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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. 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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Louis Alexander Slotin (/ˈsloʊtɪn/ SLOHT-in; 1 December 1910 – 30 May 1946) was a Canadian physicist and chemist who took part in the Manhattan Project. Born and raised in the North End of Winnipeg, Manitoba, Slotin earned both his Bachelor of Science and Master of Science degrees from the University of Manitoba, before obtaining his doctorate in physical chemistry at King's College London in 1936. Afterwards, he joined the University of Chicago as a research associate to help design a cyclotron.
In 1942, Slotin was invited to participate in the Manhattan Project, and subsequently performed experiments with uranium and plutonium cores to determine their critical mass values. After World War II, he continued his research at Los Alamos National Laboratory in New Mexico. On 21 May 1946, he accidentally triggered a supercritical nuclear chain reaction, which released a burst of hard radiation. He was rushed to the hospital and died nine days later on 30 May. Slotin had become the second fatal victim of a criticality accident in history, following Harry Daghlian, who had died of a related accident with the same plutonium "demon core" the previous year. (Full article...)
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Sir Harrie Stewart Wilson Massey FRS (16 May 1908 – 27 November 1983) was an Australian mathematical physicist who worked primarily in the fields of atomic and atmospheric physics.
A graduate of the University of Melbourne and the University of Cambridge, where he earned his doctorate at the Cavendish Laboratory, Massey became an independent lecturer in Mathematical Physics at the Queen's University of Belfast in 1933. He was appointed Goldsmid Professor of Applied Mathematics at University College London, in 1938. During the Second World War, Massey worked at the Admiralty Research Laboratory, where he helped devise countermeasures for German magnetic naval mines, and at the Admiralty Mining Establishment in Havant, where he helped develop British naval mines. In 1943, Mark Oliphant persuaded the Admiralty to release Massey to work on the Manhattan Project. He joined Oliphant's British Mission at the Radiation Laboratory at the University of California, where they worked on the electromagnetic isotope separation process. When Oliphant returned to Britain in 1945, Massey took over the Berkeley Mission. (Full article...)
The missing aircraft (9M-MRO) seen in 2013.
The analysis of communications between Malaysia Airlines Flight 370 and Inmarsat's satellite telecommunication network provide the primary source of information about Flight 370's location and possible in-flight events after it disappeared from military radar coverage at 02:22 Malaysia Standard Time (MYT) on 8 March 2014 (17:22 UTC, 7 March), one hour after communication with air traffic control ended and the aircraft departed from its planned flight path while over the South China Sea.
Flight 370 was a scheduled commercial flight with 227 passengers and 12 crew which departed Kuala Lumpur, Malaysia, at 0:41 and was scheduled to land in Beijing, China, at 6:30 China Standard Time (6:30 MYT; 22:30 UTC, 7 March). Malaysia has worked in conjunction with the Australian Transport Safety Bureau to co-ordinate the analysis, which has also involved the UK's Air Accidents Investigation Branch, Inmarsat, and US National Transportation Safety Board. Other groups have also made efforts to analyse the satellite communications, albeit challenged by a lack of publicly available information for several months after the disappearance. On 29 July 2015, debris was discovered on Réunion Island which was later confirmed to have come from Flight 370; it is the first physical evidence that Flight 370 ended in the Indian Ocean. (Full article...)
Frederick Reines (/ˈraɪnəs/ RY-nəs; March 16, 1918 – August 26, 1998) was an American physicist. He was awarded the 1995 Nobel Prize in Physics for his co-detection of the neutrino with Clyde Cowan in the neutrino experiment. He may be the only scientist in history "so intimately associated with the discovery of an elementary particle and the subsequent thorough investigation of its fundamental properties."
A graduate of Stevens Institute of Technology and New York University, Reines joined the Manhattan Project's Los Alamos Laboratory in 1944, working in the Theoretical Division in Richard Feynman's group. He became a group leader there in 1946. He participated in a number of nuclear tests, culminating in his becoming the director of the Operation Greenhouse test series in the Pacific in 1951. (Full article...)
PSR B1937+21 is a pulsar located in the constellation Vulpecula a few degrees in the sky away from the first discovered pulsar, PSR B1919+21. The name PSR B1937+21 is derived from the word "pulsar" and the declination and right ascension at which it is located, with the "B" indicating that the coordinates are for the 1950.0 epoch. PSR B1937+21 was discovered in 1982 by Don Backer, Shri Kulkarni, Carl Heiles, Michael Davis, and Miller Goss.
