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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The eye is a region of mostly calm weather at the center of a tropical cyclone. The eye of a storm is a roughly circular area, typically 30–65 kilometers (19–40 miles; 16–35 nautical miles) in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather and highest winds of the cyclone occur. The cyclone's lowest barometric pressure occurs in the eye and can be as much as 15 percent lower than the pressure outside the storm.

In strong tropical cyclones, the eye is characterized by light winds and clear skies, surrounded on all sides by a towering, symmetric eyewall. In weaker tropical cyclones, the eye is less well defined and can be covered by the central dense overcast, an area of high, thick clouds that show up brightly on satellite imagery. Weaker or disorganized storms may also feature an eyewall that does not completely encircle the eye or have an eye that features heavy rain. In all storms, however, the eye is where the barometer reading is lowest. (Full article...)

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Difference between classical and modern physics

While physics aims to discover universal laws, its theories lie in explicit domains of applicability. Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match their predictions. Albert Einstein contributed the framework of special relativity, which replaced notions of absolute time and space with spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light. Max Planck, Erwin Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Later, quantum field theory unified quantum mechanics and special relativity. General relativity allowed for a dynamical, curved spacetime, with which highly massive systems and the large-scale structure of the universe can be well-described. General relativity has not yet been unified with the other fundamental descriptions; several candidate theories of quantum gravity are being developed.

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Image 1

Wu and wife Li Minhua, c. 1943

Wu Zhonghua (Chinese: 吴仲华; 27 July 1917 – 19 September 1992), also known as Chung-Hua Wu, was a Chinese physicist. He was a National Advisory Committee for Aeronautics (NACA) researcher, Tsinghua University professor, and Founding Director of the Institute of Engineering Thermophysics of the Chinese Academy of Sciences (CAS). He pioneered the general theory of three-dimensional flow for turbomachinery, which has been widely used in aircraft engine designs. Wu and his wife Li Minhua were both academicians of the CAS.

Born in Shanghai, Wu's college education at Tsinghua University was interrupted by the Second Sino-Japanese War. He graduated from the temporary National Southwestern Associated University and was awarded a Boxer Indemnity Scholarship to study at the Massachusetts Institute of Technology in the United States. After earning his Ph.D., he joined the NACA, the predecessor of NASA, where he developed the theory of three-dimensional flow. (Full article...)
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Ronald Paul "Ron" Fedkiw (born February 27, 1968) is a full professor in the Stanford University department of computer science and a leading researcher in the field of computer graphics, focusing on topics relating to physically based simulation of natural phenomena and machine learning. His techniques have been employed in many motion pictures. He has earned recognition at the 80th Academy Awards and the 87th Academy Awards as well as from the National Academy of Sciences.

His first Academy Award was awarded for developing techniques that enabled many technically sophisticated adaptations including the visual effects in 21st century movies in the Star Wars, Harry Potter, Terminator, and Pirates of the Caribbean franchises. Fedkiw has designed a platform that has been used to create many of the movie world's most advanced special effects since it was first used on the T-X character in Terminator 3: Rise of the Machines. His second Academy Award was awarded for computer graphics techniques for special effects for large scale destruction. Although he has won an Oscar for his work, he does not design the visual effects that use his technique. Instead, he has developed a system that other award-winning technicians and engineers have used to create visual effects for some of the world's most expensive and highest-grossing movies. (Full article...)
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The Hubble Ultra-Deep Field image shows some of the most remote galaxies visible to present technology (diagonal is ~1/10 apparent Moon diameter)

The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from sub-atomic particles to entire galactic filaments. Since the early 20th century, the field of cosmology establishes that space and time emerged together at the Big Bang 13.787±0.020 billion years ago and that the universe has been expanding since then. The portion of the universe that can be seen by humans is approximately 93 billion light-years in diameter at present, but the total size of the universe is not known.

Some of the earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center. Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of universal gravitation, Isaac Newton built upon Copernicus's work as well as Johannes Kepler's laws of planetary motion and observations by Tycho Brahe. (Full article...)
Image 4

Modern photon-counting CT scanner in 2021 (Siemens NAEOTOM Alpha)

A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or radiology technologists.

CT scanners use a rotating X-ray tube and a row of detectors placed in a gantry to measure X-ray attenuations by different tissues inside the body. The multiple X-ray measurements taken from different angles are then processed on a computer using tomographic reconstruction algorithms to produce tomographic (cross-sectional) images (virtual "slices") of a body. CT scans can be used in patients with metallic implants or pacemakers, for whom magnetic resonance imaging (MRI) is contraindicated. (Full article...)
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Sir Ernest William Titterton (4 March 1916 – 8 February 1990) was a British nuclear physicist.

