Portal:Physics
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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. Physics 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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A tropical cyclone is a rapidly rotating storm system with a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane (/ˈhʌrɪkən, -keɪn/), typhoon (/taɪˈfuːn/), tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean. A typhoon occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn (120 km/h; 75 mph) or more.
Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface, which ultimately condenses into clouds and rain when moist air rises and cools to saturation. This energy source differs from that of mid-latitude cyclonic storms, such as nor'easters and European windstorms, which are powered primarily by horizontal temperature contrasts. Tropical cyclones are typically between 100 and 2,000 km (62 and 1,243 mi) in diameter. (Full article...)
Did you know -
- ... that lasers can be used to separate two isotopes very efficiently?
- ... that your feet are slightly younger than your head, because time runs slow at a lower Gravitational Potential. This is a consequence of Gravitational Time Dilation
- ...that Max Planck created a system of measurement based solely on natural units?
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Difference between classical and modern physics
While physics aims to discover universal laws, its theories lie in explicit domains of applicability. Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match their predictions. Albert Einstein contributed the framework of special relativity, which replaced notions of absolute time and space with spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light. Max Planck, Erwin Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Later, quantum field theory unified quantum mechanics and special relativity. General relativity allowed for a dynamical, curved spacetime, with which highly massive systems and the large-scale structure of the universe can be well-described. General relativity has not yet been unified with the other fundamental descriptions; several candidate theories of quantum gravity are being developed.
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These are Good articles, which meet a core set of high editorial standards.
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Electrical elastance is the reciprocal of capacitance. The SI unit of elastance is the inverse farad (F−1). The concept is not widely used by electrical and electronic engineers, as the value of capacitors is typically specified in units of capacitance rather than inverse capacitance. However, elastance is used in theoretical work in network analysis and has some niche applications, particularly at microwave frequencies.
The term elastance was coined by Oliver Heaviside through the analogy of a capacitor to a spring. The term is also used for analogous quantities in other energy domains. In the mechanical domain, it corresponds to stiffness, and it is the inverse of compliance in the fluid flow domain, especially in physiology. It is also the name of the generalized quantity in bond-graph analysis and other schemes that analyze systems across multiple domains. (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...) -
Samuel King Allison (November 13, 1900 – September 15, 1965) was an American physicist, most notable for his role in the Manhattan Project, for which he was awarded the Medal for Merit. A professor who studied X-rays, he was director of the Metallurgical Laboratory from 1943 until 1944, and later worked at the Los Alamos Laboratory — where he "rode herd" on the final stages of the project as part of the "Cowpuncher Committee", and read the countdown for the detonation of the Trinity nuclear test. After the war, he returned to the University of Chicago to direct the Institute for Nuclear Studies and was involved in the "scientists' movement", lobbying for civilian control of nuclear weapons. (Full article...) -
James Chadwick at the 1933 Solvay Conference. Chadwick had discovered the neutron the year before while working at Cavendish Laboratory.
The discovery of the neutron and its properties was central to the extraordinary developments in atomic physics in the first half of the 20th century. Early in the century, Ernest Rutherford developed a crude model of the atom, based on the gold foil experiment of Hans Geiger and Ernest Marsden. In this model, atoms had their mass and positive electric charge concentrated in a very small nucleus. By 1920, isotopes of chemical elements had been discovered, the atomic masses had been determined to be (approximately) integer multiples of the mass of the hydrogen atom, and the atomic number had been identified as the charge on the nucleus. Throughout the 1920s, the nucleus was viewed as composed of combinations of protons and electrons, the two elementary particles known at the time, but that model presented several experimental and theoretical contradictions.
The essential nature of the atomic nucleus was established with the discovery of the neutron by James Chadwick in 1932 and the determination that it was a new elementary particle, distinct from the proton. (Full article...) -
Eugene Paul Wigner (Hungarian: Wigner Jenő Pál, pronounced [ˈviɡnɛr ˈjɛnøː ˈpaːl]; November 17, 1902 – January 1, 1995) was a Hungarian-American theoretical physicist who also contributed to mathematical physics. He received the Nobel Prize in Physics in 1963 "for his contributions to the theory of the atomic nucleus and the elementary particles, particularly through the discovery and application of fundamental symmetry principles".
