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87-491: The DUMAND Project ( D eep U nderwater M uon A nd N eutrino D etector Project ) was a proposed underwater neutrino telescope to be built in the Pacific Ocean , off the shore of the island of Hawaii , five kilometers beneath the surface. It would have included thousands of strings of instruments occupying a cubic kilometer of the ocean . The proposal called for two types of detectors: optical detectors to find

174-505: A neutrino burst from supernova SN 1987A . Scientists detected 19 neutrinos from an explosion of a star inside the Large Magellanic Cloud – only 19 out of the octo-decillion (10 ) neutrinos emitted by the supernova. The Kamiokande detector was able to detect the burst of neutrinos associated with this supernova, and in 1988 it was used to directly confirm the production of solar neutrinos. The largest such detector

261-686: A detector does travel somewhat faster than the speed of light in the detector medium (although somewhat slower than the speed of light in vacuum ). The charged lepton generates a visible "optical shockwave" of Cherenkov radiation . This radiation is detected by the photomultiplier tubes and shows up as a characteristic ring-like pattern of activity in the array of photomultiplier tubes. As neutrinos can interact with atomic nuclei to produce charged leptons which emit Cherenkov radiation, this pattern can be used to infer direction, energy, and (sometimes) flavor information about incident neutrinos. Two water-filled detectors of this type ( Kamiokande and IMB ) recorded

348-630: A falling object is proportional to the square of the time elapsed. This was later confirmed by Italian scientists Jesuits Grimaldi and Riccioli between 1640 and 1650. They also calculated the magnitude of the Earth's gravity by measuring the oscillations of a pendulum. In 1657, Robert Hooke published his Micrographia , in which he hypothesised that the Moon must have its own gravity. In 1666, he added two further principles: that all bodies move in straight lines until deflected by some force and that

435-429: A force applied to an object would cause it to deviate from a geodesic. For instance, people standing on the surface of the Earth are prevented from following a geodesic path because the mechanical resistance of the Earth exerts an upward force on them. This explains why moving along the geodesics in spacetime is considered inertial. Einstein's description of gravity was quickly accepted by the majority of physicists, as it

522-470: A force, the ancient Greek philosopher Archimedes discovered the center of gravity of a triangle. He postulated that if two equal weights did not have the same center of gravity, the center of gravity of the two weights together would be in the middle of the line that joins their centers of gravity. Two centuries later, the Roman engineer and architect Vitruvius contended in his De architectura that gravity

609-399: A groundbreaking book called Philosophiæ Naturalis Principia Mathematica ( Mathematical Principles of Natural Philosophy ). In this book, Newton described gravitation as a universal force, and claimed that "the forces which keep the planets in their orbs must [be] reciprocally as the squares of their distances from the centers about which they revolve." This statement was later condensed into

696-410: A long penetrating track and is easy to spot; The length of this muon track and its curvature in the magnetic field provide energy and charge ( μ versus μ ) information. An electron in the detector produces an electromagnetic shower, which can be distinguished from hadronic showers if the granularity of the active detector is small compared to the physical extent of

783-456: A new approach to quantum mechanics) is required. Testing the predictions of general relativity has historically been difficult, because they are almost identical to the predictions of Newtonian gravity for small energies and masses. Still, since its development, an ongoing series of experimental results have provided support for the theory: In 1919, the British astrophysicist Arthur Eddington

870-435: A phenomenon called Cherenkov light . Cherenkov radiation is produced whenever charged particles such as electrons or muons are moving through a given detector medium somewhat faster than the speed of light in that medium . In a Cherenkov detector, a large volume of clear material such as water or ice is surrounded by light-sensitive photomultiplier tubes. A charged lepton produced with sufficient energy and moving through such

957-429: A simple motion, will continue to move in a straight line, unless continually deflected from it by some extraneous force, causing them to describe a circle, an ellipse, or some other curve. 3. That this attraction is so much the greater as the bodies are nearer. As to the proportion in which those forces diminish by an increase of distance, I own I have not discovered it.... Hooke's 1674 Gresham lecture, An Attempt to prove

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1044-450: A solution of cadmium chloride in water. Two scintillation detectors were placed next to the water targets. Antineutrinos with an energy above the threshold of 1.8 MeV caused charged current " Inverse beta decay " interactions with the protons in the water, producing positrons and neutrons. The resulting positrons annihilate with electrons, creating pairs of coincident photons with an energy of about 0.5 MeV each, which could be detected by

