Thompson demonstrated the conversion of mechanical work into heat.

19th century

In 1847 Joule stated the law of conservation of energy, in the form of heat as well as mechanical energy.

The behavior of electricity and magnetism was studied by Faraday, Ohm, and others. In 1855, Maxwell unified the two phenomena into a single theory of electromagnetism, described by Maxwell's equations. A prediction of this theory was that light is an electromagnetic wave.

In 1895, Röntgen discovered X-rays, which turned out to be high-frequency electromagnetic radiation. Radioactivity was discovered in 1896 by Henri Becquerel, and further studied by the Pierre Curie and Marie Curie and others. This initiated the field of nuclear physics.

In 1897, Thomson discovered the electron, the elementary particle which carries electrical current in circuits.

20th century

In 1904, Thomson proposed the first model of the atom, known as the plum pudding model. (The existence of the atom had been proposed in 1808 by Dalton.)

In 1905, Einstein formulated the theory of special relativity, unifying space and time into a single entity, spacetime. Relativity prescribes a different transformation between reference frames than classical mechanics; this necessitated the development of relativistic mechanics as a replacement for classical mechanics. In the regime of low (relative) velocities, the two theories agree. In 1915, Einstein extended special relativity to explain gravity with the general theory of relativity, which replaces Newton's law of gravitation. In the regime of low masses and energies, the two theories agree.

In 1911, Rutherford deduced from scattering experiments the existence of a compact atomic nucleus, with positively charged constituents dubbed protons. Neutrons, the neutral nuclear constituents, were discovered in 1932 by Chadwick.

Beginning in 1900, Planck, Einstein, Bohr, and others developed quantum theories to explain various anomalous experimental results by introducing discrete energy levels. In 1925, Heisenberg and Schrödinger formulated quantum mechanics, which explained the preceding quantum theories. In quantum mechanics, the outcomes of physical measurements are inherently probabilistic; the theory describes the calculation of these probabilities. It successfully describes the behavior of matter at small distance scales.

Quantum mechanics also provided the theoretical tools for condensed matter physics, which studies the physical behavior of solids and liquids, including phenomena such as crystal structures, semiconductivity, and superconductivity. The pioneers of condensed matter physics include Bloch, who created a quantum mechanical description of the behavior of electrons in crystal structures in 1928.

During World War II, research was conducted by each side into nuclear physics, for the purpose of creating a nuclear bomb. The German effort, led by Heisenberg, did not succeed, but the Allied Manhattan Project reached its goal. In America, a team led by Fermi achieved the first man-made nuclear chain reaction in 1942, and in 1945 the world's first nuclear explosive was detonated in Alamagordo, New Mexico.

Quantum field theory was formulated in order to extend quantum mechanics to be consistent with special relativity. It achieved its modern form in the late 1940s with work by Feynman, Schwinger, Tomonaga, and Dyson. They formulated the theory of quantum electrodynamics, which describes the electromagnetic interaction.

Quantum field theory provided the framework for modern particle physics, which studies fundamental forces and elementary particles. In 1954, Yang and Mills developed a class of gauge theories, which provided the framework for the Standard Model. The Standard Model, which was completed in the 1970s, successfully describes almost all elementary particles observed to date.

we need more on cosmology, black holes and Stephen Hawking

Developments since 1990

to be written -- topics should include string theory and superstring theory

Developments since 2000

to be written -- add stuff on convergence of superstring stuff to M-theory