Portal:Physics

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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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Chicago Pile-1 (CP-1) was the first artificial nuclear reactor. On 2 December 1942, the first human-made self-sustaining nuclear chain reaction was initiated in CP-1 during an experiment led by Enrico Fermi. The secret development of the reactor was the first major technical achievement for the Manhattan Project, the Allied effort to create nuclear weapons during World War II. Developed by the Metallurgical Laboratory at the University of Chicago, CP-1 was built under the west viewing stands of the original Stagg Field. Although the project's civilian and military leaders had misgivings about the possibility of a disastrous runaway reaction, they trusted Fermi's safety calculations and decided they could carry out the experiment in a densely populated area. Fermi described the reactor as "a crude pile of black bricks and wooden timbers".

After a series of attempts, the successful reactor was assembled in November 1942 by a team of about 30 that, in addition to Fermi, included scientists Leo Szilard (who had previously formulated an idea for non-fission chain reaction), Leona Woods, Herbert L. Anderson, Walter Zinn, Martin D. Whitaker, and George Weil. The reactor used natural uranium. This required a very large amount of material in order to reach criticality, along with graphite used as a neutron moderator. The reactor contained 45,000 ultra-pure graphite blocks weighing 360 short tons (330 tonnes) and was fueled by 5.4 short tons (4.9 tonnes) of uranium metal and 45 short tons (41 tonnes) of uranium oxide. Unlike most subsequent nuclear reactors, it had no radiation shielding or cooling system as it operated at very low power – about one-half watt; nonetheless, the reactor's success meant that a chain reaction could be controlled and the nuclear reaction studied and put to use. (Full article...)

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Did you know -

... that nuclear fusion reactions are probably occurring at or above the sun's photosphere; it is a process called solar surface fusion.

... that the submarine telescope ANTARES, intended to detect neutrinos, may also be used to observe bioluminescent plankton and fish?

... that a touch flash releases about a billion photons a second far less than produced in a particle accelerator?

Selected image -

The term "Copernican Revolution" was coined by the German philosopher Immanuel Kant in his 1781 work Critique of Pure Reason. It was the paradigm shift from the Ptolemaic model of the heavens, which described the cosmos as having Earth stationary at the center of the universe, to the heliocentric model with the Sun at the center of the Solar System. This revolution consisted of two phases; the first being extremely mathematical in nature and beginning with the 1543 publication of Nicolaus Copernicus’s De revolutionibus orbium coelestium, and the second phase starting in 1610 with the publication of a pamphlet by Galileo. Contributions to the "revolution" continued until finally ending with Isaac Newton's 1687 work Philosophiæ Naturalis Principia Mathematica. (Full article...)

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Ancient, medieval and Renaissance astronomers and philosophers developed many different theories about the dynamics of the celestial spheres. They explained the motions of the various nested spheres in terms of the materials of which they were made, external movers such as celestial intelligences, and internal movers such as motive souls or impressed forces. Most of these models were qualitative, although a few of them incorporated quantitative analyses that related speed, motive force and resistance. (Full article...)
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Lawrence in 1939

Ernest Orlando Lawrence (August 8, 1901 – August 27, 1958) was an American accelerator physicist who received the Nobel Prize in Physics in 1939 for his invention of the cyclotron. He is known for his work on uranium-isotope separation for the Manhattan Project, as well as for founding the Lawrence Berkeley National Laboratory and the Lawrence Livermore National Laboratory.

A graduate of the University of South Dakota and University of Minnesota, Lawrence obtained a PhD in physics at Yale in 1925. In 1928, he was hired as an associate professor of physics at the University of California, Berkeley, becoming the youngest full professor there two years later. In its library one evening, Lawrence was intrigued by a diagram of an accelerator that produced high-energy particles. He contemplated how it could be made compact, and came up with an idea for a circular accelerating chamber between the poles of an electromagnet. The result was the first cyclotron. (Full article...)
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Alvin Weinberg, c. 1960

Alvin Martin Weinberg (/ˈwaɪnbɜːrɡ/; April 20, 1915 – October 18, 2006) was an American nuclear physicist who was the administrator of Oak Ridge National Laboratory (ORNL) during and after the Manhattan Project. He came to Oak Ridge, Tennessee, in 1945 and remained there until his death in 2006. He was the first to use the term "Faustian bargain" to describe nuclear energy.

A graduate of the University of Chicago, which awarded him his doctorate in mathematical biophysics in 1939, Weinberg joined the Manhattan Project's Metallurgical Laboratory in September 1941. The following year he became part of Eugene Wigner's Theoretical Group, whose task was to design the nuclear reactors that would convert uranium into plutonium. (Full article...)
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Extended Wulff constructions refers to a number of different ways to model the structure of nanoparticles as well as larger mineral crystals. They can be used to understand the shape of gemstones and crystals with twins, and in other areas such as understanding both the shape and how nanoparticles play a role in the commercial production of chemicals using heterogeneous catalysts. Extended Wulff constructions are variants of the Wulff construction, which is used for a solid single crystal in isolation. They include cases for solid particles on substrates, those with internal boundaries and also when growth is important. Depending upon whether there are twins or a substrate, there are different cases as indicated in the decision tree figure. The simplest forms of these constructions yield the lowest Gibbs free energy (thermodynamic) shape, or the stable growth form for an isolated particle; it can be difficult to differentiate between the two in experimental data. The thermodynamic cases involve the surface energy of different facets; the term surface tension refers to liquids, not solids. The shapes found due to growth kinetics involve the growth velocity of the different surface facets. (Full article...)
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The Frisch–Peierls memorandum was the first technical exposition of a practical nuclear weapon. It was written by expatriate German-Jewish physicist Rudolf Peierls and Austrian physicist Otto Frisch in March 1940 while they were both working for Mark Oliphant at the University of Birmingham in Britain during World War II.

