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. 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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Amalie Emmy Noether (US: /ˈnʌtər/, UK: /ˈnɜːtə/; German: [ˈnøːtɐ]; 23 March 1882 – 14 April 1935) was a German mathematician who made many important contributions to abstract algebra. She proved Noether's first and second theorems, which are fundamental in mathematical physics. She was described by Pavel Alexandrov, Albert Einstein, Jean Dieudonné, Hermann Weyl and Norbert Wiener as the most important woman in the history of mathematics. As one of the leading mathematicians of her time, she developed theories of rings, fields, and algebras. In physics, Noether's theorem explains the connection between symmetry and conservation laws.
Noether was born to a Jewish family in the Franconian town of Erlangen; her father was the mathematician Max Noether. She originally planned to teach French and English after passing the required examinations but instead studied mathematics at the University of Erlangen, where her father lectured. After completing her doctorate in 1907 under the supervision of Paul Gordan, she worked at the Mathematical Institute of Erlangen without pay for seven years. At the time, women were largely excluded from academic positions. In 1915, she was invited by David Hilbert and Felix Klein to join the mathematics department at the University of Göttingen, a world-renowned center of mathematical research. The philosophical faculty objected, however, and she spent four years lecturing under Hilbert's name. Her habilitation was approved in 1919, allowing her to obtain the rank of Privatdozent. (Full article...)
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- ... that Femto satellites are the smallest types of satellites, and the Kalam SAT is one of the smallest Femto satellite ever made?
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Plasma lamps are a type of electrodeless gas-discharge lamp energized by radio frequency (RF) power. They are distinct from the novelty plasma lamps that were popular in the 1980s.
The internal-electrodeless lamp was invented by Nikola Tesla after his experimentation with high-frequency currents in evacuated glass tubes for the purposes of lighting and the study of high voltage phenomena. The first practical plasma lamps were the sulfur lamps manufactured by Fusion Lighting. This lamp suffered several practical problems and did not prosper commercially. Plasma lamps with an internal phosphor coating are called external electrode fluorescent lamps (EEFL); these external electrodes or terminal conductors provide the radio frequency electric field. (Full article...)
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These are Good articles, which meet a core set of high editorial standards.
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A waterspout near Thailand in 2016
A waterspout is a rotating column of air that occurs over a body of water, usually appearing as a funnel-shaped cloud in contact with the water and a cumuliform cloud. There are two types of waterspout, each formed by distinct mechanisms. The most common type is a weak vortex known as a "fair weather" or "non-tornadic" waterspout. The other less common type is simply a classic tornado occurring over water rather than land, known as a "tornadic", "supercellular", or "mesocyclonic" waterspout, and accurately a "tornado over water". A fair weather waterspout has a five-part life cycle: formation of a dark spot on the water surface; spiral pattern on the water surface; formation of a spray ring; development of a visible condensation funnel; and ultimately, decay. Most waterspouts do not suck up water.
While waterspouts form mostly in tropical and subtropical areas, they are also reported in Europe, Western Asia (the Middle East), Australia, New Zealand, the Great Lakes, Antarctica, and on rare occasions, the Great Salt Lake. Some are also found on the East Coast of the United States, and the coast of California. Although rare, waterspouts have been observed in connection with lake-effect snow precipitation bands. (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...) -
Decahedral PtFe1.2 nanoparticle.
A fiveling, also known as a decahedral nanoparticle, a multiply-twinned particle (MTP), a pentagonal nanoparticle, a pentatwin, or a five-fold twin is a type of twinned crystal that can exist at sizes ranging from nanometers to millimetres. It contains five different single crystals arranged around a common axis. In most cases each unit has a face centered cubic (fcc) arrangement of the atoms, although they are also known for other types of crystal structure.
