Portal:Physics

Physics is the scientific study of matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. It is one of the most fundamental scientific disciplines. A scientist who specializes in the field of physics is called a physicist.

Physics is one of the oldest academic disciplines. Over much of the past two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the Scientific Revolution in the 17th century, these natural sciences branched into separate research endeavors. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in these and other academic disciplines such as mathematics and philosophy.

Advances in physics often enable new technologies. For example, advances in the understanding of electromagnetism, solid-state physics, and nuclear physics led directly to the development of technologies that have transformed modern society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus. (Full article...)

This is a Featured article, which represents some of the best content on English Wikipedia.

A photon (from Ancient Greek φῶς, φωτός (phôs, phōtós) 'light') is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can move no faster than the speed of light measured in vacuum. The photon belongs to the class of boson particles.

As with other elementary particles, photons are best explained by quantum mechanics and exhibit wave–particle duality, their behavior featuring properties of both waves and particles. The modern photon concept originated during the first two decades of the 20th century with the work of Albert Einstein, who built upon the research of Max Planck. While Planck was trying to explain how matter and electromagnetic radiation could be in thermal equilibrium with one another, he proposed that the energy stored within a material object should be regarded as composed of an integer number of discrete, equal-sized parts. To explain the photoelectric effect, Einstein introduced the idea that light itself is made of discrete units of energy. In 1926, Gilbert N. Lewis popularized the term photon for these energy units. Subsequently, many other experiments validated Einstein's approach. (Full article...)

List of Featured articles

...that if you ever saw Jupiter's magnetic field from Earth, it would appear five times larger than the full moon?

...that the impact of a raindrop would be fatal if not for the property of fluid flow known as terminal velocity?

...that transits of Venus occur in a 243-year cycle?

The heliospheric current sheet extends to the outer reaches of the Solar System, and results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium.

These are Good articles, which meet a core set of high editorial standards.

Image 1

The Wu experiment was a particle and nuclear physics experiment conducted in 1956 by the Chinese American physicist Chien-Shiung Wu in collaboration with the Low Temperature Group of the US National Bureau of Standards. The experiment's purpose was to establish whether conservation of parity (P-conservation), which was previously established in the electromagnetic and strong interactions, also applied to weak interactions. If P-conservation was universal, a mirrored version of the world would behave identically to the mirror image of the current world. If P-conservation were violated, then it would be possible to distinguish between a mirrored version of the world and the mirror image of the current world (where left is mirrored to right and vice versa).

The experiment established that conservation of parity was violated (P-violation) by the weak interaction, thus providing a way to operationally define left and right. This result was not expected by the physics community, which had previously regarded parity as a symmetry that applied to all forces of nature. Tsung-Dao Lee and Chen-Ning Yang, the theoretical physicists who originated the idea of parity nonconservation and proposed the experiment, received the 1957 Nobel Prize in Physics for this result. While not awarded the Nobel Prize, Chien-Shiung Wu's role in the discovery was mentioned in the Nobel Prize acceptance speech of Yang and Lee, but she was not honored until 1978, when she was awarded the first Wolf Prize. (Full article...)
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Joan, Lady Curran (born Joan Elizabeth Strothers; 26 February 1916 – 10 February 1999) was a Welsh physicist who played important roles in the development of radar and the atomic bomb during the Second World War. She devised a method of releasing chaff, a radar countermeasure technique credited with reducing losses among Allied bomber crews. She also worked on the development of the proximity fuse and the electromagnetic isotope separation process for the atomic bomb.

In 1954 she became a founding member of the Scottish Society for the Parents of Mentally Handicapped Children. (Full article...)
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In mathematics, a Hilbert space is a real or complex inner product space that is also a complete metric space with respect to the metric induced by the inner product. It generalizes the notion of Euclidean space. The inner product allows lengths and angles to be defined. Furthermore, completeness means that there are enough limits in the space to allow the techniques of calculus to be used. A Hilbert space is a special case of a Banach space.

Hilbert spaces were studied beginning in the first decade of the 20th century by David Hilbert, Erhard Schmidt, and Frigyes Riesz. They are indispensable tools in the theories of partial differential equations, quantum mechanics, Fourier analysis (which includes applications to signal processing and heat transfer), and ergodic theory (which forms the mathematical underpinning of thermodynamics). John von Neumann coined the term Hilbert space for the abstract concept that underlies many of these diverse applications. The success of Hilbert space methods ushered in a very fruitful era for functional analysis. Apart from the classical Euclidean vector spaces, examples of Hilbert spaces include spaces of square-integrable functions, spaces of sequences, Sobolev spaces consisting of generalized functions, and Hardy spaces of holomorphic functions. (Full article...)
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Quantum mechanics is the fundamental physical theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. It is the foundation of all quantum physics, which includes quantum chemistry, quantum field theory, quantum technology, and quantum information science.

