Portal:Physics

The Physics Portal

Physics is the scientific study of matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. It is one of the most fundamental scientific disciplines. A scientist who specializes in the field of physics is called a physicist.

Physics is one of the oldest academic disciplines. Over much of the past two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the Scientific Revolution in the 17th century, these natural sciences branched into separate research endeavors. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in these and other academic disciplines such as mathematics and philosophy.

Advances in physics often enable new technologies. For example, advances in the understanding of electromagnetism, solid-state physics, and nuclear physics led directly to the development of technologies that have transformed modern society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus. (Full article...)

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SN 1994D (bright spot on the lower left), a Type Ia supernova within its host galaxy, NGC 4526

A supernova (pl.: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses to a neutron star or black hole, or is completely destroyed to form a diffuse nebula. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months.

The last supernova directly observed in the Milky Way was Kepler's Supernova in 1604, appearing not long after Tycho's Supernova in 1572, both of which were visible to the naked eye. Observations of recent supernova remnants within the Milky Way, coupled with studies of supernovae in other galaxies, suggest that these powerful stellar explosions occur in our galaxy approximately three times per century on average. A supernova in the Milky Way would almost certainly be observable through modern astronomical telescopes. The most recent naked-eye supernova was SN 1987A, which was the explosion of a blue supergiant star in the Large Magellanic Cloud, a satellite galaxy of the Milky Way in 1987. (Full article...)

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... 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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Archimedes' screw, also called the Archimedean screw or screwpump, is a machine historically used for transferring water from a low-lying body of water into irrigation ditches. The screw pump is commonly attributed to Archimedes on the occasion of his visit to Egypt, but this tradition may reflect only that the apparatus was unknown to the Greeks before Hellenistic times and introduced in his lifetime by unknown Greek engineers. Some writers have suggested that the device may have been in use in Assyria some 350 years earlier.

Archimedes' screw was operated by hand and could raise water efficiently
An Archimedes' screw in Huseby south of Växjö Sweden
Archimedes' screw]
Roman screw used to dewater mines in Spain
Modern Archimedes' screws which have replaced some of the windmills used to drain the polders at Kinderdijk in the Netherlands
Archimedes' screw as a form of art by Tony Cragg at 's-Hertogenbosch in the Netherlands

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Image 1

Los Alamos badge photograph, 1944

Sir Joseph Rotblat (4 November 1908 – 31 August 2005) was a Polish and British physicist. During World War II he worked on Tube Alloys and the Manhattan Project, but left the Los Alamos Laboratory on grounds of conscience after it became clear to him in 1944 that Germany had ceased development of an atomic bomb.

His work on nuclear fallout was a major contribution toward the ratification of the 1963 Partial Nuclear Test Ban Treaty. A signatory of the 1955 Russell–Einstein Manifesto, he was secretary-general of the Pugwash Conferences on Science and World Affairs from their founding until 1973 and shared, with the Pugwash Conferences, the 1995 Nobel Peace Prize "for efforts to diminish the part played by nuclear arms in international affairs and, in the longer run, to eliminate such arms." (Full article...)
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Walter Henry Zinn (December 10, 1906 – February 14, 2000) was a Canadian-born American nuclear physicist who was the first director of the Argonne National Laboratory from 1946 to 1956. He worked at the Manhattan Project's Metallurgical Laboratory during World War II, and supervised the construction of Chicago Pile-1, the world's first nuclear reactor, which went critical on December 2, 1942, at the University of Chicago. At Argonne he designed and built several new reactors, including Experimental Breeder Reactor I, the first nuclear reactor to electrically power a building, which went live on December 20, 1951. (Full article...)
Image 3
Tropical cyclones are ranked on one of five tropical cyclone intensity scales, according to their maximum sustained winds and which tropical cyclone basins they are located in. Only a few classifications are used officially by the meteorological agencies monitoring the tropical cyclones, but other scales also exist, such as accumulated cyclone energy, the Power Dissipation Index, the Integrated Kinetic Energy Index, and the Hurricane Severity Index.

Tropical cyclones that develop in the Northern Hemisphere are classified by the warning centres on one of three intensity scales. Tropical cyclones or subtropical cyclones that exist within the North Atlantic Ocean or the North-eastern Pacific Ocean are classified as either tropical depressions or tropical storms. Should a system intensify further and become a hurricane, then it will be classified on the Saffir–Simpson hurricane wind scale, and is based on the estimated maximum sustained winds over a 1-minute period. In the Western Pacific, the ESCAP/WMO Typhoon Committee uses four separate classifications for tropical cyclones that exist within the basin, which are based on the estimated maximum sustained winds over a 10-minute period. (Full article...)
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Joan, Lady Curran (born Joan Elizabeth Strothers; 26 February 1916 – 10 February 1999) was a Welsh physicist who played important roles in the development of radar and the atomic bomb during the Second World War. She devised a method of releasing chaff, a radar countermeasure technique credited with reducing losses among Allied bomber crews. She also worked on the development of the proximity fuse and the electromagnetic isotope separation process for the atomic bomb.