It is the first discovered millisecond pulsar, with a rotational period of 1.5578 milliseconds, meaning it completes 641.92 rotations per second. This period was far shorter than astronomers considered pulsars capable of reaching, and led to the suggestion that pulsars can be spun-up by accreting mass from a companion. (Full article...)
The Leibstadt Nuclear Power Plant in Switzerland
Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by nuclear fission of uranium and plutonium in nuclear power plants. Nuclear decay processes are used in niche applications such as radioisotope thermoelectric generators in some space probes such as Voyager 2. Reactors producing controlled fusion power have been operated since 1958 but have yet to generate net power and are not expected to be commercially available in the near future.
The first nuclear power plant was built in the 1950s. The global installed nuclear capacity grew to 100 GW in the late 1970s, and then expanded during the 1980s, reaching 300 GW by 1990. The 1979 Three Mile Island accident in the United States and the 1986 Chernobyl disaster in the Soviet Union resulted in increased regulation and public opposition to nuclear power plants. Nuclear power plants supplied 2,602 terawatt hours (TWh) of electricity in 2023, equivalent to about 9% of global electricity generation, and were the second largest low-carbon power source after hydroelectricity. As of November 2024,[update] there are 415 civilian fission reactors in the world, with overall capacity of 374 GW, 66 under construction and 87 planned, with a combined capacity of 72 GW and 84 GW, respectively. The United States has the largest fleet of nuclear reactors, generating almost 800 TWh per year with an average capacity factor of 92%. The average global capacity factor is 89%. Most new reactors under construction are generation III reactors in Asia. (Full article...)
Val Logsdon Fitch (March 10, 1923 – February 5, 2015) was an American nuclear physicist who, with co-researcher James Cronin, was awarded the 1980 Nobel Prize in Physics for a 1964 experiment using the Alternating Gradient Synchrotron at Brookhaven National Laboratory that proved that certain subatomic reactions do not adhere to fundamental symmetry principles. Specifically, they proved, by examining the decay of K-mesons, that a reaction run in reverse does not retrace the path of the original reaction, which showed that the reactions of subatomic particles are not indifferent to time. Thus the phenomenon of CP violation was discovered. This demolished the faith that physicists had that natural laws were governed by symmetry.
Born on a cattle ranch near Merriman, Nebraska, Fitch was drafted into the U.S. Army during World War II, and worked on the Manhattan Project at the Los Alamos Laboratory in New Mexico. He later graduated from McGill University, and completed his PhD in physics in 1954 at Columbia University. He was a member of the faculty at Princeton University from 1954 until his retirement in 2005. (Full article...)
Harold Melvin Agnew (March 28, 1921 – September 29, 2013) was an American physicist, best known for having flown as a scientific observer on the Hiroshima bombing mission and, later, as the third director of the Los Alamos National Laboratory.
Agnew joined the Metallurgical Laboratory at the University of Chicago in 1942, and helped build Chicago Pile-1, the world's first nuclear reactor. In 1943, he joined the Los Alamos Laboratory, where he worked with the Cockcroft–Walton generator. After the war ended, he returned to the University of Chicago, where he completed his graduate work under Enrico Fermi. (Full article...)
Atomic model of an icosahedral nanoparticle, with red atoms at the five-fold axes
An icosahedral twin is an atomic structure found in atomic clusters and also nanoparticles with some thousands of atoms. Their atomic structure is slightly different from what is found for bulk materials, and contains five-fold symmetries. They have been analyzed in many areas of science including crystal growth, crystallography, chemical physics, surface science and materials science, and are sometimes considered as beautiful due to their high symmetry.
The simplest form of these clusters is twenty interlinked tetrahedral crystals joined along triangular (e.g. cubic-(111)) faces, although more complex variants of the outer surface also occur. A related structure has five units similarly arranged with twinning, which were known as "fivelings" in the 19th century, and more recently as "decahedral multiply twinned particles", "pentagonal particles" or "star particles".: 9–13 A variety of different methods (e.g. condensing metal nanoparticles in argon, deposition on a substrate, wet chemical synthesis) lead to the icosahedral form, and they also occur in virus capsids. (Full article...)