The memorandum contained some of the first calculations about the size of the critical mass of fissile material needed for an atomic bomb. It revealed that the amount required might be small enough to incorporate into a bomb that could be delivered by air. It also anticipated the strategic and moral implications of nuclear weapons. (Full article...)
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Kenneth Tompkins Bainbridge (July 27, 1904 – July 14, 1996) was an American physicist at Harvard University who worked on cyclotron research. His accurate measurements of mass differences between nuclear isotopes allowed him to confirm Albert Einstein's mass–energy equivalence concept. He was the Director of the Manhattan Project's Trinity nuclear test, which took place July 16, 1945. Bainbridge described the Trinity explosion as a "foul and awesome display". He remarked to J. Robert Oppenheimer immediately after the test, "Now we are all sons of bitches." This marked the beginning of his dedication to ending the testing of nuclear weapons and to efforts to maintain civilian control of future developments in that field. (Full article...)
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A series of 5, 2, 1, 0.5 and 0.2 kilogram weights, made of cast iron

The kilogram (also spelled kilogramme) is the base unit of mass in the International System of Units (SI), equal to one thousand grams. It has the unit symbol kg. The word "kilogram" is formed from the combination of the metric prefix kilo- (meaning one thousand) and gram; it is colloquially shortened to "kilo" (plural "kilos").

The kilogram is an SI base unit, defined ultimately in terms of three defining constants of the SI, namely a specific transition frequency of the caesium-133 atom, the speed of light, and the Planck constant. A properly equipped metrology laboratory can calibrate a mass measurement instrument such as a Kibble balance as a primary standard for the kilogram mass. (Full article...)
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Fredrik Carl Mülertz Størmer (Norwegian pronunciation: [fʁɛdʁɪk kaːl ˈmʏlɐːt͡s ̍ˈʃtøːmɐː]) (3 September 1874 – 13 August 1957) was a Norwegian mathematician and astrophysicist. In mathematics, he is known for his work in number theory, including the calculation of $π$ and Størmer's theorem on consecutive smooth numbers. In physics, he is known for studying the movement of charged particles in the magnetosphere and the formation of aurorae, and for his book on these subjects, From the Depths of Space to the Heart of the Atom. He worked for many years as a professor of mathematics at the University of Oslo in Norway. A crater on the far side of the Moon is named after him. (Full article...)
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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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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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The physics of a bouncing ball concerns the physical behaviour of bouncing balls, particularly its motion before, during, and after impact against the surface of another body. Several aspects of a bouncing ball's behaviour serve as an introduction to mechanics in high school or undergraduate level physics courses. However, the exact modelling of the behaviour is complex and of interest in sports engineering.

The motion of a ball is generally described by projectile motion (which can be affected by gravity, drag, the Magnus effect, and buoyancy), while its impact is usually characterized through the coefficient of restitution (which can be affected by the nature of the ball, the nature of the impacting surface, the impact velocity, rotation, and local conditions such as temperature and pressure). To ensure fair play, many sports governing bodies set limits on the bounciness of their ball and forbid tampering with the ball's aerodynamic properties. The bounciness of balls has been a feature of sports as ancient as the Mesoamerican ballgame. (Full article...)
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A NASA portrait of Levine

Joel S. Levine (born 1942) is an American planetary scientist, author, and research professor in applied science at the College of William & Mary, specializing in the atmospheres of the Moon, Earth, and Mars. He has worked as a senior research scientist at NASA, developing scientific models of the evolution of the Earth's early atmosphere, as well as creating models of the Martian atmosphere for use during the Viking 1 and 2 Mars Orbiter and Lander Missions, and was principal investigator and chief scientist of the proposed ARES Mars Airplane Mission. He also formed and led the "Charters of Freedom Research Team," a group of 12 NASA scientists who worked with the National Archive and Records Administration (NARA) to preserve the United States Declaration of Independence, the Constitution, and the Bill of Rights when small white spots began appearing on the documents in 1988. Levine's past work also includes assisting in the design of the rescue vehicle that saved 33 Chilean miners in the 2010 Copiapó mining accident, as well as original research on the feasibility of the "nuclear winter" hypothesis, and the effects of uncontrolled fires on global warming.