1131-493: A sufficiently large and compact object. General relativity states that gravity acts on light and matter equally, meaning that a sufficiently massive object could warp light around it and create a gravitational lens . This phenomenon was first confirmed by observation in 1979 using the 2.1 meter telescope at Kitt Peak National Observatory in Arizona, which saw two mirror images of the same quasar whose light had been bent around

1218-501: A tank filled with a chlorine-containing fluid such as tetrachloroethylene . A neutrino occasionally converts a chlorine -37 atom into one of argon -37 via the charged current interaction. The threshold neutrino energy for this reaction is 0.814 MeV. The fluid is periodically purged with helium gas which would remove the argon. The helium is then cooled to separate out the argon, and the argon atoms are counted based on their electron capture radioactive decays. A chlorine detector in

1305-526: A theory of general relativity which was able to accurately model Mercury's orbit. In general relativity, the effects of gravitation are ascribed to spacetime curvature instead of a force. Einstein began to toy with this idea in the form of the equivalence principle , a discovery which he later described as "the happiest thought of my life." In this theory, free fall is considered to be equivalent to inertial motion, meaning that free-falling inertial objects are accelerated relative to non-inertial observers on

1392-405: A theory of gravity consistent with quantum mechanics , a quantum gravity theory, which would allow gravity to be united in a common mathematical framework (a theory of everything ) with the other three fundamental interactions of physics. Gravitation , also known as gravitational attraction, is the mutual attraction between all masses in the universe. Gravity is the gravitational attraction at

1479-412: A tower. In the late 16th century, Galileo Galilei 's careful measurements of balls rolling down inclines allowed him to firmly establish that gravitational acceleration is the same for all objects. Galileo postulated that air resistance is the reason that objects with a low density and high surface area fall more slowly in an atmosphere. In 1604, Galileo correctly hypothesized that the distance of

1566-407: A very large active detector volume. Tracking calorimeters are only useful for high-energy ( GeV range) neutrinos. At these energies, neutral current interactions appear as a shower of hadronic debris and charged current interactions are identified by the presence of the charged lepton's track (possibly alongside some form of hadronic debris). A muon produced in a charged current interaction leaves

1653-441: Is a fundamental interaction primarily observed as mutual attraction between all things that have mass . Gravity is, by far, the weakest of the four fundamental interactions, approximately 10 times weaker than the strong interaction , 10 times weaker than the electromagnetic force and 10 times weaker than the weak interaction . As a result, it has no significant influence at the level of subatomic particles . However, gravity

1740-534: Is a large volume of water surrounded by phototubes that watch for the Cherenkov radiation emitted when an incoming neutrino creates an electron or muon in the water. The Sudbury Neutrino Observatory was similar, but used heavy water as the detecting medium. Other detectors have consisted of large volumes of chlorine or gallium which are periodically checked for excesses of argon or germanium , respectively, which are created by neutrinos interacting with

1827-458: Is especially vexing to physicists because the other three fundamental forces (strong force, weak force and electromagnetism) were reconciled with a quantum framework decades ago. As a result, modern researchers have begun to search for a theory that could unite both gravity and quantum mechanics under a more general framework. One path is to describe gravity in the framework of quantum field theory , which has been successful to accurately describe

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1914-409: Is most accurately described by the general theory of relativity , proposed by Albert Einstein in 1915, which describes gravity not as a force, but as the curvature of spacetime , caused by the uneven distribution of mass, and causing masses to move along geodesic lines. The most extreme example of this curvature of spacetime is a black hole , from which nothing—not even light—can escape once past

2001-543: Is not dependent on a substance's weight but rather on its "nature". In the 6th century CE, the Byzantine Alexandrian scholar John Philoponus proposed the theory of impetus, which modifies Aristotle's theory that "continuation of motion depends on continued action of a force" by incorporating a causative force that diminishes over time. In 628 CE, the Indian mathematician and astronomer Brahmagupta proposed

2088-456: Is often expressed in the form G μ ν + Λ g μ ν = κ T μ ν , {\displaystyle G_{\mu \nu }+\Lambda g_{\mu \nu }=\kappa T_{\mu \nu },} where G μν is the Einstein tensor , g μν is the metric tensor , T μν is the stress–energy tensor , Λ