They nucleate at quite small sizes in the nanometer range, but can be grown much larger. They have been found in mineral crystals excavated from mines such as pentagonite or native gold from Ukraine, in rods of metals grown via electrochemical processes and in nanoparticles produced by the condensation of metals either onto substrates or in inert gases. They have been investigated for their potential uses in areas such as improving the efficiency of solar cell or heterogeneous catalysis for more efficient production of chemicals. Information about them is distributed across a diverse range of scientific disciplines, mainly chemistry, materials science, mineralogy, nanomaterials and physics. Because many different names have been used, sometimes the information in the different disciplines or within any one discipline is fragmented and overlapping. (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...) -
Fredrik Carl Mülertz Størmer (3 September 1874 – 13 August 1957) was a Norwegian mathematician and astrophysicist. In mathematics, he is known for his work in number theory, including the calculation of π and Størmer's theorem on consecutive smooth numbers. In physics, he is known for studying the movement of charged particles in the magnetosphere and the formation of aurorae, and for his book on these subjects, From the Depths of Space to the Heart of the Atom. He worked for many years as a professor of mathematics at the University of Oslo in Norway. A crater on the far side of the Moon is named after him. (Full article...) -
James Franck (German pronunciation: [ˈdʒɛɪ̯ms ˈfʁaŋk] ⓘ; 26 August 1882 – 21 May 1964) was a German physicist who won the 1925 Nobel Prize in Physics with Gustav Hertz "for their discovery of the laws governing the impact of an electron upon an atom". He completed his doctorate in 1906 and his habilitation in 1911 at the Frederick William University in Berlin, where he lectured and taught until 1918, having reached the position of professor extraordinarius. He served as a volunteer in the German Army during World War I. He was seriously injured in 1917 in a gas attack and was awarded the Iron Cross 1st Class.
Franck became the Head of the Physics Division of the Kaiser Wilhelm Gesellschaft for Physical Chemistry. In 1920, Franck became professor ordinarius of experimental physics and Director of the Second Institute for Experimental Physics at the University of Göttingen. While there he worked on quantum physics with Max Born, who was Director of the Institute of Theoretical Physics. His work included the Franck–Hertz experiment, an important confirmation of the Bohr model of the atom. He promoted the careers of women in physics, notably Lise Meitner, Hertha Sponer and Hilde Levi. (Full article...) -
Schiehallion's isolated position and symmetrical shape were well-suited to the experiment.
The Schiehallion experiment was an 18th-century experiment to determine the mean density of the Earth. Funded by a grant from the Royal Society, it was conducted in the summer of 1774 around the Scottish mountain of Schiehallion, Perthshire. The experiment involved measuring the tiny deflection of the vertical due to the gravitational attraction of a nearby mountain. Schiehallion was considered the ideal location after a search for candidate mountains, thanks to its isolation and almost symmetrical shape.
The experiment had previously been considered, but rejected, by Isaac Newton as a practical demonstration of his theory of gravitation; however, a team of scientists, notably Nevil Maskelyne, the Astronomer Royal, was convinced that the effect would be detectable and undertook to conduct the experiment. The deflection angle depended on the relative densities and volumes of the Earth and the mountain: if the density and volume of Schiehallion could be ascertained, then so could the density of the Earth. Once this was known, it would in turn yield approximate values for those of the other planets, their moons, and the Sun, previously known only in terms of their relative ratios. (Full article...) -
A depiction of the ultrasound signals emitted by a bat, and the echo from a nearby object
Echolocation, also called bio sonar, is a biological active sonar used by several animal groups, both in the air and underwater. Echolocating animals emit calls and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects. Echolocation is used for navigation, foraging, and hunting prey.
Echolocation calls can be frequency modulated (FM, varying in pitch during the call) or constant frequency (CF). FM offers precise range discrimination to localize the prey, at the cost of reduced operational range. CF allows both the prey's velocity and its movements to be detected by means of the Doppler effect. FM may be best for close, cluttered environments, while CF may be better in open environments or for hunting while perched. (Full article...) -
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...) -
In a nuclear weapon, a tamper is an optional layer of dense material surrounding the fissile material. It is used in nuclear weapon design to reduce the critical mass and to delay the expansion of the reacting material through its inertia, which delays the thermal expansion of the fissioning fuel mass, keeping it supercritical longer. Often the same layer serves both as tamper and as neutron reflector. The weapon disintegrates as the reaction proceeds, and this stops the reaction, so the use of a tamper makes for a longer-lasting, more energetic and more efficient explosion. The yield can be further enhanced using a fissionable tamper.
The first nuclear weapons used heavy natural uranium or tungsten carbide tampers, but a heavy tamper necessitates a larger high-explosive implosion system and makes the entire device larger and heavier. The primary stage of a modern thermonuclear weapon may instead use a lightweight beryllium reflector, which is also transparent to X-rays when ionized, allowing the primary's energy output to escape quickly to be used in compressing the secondary stage. More exotic tamper materials such as gold are used for special purposes like emitting large amounts of X-rays or altering the amount of nuclear fallout. (Full article...) -
Facsimile of the Einstein–Szilard letter
The Einstein–Szilard letter was a letter written by Leo Szilard and signed by Albert Einstein on August 2, 1939, that was sent to President of the United States Franklin D. Roosevelt. Written by Szilard in consultation with fellow Hungarian physicists Edward Teller and Eugene Wigner, the letter warned that Germany might develop atomic bombs and suggested that the United States should start its own nuclear program. It prompted action by Roosevelt, which eventually resulted in the Manhattan Project, the development of the first atomic bombs, and the use of these bombs on the cities of Hiroshima and Nagasaki. (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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The state of a vibrating string can be modeled as a point in a Hilbert space. The decomposition of a vibrating string into its vibrations in distinct overtones is given by the projection of the point onto the coordinate axes in the space.
