Portal:Physics
The Physics Portal
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...)
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The speed of light in vacuum, commonly denoted c, is a universal physical constant exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1⁄299792458 second. According to the special theory of relativity, c is the upper limit for the speed at which conventional matter, or energy, can travel through space.
All forms of electromagnetic radiation, including visible light, travel at the speed of light. For many practical purposes, light and other electromagnetic waves will appear to propagate instantaneously, but for long distances and sensitive measurements, their finite speed has noticeable effects. Much starlight viewed on Earth is from the distant past, allowing humans to study the history of the universe by viewing distant objects. When communicating with distant space probes, it can take hours for signals to travel. In computing, the speed of light fixes the ultimate minimum communication delay. The speed of light can be used in time of flight measurements to measure large distances to extremely high precision. (Full article...)
Did you know -
- ... that nuclear fusion reactions are probably occurring at or above the sun's photosphere; it is a process called solar surface fusion.
- ... that the submarine telescope ANTARES, intended to detect neutrinos, may also be used to observe bioluminescent plankton and fish?
- ... that a touch flash releases about a billion photons a second far less than produced in a particle accelerator?
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An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the early 1800s, was the first practical electric light. It was widely used starting in the 1870s for street and large building lighting until it was superseded by the incandescent light in the early 20th century. It continued in use in more specialized applications where a high intensity point light source was needed, such as searchlights and movie projectors until after World War II.
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The 15 kW xenon short-arc lamp used in the IMAX projection system -
A mercury arc lamp from a fluorescence microscope -
A krypton long arc lamp (top) is shown above a xenon flashtube. The two lamps, used for laser pumping, are very different in the shape of the electrodes, in particular, the cathode, (on the left). -
A krypton arc lamp during operation. -
An electric arc, demonstrating the “arch” effect
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Klaus Emil Julius Fuchs (29 December 1911 – 28 January 1988) was a German theoretical physicist and atomic spy who supplied information from the American, British, and Canadian Manhattan Project to the Soviet Union during and shortly after World War II. While at the Los Alamos Laboratory, Fuchs was responsible for many significant theoretical calculations relating to the first nuclear weapons and, later, early models of the hydrogen bomb. After his conviction in 1950, he served nine years in prison in the United Kingdom, then migrated to East Germany where he resumed his career as a physicist and scientific leader.
The son of a Lutheran pastor, Fuchs attended the University of Leipzig, where his father was a professor of theology, and became involved in student politics, joining the student branch of the Social Democratic Party of Germany (SPD), and the Reichsbanner Schwarz-Rot-Gold, an SPD-allied paramilitary organisation. He was expelled from the SPD in 1932, and joined the Communist Party of Germany (KPD). He went into hiding after the 1933 Reichstag fire and the subsequent persecution of communists in Nazi Germany, and fled to the United Kingdom, where he received his PhD from the University of Bristol under the supervision of Nevill Francis Mott, and his DSc from the University of Edinburgh, where he worked as an assistant to Max Born. (Full article...) -
Flash X-Ray images of the converging shock waves formed during a test of the high explosive lens system.
The RaLa Experiment, or RaLa, was a series of tests during and after the Manhattan Project designed to study the behavior of converging shock waves to achieve the spherical implosion necessary for compression of the plutonium pit of the nuclear weapon. The experiment used significant amounts of a short-lived radioisotope lanthanum-140, a potent source of gamma radiation; the RaLa is a contraction of Radioactive Lanthanum. The method was proposed by Robert Serber and developed by a team led by the Italian experimental physicist Bruno Rossi.
The tests were performed with 1⁄8 inch (3.2 mm) spheres of radioactive lanthanum, equal to about 100 curies (3.7 TBq) and later 1,000 Ci (37 TBq), located in the center of a simulated nuclear device. The explosive lenses were designed primarily using this series of tests. Some 254 tests were conducted between September 1944 and March 1962. In his history of the Los Alamos project, David Hawkins wrote: “RaLa became the most important single experiment affecting the final bomb design”. (Full article...) -
Ernest Orlando Lawrence (August 8, 1901 – August 27, 1958) was an American physicist who received the Nobel Prize in Physics in 1939 for his invention of the cyclotron. He is known for his work on uranium-isotope separation for the Manhattan Project, as well as for founding the Lawrence Berkeley National Laboratory and the Lawrence Livermore National Laboratory.