In 1954 she became a founding member of the Scottish Society for the Parents of Mentally Handicapped Children. (Full article...)
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Franck in 1925

James Franck (German: [ˈdʒɛɪ̯ms ˈfʁaŋk] ; 26 August 1882 – 21 May 1964) was a German-American physicist who received 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...)
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Dr. Mujaddid Ahmed Ijaz in 1987

Mujaddid Ahmed Ijaz, Ph.D. (Urdu: مجدد احمد اعجا ز; June 12, 1937 – July 9, 1992), was a Pakistani-American experimental physicist noted for his role in discovering new isotopes that expanded the neutron-deficient side of the atomic chart. Some of the isotopes he discovered enabled significant advances in medical research, particularly in the treatment of cancer, and further advanced the experimental understanding of nuclear structures. Ijaz conducted his research work at Oak Ridge National Laboratories (ORNL). He and his ORNL colleagues published more than 60 papers in physics journals announcing isotope discoveries and other results of their accelerator experiments from 1968 until 1983.

Ijaz participated in the U.S. Atoms for Peace initiative during the 1970s. The program provided a number of third-world countries, including Pakistan, with civilian nuclear reactor technology to develop energy for peaceful purposes. As a tenured professor of physics at Virginia Tech, he acted as thesis adviser to graduate students from around the world in experimental physics disciplines. Ijaz made extensive trips abroad during his career, including sabbaticals as a visiting professor at Saudi Arabia's King Fahd University of Petroleum and Minerals. in the early 1980s and as a visiting faculty member at the Abdus Salam International Centre for Theoretical Physics in Trieste, Italy in 1985. He retired Professor Emeritus of Physics from Virginia Tech in December 1991 after a 27-year career in teaching and research. Ijaz and his wife emigrated to the United States and settled in Virginia, where they had five children. He died in 1992 after a battle with cancer. (Full article...)
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Foster's reactance theorem is an important theorem in the fields of electrical network analysis and synthesis. The theorem states that the reactance of a passive, lossless two-terminal (one-port) network always strictly monotonically increases with frequency. It is easily seen that the reactances of inductors and capacitors individually increase or decrease with frequency respectively and from that basis a proof for passive lossless networks generally can be constructed. The proof of the theorem was presented by Ronald Martin Foster in 1924, although the principle had been published earlier by Foster's colleagues at American Telephone & Telegraph.

The theorem can be extended to admittances and the encompassing concept of immittances. A consequence of Foster's theorem is that zeros and poles of the reactance must alternate with frequency. Foster used this property to develop two canonical forms for realising these networks. Foster's work was an important starting point for the development of network synthesis. (Full article...)
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Robert F. Christy c. 1959

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...)
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Arne Edwin Slettebak (August 8, 1925 – May 20, 1999) was an American astronomer who served as chair of the astronomy department at the Ohio State University from 1962 to 1987 and director of the Perkins Observatory from 1959 to 1978.

Slettebak was born in the Free City of Danzig before emigrating to the United States at a young age. He obtained a degree in physics in 1945 and his doctorate in astronomy in 1949, the latter under the supervision of William Wilson Morgan with a thesis on O-type and B-type stars. Slettebak joined the Ohio State University shortly after graduating and was instrumental in re-establishing a separate astronomy department there. His principal research interests were in stellar rotation and Be stars, and he published over 90 papers, abstracts and articles. (Full article...)
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Agnew in 1955

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...)
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Elda Emma Anderson, physicist and health researcher

Elda Emma Anderson (October 5, 1899 – April 17, 1961) was an American physicist and health researcher. During World War II, she worked on the Manhattan Project at Princeton University and the Los Alamos National Laboratory, where she prepared the first sample of pure uranium-235 at the laboratory. A graduate of the University of Wisconsin, she became professor of physics at Milwaukee-Downer College in 1929. After the war, she became interested in health physics. She worked in the Health Physics Division of the Oak Ridge National Laboratory, and established the professional certification agency known as the American Board of Health Physics. (Full article...)
Image 12

Birch, c. 1970

Albert Francis Birch (August 22, 1903 – January 30, 1992) was an American geophysicist. He is considered one of the founders of solid Earth geophysics. He is also known for his part in the atomic bombing of Hiroshima and Nagasaki.

