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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The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). It is an icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law, which states that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident. The table is divided into four roughly rectangular areas called blocks. Elements in the same group tend to show similar chemical characteristics.
Vertical, horizontal and diagonal trends characterize the periodic table. Metallic character increases going down a group and from right to left across a period. Nonmetallic character increases going from the bottom left of the periodic table to the top right. (Full article...)
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A ferrofluid on a glass plate, being affected by a rare-earth magnet
Image credit: Gregory Maxwell
A ferrofluid is a liquid which becomes strongly polarised in the presence of a magnetic field. Ferrofluids are composed of nanoscale ferromagnetic particles suspended in a carrier fluid, usually an organic solvent or water. The ferromagnetic nano-particles are coated with a surfactant to prevent their agglomeration (due to van der Waals and magnetic forces). Although the name may suggest otherwise, ferrofluids do not display ferromagnetism, since they do not retain magnetisation in the absence of an externally applied field. In fact, ferrofluids display paramagnetism, and are often referred as being "superparamagnetic" due to their large magnetic susceptibility. True ferromagnetic fluids are difficult to create at present.
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Alvin Cushman Graves (November 4, 1909 – July 28, 1965) was an American nuclear physicist who served at the Manhattan Project's Metallurgical Laboratory and the Los Alamos Laboratory during World War II. After the war, he became the head of the J (Test) Division at Los Alamos and was director or assistant director of numerous nuclear weapons tests during the 1940s and 1950s. Graves was severely injured in the 1946 laboratory criticality accident in Los Alamos that killed Louis Slotin, but recovered. (Full article...) -
Adriana C. Ocampo Uria (born January 5, 1955) is a Colombian planetary geologist and a Science Program Manager at NASA Headquarters. In 1970, Ocampo emigrated to California and completed her Master in Sciences at California State University, Northridge and finished her PhD at the Vrije Universiteit in the Netherlands. During high school and graduate studies she worked at the Jet Propulsion Laboratory, where she serves as the science coordinator for many planetary missions (Viking, Mars Observer, Voyager, Galileo Galileo Mission, etc.).
She was the first to recognize, using satellite images, that a ring of cenotes or sinkholes, is the only surface impression of the buried Chicxulub crater. This research contributed significantly to the understanding of this impact crater. Ocampo has subsequently led at least seven research expeditions to the Chicxulub site. and to Belize K/Pg ejecta sites, which she discovered and are the subject of her MSc and PhD. She continues to search for new impact craters, and with her team, in 2017, reported on a possible crater near Cali, Colombia. (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...) -
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...) -
Norman Foster Ramsey Jr. (August 27, 1915 – November 4, 2011) was an American physicist who was awarded the 1989 Nobel Prize in Physics for the invention of the separated oscillatory field method (see Ramsey interferometry), which had important applications in the construction of atomic clocks. A physics professor at Harvard University for most of his career, Ramsey also held several posts with such government and international agencies as NATO and the United States Atomic Energy Commission. Among his other accomplishments are helping to found the United States Department of Energy's Brookhaven National Laboratory and Fermilab. (Full article...) -
DU Spectrophotometer, National Technical Laboratories, 1947
The DU spectrophotometer or Beckman DU, introduced in 1941, was the first commercially viable scientific instrument for measuring the amount of ultraviolet light absorbed by a substance. This model of spectrophotometer enabled scientists to easily examine and identify a given substance based on its absorption spectrum, the pattern of light absorbed at different wavelengths. Arnold O. Beckman's National Technical Laboratories (later Beckman Instruments) developed three in-house prototype models (A, B, C) and one limited distribution model (D) before moving to full commercial production with the DU. Approximately 30,000 DU spectrophotometers were manufactured and sold between 1941 and 1976.
Sometimes referred to as a UV–Vis spectrophotometer because it measured both the ultraviolet (UV) and visible spectra, the DU spectrophotometer is credited as being a truly revolutionary technology. It yielded more accurate results than previous methods for determining the chemical composition of a complex substance, and substantially reduced the time needed for an accurate analysis from weeks or hours to minutes. The Beckman DU was essential to several critical secret research projects during World War II, including the development of penicillin and synthetic rubber. (Full article...) -
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...) -
Hans Albrecht Bethe (/ˈbɛθə/; German: [ˈhans ˈbeːtə] ; July 2, 1906 – March 6, 2005) was a German-American physicist who made major contributions to nuclear physics, astrophysics, quantum electrodynamics and solid-state physics, and received the Nobel Prize in Physics in 1967 for his work on the theory of stellar nucleosynthesis. For most of his career, Bethe was a professor at Cornell University.
During World War II, he was head of the Theoretical Division at the secret Los Alamos laboratory that developed the first atomic bombs. There he played a key role in calculating the critical mass of the weapons and developing the theory behind the implosion method used in both the Trinity test and the "Fat Man" weapon dropped on Nagasaki in August 1945. (Full article...) -
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...) -
Henri Coutard (27 August 1876 – 16 March 1950) was a French radiation therapist. He is known for his studies of radiation therapy for the treatment of laryngeal cancer and the development of the "protracted-fractional method" of radiation dosing.