A graduate of the University of Birmingham, Titterton worked in a research position under Mark Oliphant, who recruited him to work on radar for the British Admiralty during the first part of the Second World War. In 1943, he joined the Manhattan Project's Los Alamos Laboratory, where he helped develop the first atomic bombs. He eventually became one of the laboratory's group leaders. He participated in the Operation Crossroads nuclear tests at the Bikini Atoll in 1946, where he performed the countdown for both tests. With the passage of the Atomic Energy Act of 1946, known as the McMahon Act, all British government employees had to leave. He was the last member of the British Mission to do so, in April 1947. (Full article...)
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Sir Harrie Stewart Wilson Massey (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...)
Image 7

Jackson in 1979

Mary Jackson (née Winston; April 9, 1921 – February 11, 2005) was an American mathematician and aerospace engineer at the National Advisory Committee for Aeronautics (NACA), which in 1958 was succeeded by the National Aeronautics and Space Administration (NASA). She worked at Langley Research Center in Hampton, Virginia, for most of her career. She started as a computer at the segregated West Area Computing division in 1951. In 1958, after taking engineering classes, she became NASA's first black female engineer.

After 34 years at NASA, Jackson had earned the most senior engineering title available. She realized she could not earn further promotions without becoming a supervisor. She accepted a demotion to become a manager of both the Federal Women's Program, in the NASA Office of Equal Opportunity Programs and of the Affirmative Action Program. In this role, she worked to influence the hiring and promotion of women in NASA's science, engineering, and mathematics careers. (Full article...)
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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...)
Image 9
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...)
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Sir Leslie Harold Martin, (21 December 1900 – 1 February 1983) was an Australian physicist. He was one of the 24 Founding Fellows of the Australian Academy of Science and had a significant influence on the structure of higher education in Australia as chairman of the Australian Universities Commission from 1959 until 1966. He was Professor of Physics at the University of Melbourne from 1945 to 1959, and Dean of the Faculty of Military Studies and Professor of Physics at the University of New South Wales at the Royal Military College, Duntroon, in Canberra from 1967 to 1970. He was the Defence Scientific Adviser and chairman of the Defence Research and Development Policy Committee from 1948 to 1968, and a member of the Australian Atomic Energy Commission from 1958 to 1968. In this role he was an official observer at several British nuclear weapons tests in Australia. (Full article...)
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William George Penney, Baron Penney, (24 June 1909 – 3 March 1991) was an English mathematician and professor of mathematical physics at the Imperial College London and later the rector of Imperial College London. He had a leading role in the development of High Explosive Research, Britain's clandestine nuclear programme that started in 1942 during the Second World War which produced the first British atomic bomb in 1952.

As the head of the British delegation working on the Manhattan Project at Los Alamos Laboratory, Penney initially carried out calculations to predict the damage effects generated by the blast wave of an atomic bomb. Upon returning home, Penney directed the British nuclear weapons directorate, codenamed Tube Alloys and directed scientific research at the Atomic Weapons Research Establishment which resulted in the first detonation of a British nuclear bomb in Operation Hurricane in 1952. After the test, Penney became chief advisor to the new United Kingdom Atomic Energy Authority (UKAEA). He was later chairman of the authority, which he used in international negotiations to control nuclear testing with the Partial Nuclear Test Ban Treaty. (Full article...)
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As seen from the orbiting Earth, the Sun appears to move with respect to the fixed stars, and the ecliptic is the yearly path the Sun follows on the celestial sphere. This process repeats itself in a cycle lasting a little over 365 days.

The ecliptic or ecliptic plane is the orbital plane of Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making.

From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic against the background of stars – specifically the Zodiac constellations. The planets of the Solar System can also be seen along the ecliptic, because their orbital planes are very close to Earth's. The Moon's orbital plane is also similar to Earth's; the ecliptic is so named because the ancients noted that eclipses only occur when the Moon is crossing it. (Full article...)
Image 13

Seaborg in 1964

Glenn Theodore Seaborg (/ˈsiːbɔːrɡ/ SEE-borg; April 19, 1912 – February 25, 1999) was an American chemist whose involvement in the synthesis, discovery and investigation of ten transuranium elements earned him a share of the 1951 Nobel Prize in Chemistry. His work in this area also led to his development of the actinide concept and the arrangement of the actinide series in the periodic table of the elements.