Quantum mechanics can describe many systems that classical physics cannot. Classical physics can describe many aspects of nature at an ordinary (macroscopic and (optical) microscopic) scale, but is not sufficient for describing them at very small submicroscopic (atomic and subatomic) scales. Classical mechanics can be derived from quantum mechanics as an approximation that is valid at ordinary scales. (Full article...)
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Matthew L. Sands Los Alamos ID badge photo

Matthew Linzee Sands (October 20, 1919 – September 13, 2014) was an American physicist and educator best known as a co-author of the Feynman Lectures on Physics. A graduate of Rice University, Sands served with the Naval Ordnance Laboratory and the Manhattan Project's Los Alamos Laboratory during World War II.

After the war, Sands studied cosmic rays for his doctorate at the Massachusetts Institute of Technology (MIT) under the supervision of Bruno Rossi. Sands went to the California Institute of Technology (Caltech) in 1950, and helped build and operate its 1.5 GeV electron synchrotron. He became deputy director for the construction and early operation of the Stanford Linear Accelerator Center (SLAC) in 1963. Sands later joined the University of California, Santa Cruz (UCSC) as a professor of physics, and served as its Vice Chancellor for Science from 1969 to 1972. In 1998, The American Physical Society awarded him the Robert R. Wilson Prize "for his many contributions to accelerator physics and the development of electron-positron and proton colliders." (Full article...)
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Prescod-Weinstein at "Becoming Interplanetary" talk at the Library of Congress, 2018

Chanda Prescod-Weinstein (born c. 1982) is an American theoretical cosmologist and particle physicist at the University of New Hampshire. She is also an advocate of increasing diversity in science. (Full article...)
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Alvarez with a magnetic monopole detector in 1969

Luis Walter Alvarez (June 13, 1911 – September 1, 1988) was an American experimental physicist, inventor, and professor who was awarded the Nobel Prize in Physics in 1968 for his discovery of resonance states in particle physics using the hydrogen bubble chamber. In 2007 the American Journal of Physics commented, "Luis Alvarez was one of the most brilliant and productive experimental physicists of the twentieth century."

After receiving his PhD from the University of Chicago in 1936, Alvarez went to work for Ernest Lawrence at the Radiation Laboratory at the University of California, Berkeley. Alvarez devised a set of experiments to observe K-electron capture in radioactive nuclei, predicted by the beta decay theory but never before observed. He produced tritium using the cyclotron and measured its lifetime. In collaboration with Felix Bloch, he measured the magnetic moment of the neutron. (Full article...)
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A NASA portrait of Levine

Joel S. Levine (born 1942) is an American planetary scientist, author, and research professor in applied science at the College of William & Mary, specializing in the atmospheres of the Moon, Earth, and Mars. He has worked as a senior research scientist at NASA, developing scientific models of the evolution of the Earth's early atmosphere, as well as creating models of the Martian atmosphere for use during the Viking 1 and 2 Mars Orbiter and Lander Missions, and was principal investigator and chief scientist of the proposed ARES Mars Airplane Mission. He also formed and led the "Charters of Freedom Research Team," a group of 12 NASA scientists who worked with the National Archive and Records Administration (NARA) to preserve the United States Declaration of Independence, the Constitution, and the Bill of Rights when small white spots began appearing on the documents in 1988. Levine's past work also includes assisting in the design of the rescue vehicle that saved 33 Chilean miners in the 2010 Copiapó mining accident, as well as original research on the feasibility of the "nuclear winter" hypothesis, and the effects of uncontrolled fires on global warming.

Levine is married to Arlene Spielholz, a former NASA scientist who studied the psychological effects of astronauts spending long time periods in space, and has a daughter and grandson. (Full article...)
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Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to form images of the organs in the body. MRI does not involve X-rays or the use of ionizing radiation, which distinguishes it from computed tomography (CT) and positron emission tomography (PET) scans. MRI is a medical application of nuclear magnetic resonance (NMR) which can also be used for imaging in other NMR applications, such as NMR spectroscopy.