Levine is married to Arlene Spielholz, a former NASA scientist who studied the psychological effects of astronauts spending long time periods in space, and has a daughter and grandson. (Full article...)
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Prescod-Weinstein at "Becoming Interplanetary" talk at the Library of Congress, 2018

Chanda Prescod-Weinstein (born c. 1982) is an American theoretical cosmologist and particle physicist at the University of New Hampshire. She is also an advocate of increasing diversity in science. (Full article...)
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Roman copy (in marble) of a Greek bronze bust of Aristotle by Lysippos (c. 330 BC), with modern alabaster mantle

Aristotle (Attic Greek: Ἀριστοτέλης, romanized: Aristotélēs; 384–322 BC) was an Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, and the arts. As the founder of the Peripatetic school of philosophy in the Lyceum in Athens, he began the wider Aristotelian tradition that followed, which set the groundwork for the development of modern science.

Little is known about Aristotle's life. He was born in the city of Stagira in northern Greece during the Classical period. His father, Nicomachus, died when Aristotle was a child, and he was brought up by a guardian. At around eighteen years old, he joined Plato's Academy in Athens and remained there until the age of thirty seven (c. 347 BC). Shortly after Plato died, Aristotle left Athens and, at the request of Philip II of Macedon, tutored his son Alexander the Great beginning in 343 BC. He established a library in the Lyceum, which helped him to produce many of his hundreds of books on papyrus scrolls. (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...)

August anniversaries

2 August 1932 – The positron is discovered by Carl D. Anderson.
2 August 1939 – Einstein and Leó Szilárd urge Franklin D. Roosevelt to begin the Manhattan Project.
3 August 1958 – USS Nautilus under the Arctic ice cap.
3 August 1972 – U.S. Senate ratifies Anti-Ballistic Missile Treaty.

Birthdays

1820 - John Tyndall 2 August
1871 - Ernest Rutherford 30 August
1887 - Erwin Schrödinger 12 August
1902 - Paul Dirac 8 August
1931 – Roger Penrose 8 August
1934 - Valery Bykovsky 2 August
1951 - Edward Witten 26 August
1959 – Koichi Tanaka 3 August
1776 - Amedeo Avogadro. 9 August

Deaths

2 August 1922 – Alexander Graham Bell
3 August 1942 – Richard Willstätter, Nobel laureate
28 August 2006 - Melvin Schwartz, Nobel laureate

General images

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

Image 1Star 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 2The 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 3James Clerk Maxwell (1831–1879) (from History of physics)
Image 4A replica of the first point-contact transistor in Bell labs (from Condensed matter physics)
Image 5Composite montage comparing Jupiter (left) and its four Galilean moons (from top: Io, Europa, Ganymede, Callisto) (from History of physics)
Image 6One 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 7Werner Heisenberg (1901–1976) (from History of physics)
Image 8Classical 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 9Einstein 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 10Christiaan Huygens (1629–1695) (from History of physics)
Image 11The 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 12William Thomson (Lord Kelvin)
(1824–1907) (from History of physics)
Image 13Richard Feynman's Los Alamos ID badge (from History of physics)
Image 14René Descartes (1596–1650) (from History of physics)
Image 15Alessandro Volta (1745–1827) (from History of physics)
Image 16Galileo Galilei (1564–1642), early proponent of the modern scientific worldview and method (from History of physics)
Image 17A 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 18A page from al-Khwārizmī's Algebra. (from History of physics)
Image 19Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957. (from History of physics)
Image 20Classical 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 21Max Planck (1858–1947) (from History of physics)
Image 22Aristotle (384–322 BCE) (from History of physics)
Image 23The quantum Hall effect: Components of the Hall resistivity as a function of the external magnetic field (from Condensed matter physics)
Image 24Rudolf Clausius (1822–1888) (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 26The ancient Greek mathematician Archimedes, developer of ideas regarding fluid mechanics and buoyancy. (from History of physics)
Image 27Ludwig Boltzmann (1844–1906) (from History of physics)
Image 28Johannes Kepler (1571–1630) (from History of physics)
Image 29A 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 30Michael Faraday (1791–1867) (from History of physics)
Image 31The Standard Model (from History of physics)
Image 32Albert Einstein (1879–1955), ca. 1905 (from History of physics)
Image 33A Newton's cradle, named after physicist Isaac Newton (from History of physics)
Image 34Nicolaus Copernicus (1473–1543) developed a heliocentric model of the Solar System. (from History of physics)
Image 35Marie Skłodowska-Curie
(1867–1934) received Nobel prizes in physics (1903) and chemistry (1911). (from History of physics)
Image 36Gottfried Leibniz (1646–1716) (from History of physics)
Image 37Computer 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 38Heike Kamerlingh Onnes and Johannes van der Waals with the helium liquefactor at Leiden in 1908 (from Condensed matter physics)
Image 39Artist'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 40Ibn al-Haytham (c. 965–1040). (from History of physics)
Image 41Sir Isaac Newton (1642–1727) (from History of physics)
Image 42Daniel Bernoulli (1700–1782) (from History of physics)
Image 43Image of X-ray diffraction pattern from a protein crystal (from Condensed matter physics)
Image 44J.J. Thomson (1856–1940), discoverer of electron and isotopy, and inventor of mass spectrometer, received 1906 Nobel Prize in Physics. (from History of physics)

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

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