During World War II, Birch participated in the Manhattan Project, working on the design and development of the gun-type nuclear weapon known as Little Boy. He oversaw its manufacture, and went to Tinian to supervise its assembly and loading into Enola Gay, the Boeing B-29 Superfortress tasked with dropping the bomb. (Full article...)
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Portrait by Christian Albrecht Jensen, 1840 (copy from Gottlieb Biermann, 1887)

Johann Carl Friedrich Gauss (/ɡaʊs/ ; German: Gauß [kaʁl ˈfʁiːdʁɪç ˈɡaʊs] ; Latin: Carolus Fridericus Gauss; 30 April 1777 – 23 February 1855) was a German mathematician, astronomer, geodesist, and physicist, who contributed to many fields in mathematics and science. He was director of the Göttingen Observatory in Germany and professor of astronomy from 1807 until his death in 1855.

While studying at the University of Göttingen, he propounded several mathematical theorems. As an independent scholar, he wrote the masterpieces Disquisitiones Arithmeticae and Theoria motus corporum coelestium. Gauss produced the second and third complete proofs of the fundamental theorem of algebra. In number theory, he made numerous contributions, such as the composition law, the law of quadratic reciprocity and the Fermat polygonal number theorem. He also contributed to the theory of binary and ternary quadratic forms, the construction of the heptadecagon, and the theory of hypergeometric series. Due to Gauss' extensive and fundamental contributions to science and mathematics, more than 100 mathematical and scientific concepts are named after him. (Full article...)
Image 14

Szilard, c. 1960

Leo Szilard (/ˈsɪlɑːrd/; Hungarian: Leó Szilárd [ˈlɛoː ˈsilaːrd]; born Leó Spitz; February 11, 1898 – May 30, 1964) was a Hungarian-born physicist, biologist and inventor who made numerous important discoveries in nuclear physics and the biological sciences. He conceived the nuclear chain reaction in 1933, and patented the idea in 1936. In late 1939 he wrote the letter for Albert Einstein's signature that resulted in the Manhattan Project that built the atomic bomb, and then in 1945 wrote the Szilard petition asking president Harry S. Truman to demonstrate the bomb without dropping it on civilians. According to György Marx, he was one of the Hungarian scientists known as The Martians.

Szilard initially attended Palatine Joseph Technical University in Budapest, but his engineering studies were interrupted by service in the Austro-Hungarian Army during World War I. He left Hungary for Germany in 1919, enrolling at Technische Hochschule (Institute of Technology) in Berlin-Charlottenburg (now Technische Universität Berlin), but became bored with engineering and transferred to Friedrich Wilhelm University, where he studied physics. He wrote his doctoral thesis on Maxwell's demon, a long-standing puzzle in the philosophy of thermal and statistical physics. Szilard was the first scientist of note to recognize the connection between thermodynamics and information theory. (Full article...)
Image 15
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...)

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July anniversaries

July 1654 – Blaise Pascal's letters to Pierre de Fermat on the "Problem of Points"
July 1820 – Hans Christian Ørsted published pamphlet about the relation between electricity and magnetism
July 1849 – Fizeau publishes results of speed of light experiment.
July 1914 – AT&T tested the first working transcontinental telephone line when the president of the company spoke from one coast to the other. Months later Alexander Graham Bell repeated his famous statement over the phone in New York City which was heard by Dr. Watson in San Francisco.
July 1957 – John Bardeen, Leon Cooper and Robert Schrieffer submit detailed research report, "Theory of Superconductivity" to the Physical Review (it was published in December).
July 1994 – Comet Shoemaker–Levy 9 collides with Jupiter.
16 July 1945 – Trinity test, named by J. Robert Oppenheimer.
16 July 1969 – Apollo 11 launched.
20 July 1969 – Apollo 11 landed on the Moon.
23 July 1995 – Comet Hale-Bopp discovered.
2 July 1876 - Harriet Brooks was born; noted for research in nuclear transmutations and for discovering the Atomic recoil.

General images

The following are images from various physics-related articles on Wikipedia.