In mathematics, Hilbert spaces (named after David Hilbert) allow the methods of linear algebra and calculus to be generalized from (finite-dimensional) Euclidean vector spaces to spaces that may be infinite-dimensional. Hilbert spaces arise naturally and frequently in mathematics and physics, typically as function spaces. Formally, a Hilbert space is a vector space equipped with an inner product that induces a distance function for which the space is a complete metric space. 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...) -
A History of the Theories of Aether and Electricity is any of three books written by British mathematician Sir Edmund Taylor Whittaker FRS FRSE on the history of electromagnetic theory, covering the development of classical electromagnetism, optics, and aether theories. The book's first edition, subtitled from the Age of Descartes to the Close of the Nineteenth Century, was published in 1910 by Longmans, Green. The book covers the history of aether theories and the development of electromagnetic theory up to the 20th century. A second, extended and revised, edition consisting of two volumes was released in the early 1950s by Thomas Nelson, expanding the book's scope to include the first quarter of the 20th century. The first volume, subtitled The Classical Theories, was published in 1951 and served as a revised and updated edition to the first book. The second volume, subtitled The Modern Theories (1900–1926), was published two years later in 1953, extended this work covering the years 1900 to 1926. Notwithstanding a notorious controversy on Whittaker's views on the history of special relativity, covered in volume two of the second edition, the books are considered authoritative references on the history of electricity and magnetism as well as classics in the history of physics.
The original book was well-received, but it ran out of print by the early 1920s. Whittaker believed that a new edition should include the developments in physics that took part at the turn of the twentieth century and declined to have it reprinted. He wrote the second edition of the book after his retirement and published The Classical Theories in 1951, which also received critical acclaim. In the 1953 second volume, The Modern Theories (1900–1926), Whittaker argued that Henri Poincaré and Hendrik Lorentz developed the theory of special relativity before Albert Einstein, a claim that has been rejected by most historians of science. Though overall reviews of the book were generally positive, due to its role in this relativity priority dispute, it receives far fewer citations than the other volumes, outside of references to the controversy. (Full article...)
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January anniversaries
1 January
- 1894 - Satyendra Nath Bose's birthday.
- 1801 - Giuseppe Piazzi is the first to notice the dwarf planet Ceres. However, very soon astronomers lose sight of its orbital path. After some months, Giuseppe Piazzi finally calculates its correct position on December 31.
- 1985 - Ernie Wise, a comedian, places the first mobile phone call in the UK.
2 January
- 2 January 1822 - Rudolf Clausius was born.
8 January
- 8 January 1942 - Stephen Hawking was born, on the same day that Galileo Galilei died in 1642.
15 January
- 15 January 1908 - Edward Teller was born.
General images
The following are images from various physics-related articles on Wikipedia.
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Sir Isaac Newton (1642–1727) (from History of physics) -
William Thomson (Lord Kelvin)
(1824–1907) (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) -
Image of X-ray diffraction pattern from a protein crystal (from Condensed matter 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) -
Albert Einstein (1879–1955), photographed here in around 1905 (from History of physics) -
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Max Planck (1858–1947) (from History of physics) -
Rudolf Clausius (1822–1888) (from History of physics) -
An artist's rendition of Kepler-62f, a potentially habitable exoplanet discovered using data transmitted by the Kepler space telescope, named after Kepler. (from History of 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) -
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) -
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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) -
Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter 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) -
Alessandro Volta (1745–1827) (from History of physics) -
Ludwig Boltzmann (1844–1906) (from History of physics) -
Richard Feynman's Los Alamos ID badge (from History of physics) -
Gottfried Leibniz (1646–1716) (from History of physics) -
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Daniel Bernoulli (1700–1782) (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) -
Johannes Kepler.(1571–1630) (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) -
Christiaan Huygens (1629–1695) (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) -
Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics) -
A composite montage comparing Jupiter (lefthand side) and its four Galilean moons (top to bottom: Io, Europa, Ganymede, Callisto) (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) -
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) -
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) -
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René Descartes (1596–1650) (from History of physics) -
Michael Faraday (1791–1867) (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) -
Marie Skłodowska-Curie
(1867–1934) was awarded two Nobel prizes, Physics (1903) and Chemistry (1911) (from History of physics) -
James Clerk Maxwell (1831–1879) (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)
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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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