A graduate of the University of South Dakota and University of Minnesota, Lawrence obtained a PhD in physics at Yale in 1925. In 1928, he was hired as an associate professor of physics at the University of California, Berkeley, becoming the youngest full professor there two years later. In its library one evening, Lawrence was intrigued by a diagram of an accelerator that produced high-energy particles. He contemplated how it could be made compact, and came up with an idea for a circular accelerating chamber between the poles of an electromagnet. The result was the first cyclotron. (Full article...) -
Geocentric celestial spheres; Peter Apian's Cosmographia (Antwerp, 1539)
The celestial spheres, or celestial orbs, were the fundamental entities of the cosmological models developed by Plato, Eudoxus, Aristotle, Ptolemy, Copernicus, and others. In these celestial models, the apparent motions of the fixed stars and planets are accounted for by treating them as embedded in rotating spheres made of an aetherial, transparent fifth element (quintessence), like gems set in orbs. Since it was believed that the fixed stars did not change their positions relative to one another, it was argued that they must be on the surface of a single starry sphere.
In modern thought, the orbits of the planets are viewed as the paths of those planets through mostly empty space. Ancient and medieval thinkers, however, considered the celestial orbs to be thick spheres of rarefied matter nested one within the other, each one in complete contact with the sphere above it and the sphere below. When scholars applied Ptolemy's epicycles, they presumed that each planetary sphere was exactly thick enough to accommodate them. By combining this nested sphere model with astronomical observations, scholars calculated what became generally accepted values at the time for the distances to the Sun: about 4 million miles (6.4 million kilometres), to the other planets, and to the edge of the universe: about 73 million miles (117 million kilometres). The nested sphere model's distances to the Sun and planets differ significantly from modern measurements of the distances, and the size of the universe is now known to be inconceivably large and continuously expanding. (Full article...) -
Arne Edwin Slettebak (August 8, 1925 – May 20, 1999) was an American astronomer who served as chair of the astronomy department at the Ohio State University from 1962 to 1987 and director of the Perkins Observatory from 1959 to 1978.
Slettebak was born in the Free City of Danzig before emigrating to the United States at a young age. He obtained a degree in physics in 1945 and his doctorate in astronomy in 1949, the latter under the supervision of William Wilson Morgan with a thesis on O-type and B-type stars. Slettebak joined the Ohio State University shortly after graduating and was instrumental in re-establishing a separate astronomy department there. His principal research interests were in stellar rotation and Be stars, and he published over 90 papers, abstracts and articles. (Full article...) -
James Clerk Maxwell FRS FRSE (13 June 1831 – 5 November 1879) was a Scottish physicist and mathematician who was responsible for the classical theory of electromagnetic radiation, which was the first theory to describe electricity, magnetism and light as different manifestations of the same phenomenon. Maxwell's equations for electromagnetism achieved the second great unification in physics, where the first one had been realised by Isaac Newton. Maxwell was also key in the creation of statistical mechanics.
With the publication of "A Dynamical Theory of the Electromagnetic Field" in 1865, Maxwell demonstrated that electric and magnetic fields travel through space as waves moving at the speed of light. He proposed that light is an undulation in the same medium that is the cause of electric and magnetic phenomena. The unification of light and electrical phenomena led to his prediction of the existence of radio waves, and the paper contained his final version of his equations, which he had been working on since 1856. As a result of his equations, and other contributions such as introducing an effective method to deal with network problems and linear conductors, he is regarded as a founder of the modern field of electrical engineering. In 1871, Maxwell became the first Cavendish Professor of Physics, serving until his death in 1879. (Full article...) -
Katharine "Kay" Way (February 20, 1902 – December 9, 1995) was an American physicist best known for her work on the Nuclear Data Project. During World War II, she worked for the Manhattan Project at the Metallurgical Laboratory in Chicago. She became an adjunct professor at Duke University in 1968. (Full article...)
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Fourteenth-century drawing of angels turning the celestial spheres
Ancient, medieval and Renaissance astronomers and philosophers developed many different theories about the dynamics of the celestial spheres. They explained the motions of the various nested spheres in terms of the materials of which they were made, external movers such as celestial intelligences, and internal movers such as motive souls or impressed forces. Most of these models were qualitative, although a few of them incorporated quantitative analyses that related speed, motive force and resistance. (Full article...) -
Nikola Tesla (/ˈnɪkələ ˈtɛslə/; Serbian Cyrillic: Никола Тесла [nǐkola têsla]; 10 July 1856 – 7 January 1943) was a Serbian-American engineer, futurist, and inventor. He is known for his contributions to the design of the modern alternating current (AC) electricity supply system.