2175-608: Is sensitive to lower-energy neutrinos. A neutrino is able to react with an atom of gallium-71, converting it into an atom of the unstable isotope germanium-71. The germanium was then chemically extracted and concentrated. Neutrinos were thus detected by measuring the radioactive decay of germanium. This latter method is nicknamed the " Alsace-Lorraine " technique in a joke-reference to the Ga → Ge → Ga reaction sequence. The SAGE experiment in Russia used about 50 tons of gallium , and

2262-545: Is the cosmological constant , G {\displaystyle G} is the Newtonian constant of gravitation and c {\displaystyle c} is the speed of light . The constant κ = 8 π G c 4 {\displaystyle \kappa ={\frac {8\pi G}{c^{4}}}} is referred to as the Einstein gravitational constant. A major area of research

2349-445: Is the discovery of exact solutions to the Einstein field equations. Solving these equations amounts to calculating a precise value for the metric tensor (which defines the curvature and geometry of spacetime) under certain physical conditions. There is no formal definition for what constitutes such solutions, but most scientists agree that they should be expressable using elementary functions or linear differential equations . Some of

2436-520: Is the most significant interaction between objects at the macroscopic scale , and it determines the motion of planets , stars , galaxies , and even light . On Earth , gravity gives weight to physical objects , and the Moon's gravity is responsible for sublunar tides in the oceans. The corresponding antipodal tide is caused by the inertia of the Earth and Moon orbiting one another. Gravity also has many important biological functions, helping to guide

2523-451: Is the water-filled Super-Kamiokande . This detector uses 50,000 tons of pure water surrounded by 11,000 photomultiplier tubes buried 1 km underground. The Sudbury Neutrino Observatory (SNO) used 1,000 tonnes of ultrapure heavy water contained in a 12 metre-diameter vessel made of acrylic plastic surrounded by a cylinder of ultrapure ordinary water 22 metres in diameter and 34 metres high. In addition to

2610-591: The Big Bang , and others are generated by nuclear reactions inside stars, planets, and by other interstellar processes. According to scientists' speculations, some may also originate from events in the universe such as "colliding black holes, gamma ray bursts from exploding stars, and/or violent events at the cores of distant galaxies". Despite how common they are, neutrinos are extremely difficult to detect, due to their low mass and lack of electric charge. Unlike other particles, neutrinos only interact via gravity and

2697-401: The Cherenkov radiation emitted by secondary particles traveling faster than the speed of light in water, resulting from collisions by neutrinos , and hydrophones to listen for the acoustic signals generated by the interactions. Sophisticated signal processing would have combined the signals from many optical and acoustic sensors, allowing scientists to determine the direction from which

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2784-570: The GALLEX / GNO experiments in Italy about 30 tons of gallium as reaction mass. The price of gallium is prohibitive, so this experiment is difficult to afford on large-scale. Larger experiments have therefore turned to a less costly reaction mass. Radiochemical detection methods are only useful for counting neutrinos; they provide almost no information on neutrino energy or direction of travel. "Ring-imaging" Cherenkov detectors take advantage of

2871-481: The International System of Units (SI). The force of gravity on Earth is the resultant (vector sum) of two forces: (a) The gravitational attraction in accordance with Newton's universal law of gravitation, and (b) the centrifugal force, which results from the choice of an earthbound, rotating frame of reference. The force of gravity is weakest at the equator because of the centrifugal force caused by

2958-480: The South Pole . The ice itself is the detector medium. The direction of incident neutrinos is determined by recording the arrival time of individual photons using a three-dimensional array of detector modules each containing one photomultiplier tube. This method allows detection of neutrinos above 50 GeV with a spatial resolution of approximately 2  degrees . AMANDA was used to generate neutrino maps of

3045-420: The weak interaction . The two types of weak interactions they (rarely) engage in are neutral current (which involves the exchange of a Z boson and only results in deflection) and charged current (which involves the exchange of a W boson and causes the neutrino to convert into a charged lepton : an electron , a muon , or a tauon , or one of their antiparticles, if an antineutrino). According to

