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The expansion of the universe according to the Big Bang theory in physics

Physics is the natural science of matter, involving the 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, with its main goal being to understand how the universe behaves. A scientist who specializes in the field of physics is called a physicist.

Physics is one of the oldest academic disciplines and, through its inclusion of astronomy, perhaps the oldest. 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 emerged as unique research endeavors in their own right. 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

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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Image of Sirius A and Sirius B taken by the Hubble Space Telescope. Sirius B, which is a white dwarf, can be seen as a faint point of light to the lower left of the much brighter Sirius A.

A

Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910. The name white dwarf was coined by Willem Jacob Luyten
in 1922.

White dwarfs are thought to be the final
evolutionary state of stars whose mass is not high enough to become a neutron star or black hole. This includes over 97% of the stars in the Milky Way. After the hydrogen-fusing period of a main-sequence star of low or medium mass ends, such a star will expand to a red giant during which it fuses helium to carbon and oxygen in its core by the triple-alpha process. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon (around 1 billion K), an inert mass of carbon and oxygen will build up at its center. After such a star sheds its outer layers and forms a planetary nebula, it will leave behind a core, which is the remnant white dwarf. Usually, white dwarfs are composed of carbon and oxygen (CO white dwarf). If the mass of the progenitor is between 7 and 9 solar masses (M), the core temperature will be sufficient to fuse carbon but not neon, in which case an oxygen–neon–magnesium (ONeMg or ONe) white dwarf may form. Stars of very low mass will be unable to fuse helium; hence, a helium white dwarf may form by mass loss in binary systems. (Full article...)
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  • ... that Aristotle's ideas of physics held that because an object could not move without an immediate source of energy, arrows created a vacuum behind them that pushed them through the air.

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Date 1535: "Representations to the Teaching of Optics" edited and printed by Johannes Petreius. This was originally printed on paper. See here for more information.

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  • Image 5 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 energy and matter, and the structures they form, from sub-atomic particles to entire galactic filaments. Space and time, according to the prevailing cosmological theory of the Big Bang, emerged together 13.787±0.020 billion years ago, and the universe has been expanding ever since. Today the universe has expanded into an age and size that is physically only in parts observable as the observable universe, which is approximately 93 billion light-years in diameter at the present day, while the spatial size, if any, of the entire universe is unknown. 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...)

    sub-atomic particles to entire galactic filaments. Space and time, according to the prevailing cosmological theory of the Big Bang, emerged together 13.787±0.020 billion years ago, and the universe has been expanding ever since. Today the universe has expanded into an age and size that is physically only in parts observable as the observable universe, which is approximately 93 billion light-years in diameter at the present day, while the spatial size, if any, of the entire universe is unknown.

    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 6 Wheeler in 1985 John Archibald Wheeler (July 9, 1911 – April 13, 2008) was an American theoretical physicist. He was largely responsible for reviving interest in general relativity in the United States after World War II. Wheeler also worked with Niels Bohr to explain the basic principles of nuclear fission. Together with Gregory Breit, Wheeler developed the concept of the Breit–Wheeler process. He is best known for popularizing the term "black hole" for objects with gravitational collapse already predicted during the early 20th century, for inventing the terms "quantum foam", "neutron moderator", "wormhole" and "it from bit", and for hypothesizing the "one-electron universe". Stephen Hawking called Wheeler the "hero of the black hole story". At 21, Wheeler earned his doctorate at Johns Hopkins University under the supervision of Karl Herzfeld. He studied under Breit and Bohr on a National Research Council fellowship. In 1939 he collaborated with Bohr on a series of papers using the liquid drop model to explain the mechanism of fission. During World War II, he worked with the Manhattan Project's Metallurgical Laboratory in Chicago, where he helped design nuclear reactors, and then at the Hanford Site in Richland, Washington, where he helped DuPont build them. He returned to Princeton after the war but returned to government service to help design and build the hydrogen bomb in the early 1950s. He and Edward Teller were the main civilian proponents of thermonuclear weapons. (Full article...)

    hydrogen bomb in the early 1950s. He and Edward Teller were the main civilian proponents of thermonuclear weapons. (Full article...
    )
  • Image 7 Figure 1: Selected area diffraction pattern of a twinned austenite crystal in a piece of steel Electron diffraction is a generic term for phenomena associated with changes in the direction of electron beams due to elastic interactions with atoms. It occurs due to elastic scattering, when there is no change in the energy of the electrons. The negatively charged electrons are scattered due to Coulomb forces when they interact with both the positively charged atomic core and the negatively charged electrons around the atoms. The resulting map of the directions of the electrons far from the sample is called a diffraction pattern, see for instance Figure 1. Beyond patterns showing the directions of electrons, electron diffraction also plays a major role in the contrast of images in electron microscopes. This article provides an overview of electron diffraction and electron diffraction patterns, collective referred to by the generic name electron diffraction. This includes aspects of how in a general way electrons can act as waves, and diffract and interact with matter. It also involves the extensive history behind modern electron diffraction, how the combination of developments in the 19th century in understanding and controlling electrons in vacuum and the early 20th century developments with electron waves were combined with early instruments, giving birth to electron microscopy and diffraction in 1920–1935. While this was the birth, there have been a large number of further developments since then. (Full article...)
    atoms. It occurs due to elastic scattering, when there is no change in the energy of the electrons. The negatively charged electrons are scattered due to Coulomb forces when they interact with both the positively charged atomic core and the negatively charged electrons around the atoms. The resulting map of the directions of the electrons far from the sample is called a diffraction pattern, see for instance Figure 1. Beyond patterns showing the directions of electrons, electron diffraction also plays a major role in the contrast of images in electron microscopes.