MRI is widely used in hospitals and clinics for medical diagnosis, staging and follow-up of disease. Compared to CT, MRI provides better contrast in images of soft tissues, e.g. in the brain or abdomen. However, it may be perceived as less comfortable by patients, due to the usually longer and louder measurements with the subject in a long, confining tube, although "open" MRI designs mostly relieve this. Additionally, implants and other non-removable metal in the body can pose a risk and may exclude some patients from undergoing an MRI examination safely. (Full article...)
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Born, 1930s

Max Born (German: [ˈmaks ˈbɔʁn] ; 11 December 1882 – 5 January 1970) was a German-British theoretical physicist who was instrumental in the development of quantum mechanics. He also made contributions to solid-state physics and optics, and supervised the work of a number of notable physicists in the 1920s and 1930s. Born shared the 1954 Nobel Prize in Physics with Walther Bothe "for his fundamental research in quantum mechanics, especially in the statistical interpretation of the wave function".

Born entered the University of Göttingen in 1904, where he met the three renowned mathematicians Felix Klein, David Hilbert, and Hermann Minkowski. He wrote his PhD thesis on the subject of the stability of elastic wires and tapes, winning the university's Philosophy Faculty Prize. In 1905, he began researching special relativity with Minkowski, and subsequently wrote his habilitation thesis on the Thomson model of the atom. A chance meeting with Fritz Haber in Berlin in 1918 led to discussion of how an ionic compound is formed when a metal reacts with a halogen, which is today known as the Born–Haber cycle. (Full article...)
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Elda Emma Anderson, physicist and health researcher

Elda Emma Anderson (October 5, 1899 – April 17, 1961) was an American physicist and health researcher. During World War II, she worked on the Manhattan Project at Princeton University and the Los Alamos National Laboratory, where she prepared the first sample of pure uranium-235 at the laboratory. A graduate of the University of Wisconsin, she became professor of physics at Milwaukee-Downer College in 1929. After the war, she became interested in health physics. She worked in the Health Physics Division of the Oak Ridge National Laboratory, and established the professional certification agency known as the American Board of Health Physics. (Full article...)
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In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it.

This is in contrast to an ordinary resistor, in which an increase in applied voltage causes a proportional increase in current in accordance with Ohm's law, resulting in a positive resistance. Under certain conditions, negative resistance can increase the power of an electrical signal, amplifying it. (Full article...)
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A geostationary orbit, also referred to as a geosynchronous equatorial orbit (GEO), is a circular geosynchronous orbit 35,786 km (22,236 mi) in altitude above Earth's equator, 42,164 km (26,199 mi) in radius from Earth's center, and following the direction of Earth's rotation.

An object in such an orbit has an orbital period equal to Earth's rotational period, one sidereal day, and so to ground observers it appears motionless, in a fixed position in the sky. The concept of a geostationary orbit was popularised by the science fiction writer Arthur C. Clarke in the 1940s as a way to revolutionise telecommunications, and the first satellite to be placed in this kind of orbit was launched in 1963. (Full article...)
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Amedeo Avogadro, the constant's namesake

The Avogadro constant, commonly denoted $N A$ or $L$ , is an SI defining constant with an exact value of 6.02214076×10²³ mol⁻¹ when expressed in reciprocal moles. It defines the ratio of the number of constituent particles to the amount of substance in a sample, where the particles in question are any designated elementary entity, such as molecules, atoms, ions, ion pairs. The numerical value of this constant when expressed in terms of the mole is known as the Avogadro number, commonly denoted $N 0$ . The Avogadro number is an exact number equal to the number of constituent particles in one mole of any substance (by definition of the mole), historically derived from the experimental determination of the number of atoms in 12 grams of carbon-12 (¹²C) before the 2019 revision of the SI, i.e. the gram-to-dalton mass-unit ratio, g/Da. Both the constant and the number are named after the Italian physicist and chemist Amedeo Avogadro.

The Avogadro constant is used as a proportionality factor in relating the amount of substance $n (X)$ , in a sample of a substance $X$ , to the corresponding number of elementary entities $N (X)$ :
: $n(\mathrm {X} )={\frac {N(\mathrm {X} )}{N_{\mathrm {A} }}}$ (Full article...)
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In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved. QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons and represents the quantum counterpart of classical electromagnetism giving a complete account of matter and light interaction.

In technical terms, QED can be described as a perturbation theory of the electromagnetic quantum vacuum. Richard Feynman called it "the jewel of physics" for its extremely accurate predictions of quantities like the anomalous magnetic moment of the electron and the Lamb shift of the energy levels of hydrogen. It is the most precise and stringently tested theory in physics. (Full article...)