Born and raised in the Austrian Empire, Tesla first studied engineering and physics in the 1870s without receiving a degree. He then gained practical experience in the early 1880s working in telephony and at Continental Edison in the new electric power industry. In 1884 he immigrated to the United States, where he became a naturalized citizen. He worked for a short time at the Edison Machine Works in New York City before he struck out on his own. With the help of partners to finance and market his ideas, Tesla set up laboratories and companies in New York to develop a range of electrical and mechanical devices. His AC induction motor and related polyphase AC patents, licensed by Westinghouse Electric in 1888, earned him a considerable amount of money and became the cornerstone of the polyphase system which that company eventually marketed. (Full article...) -
Aage Niels Bohr (Danish: [ˈɔːwə ˈne̝ls ˈpoɐ̯ˀ] ⓘ; 19 June 1922 – 8 September 2009) was a Danish nuclear physicist who shared the Nobel Prize in Physics in 1975 with Ben Roy Mottelson and James Rainwater "for the discovery of the connection between collective motion and particle motion in atomic nuclei and the development of the theory of the structure of the atomic nucleus based on this connection". His father was Niels Bohr.
Starting from Rainwater's concept of an irregular-shaped liquid drop model of the nucleus, Bohr and Mottelson developed a detailed theory that was in close agreement with experiments. (Full article...) -
Sir John Douglas Cockcroft (27 May 1897 – 18 September 1967) was a British physicist who shared the 1951 Nobel Prize in Physics with Ernest Walton for their splitting of the atomic nucleus, which was instrumental in the development of nuclear power.
After service on the Western Front with the Royal Field Artillery during the Great War, Cockcroft studied electrical engineering at Manchester Municipal College of Technology whilst he was an apprentice at Metropolitan Vickers Trafford Park and was also a member of their research staff. He then won a scholarship to St. John's College, Cambridge, where he sat the tripos exam in June 1924, becoming a wrangler. Ernest Rutherford accepted Cockcroft as a research student at the Cavendish Laboratory, and Cockcroft completed his doctorate under Rutherford's supervision in 1928. With Walton and Mark Oliphant, he built what became known as a Cockcroft–Walton generator. Cockcroft and Walton used this to perform the first artificial disintegration of an atomic nucleus, a feat popularly known as splitting the atom. (Full article...) -
Albert Francis Birch (August 22, 1903 – January 30, 1992) was an American geophysicist. He is considered one of the founders of solid Earth geophysics. He is also known for his part in the atomic bombing of Hiroshima and Nagasaki.
During World War II, Birch participated in the Manhattan Project, working on the design and development of the gun-type nuclear weapon known as Little Boy. He oversaw its manufacture, and went to Tinian to supervise its assembly and loading into Enola Gay, the Boeing B-29 Superfortress tasked with dropping the bomb. (Full article...) -
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...) -
Christiaan Huygens, Lord of Zeelhem, FRS (/ˈhaɪɡənz/ HY-gənz, US also /ˈhɔɪɡənz/ HOY-gənz; Dutch: [ˈkrɪstijaːn ˈɦœyɣə(n)s] ⓘ; also spelled Huyghens; Latin: Hugenius; 14 April 1629 – 8 July 1695) was a Dutch mathematician, physicist, engineer, astronomer, and inventor who is regarded as a key figure in the Scientific Revolution. In physics, Huygens made seminal contributions to optics and mechanics, while as an astronomer he studied the rings of Saturn and discovered its largest moon, Titan. As an engineer and inventor, he improved the design of telescopes and invented the pendulum clock, the most accurate timekeeper for almost 300 years. A talented mathematician and physicist, his works contain the first idealization of a physical problem by a set of mathematical parameters, and the first mathematical and mechanistic explanation of an unobservable physical phenomenon.
Huygens first identified the correct laws of elastic collision in his work De Motu Corporum ex Percussione, completed in 1656 but published posthumously in 1703. In 1659, Huygens derived geometrically the formula in classical mechanics for the centrifugal force in his work De vi Centrifuga, a decade before Isaac Newton. In optics, he is best known for his wave theory of light, which he described in his Traité de la Lumière (1690). His theory of light was initially rejected in favour of Newton's corpuscular theory of light, until Augustin-Jean Fresnel adapted Huygens's principle to give a complete explanation of the rectilinear propagation and diffraction effects of light in 1821. Today this principle is known as the Huygens–Fresnel principle. (Full article...) -
Incoming wave (red) reflected at the wall produces the outgoing wave (blue), both being overlaid resulting in the clapotis (black).