Image 1Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter physics)
Image 2René Descartes (1596–1650) (from History of physics)
Image 3Marie Skłodowska-Curie
(1867–1934) received Nobel prizes in physics (1903) and chemistry (1911). (from History of physics)
Image 4Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics)
Image 5The first Bose–Einstein condensate observed in a gas of ultracold rubidium atoms. The blue and white areas represent higher density. (from Condensed matter physics)
Image 6Aristotle (384–322 BCE) (from History of physics)
Image 7A Newton's cradle, named after physicist Isaac Newton (from History of physics)
Image 8One 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)
Image 9A replica of the first point-contact transistor in Bell labs (from Condensed matter physics)
Image 10A 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 11Werner Heisenberg (1901–1976) (from History of physics)
Image 12Classical 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)
Image 13Galileo Galilei (1564–1642), early proponent of the modern scientific worldview and method (from History of physics)
Image 141927 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)
Image 15Alessandro Volta (1745–1827) (from History of physics)
Image 16Gottfried Leibniz (1646–1716) (from History of physics)
Image 17Johannes Kepler (1571–1630) (from History of physics)
Image 18J.J. Thomson (1856–1940), discoverer of electron and isotopy, and inventor of mass spectrometer, received 1906 Nobel Prize in Physics. (from History of physics)
Image 19Michael Faraday (1791–1867) (from History of physics)
Image 20The 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 21Daniel Bernoulli (1700–1782) (from History of physics)
Image 22Ludwig Boltzmann (1844–1906) (from History of physics)
Image 23Composite montage comparing Jupiter (left) and its four Galilean moons (from top: Io, Europa, Ganymede, Callisto) (from History of physics)
Image 24Nicolaus Copernicus (1473–1543) developed a heliocentric model of the Solar System. (from History of physics)
Image 25Star 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)
Image 26The Standard Model (from History of physics)
Image 27Classical 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)
Image 28Einstein 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)
Image 29James Clerk Maxwell (1831–1879) (from History of physics)
Image 30Max Planck (1858–1947) (from History of physics)
Image 31Ibn al-Haytham (c. 965–1040). (from History of physics)
Image 32Sir Isaac Newton (1642–1727) (from History of physics)
Image 33Albert Einstein (1879–1955), ca. 1905 (from History of physics)
Image 34Richard Feynman's Los Alamos ID badge (from History of physics)
Image 35A 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)
Image 36Artist's rendition of Kepler-62f, a potentially habitable exoplanet discovered using data transmitted by Kepler space telescope, named for Kepler (from History of physics)
Image 37Rudolf Clausius (1822–1888) (from History of physics)
Image 38The quantum Hall effect: Components of the Hall resistivity as a function of the external magnetic field (from Condensed matter physics)
Image 39The ancient Greek mathematician Archimedes, developer of ideas regarding fluid mechanics and buoyancy. (from History of physics)
Image 40William Thomson (Lord Kelvin)
(1824–1907) (from History of physics)
Image 41A page from al-Khwārizmī's Algebra. (from History of physics)
$Image 42Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics)$

Image 42Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics)
Image 43Christiaan Huygens (1629–1695) (from History of physics)
Image 44Computer 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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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.

Fundamental Concepts	Classical Physics	Modern Physics	Cross Discipline Topics
Continuum	Solid Mechanics	Fluid Mechanics	Geophysics
Motion	Classical Mechanics	Analytical mechanics	Mathematical Physics
Kinetics	Kinematics	Kinematic chain	Robotics
Matter	Classical states	Modern states	Nanotechnology
Energy	Chemical Physics	Plasma Physics	Materials Science
Cold	Cryophysics	Cryogenics	Superconductivity
Heat	Heat transfer	Transport Phenomena	Combustion
Entropy	Thermodynamics	Statistical mechanics	Phase transitions
Particle	Particulates	Particle physics	Particle accelerator
Antiparticle	Antimatter	Annihilation physics	Gamma ray
Waves	Oscillation	Quantum oscillation	Vibration
Gravity	Gravitation	Gravitational wave	Celestial mechanics
Vacuum	Pressure physics	Vacuum state physics	Quantum fluctuation
Random	Statistics	Stochastic process	Brownian motion
Spacetime	Special Relativity	General Relativity	Black holes
Quantum	Quantum mechanics	Quantum field theory	Quantum computing
Radiation	Radioactivity	Radioactive decay	Cosmic ray
Light	Optics	Quantum optics	Photonics
Electrons	Solid State	Condensed Matter	Symmetry breaking
Electricity	Electrical circuit	Electronics	Integrated circuit
Electromagnetism	Electrodynamics	Quantum Electrodynamics	Chemical Bonds
Strong interaction	Nuclear Physics	Quantum Chromodynamics	Quark model
Weak interaction	Atomic Physics	Electroweak theory	Radioactivity
Standard Model	Fundamental interaction	Grand Unified Theory	Higgs boson
Information	Information science	Quantum information	Holographic principle
Life	Biophysics	Quantum Biology	Astrobiology
Conscience	Neurophysics	Quantum mind	Quantum brain dynamics
Cosmos	Astrophysics	Cosmology	Observable universe
Cosmogony	Big Bang	Mathematical universe	Multiverse
Chaos	Chaos theory	Quantum chaos	Perturbation theory
Complexity	Dynamical system	Complex system	Emergence
Quantization	Canonical quantization	Loop quantum gravity	Spin foam
Unification	Quantum gravity	String theory	Theory of Everything