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Physics

Physics is very closely related to the other natural sciences, particularly chemistry, the science of molecules and the chemical compounds that they form in bulk. Chemistry draws on many fields of physics, particularly quantum mechanics, thermodynamics and electromagnetism. However, chemical phenomena are sufficiently varied and complex that chemistry is usually regarded as a separate discipline. Nevertheless, it is widely accepted among chemists and physicists that the laws of physics describe at the most fundamental level all chemical interactions.

In fact, many physicists take the position that physics is the only fundamental science. Their argument runs as follows: all sciences--biology, chemistry, geology, etc.--are concerned with matter; all matter is composed of atoms; physics describes the dynamics and internal configurations of atoms. Extension of this physico-centric view can result in profound philosophical consequences. For example, if one accepts that the human brain controls all human behavior, and if one accepts that the brain is composed entirely of atoms whose behavior is completely described by laws of physics, then one may reasonably question whether a person has the free will to control his behavior. Nevertheless it is not the task of physics to answer philosophical questions.

A common goal of theoretical physicists is to reduce the description of the physical world to a minimal set of laws governing a finite set of fundamental constituent elements in the universe. That the physical world can necessarily be completely reduced in such a way is unclear; one could conceive of a world comprised of an infinite variety of particles behaving in accordance with an infinite number of laws, or perhaps behaving entirely randomly on occasion. However, thanks to experimental physicists, physics have been remarkably successful to date at this reduction process, and the reduction trend is evident in the names of some of the proposed theories listed below.

Physics, like other sciences, is often subdivided into categories: theoretical physics and experimental physics or fundamental research and applied physics. Theoretical physicists seek new fundamental knowledge about the universe, using the observations of experimental physicists. Experimental physicists perform experiments designed to be able to decide which theory is true. Experimental physics often finds completely new phenomena with no existing theory, e.g. electromagnetism, radioactivity were discovered this way. Fundamental research quests for the basic structure of nature while applied physicists apply existing knowledge to analyze complex systems in order to use them in practical life and economy. Both fundamental research and applied research has theoretical and experimental aspects. As an example, a particularly fertile area of applied physics is solid-state physics, in which researchers use the more fundamental laws of quantum mechanics and electromagnetism to analyze the behavior of atoms that comprise a solid.

Below is an overview of the major subfields and concepts in physics, followed by a brief outline of the history of physics and its subfields. A more comprehensive list of physics topics is also available.

Overview of physics

Theories

Main article: Theories of Physics

Central theories

Classical mechanics -- Thermodynamics -- Statistical mechanics -- Electromagnetism -- Special relativity -- General relativity -- Quantum mechanics -- Quantum field theory -- Standard Model -- Fluid dynamics

Proposed theories

Theory of everything -- Grand unification theory -- M-theory -- Loop quantum gravity -- Emergence -- Process Physics

Fringe theories

Cold fusion -- Dynamic theory of gravity -- Luminiferous aether -- Orgone energy -- Reciprocal System of Theory -- Steady state theory -- Time Cube -- Unified field theory -- Variable speed of light

Concepts

Matter -- Antimatter -- Elementary particle -- Boson -- Fermion

Symmetry -- Motion -- Conservation law -- Mass -- Energy -- Momentum -- Angular momentum -- Spin

Time -- Space -- Dimension -- Spacetime -- Length -- Velocity -- Force -- Torque

Wave -- Wavefunction -- Quantum entanglement -- Harmonic oscillator -- Magnetism -- Electricity -- Electromagnetic radiation -- Temperature -- Entropy -- Physical information -- Vacuum energy -- Zero-point energy

Phase transitions -- Critical phenomena -- Self-organization -- Spontaneous symmetry breaking -- Superconductivity -- Superfluidity -- Quantum phase transitions

Fundamental forces

Gravitational -- Electromagnetic -- Weak -- Strong

Particles

Main article: Particless

Atom -- Electron -- Gluon -- Graviton -- Neutrino -- Neutron -- Quark -- Photino -- Photon -- Proton -- W and Z bosons -- Particle radiation -- Phonon -- Roton

Bosons -- Fermions -- Supersymmetry -- Higgs boson

Subfields of physics

Accelerator physics -- Acoustics -- Astrophysics -- Atomic, Molecular, and Optical physics -- Computational physics -- Condensed matter physics -- Cosmology -- Cryogenics -- Fluid dynamics -- Polymer physics -- Optics -- Materials physics -- Nuclear physics -- Plasma physics -- Particle physics (or High Energy Physics) -- Vehicle dynamics

Methods

Scientific method -- Physical quantity -- Measurement -- Measuring instruments -- Dimensional analysis -- Statistics--Scaling

Tables

List of physical laws -- Physical constants -- SI base units -- SI derived units -- SI prefixes -- Unit conversions

History

History of Physics -- Famous Physicists -- Nobel Prize in physics

Related Fields

Astronomy -- Biophysics -- Cycles -- Electronics -- Engineering -- Geophysics -- Materials science -- Mathematical physics -- Medical physics -- Physical chemistry -- Physics of computation

A brief history of physics

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. These theories were largely couched in philosophical terms, and never verified by systematic experimental testing. There were exceptions and there are anachronisms: for example, the Greek thinker Archimedes derived many correct quantitative descriptions of mechanics and hydrostatics.

During the early 17th century, Galileo pioneered the use of experiment to validate physical theories, which is the key idea in the scientific method. Galileo formulated and successfully tested several results in dynamics, in particular the Law of Inertia. In 1687, 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.

From the 18th century onwards, thermodynamics was developed by Boyle, Young, and many others. In 1733, 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, and 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, Roentgen discovered X-rays, which turned out to be high-frequency electromagnetic radiation. Radioactivity was discovered in 1896 by Henri Becquerel, and further studied by 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. In 1904, he 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 replace
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