1 June 1831 – James Clark Ross discovers the North Magnetic Pole.
1 June 1869 – Thomas Edison receives a patent for his electric voting machine.
1 June 1910 – Robert Falcon Scott expedition leaves England for South Pole.
1 June 1978 – First Patent Cooperation Treaty international filings.
1 June 1980 – Cable News Network (CNN) begins broadcasting.
1 June 1990 – Bush and Gorbachev sign chemical weapons ban.
1 June 2000 – Patent Law Treaty is signed.
2 June 1966 – Surveyor 1 lands on the Moon.
2 June 2003 - ESA launches Mars Express probe to Mars.
3 June 1965 - First American spacewalk, mission Gemini IV
3 June 1973 – A Soviet supersonic Tupolev Tu-144 crashes.
4 June 781 BC – First historic solar eclipse is recorded in China.
4 June 1973 – A patent for the ATM is granted.
4 June 1996 - First flight. Ariane 5 rocket explodes after roughly 20 seconds.
5 June 1977 – Apple II, personal computer goes on sale.

The following are images from various physics-related articles on Wikipedia.

Image 1James Clerk Maxwell (1831–1879) (from History of physics)
Image 2A Newton's cradle, named after physicist Isaac Newton (from History of physics)
Image 3Richard Feynman's Los Alamos ID badge (from History of physics)
Image 4Marie Skłodowska-Curie
(1867–1934) received Nobel prizes in physics (1903) and chemistry (1911). (from History of physics)
Image 5Nicolaus Copernicus (1473–1543) developed a heliocentric model of the Solar System. (from History of physics)
Image 6Classical physics (Rayleigh–Jeans law, black line) failed to explain black-body radiation – the so-called ultraviolet catastrophe. The quantum description (Planck's law, colored lines) is said to be modern physics. (from Modern physics)
Image 7William Thomson (Lord Kelvin)
(1824–1907) (from History of physics)
Image 8J.J. Thomson (1856–1940), discoverer of electron and isotopy, and inventor of mass spectrometer, received 1906 Nobel Prize in Physics. (from History of physics)
Image 9One possible signature of a Higgs boson from a simulated proton–proton collision. It decays almost immediately into two jets of hadrons and two electrons, visible as lines. (from History of physics)
Image 10A page from al-Khwārizmī's Algebra. (from History of physics)
Image 11A Feynman diagram representing (left to right) the production of a photon (blue sine wave) from the annihilation of an electron and its complementary antiparticle, the positron. The photon becomes a quark–antiquark pair and a gluon (green spiral) is released. (from History of physics)
Image 12Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter physics)
Image 13Artist's rendition of Kepler-62f, a potentially habitable exoplanet discovered using data transmitted by Kepler space telescope, named for Kepler (from History of physics)
Image 14Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics)
Image 15Einstein proposed that gravitation results from masses (or their equivalent energies) curving ("bending") the spacetime in which they exist, altering the paths they follow within it. (from History of physics)
Image 16Christiaan Huygens (1629–1695) (from History of physics)
Image 17The first Bose–Einstein condensate observed in a gas of ultracold rubidium atoms. The blue and white areas represent higher density. (from Condensed matter physics)
Image 18A replica of the first point-contact transistor in Bell labs (from Condensed matter physics)
Image 19The quantum Hall effect: Components of the Hall resistivity as a function of the external magnetic field (from Condensed matter physics)
Image 20Rudolf Clausius (1822–1888) (from History of physics)
Image 21Galileo Galilei (1564–1642), early proponent of the modern scientific worldview and method (from History of physics)
Image 221927 Solvay Conference included prominent physicists Albert Einstein, Werner Heisenberg, Max Planck, Hendrik Lorentz, Niels Bohr, Marie Curie, Erwin Schrödinger, Paul Dirac (from History of physics)
Image 23Alessandro Volta (1745–1827) (from History of physics)
Image 24The Hindu-Arabic numeral system. The inscriptions on the edicts of Ashoka (3rd century BCE) display this number system being used by the Imperial Mauryas. (from History of physics)
Image 25Composite montage comparing Jupiter (left) and its four Galilean moons (from top: Io, Europa, Ganymede, Callisto) (from History of physics)
Image 26Computer simulation of nanogears made of fullerene molecules. It is hoped that advances in nanoscience will lead to machines working on the molecular scale. (from Condensed matter physics)
Image 27Ibn al-Haytham (c. 965–1040). (from History of physics)
Image 28Daniel Bernoulli (1700–1782) (from History of physics)
Image 29The ancient Greek mathematician Archimedes, developer of ideas regarding fluid mechanics and buoyancy. (from History of physics)
Image 30Albert Einstein (1879–1955), ca. 1905 (from History of physics)
Image 31The Standard Model (from History of physics)
Image 32Michael Faraday (1791–1867) (from History of physics)
Image 33Aristotle (384–322 BCE) (from History of physics)
Image 34Star maps by the 11th century Chinese polymath Su Song are the oldest known woodblock-printed star maps to have survived to the present day. This example, dated 1092, employs the cylindricalequirectangular projection. (from History of physics)
Image 35Johannes Kepler (1571–1630) (from History of physics)
Image 36Gottfried Leibniz (1646–1716) (from History of physics)
Image 37René Descartes (1596–1650) (from History of physics)
Image 38Max Planck (1858–1947) (from History of physics)
Image 39A magnet levitating above a high-temperature superconductor. Today some physicists are working to understand high-temperature superconductivity using the AdS/CFT correspondence. (from Condensed matter physics)
Image 40Classical physics is usually concerned with everyday conditions: speeds are much lower than the speed of light, sizes are much greater than that of atoms, yet very small in astronomical terms. Modern physics, however, is concerned with high velocities, small distances, and very large energies. (from Modern physics)
Image 41Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics)
Image 42Werner Heisenberg (1901–1976) (from History of physics)
Image 43Sir Isaac Newton (1642–1727) (from History of physics)
Image 44Ludwig Boltzmann (1844–1906) (from History of physics)