    This article provides an overview of electron diffraction and electron diffraction patterns, collective referred to by the generic name electron diffraction. This includes aspects of how in a general way electrons can act as waves, and diffract and interact with matter. It also involves the extensive history behind modern electron diffraction, how the combination of developments in the 19th century in understanding and controlling electrons in vacuum and the early 20th century developments with electron waves were combined with early instruments, giving birth to electron microscopy and diffraction in 1920–1935. While this was the birth, there have been a large number of further developments since then. (Full article...
    )
  • Image 8 Two geostationary satellites in the same orbit A geostationary orbit, also referred to as a geosynchronous equatorial orbit (GEO), is a circular geosynchronous orbit 35,786 km (22,236 mi) in altitude above Earth's equator, 42,164 km (26,199 mi) in radius from Earth's center, and following the direction of Earth's rotation. An object in such an orbit has an orbital period equal to Earth's rotational period, one sidereal day, and so to ground observers it appears motionless, in a fixed position in the sky. The concept of a geostationary orbit was popularised by the science fiction writer Arthur C. Clarke in the 1940s as a way to revolutionise telecommunications, and the first satellite to be placed in this kind of orbit was launched in 1963. (Full article...)
    Two geostationary satellites in the same orbit

    A geostationary orbit, also referred to as a geosynchronous equatorial orbit (GEO), is a circular geosynchronous orbit 35,786 km (22,236 mi) in altitude above Earth's equator, 42,164 km (26,199 mi) in radius from Earth's center, and following the direction of Earth's rotation.

    An object in such an orbit has an orbital period equal to Earth's rotational period, one sidereal day, and so to ground observers it appears motionless, in a fixed position in the sky. The concept of a geostationary orbit was popularised by the science fiction writer Arthur C. Clarke in the 1940s as a way to revolutionise telecommunications, and the first satellite to be placed in this kind of orbit was launched in 1963. (Full article...)
  • Image 9 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...)
    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...
    )
  • Image 10 An electron backscatter diffraction pattern of monocrystalline silicon, taken at 20 kV with a field-emission electron source Electron backscatter diffraction (EBSD) is a scanning electron microscopy (SEM) technique used to study the crystallographic structure of materials. EBSD is carried out in a scanning electron microscope equipped with an EBSD detector comprising at least a phosphorescent screen, a compact lens and a low-light camera. In the microscope an incident beam of electrons hits a tilted sample. As backscattered electrons leave the sample, they interact with the atoms and are both elastically diffracted and lose energy, leaving the sample at various scattering angles before reaching the phosphor screen forming Kikuchi patterns (EBSPs). The EBSD spatial resolution depends on many factors, including the nature of the material under study and the sample preparation. They can be indexed to provide information about the material's grain structure, grain orientation, and phase at the micro-scale. EBSD is used for impurities and defect studies, plastic deformation, and statistical analysis for average misorientation, grain size, and crystallographic texture. EBSD can also be combined with energy-dispersive X-ray spectroscopy (EDS), cathodoluminescence (CL), and wavelength-dispersive X-ray spectroscopy (WDS) for advanced phase identification and materials discovery. The change and sharpness of the electron backscatter patterns (EBSPs) provide information about lattice distortion in the diffracting volume. Pattern sharpness can be used to assess the level of plasticity. Changes in the EBSP zone axis position can be used to measure the residual stress and small lattice rotations. EBSD can also provide information about the density of geometrically necessary dislocations (GNDs). However, the lattice distortion is measured relative to a reference pattern (EBSP0). The choice of reference pattern affects the measurement precision; e.g., a reference pattern deformed in tension will directly reduce the tensile strain magnitude derived from a high-resolution map while indirectly influencing the magnitude of other components and the spatial distribution of strain. Furthermore, the choice of EBSP0 slightly affects the GND density distribution and magnitude. (Full article...)
    wavelength-dispersive X-ray spectroscopy (WDS) for advanced phase identification and materials discovery.