Joseph Sidney Gelders (November 20, 1898 – March 1, 1950) was an American physicist who later became an antiracist, civil rights activist, labor organizer, and communist. In the mid-1930s, he served as the secretary and southern-U.S. representative of the National Committee for the Defense of Political Prisoners. In September 1936, Gelders was kidnapped, beaten, and nearly killed by members of the Ku Klux Klan for his civil rights and labor organizing activities. After his recovery, Gelders continued his activism and cofounded the Southern Conference for Human Welfare and the National Committee to Abolish the Poll Tax. He collaborated closely with other activists including Lucy Randolph Mason and Virginia Foster Durr. Internal injuries sustained during his kidnapping and assault led to Gelders' death on March 1, 1950. (Full article...)
Nikola Tesla (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...)
The SI system after the 2019 definition: Base units as defined in terms of physical constants and other base units. Here, means is used in the definition of .
In 2019, four of the seven SI base units specified in the International System of Quantities were redefined in terms of natural physical constants, rather than human artefacts such as the standard kilogram. Effective 20 May 2019, the 144th anniversary of the Metre Convention, the kilogram, ampere, kelvin, and mole are defined by setting exact numerical values, when expressed in SI units, for the Planck constant (h), the elementary electric charge (e), the Boltzmann constant (kB), and the Avogadro constant (NA), respectively. The second, metre, and candela had previously been redefined using physical constants. The four new definitions aimed to improve the SI without changing the value of any units, ensuring continuity with existing measurements. In November 2018, the 26th General Conference on Weights and Measures (CGPM) unanimously approved these changes, which the International Committee for Weights and Measures (CIPM) had proposed earlier that year after determining that previously agreed conditions for the change had been met. These conditions were satisfied by a series of experiments that measured the constants to high accuracy relative to the old SI definitions, and were the culmination of decades of research.
The previous major change of the metric system occurred in 1960 when the International System of Units (SI) was formally published. At this time the metre was redefined: the definition was changed from the prototype of the metre to a certain number of wavelengths of a spectral line of a krypton-86 radiation, making it derivable from universal natural phenomena. The kilogram remained defined by a physical prototype, leaving it the only artefact upon which the SI unit definitions depended. At this time the SI, as a coherent system, was constructed around seven base units, powers of which were used to construct all other units. With the 2019 redefinition, the SI is constructed around seven defining constants, allowing all units to be constructed directly from these constants. The designation of base units is retained but is no longer essential to define the SI units. (Full article...)- 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...)
Maria Goeppert-Mayer (German: [maˈʁiːa ˈɡœpɐt ˈmaɪɐ] ⓘ; née Göppert; June 28, 1906 – February 20, 1972) was a German–American theoretical physicist who shared the 1963 Nobel Prize in Physics with J. Hans D. Jensen and Eugene Wigner. One half of the prize was awarded jointly to Goeppert-Mayer and Jensen "for their discoveries concerning nuclear shell structure". She was the second woman to win a Nobel Prize in Physics, the first being Marie Curie in 1903. In 1986, the Maria Goeppert-Mayer Award for early-career women physicists was established in her honor.
A graduate of the University of Göttingen, Goeppert-Mayer wrote her doctoral thesis on the theory of possible two-photon absorption by atoms. At the time, the chances of experimentally verifying her thesis seemed remote, but the development of the laser in the 1960s later permitted this. Today, the unit for the two-photon absorption cross section is called the Goeppert-Mayer (GM) unit. (Full article...)
Figure 2: The radius r of the green and blue planets are the same, but their angular speed differs by a factor k. Examples of such orbits are shown in Figures 1 and 3–5.
In classical mechanics, Newton's theorem of revolving orbits identifies the type of central force needed to multiply the angular speed of a particle by a factor k without affecting its radial motion (Figures 1 and 2). Newton applied his theorem to understanding the overall rotation of orbits (apsidal precession, Figure 3) that is observed for the Moon and planets. The term "radial motion" signifies the motion towards or away from the center of force, whereas the angular motion is perpendicular to the radial motion.
Isaac Newton derived this theorem in Propositions 43–45 of Book I of his Philosophiæ Naturalis Principia Mathematica, first published in 1687. In Proposition 43, he showed that the added force must be a central force, one whose magnitude depends only upon the distance r between the particle and a point fixed in space (the center). In Proposition 44, he derived a formula for the force, showing that it was an inverse-cube force, one that varies as the inverse cube of r. In Proposition 45 Newton extended his theorem to arbitrary central forces by assuming that the particle moved in nearly circular orbit. (Full article...)
A simulated particle collision in the LHC.