3132-485: The Annual Motion of the Earth , explained that gravitation applied to "all celestial bodies" In 1684, Newton sent a manuscript to Edmond Halley titled De motu corporum in gyrum ('On the motion of bodies in an orbit') , which provided a physical justification for Kepler's laws of planetary motion . Halley was impressed by the manuscript and urged Newton to expand on it, and a few years later Newton published

3219-649: The Big Bang. Neutron star and black hole formation also create detectable amounts of gravitational radiation. This research was awarded the Nobel Prize in Physics in 2017. In December 2012, a research team in China announced that it had produced measurements of the phase lag of Earth tides during full and new moons which seem to prove that the speed of gravity is equal to the speed of light. This means that if

3306-457: The Earth's rotation and because points on the equator are furthest from the center of the Earth. The force of gravity varies with latitude and increases from about 9.780 m/s at the Equator to about 9.832 m/s at the poles. General relativity predicts that energy can be transported out of a system through gravitational radiation. The first indirect evidence for gravitational radiation

3393-463: The Earth) is surrounded by its own gravitational field, which can be conceptualized with Newtonian physics as exerting an attractive force on all objects. Assuming a spherically symmetrical planet, the strength of this field at any given point above the surface is proportional to the planetary body's mass and inversely proportional to the square of the distance from the center of the body. The strength of

3480-622: The Sun suddenly disappeared, the Earth would keep orbiting the vacant point normally for 8 minutes, which is the time light takes to travel that distance. The team's findings were released in Science Bulletin in February 2013. In October 2017, the LIGO and Virgo detectors received gravitational wave signals within 2 seconds of gamma ray satellites and optical telescopes seeing signals from

3567-436: The atmospheric muon incident flux is isotropic, a localised and anisotropic detection is discriminated in relation to the background betraying a cosmic event. For lower-energy experiments, the cosmic rays are not directly the problem. Instead, the spallation neutrons and radioisotopes produced by the cosmic rays may mimic the desired signals. For these experiments, the solution is to place the detector deep underground so that

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3654-503: The attractive force is stronger for closer bodies. In a communication to the Royal Society in 1666, Hooke wrote I will explain a system of the world very different from any yet received. It is founded on the following positions. 1. That all the heavenly bodies have not only a gravitation of their parts to their own proper centre, but that they also mutually attract each other within their spheres of action. 2. That all bodies having

3741-422: The black hole's event horizon . However, for most applications, gravity is well approximated by Newton's law of universal gravitation , which describes gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them. Current models of particle physics imply that

3828-803: The detector from atmospheric muons. Secondly, these environments are transparent and dark, vital criteria in order to detect the faint Cherenkov light . In practice, because of Potassium 40 decay, even the abyss is not completely dark, so this decay must be used as a baseline. Located at a depth of about 2.5 km in the Mediterranean Sea , the ANTARES telescope (Astronomy with a Neutrino Telescope and Abyss environmental Research) has been fully operational since 30 May 2008. Consisting of an array of twelve separate 350  meter -long vertical detector strings 70 meters apart, each with 75  photomultiplier optical modules, this detector uses

3915-427: The detector planes provide the tracking information. Steel is a popular absorber choice, being relatively dense and inexpensive and having the advantage that it can be magnetised. The active detector is often liquid or plastic scintillator, read out with photomultiplier tubes, although various kinds of ionisation chambers have also been used. The NOνA proposal suggests eliminating the absorber planes in favor of using

4002-498: The earliest instance of gravity in the universe, possibly in the form of quantum gravity , supergravity or a gravitational singularity , along with ordinary space and time , developed during the Planck epoch (up to 10 seconds after the birth of the universe), possibly from a primeval state, such as a false vacuum , quantum vacuum or virtual particle , in a currently unknown manner. Scientists are currently working to develop

4089-409: The earth above can reduce the cosmic ray rate to acceptable levels. Neutrino detectors can be aimed at astrophysics observations, since many astrophysical events are believed to emit neutrinos. Underwater neutrino telescopes: Under-ice neutrino telescopes: Underground neutrino observatories: Others: Gravity In physics, gravity (from Latin gravitas  'weight' )

4176-472: The exceedingly rare occasions when a neutrino does interact with an atom of ice or water. The Radio Ice Cherenkov Experiment uses antennas to detect Cherenkov radiation from high-energy neutrinos in Antarctica. The Antarctic Impulse Transient Antenna (ANITA) is a balloon-borne device flying over Antarctica and detecting Askaryan radiation , produced as cosmic ultra-high-energy neutrinos travel through