Other: Physics in fiction | Physics lists | Physics software | Physics stubs

Classical physics traditionally includes the fields of mechanics, optics, electricity, magnetism, acoustics and thermodynamics. The term Modern physics is normally used for fields which rely heavily on quantum theory, including quantum mechanics, atomic physics, nuclear physics, particle physics and condensed matter physics. General and special relativity are usually considered to be part of modern physics as well.

Fundamental Concepts	Classical Physics	Modern Physics	Cross Discipline Topics
Continuum	Solid Mechanics	Fluid Mechanics	Geophysics
Motion	Classical Mechanics	Analytical mechanics	Mathematical Physics
Kinetics	Kinematics	Kinematic chain	Robotics
Matter	Classical states	Modern states	Nanotechnology
Energy	Chemical Physics	Plasma Physics	Materials Science
Cold	Cryophysics	Cryogenics	Superconductivity
Heat	Heat transfer	Transport Phenomena	Combustion
Entropy	Thermodynamics	Statistical mechanics	Phase transitions
Particle	Particulates	Particle physics	Particle accelerator
Antiparticle	Antimatter	Annihilation physics	Gamma ray
Waves	Oscillation	Quantum oscillation	Vibration
Gravity	Gravitation	Gravitational wave	Celestial mechanics
Vacuum	Pressure physics	Vacuum state physics	Quantum fluctuation
Random	Statistics	Stochastic process	Brownian motion
Spacetime	Special Relativity	General Relativity	Black holes
Quantum	Quantum mechanics	Quantum field theory	Quantum computing
Radiation	Radioactivity	Radioactive decay	Cosmic ray
Light	Optics	Quantum optics	Photonics
Electrons	Solid State	Condensed Matter	Symmetry breaking
Electricity	Electrical circuit	Electronics	Integrated circuit
Electromagnetism	Electrodynamics	Quantum Electrodynamics	Chemical Bonds
Strong interaction	Nuclear Physics	Quantum Chromodynamics	Quark model
Weak interaction	Atomic Physics	Electroweak theory	Radioactivity
Standard Model	Fundamental interaction	Grand Unified Theory	Higgs boson
Information	Information science	Quantum information	Holographic principle
Life	Biophysics	Quantum Biology	Astrobiology
Conscience	Neurophysics	Quantum mind	Quantum brain dynamics
Cosmos	Astrophysics	Cosmology	Observable universe
Cosmogony	Big Bang	Mathematical universe	Multiverse
Chaos	Chaos theory	Quantum chaos	Perturbation theory
Complexity	Dynamical system	Complex system	Emergence
Quantization	Canonical quantization	Loop quantum gravity	Spin foam
Unification	Quantum gravity	String theory	Theory of Everything

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