Born in Marolles-les-Braults in the French department of Sarthe, Coutard attended medical school at University of Paris and graduated in 1902. He served in the French Army and lived for several years in the Jura Mountains before returning to Paris to study the medical applications of radium. During World War I, he worked in one of the radiological ambulance units overseen by the Polish-French physicist and chemist Marie Curie. He became the chief of the X-ray department at the Radium Institute of the University of Paris in 1919, working closely with Claudius Regaud and other scientists. Coutard's early work demonstrating the efficacy of radiating patients with laryngeal cancer led to the adoption of radiation therapy as a primary course of cancer treatment. The protracted-fractional method consisted of long durations of radiation applied over several weeks. (Full article...) -
Augustin-Jean Fresnel (10 May 1788 – 14 July 1827) was a French civil engineer and physicist whose research in optics led to the almost unanimous acceptance of the wave theory of light, excluding any remnant of Newton's corpuscular theory, from the late 1830s until the end of the 19th century. He is perhaps better known for inventing the catadioptric (reflective/refractive) Fresnel lens and for pioneering the use of "stepped" lenses to extend the visibility of lighthouses, saving countless lives at sea. The simpler dioptric (purely refractive) stepped lens, first proposed by Count Buffon and independently reinvented by Fresnel, is used in screen magnifiers and in condenser lenses for overhead projectors.
By expressing Huygens's principle of secondary waves and Young's principle of interference in quantitative terms, and supposing that simple colors consist of sinusoidal waves, Fresnel gave the first satisfactory explanation of diffraction by straight edges, including the first satisfactory wave-based explanation of rectilinear propagation. Part of his argument was a proof that the addition of sinusoidal functions of the same frequency but different phases is analogous to the addition of forces with different directions. By further supposing that light waves are purely transverse, Fresnel explained the nature of polarization, the mechanism of chromatic polarization, and the transmission and reflection coefficients at the interface between two transparent isotropic media. Then, by generalizing the direction-speed-polarization relation for calcite, he accounted for the directions and polarizations of the refracted rays in doubly-refractive crystals of the biaxial class (those for which Huygens's secondary wavefronts are not axisymmetric). The period between the first publication of his pure-transverse-wave hypothesis, and the submission of his first correct solution to the biaxial problem, was less than a year. (Full article...) -
Sir John Douglas Cockcroft (27 May 1897 – 18 September 1967) was an English physicist who shared the 1951 Nobel Prize in Physics with Ernest Walton for splitting 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...) -
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...) -
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...) -
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...)
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December anniversaries
- 1610 – Galileo Galilei observes phases of Venus.
- 1900 - The peer reviewed journal "Nature" reports on Duddell's "Singing Arc" American Physical Society.
- 1942 - First self-sustained nuclear chain reaction at the University of Chicago under the supervision of Enrico Fermi. American Physical Society
- 1968 – Apollo 8 Launched
- 1995 – Hubble Deep Field images taken.
Births
- 1852 - Henri Becquerel
- 1900 - George Eugene Uhlenbeck
- 25 December, 1642 - Isaac Newton
- 5 December, 1901 - Werner Heisenberg
- 18 December, 1856 - J. J. Thomson
General images
The following are images from various physics-related articles on Wikipedia.
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Michael Faraday (1791–1867) (from History of physics) -
Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter 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) -
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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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) -
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Sir Isaac Newton (1642–1727) (from History of physics) -
Galileo Galilei, early proponent of the modern scientific worldview and method (1564–1642) (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) -
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) -
Richard Feynman's Los Alamos ID badge (from History of physics) -
Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics) -
Alessandro Volta (1745–1827) (from History of physics) -
James Clerk Maxwell (1831–1879) (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) -
Albert Einstein (1879–1955), photographed here in around 1905 (from History of physics) -
Rudolf Clausius (1822–1888) (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) -
Marie Skłodowska-Curie
(1867–1934) was awarded two Nobel prizes, Physics (1903) and Chemistry (1911) (from History of physics) -
Christiaan Huygens (1629–1695) (from History of physics) -
Max Planck (1858–1947) (from History of physics) -
Johannes Kepler.(1571–1630) (from History of physics) -
Werner Heisenberg (1901–1976) (from History of physics) -
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Daniel Bernoulli (1700–1782) (from History of 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) -
The Standard Model (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) -
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) -
Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics) -
William Thomson (Lord Kelvin)
(1824–1907) (from History of physics) -
René Descartes (1596–1650) (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) -
Ludwig Boltzmann (1844–1906) (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) -
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) -
A composite montage comparing Jupiter (lefthand side) and its four Galilean moons (top to bottom: Io, Europa, Ganymede, Callisto) (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 quantum Hall effect: Components of the Hall resistivity as a function of the external magnetic field (from Condensed matter physics) -
Gottfried Leibniz (1646–1716) (from History of physics)
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Categories
Fundamentals: Concepts in physics | Constants | Physical quantities | Units of measure | Mass | Length | Time | Space | Energy | Matter | Force | Gravity | Electricity | Magnetism | Waves
Basic physics: Mechanics | Electromagnetism | Statistical mechanics | Thermodynamics | Quantum mechanics | Theory of relativity | Optics | Acoustics
Specific fields: Acoustics | Astrophysics | Atomic physics | Molecular physics | Optical physics | Computational physics | Condensed matter physics | Nuclear physics | Particle physics | Plasma physics
Tools: Detectors | Interferometry | Measurement | Radiometry | Spectroscopy | Transducers
Background: Physicists | History of physics | Philosophy of physics | Physics education | Physics journals | Physics organizations
Other: Physics in fiction | Physics lists | Physics software | Physics stubs
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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