4263-471: The fall of bodies. The mid-16th century Italian physicist Giambattista Benedetti published papers claiming that, due to specific gravity , objects made of the same material but with different masses would fall at the same speed. With the 1586 Delft tower experiment , the Flemish physicist Simon Stevin observed that two cannonballs of differing sizes and weights fell at the same rate when dropped from

4350-414: The flavor of the neutrino. Most neutrino experiments must address the flux of cosmic rays that bombard the Earth's surface. The higher-energy (>50 MeV or so) neutrino experiments often cover or surround the primary detector with a "veto" detector which reveals when a cosmic ray passes into the primary detector, allowing the corresponding activity in the primary detector to be ignored ("vetoed"). Since

4437-433: The following inverse-square law: F = G m 1 m 2 r 2 , {\displaystyle F=G{\frac {m_{1}m_{2}}{r^{2}}},} where F is the force, m 1 and m 2 are the masses of the objects interacting, r is the distance between the centers of the masses and G is the gravitational constant 6.674 × 10  m ⋅kg ⋅s . Newton's Principia

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4524-430: The former Homestake Mine near Lead, South Dakota , containing 520  short tons (470  metric tons ) of fluid, was the first to detect the solar neutrinos, and made the first measurement of the deficit of electron neutrinos from the sun (see Solar neutrino problem ). A similar detector design, with a much lower detection threshold of 0.233 MeV, uses a gallium (Ga) → germanium (Ge) transformation which

4611-409: The framework for the understanding of gravity. Physicists continue to work to find solutions to the Einstein field equations that form the basis of general relativity and continue to test the theory, finding excellent agreement in all cases. The Einstein field equations are a system of 10 partial differential equations which describe how matter affects the curvature of spacetime. The system

4698-458: The galaxy YGKOW G1 . Frame dragging , the idea that a rotating massive object should twist spacetime around it, was confirmed by Gravity Probe B results in 2011. In 2015, the LIGO observatory detected faint gravitational waves , the existence of which had been predicted by general relativity. Scientists believe that the waves emanated from a black hole merger that occurred 1.5 billion light-years away. Every planetary body (including

4785-523: The gravitational field is numerically equal to the acceleration of objects under its influence. The rate of acceleration of falling objects near the Earth's surface varies very slightly depending on latitude, surface features such as mountains and ridges, and perhaps unusually high or low sub-surface densities. For purposes of weights and measures, a standard gravity value is defined by the International Bureau of Weights and Measures , under

4872-472: The ground. In contrast to Newtonian physics , Einstein believed that it was possible for this acceleration to occur without any force being applied to the object. Einstein proposed that spacetime is curved by matter, and that free-falling objects are moving along locally straight paths in curved spacetime. These straight paths are called geodesics . As in Newton's first law of motion, Einstein believed that

4959-487: The growth of plants through the process of gravitropism and influencing the circulation of fluids in multicellular organisms . The gravitational attraction between the original gaseous matter in the universe caused it to coalesce and form stars which eventually condensed into galaxies, so gravity is responsible for many of the large-scale structures in the universe. Gravity has an infinite range, although its effects become weaker as objects get farther away. Gravity

5046-693: The ice below and produce a shower of secondary charged particles, which emits a cone of coherent radiation in the radio or microwave part of the electromagnetic spectrum. Currently the Radio Neutrino Observatory Greenland is being built, exploiting the Askaryan effect in ice to detect neutrinos with energies >10 PeV. Tracking calorimeters such as the MINOS detectors use alternating planes of absorber material and detector material. The absorber planes provide detector mass while

5133-440: The idea that gravity is an attractive force that draws objects to the Earth and used the term gurutvākarṣaṇ to describe it. In the ancient Middle East , gravity was a topic of fierce debate. The Persian intellectual Al-Biruni believed that the force of gravity was not unique to the Earth, and he correctly assumed that other heavenly bodies should exert a gravitational attraction as well. In contrast, Al-Khazini held

5220-596: The idea that time runs more slowly in the presence of a gravitational field. The time delay of light passing close to a massive object was first identified by Irwin I. Shapiro in 1964 in interplanetary spacecraft signals. In 1971, scientists discovered the first-ever black hole in the galaxy Cygnus . The black hole was detected because it was emitting bursts of x-rays as it consumed a smaller star, and it came to be known as Cygnus X-1 . This discovery confirmed yet another prediction of general relativity, because Einstein's equations implied that light could not escape from