A graduate of the Technical Hochschule Berlin (now Technische Universität Berlin), Wigner worked as an assistant to Karl Weissenberg and Richard Becker at the Kaiser Wilhelm Institute in Berlin, and David Hilbert at the University of Göttingen. Wigner and Hermann Weyl were responsible for introducing group theory into physics, particularly the theory of symmetry in physics. Along the way he performed ground-breaking work in pure mathematics, in which he authored a number of mathematical theorems. In particular, Wigner's theorem is a cornerstone in the mathematical formulation of quantum mechanics. He is also known for his research into the structure of the atomic nucleus. In 1930, Princeton University recruited Wigner, along with John von Neumann, and he moved to the United States, where he obtained citizenship in 1937. (Full article...) -
Quantum Reality is a 1985 popular science book by physicist Nick Herbert, a member of the Fundamental Fysiks Group which was formed to explore the philosophical implications of quantum theory. The book attempts to address the ontology of quantum objects, their attributes, and their interactions, without reliance on advanced mathematical concepts. Herbert discusses the most common interpretations of quantum mechanics and their consequences in turn, highlighting the conceptual advantages and drawbacks of each. (Full article...)
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Units in everyday use by country as of 2019
The history of the metric system began during the Age of Enlightenment with measures of length and weight derived from nature, along with their decimal multiples and fractions. The system became the standard of France and Europe within half a century. Other measures with unity ratios were added, and the system went on to be adopted across the world.
The first practical realisation of the metric system came in 1799, during the French Revolution, after the existing system of measures had become impractical for trade, and was replaced by a decimal system based on the kilogram and the metre. The basic units were taken from the natural world. The unit of length, the metre, was based on the dimensions of the Earth, and the unit of mass, the kilogram, was based on the mass of a volume of water of one litre (a cubic decimetre). Reference copies for both units were manufactured in platinum and remained the standards of measure for the next 90 years. After a period of reversion to the mesures usuelles due to unpopularity of the metric system, the metrication of France and much of Europe was complete by the 1850s. (Full article...) -
The expanding remnant of SN 1987A, a peculiar Type II supernova in the Large Magellanic Cloud. NASA image.
A Type II supernova or SNII (plural: supernovae) results from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun (M☉) to undergo this type of explosion. Type II supernovae are distinguished from other types of supernovae by the presence of hydrogen in their spectra. They are usually observed in the spiral arms of galaxies and in H II regions, but not in elliptical galaxies; those are generally composed of older, low-mass stars, with few of the young, very massive stars necessary to cause a supernova.
Stars generate energy by the nuclear fusion of elements. Unlike the Sun, massive stars possess the mass needed to fuse elements that have an atomic mass greater than hydrogen and helium, albeit at increasingly higher temperatures and pressures, causing correspondingly shorter stellar life spans. The degeneracy pressure of electrons and the energy generated by these fusion reactions are sufficient to counter the force of gravity and prevent the star from collapsing, maintaining stellar equilibrium. The star fuses increasingly higher mass elements, starting with hydrogen and then helium, progressing up through the periodic table until a core of iron and nickel is produced. Fusion of iron or nickel produces no net energy output, so no further fusion can take place, leaving the nickel–iron core inert. Due to the lack of energy output creating outward thermal pressure, the core contracts due to gravity until the overlying weight of the star can be supported largely by electron degeneracy pressure. (Full article...) -
Sir Chandrasekhara Venkata Raman FRS (/ˈrɑːmən/; 7 November 1888 – 21 November 1970) known as C. V. Raman or just Venkata Raman, was an Indian physicist known for his work in the field of light scattering. Using a spectrograph that he developed, he and his student K. S. Krishnan discovered that when light traverses a transparent material, the deflected light changes its wavelength. This phenomenon, a hitherto unknown type of scattering of light, which they called "modified scattering" was subsequently termed the Raman effect or Raman scattering. Raman received the 1930 Nobel Prize in Physics for the discovery and was the first Asian and the first non-White to receive a Nobel Prize in any branch of science.