Seaborg spent most of his career as an educator and research scientist at the University of California, Berkeley, serving as a professor, and, between 1958 and 1961, as the university's second chancellor. He advised ten US presidents—from Harry S. Truman to Bill Clinton—on nuclear policy and was Chairman of the United States Atomic Energy Commission from 1961 to 1971, where he pushed for commercial nuclear energy and the peaceful applications of nuclear science. Throughout his career, Seaborg worked for arms control. He was a signatory to the Franck Report and contributed to the Limited Test Ban Treaty, the Nuclear Non-Proliferation Treaty and the Comprehensive Test Ban Treaty. He was a well-known advocate of science education and federal funding for pure research. Toward the end of the Eisenhower administration, he was the principal author of the Seaborg Report on academic science, and, as a member of President Ronald Reagan's National Commission on Excellence in Education, he was a key contributor to its 1983 report "A Nation at Risk". (Full article...)
Image 14

Alvarez with a magnetic monopole detector in 1969

Luis Walter Alvarez (June 13, 1911 – September 1, 1988) was an American experimental physicist, inventor, and professor who was awarded the Nobel Prize in Physics in 1968 for his discovery of resonance states in particle physics using the hydrogen bubble chamber. In 2007 the American Journal of Physics commented, "Luis Alvarez was one of the most brilliant and productive experimental physicists of the twentieth century."

After receiving his PhD from the University of Chicago in 1936, Alvarez went to work for Ernest Lawrence at the Radiation Laboratory at the University of California, Berkeley. Alvarez devised a set of experiments to observe K-electron capture in radioactive nuclei, predicted by the beta decay theory but never before observed. He produced tritium using the cyclotron and measured its lifetime. In collaboration with Felix Bloch, he measured the magnetic moment of the neutron. (Full article...)
Image 15

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...)

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April anniversaries

1 April 1997 – Comet Hale-Bopp at perihelion
12 April 1633 – Galileo Galilei's trial starts
15 April 1707 – Leonhard Euler's birthday
18 April 1955 – Albert Einstein's death
22 April 1904 – J. Robert Oppenheimer's birthday
23 April 1858 – Max Planck's birthday
24 April 1990 – Hubble Space Telescope launched
25 April 1990 – Hubble Space Telescope deployed from the shuttle Discovery
30 April 1777 – Carl Friedrich Gauss's birthday

General images

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

Image 1Albert Einstein (1879–1955), ca. 1905 (from History of physics)
Image 2A replica of the first point-contact transistor in Bell labs (from Condensed matter physics)
$Image 3Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics)$

Image 3Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics)
Image 4The 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 5A 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 6Composite montage comparing Jupiter (left) and its four Galilean moons (from top: Io, Europa, Ganymede, Callisto) (from History of physics)
Image 7Werner Heisenberg (1901–1976) (from History of physics)
Image 8Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter physics)
Image 9Michael Faraday (1791–1867) (from History of physics)
Image 10Computer 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)
Image 11Einstein 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 12The 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 13Ibn al-Haytham (c. 965–1040). (from History of physics)
Image 14J.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 15Rudolf Clausius (1822–1888) (from History of physics)
Image 16Marie Skłodowska-Curie
(1867–1934) received Nobel prizes in physics (1903) and chemistry (1911). (from History of physics)
Image 17René Descartes (1596–1650) (from History of physics)
Image 18Classical 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 19Max Planck (1858–1947) (from History of physics)
Image 20Artist'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 21Sir Isaac Newton (1642–1727) (from History of physics)
Image 22William Thomson (Lord Kelvin)
(1824–1907) (from History of physics)
Image 23One 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 24Nicolaus Copernicus (1473–1543) developed a heliocentric model of the Solar System. (from History of physics)
Image 251927 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 26Gottfried Leibniz (1646–1716) (from History of physics)
Image 27Ludwig Boltzmann (1844–1906) (from History of physics)
Image 28Star 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 29Alessandro Volta (1745–1827) (from History of physics)
Image 30Galileo Galilei (1564–1642), early proponent of the modern scientific worldview and method (from History of physics)
Image 31Richard Feynman's Los Alamos ID badge (from History of physics)
Image 32Classical 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 33The ancient Greek mathematician Archimedes, developer of ideas regarding fluid mechanics and buoyancy. (from History of physics)
Image 34Christiaan Huygens (1629–1695) (from History of physics)
Image 35The Standard Model (from History of physics)
Image 36Aristotle (384–322 BCE) (from History of physics)
Image 37A Newton's cradle, named after physicist Isaac Newton (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 39Daniel Bernoulli (1700–1782) (from History of physics)
Image 40Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics)
Image 41Johannes Kepler (1571–1630) (from History of physics)
Image 42A 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 43James Clerk Maxwell (1831–1879) (from History of physics)
Image 44A page from al-Khwārizmī's Algebra. (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.

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