5307-457: The interactions of three or more massive bodies (the " n -body problem"), and some scientists suspect that the Einstein field equations will never be solved in this context. However, it is still possible to construct an approximate solution to the field equations in the n -body problem by using the technique of post-Newtonian expansion . In general, the extreme nonlinearity of the Einstein field equations makes it difficult to solve them in all but

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5394-605: The laws of physics neutrinos must have mass, but only a "smidgen of rest mass" – perhaps less than a "millionth as much as an electron" – so the gravitational force caused by neutrinos has so far proved too weak to detect, leaving the weak interaction as the main method of detection: Antineutrinos were first detected near the Savannah River nuclear reactor by the Cowan–Reines neutrino experiment in 1956. Frederick Reines and Clyde Cowan used two targets containing

5481-468: The mass in the Universe towards it. He also thought that the speed of a falling object should increase with its weight, a conclusion that was later shown to be false. While Aristotle's view was widely accepted throughout Ancient Greece, there were other thinkers such as Plutarch who correctly predicted that the attraction of gravity was not unique to the Earth. Although he did not understand gravity as

5568-429: The most notable solutions of the equations include: Today, there remain many important situations in which the Einstein field equations have not been solved. Chief among these is the two-body problem , which concerns the geometry of spacetime around two mutually interacting massive objects, such as the Sun and the Earth, or the two stars in a binary star system . The situation gets even more complicated when considering

5655-405: The most specific cases. Despite its success in predicting the effects of gravity at large scales, general relativity is ultimately incompatible with quantum mechanics . This is because general relativity describes gravity as a smooth, continuous distortion of spacetime, while quantum mechanics holds that all forces arise from the exchange of discrete particles known as quanta . This contradiction

5742-425: The neutrino arrived, and to rule out false signals arising from other particles or acoustic sources. Because of the nature of the interaction between neutrinos and protons, DUMAND would have been most sensitive to ultra-high energy neutrinos , and completely insensitive to solar neutrinos . Work began in about 1976, at Keahole Point , but the project cancelled in 1995 due to technical difficulties. Although it

5829-602: The neutrino interactions visible in a regular water detector, a neutrino can break up the deuterium in heavy water. The resulting free neutron is subsequently captured, releasing a burst of gamma rays that can be detected. All three neutrino flavors participate equally in this dissociation reaction. The MiniBooNE detector employs pure mineral oil as its detection medium. Mineral oil is a natural scintillator , so charged particles without sufficient energy to produce Cherenkov light still produce scintillation light. Low-energy muons and protons, invisible in water, can be detected. Thus

5916-524: The northern sky to search for extraterrestrial neutrino sources and to search for dark matter . AMANDA has been upgraded to the IceCube observatory, eventually increasing the volume of the detector array to one cubic kilometer. Ice Cube sits deep underneath the South Pole in a cubic kilometre of perfectly clear, bubble-free ancient ice. Like AMANDA it relies on detecting the flickers of light emitted on

6003-422: The orbit of the planet Mercury which could not be explained by Newton's theory: the perihelion of the orbit was increasing by about 42.98 arcseconds per century. The most obvious explanation for this discrepancy was an as-yet-undiscovered celestial body, such as a planet orbiting the Sun even closer than Mercury, but all efforts to find such a body turned out to be fruitless. In 1915, Albert Einstein developed

6090-666: The original substance. MINOS used a solid plastic scintillator watched by phototubes; Borexino uses a liquid pseudocumene scintillator also watched by phototubes; and the NOνA detector uses a liquid scintillator watched by avalanche photodiodes . The proposed acoustic detection of neutrinos via the thermoacoustic effect is the subject of dedicated studies done by the ANTARES , IceCube , and KM3NeT collaborations. Neutrinos are omnipresent in nature: every second, tens of billions of them "pass through every square centimetre of our bodies without us ever noticing." Many were created during

6177-465: The other fundamental interactions . The electromagnetic force arises from an exchange of virtual photons , where the QFT description of gravity is that there is an exchange of virtual gravitons . This description reproduces general relativity in the classical limit . However, this approach fails at short distances of the order of the Planck length , where a more complete theory of quantum gravity (or