Born to Tamil Brahmin parents, completing his secondary and higher secondary education from St Aloysius' Anglo-Indian High School at the age of 11 and 13, respectively. He topped the bachelor's degree examination of the University of Madras with honours in physics from Presidency College at age 16. His first research paper, on diffraction of light, was published in 1906 while he was still a graduate student. The next year he obtained a master's degree. He joined the Indian Finance Service in Calcutta as Assistant Accountant General at age 19. There he became acquainted with the Indian Association for the Cultivation of Science (IACS), the first research institute in India, which allowed him to carry out independent research and where he made his major contributions in acoustics and optics. (Full article...) -
A Type Ia supernova (read: "type one-A") is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.
Physically, carbon–oxygen white dwarfs with a low rate of rotation are limited to below 1.44 solar masses (M☉). Beyond this "critical mass", they reignite and in some cases trigger a supernova explosion; this critical mass is often referred to as the Chandrasekhar mass, but is marginally different from the absolute Chandrasekhar limit, where electron degeneracy pressure is unable to prevent catastrophic collapse. If a white dwarf gradually accretes mass from a binary companion, or merges with a second white dwarf, the general hypothesis is that a white dwarf's core will reach the ignition temperature for carbon fusion as it approaches the Chandrasekhar mass. Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction, releasing enough energy (1×1044 J) to unbind the star in a supernova explosion. (Full article...) -
Edward Uhler Condon (March 2, 1902 – March 26, 1974) was an American nuclear physicist, a pioneer in quantum mechanics, and a participant during World War II in the development of radar and, very briefly, of nuclear weapons as part of the Manhattan Project. The Franck–Condon principle and the Slater–Condon rules are co-named after him.
He was the director of the National Bureau of Standards (now NIST) from 1945 to 1951. In 1946, Condon was president of the American Physical Society, and in 1953 was president of the American Association for the Advancement of Science. (Full article...) -
The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from sub-atomic particles to entire galactic filaments. Since the early 20th century, the field of cosmology establishes that space and time emerged together at the Big Bang 13.787±0.020 billion years ago and that the universe subsequently expanded. Today, the universe has expanded into an age and size that is only partially observable from Earth; while the spatial size of the entire universe is unknown, the smaller observable universe is approximately 93 billion light-years in diameter at present.
Some of the earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center. Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of universal gravitation, Isaac Newton built upon Copernicus's work as well as Johannes Kepler's laws of planetary motion and observations by Tycho Brahe. (Full article...) -
Robert Frederick Christy (May 14, 1916 – October 3, 2012) was a Canadian-American theoretical physicist and later astrophysicist who was one of the last surviving people to have worked on the Manhattan Project during World War II. He briefly served as acting president of California Institute of Technology (Caltech).
A graduate of the University of British Columbia (UBC) in the 1930s where he studied physics, he followed George Volkoff, who was a year ahead of him, to the University of California, Berkeley, where he was accepted as a graduate student by Robert Oppenheimer, the leading theoretical physicist in the United States at that time. Christy received his doctorate in 1941 and joined the physics department of Illinois Institute of Technology. (Full article...) -
An extratropical cyclone near Iceland
In meteorology, a cyclone (/ˈsaɪ.kloʊn/) is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above (opposite to an anticyclone). Cyclones are characterized by inward-spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale (the synoptic scale). Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes, and dust devils lie within the smaller mesoscale.
Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream. (Full article...) -
A kilogram mass and three metric measuring devices: a tape measure in centimetres, a thermometer in degrees Celsius, and a multimeter that measures potential in volts, current in amperes and resistance in ohms.