    The change and sharpness of the electron backscatter patterns (EBSPs) provide information about lattice distortion in the diffracting volume. Pattern sharpness can be used to assess the level of plasticity. Changes in the EBSP zone axis position can be used to measure the residual stress and small lattice rotations. EBSD can also provide information about the density of geometrically necessary dislocations (GNDs). However, the lattice distortion is measured relative to a reference pattern (EBSP0). The choice of reference pattern affects the measurement precision; e.g., a reference pattern deformed in tension will directly reduce the tensile strain magnitude derived from a high-resolution map while indirectly influencing the magnitude of other components and the spatial distribution of strain. Furthermore, the choice of EBSP0 slightly affects the GND density distribution and magnitude. (Full article...
    )
  • Image 11 The radioactive beta decay is due to the weak interaction, which transforms a neutron into a proton, an electron, and an electron antineutrino. In nuclear physics and particle physics, the weak interaction, also called the weak force is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction, and gravitation. It is the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms: The weak interaction participates in nuclear fission and nuclear fusion. The theory describing its behaviour and effects is sometimes called quantum flavourdynamics (QFD); however, the term QFD is rarely used, because the weak force is better understood by electroweak theory (EWT). The effective range of the weak force is limited to subatomic distances and is less than the diameter of a proton. (Full article...)
    subatomic particles that is responsible for the radioactive decay of atoms: The weak interaction participates in nuclear fission and nuclear fusion. The theory describing its behaviour and effects is sometimes called quantum flavourdynamics (QFD); however, the term QFD is rarely used, because the weak force is better understood by electroweak theory (EWT).

    The effective range of the weak force is limited to subatomic distances and is less than the diameter of a proton. (Full article...
    )
  • Image 12 Woods at the University of Chicago in 1946 Leona Harriet Woods (August 9, 1919 – November 10, 1986), later known as Leona Woods Marshall and Leona Woods Marshall Libby, was an American physicist who helped build the first nuclear reactor and the first atomic bomb. At age 23, she was the youngest and only female member of the team which built and experimented with the world's first nuclear reactor (then called a pile), Chicago Pile-1, in a project led by her mentor Enrico Fermi. In particular, Woods was instrumental in the construction and then utilization of geiger counters for analysis during experimentation. She was the only woman present when the reactor went critical. She worked with Fermi on the Manhattan Project, and she subsequently helped evaluate the cross section of xenon, which had poisoned the first Hanford production reactor when it began operation. (Full article...)

    atomic bomb.

    At age 23, she was the youngest and only female member of the team which built and experimented with the world's first nuclear reactor (then called a pile), Chicago Pile-1, in a project led by her mentor Enrico Fermi. In particular, Woods was instrumental in the construction and then utilization of geiger counters for analysis during experimentation. She was the only woman present when the reactor went critical. She worked with Fermi on the Manhattan Project, and she subsequently helped evaluate the cross section of xenon, which had poisoned the first Hanford production reactor when it began operation. (Full article...
    )
  • Image 13 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...)

    cosmologist and particle physicist at the University of New Hampshire. She is also an advocate of increasing diversity in science. (Full article...
    )
  • Image 14 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...)

    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...
    )
  • Image 15 Pontecorvo in 1955 Bruno Pontecorvo (Italian: [ponteˈkɔrvo]; Russian: Бру́но Макси́мович Понтеко́рво, Bruno Maksimovich Pontecorvo; 22 August 1913 – 24 September 1993) was an Italian and Soviet nuclear physicist, an early assistant of Enrico Fermi and the author of numerous studies in high energy physics, especially on neutrinos. A convinced communist, he defected to the Soviet Union in 1950, where he continued his research on the decay of the muon and on neutrinos. The prestigious Pontecorvo Prize was instituted in his memory in 1995. The fourth of eight children of a wealthy Jewish-Italian family, Pontecorvo studied physics at the Sapienza University of Rome, under Fermi, becoming the youngest of his Via Panisperna boys. In 1934 he participated in Fermi's famous experiment showing the properties of slow neutrons that led the way to the discovery of nuclear fission. He moved to Paris in 1936, where he conducted research under Irène and Frédéric Joliot-Curie. Influenced by his cousin, Emilio Sereni, he joined the Italian Communist Party, whose leader were in Paris as refugees, and as did his sisters Giuliana and Laura and brother Gillo. The Italian Fascist regime's 1938 racial laws against Jews caused his family members to leave Italy for Britain, France and the United States. (Full article...)

    Pontecorvo in 1955

    Bruno Pontecorvo (Italian: [ponteˈkɔrvo]; Russian: Бру́но Макси́мович Понтеко́рво, Bruno Maksimovich Pontecorvo; 22 August 1913 – 24 September 1993) was an Italian and Soviet nuclear physicist, an early assistant of Enrico Fermi and the author of numerous studies in high energy physics, especially on neutrinos. A convinced communist, he defected to the Soviet Union in 1950, where he continued his research on the decay of the muon and on neutrinos. The prestigious Pontecorvo Prize was instituted in his memory in 1995.

    The fourth of eight children of a wealthy Jewish-Italian family, Pontecorvo studied physics at the Sapienza University of Rome, under Fermi, becoming the youngest of his Via Panisperna boys. In 1934 he participated in Fermi's famous experiment showing the properties of slow neutrons that led the way to the discovery of nuclear fission. He moved to Paris in 1936, where he conducted research under Irène and Frédéric Joliot-Curie. Influenced by his cousin, Emilio Sereni, he joined the Italian Communist Party, whose leader were in Paris as refugees, and as did his sisters Giuliana and Laura and brother Gillo. The Italian Fascist regime's 1938 racial laws against Jews caused his family members to leave Italy for Britain, France and the United States. (Full article...)
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