In hydrodynamics, a clapotis (from French for "lapping of water") is a non-breaking standing wave pattern, caused for example, by the reflection of a traveling surface wave train from a near vertical shoreline like a breakwater, seawall or steep cliff.
The resulting clapotic wave does not travel horizontally, but has a fixed pattern of nodes and antinodes.
These waves promote erosion at the toe of the wall, and can cause severe damage to shore structures. The term was coined in 1877 by French mathematician and physicist Joseph Valentin Boussinesq who called these waves 'le clapotis' meaning "the lapping".
In the idealized case of "full clapotis" where a purely monotonic incoming wave is completely reflected normal to a solid vertical wall,
the standing wave height is twice the height of the incoming waves at a distance of one half wavelength from the wall.
In this case, the circular orbits of the water particles in the deep-water wave are converted to purely linear motion, with vertical velocities at the antinodes, and horizontal velocities at the nodes. (Full article...)
April anniversaries
- 1 April 1997 – Comet Hale-Bopp at perihelion
- 12 April 1633 – Galileo Galilei's trial starts
- 15 April 1707 – Leonhard Euler's birthday
- 18 April 1955 – Albert Einstein's death
- 22 April 1904 – J. Robert Oppenheimer's birthday
- 23 April 1858 – Max Planck's birthday
- 24 April 1990 – Hubble Space Telescope launched
- 25 April 1990 – Hubble Space Telescope deployed from the shuttle Discovery
- 30 April 1777 – Carl Friedrich Gauss's birthday
General images
The following are images from various physics-related articles on Wikipedia.
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Christiaan Huygens (1629–1695) (from History of physics) -
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J.J. Thomson (1856–1940), discoverer of electron and isotopy, and inventor of mass spectrometer, received 1906 Nobel Prize in Physics. (from History of physics) -
James Clerk Maxwell (1831–1879) (from History of physics) -
Artist's rendition of Kepler-62f, a potentially habitable exoplanet discovered using data transmitted by Kepler space telescope, named for Kepler (from History of physics) -
One 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) -
The quantum Hall effect: Components of the Hall resistivity as a function of the external magnetic field (from Condensed matter physics) -
Computer 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) -
Ludwig Boltzmann (1844–1906) (from History of physics) -
Sir Isaac Newton (1642–1727) (from History of physics) -
Rudolf Clausius (1822–1888) (from History of physics) -
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Classical 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) -
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Gottfried Leibniz (1646–1716) (from History of physics) -
Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics) -
Alessandro Volta (1745–1827) (from History of physics) -
Albert Einstein (1879–1955), ca. 1905 (from History of physics) -
Nicolaus Copernicus (1473–1543) developed a heliocentric model of the Solar System. (from History of physics) -
Richard Feynman's Los Alamos ID badge (from History of physics) -
Classical 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) -
Johannes Kepler (1571–1630) (from History of physics) -
A 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) -
Marie Skłodowska-Curie
(1867–1934) received Nobel prizes in physics (1903) and chemistry (1911). (from History of physics) -
The ancient Greek mathematician Archimedes, developer of ideas regarding fluid mechanics and buoyancy. (from History of physics) -
René Descartes (1596–1650) (from History of physics) -
1927 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) -
Michael Faraday (1791–1867) (from History of physics) -
Max Planck (1858–1947) (from History of physics) -
Einstein 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) -
Daniel Bernoulli (1700–1782) (from History of physics) -
Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter physics) -
The 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) -
The first Bose–Einstein condensate observed in a gas of ultracold rubidium atoms. The blue and white areas represent higher density. (from Condensed matter physics) -
William Thomson (Lord Kelvin)
(1824–1907) (from History of physics) -
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Galileo Galilei (1564–1642), early proponent of the modern scientific worldview and method (from History of physics) -
Composite montage comparing Jupiter (left) and its four Galilean moons (from top: Io, Europa, Ganymede, Callisto) (from History of physics) -
The Standard Model (from History of physics) -
Star 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) -
Werner Heisenberg (1901–1976) (from History of physics) -
Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics) -
A 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)
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Physics topics
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.
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