The metric system is a decimal-based system of measurement. The current international standard for the metric system is the International System of Units (Système international d'unités or SI), in which all units can be expressed in terms of seven base units: the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). These can be made into larger or smaller units with the use of metric prefixes.
SI derived units are named combinations – such as the hertz (cycles per second), newton (kg⋅m/s2), and tesla (1 kg⋅s−2⋅A−1) – or a shifted scale, in the case of degrees Celsius. Certain units have been officially accepted for use with the SI. Some of these are decimalised, like the litre and electronvolt, and are considered "metric". Others, like the astronomical unit are not. Ancient non-metric but SI-accepted multiples of time (minute and hour) and angle (degree, arcminute, and arcsecond) are sexagesimal (base 60). (Full article...)
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November anniversaries
- 1952 - detonation of the first Hydrogen bomb, code named "Ivy Mike".
- 1947 - invention of the first transistor, between November 17 to December 23. APS.
- 1930 - Patent granted for Einstein-Szilard refrigerator designed by Albert Einstein and Leó Szilárd. APS.
- 1919 - Elmer Imes's published work presented the first accurate measurement of the distance between atoms in molecules with high resolution infrared spectroscopy. APS.
- 1915 – Einstein's presentation to the Prussian Academy of Science specifies how the geometry of space and time is influenced by whatever matter is present. (see: General relativity and APS)
- 1895 - Wilhelm Conrad Roentgen discovers X-rays.
- 1887 - Michelson–Morley experiment provided strong evidence against the luminiferous ether. APS.
- 1872 - death of Mary Somerville who gained an international reputation as a scientist in the intervals of raising a family of six children. APS
- 1783 - John Michell predicted the existence of black holes, and the possibility of a luminous twin to aid in detection. APS
- 1676 – using his first quantitative measurement of the speed of light, Ole Rømer accurately predicts the delay of eclipse of Io
Births
- 1934 – Carl Sagan
- 1932 - Melvin Schwartz
- 1929 - Richard E. Taylor
- 1925 - Simon van der Meer
- 1902 - Eugene Wigner
- 1837 - Johannes Diderik van der Waals
- 1867 - Marie Curie (Nov. 7)
- 1828 - Balfour Stewart
- 1878 - Lise Meitner (Nov. 7)
- 1887 - Henry Moseley
- 1888 - C V Raman (Nov. 7)
- 1892 - Dmitri Skobeltsyn (Nov. 24)
General images
The following are images from various physics-related articles on Wikipedia.
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A composite montage comparing Jupiter (lefthand side) and its four Galilean moons (top to bottom: Io, Europa, Ganymede, Callisto) (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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The Standard Model (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) -
Albert Einstein (1879–1955), photographed here in around 1905 (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 cylindrical equirectangular projection. (from History of physics) -
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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) -
Einstein proposed that gravitation is a result of masses (or their equivalent energies) curving ("bending") the spacetime in which they exist, altering the paths they follow within it. (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) -
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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) -
Richard Feynman's Los Alamos ID badge (from History of physics) -
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Marie Skłodowska-Curie
(1867–1934) She was awarded two Nobel prizes, Physics (1903) and Chemistry (1911) (from History of physics) -
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Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics) -
J. J. Thomson (1856–1940) discovered the electron and isotopy and also invented the mass spectrometer. He was awarded the Nobel Prize in Physics in 1906. (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) -
Sir Isaac Newton
(1642–1727) (from History of physics) -
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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) -
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Galileo Galilei, early proponent of the modern scientific worldview and method
(1564–1642) (from History of physics) -
The ancient Greek mathematician Archimedes, developer of ideas regarding fluid mechanics and buoyancy. (from History of physics) -
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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 Polish astronomer Nicolaus Copernicus (1473–1543) is remembered for his development of a heliocentric model of the Solar System. (from History of physics) -
William Thomson (Lord Kelvin)
(1824–1907) (from History of physics) -
Christiaan Huygens
(1629–1695) (from History of physics) -
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) -
Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter physics) -
Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (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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