The safety of high energy particle collisions was a topic of widespread discussion and topical interest during the time when the Relativistic Heavy Ion Collider (RHIC) and later the Large Hadron Collider (LHC)—currently the world's largest and most powerful particle accelerator—were being constructed and commissioned. Concerns arose that such high energy experiments—designed to produce novel particles and forms of matter—had the potential to create harmful states of matter or even doomsday scenarios. Claims escalated as commissioning of the LHC drew closer, around 2008–2010. The claimed dangers included the production of stable micro black holes and the creation of hypothetical particles called strangelets, and these questions were explored in the media, on the Internet and at times through the courts.
To address these concerns in the context of the LHC, CERN mandated a group of independent scientists to review these scenarios. In a report issued in 2003, they concluded that, like current particle experiments such as the RHIC, the LHC particle collisions pose no conceivable threat. A second review of the evidence commissioned by CERN was released in 2008. The report, prepared by a group of physicists affiliated to CERN but not involved in the LHC experiments, reaffirmed the safety of the LHC collisions in light of further research conducted since the 2003 assessment. It was reviewed and endorsed by a CERN committee of 20 external scientists and by the Executive Committee of the Division of Particles & Fields of the American Physical Society, and was later published in the peer-reviewed Journal of Physics G by the UK Institute of Physics, which also endorsed its conclusions. (Full article...)
September anniversaries
- 6 September 1809 - Sir George Cayley identifies the four aerodynamic forces
- 3 September 1821 - Faraday discovers electromagnetic rotation (the principle behind the electric motor).
- - September 1911 - The Sackur-Tetrode Equation is published in Annalen der Physik.
- 29 September 1904 - Nature publishes Wood's letter discrediting N-rays.
- 27 September 1905 - E=mc2 --- Annalen der Physik publishes the Mass–Energy equivalence
- 9 September 1934: The American Rocket Society (ARS) launched Rocket No. 4 to 400 feet.
- 17 September 1959 - The first powered X-15 flight.
- 9 September 1959 - The Atlas 10-D rocket is launched.
- 1 September 1974 - Pioneer 11 sends polar images of Jupiter.
- 20 September 1979 - The High Energy Astronomical Observatory (HEAO) 3 is launched.
- - September 1981 - Invention of the scanning tunneling microscope.
Births
- 22 September 1791 Michael Faraday (d.1867)
- 29 September 1901 Enrico Fermi
Deaths
- 5 September 1906 - Ludwig Boltzmann
- 7 September 1783 - Leonhard Euler
- 9 September 2003 - Edward Teller
General images
The following are images from various physics-related articles on Wikipedia.
The Voltaic pile, the first battery was invented by Alessandro Volta in 1800 (from History of physics)
Sir Isaac Newton (1642–1727) (from History of physics)
Johannes Kepler's first law of planetary motion states that planets move in elliptical orbits about the Sun. (from History of physics)
Maxwell's demon, thought experiment by James Clerk Maxwell to describe the kinetic theory of gases and describe how a microscopic creature could lead to violations of the second law of thermodynamics. (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)
Hydrogen emission spectrum is discrete (here in log scale). The lines can only be explained with quantum mechanics. (from History of physics)
The Standard Model (from History of physics)
Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics)
The ancient Greek mathematician Archimedes, developer of ideas regarding fluid mechanics and buoyancy. (from History of physics)
An engraving of Benjamin Franklin's kite experiment used to study lightning. (from History of physics)
Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter physics)
Christiaan Huygens (1629–1695) (from History of physics)
Newton's cannonball, a though experiment by Newton relating the motion of a projectile and orbiting of planets. (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)
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)
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)
Albert Einstein (1879–1955), ca. 1905 (from History of physics)
Magdeburg hemispheres, an experiment by Otto von Guericke where two metal hemispheres are held together by vacuum and cannot be separated even if largue forces are applied. (from History of physics)
Marie Skłodowska-Curie
(1867–1934) received Nobel prizes in physics (1903) and chemistry (1911). (from History of physics)
Image of X-ray diffraction pattern from a protein crystal (from Condensed matter 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)
Galileo Galilei (1564–1642), early proponent of the modern scientific worldview and method (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)
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)
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)
Crookes tube used to study cathode rays. It lead to the discovery of the electron by J. J. Thomson. (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)
The quantum Hall effect: Components of the Hall resistivity as a function of the external magnetic field (from Condensed matter physics)
Composite montage comparing Jupiter (left) and its four Galilean moons (from top: Io, Europa, Ganymede, Callisto) (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)
James Prescott Joule's apparatus for measuring the mechanical equivalent of heat which the "work" of the falling weight is converted into the "heat" of agitation in the water. (from History of physics)
Richard Feynman's Los Alamos ID badge (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)
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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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