6264-502: The planet's actual trajectory. In order to explain this discrepancy, many astronomers speculated that there might be a large object beyond the orbit of Uranus which was disrupting its orbit. In 1846, the astronomers John Couch Adams and Urbain Le Verrier independently used Newton's law to predict Neptune's location in the night sky, and the planet was discovered there within a day. Eventually, astronomers noticed an eccentricity in

6351-752: The same position as Aristotle that all matter in the Universe is attracted to the center of the Earth. In the mid-16th century, various European scientists experimentally disproved the Aristotelian notion that heavier objects fall at a faster rate. In particular, the Spanish Dominican priest Domingo de Soto wrote in 1551 that bodies in free fall uniformly accelerate. De Soto may have been influenced by earlier experiments conducted by other Dominican priests in Italy, including those by Benedetto Varchi , Francesco Beato, Luca Ghini , and Giovan Bellaso which contradicted Aristotle's teachings on

6438-423: The scientific community. In 1959, American physicists Robert Pound and Glen Rebka performed an experiment in which they used gamma rays to confirm the prediction of gravitational time dilation . By sending the rays down a 74-foot tower and measuring their frequency at the bottom, the scientists confirmed that light is redshifted as it moves towards a source of gravity. The observed redshift also supported

6525-641: The shower. Tau leptons decay essentially immediately to either another charged lepton or pions , and cannot be observed directly in this kind of detector. (To directly observe taus, one typically looks for a kink in tracks in photographic emulsion.) At low energies, a neutrino can scatter from the entire nucleus of an atom, rather than the individual nucleons, in a process known as coherent neutral current neutrino-nucleus elastic scattering or coherent neutrino scattering . This effect has been used to make an extremely small neutrino detector. Unlike most other detection methods, coherent scattering does not depend on

6612-431: The surface of a planet or other celestial body; gravity may also include, in addition to gravitation, the centrifugal force resulting from the planet's rotation (see § Earth's gravity ) . The nature and mechanism of gravity were explored by a wide range of ancient scholars. In Greece , Aristotle believed that objects fell towards the Earth because the Earth was the center of the Universe and attracted all of

6699-594: The surrounding sea water as the detector medium. The next generation deep sea neutrino telescope KM3NeT will have a total instrumented volume of about 5 km . The detector will be distributed over three installation sites in the Mediterranean. Implementation of the first phase of the telescope was started in 2013. The Antarctic Muon And Neutrino Detector Array (AMANDA) operated from 1996–2004. This detector used photomultiplier tubes mounted in strings buried deep (1.5–2 km) inside Antarctic glacial ice near

6786-558: The total antineutrino flux . The detected antineutrinos thus all carried an energy greater than 1.8 MeV, which is the threshold for the reaction channel used (1.8 MeV is the energy needed to create a positron and a neutron from a proton). Only about 3% of the antineutrinos from a nuclear reactor carry enough energy for the reaction to occur. A more recently built and much larger KamLAND detector used similar techniques to study oscillations of antineutrinos from 53 Japanese nuclear power plants. A smaller, but more radiopure Borexino detector

6873-428: The two scintillation detectors above and below the target. The neutrons were captured by cadmium nuclei, resulting in delayed gamma rays of about 8 MeV that were detected a few microseconds after the photons from a positron annihilation event. This experiment was designed by Cowan and Reines to give a unique signature for antineutrinos, to prove the existence of these particles. It was not the experimental goal to measure

6960-572: The use of natural environment as a measurement medium emerged. Since the neutrino flux incoming to earth decreases with increasing energy, the size of neutrino detectors must increase too. Though building a kilometer-sized cube detector underground covered by thousands of photomultiplier would be prohibitively expensive, detection volumes of this magnitude can be achieved by installing Cherenkov detector arrays deep inside already existing natural water or ice formations, with several other advantages. Firstly, hundreds of meters of water or ice partly protect

7047-421: Was able to confirm the predicted gravitational lensing of light during that year's solar eclipse . Eddington measured starlight deflections twice those predicted by Newtonian corpuscular theory, in accordance with the predictions of general relativity. Although Eddington's analysis was later disputed, this experiment made Einstein famous almost overnight and caused general relativity to become widely accepted in

7134-468: Was able to explain a wide variety of previously baffling experimental results. In the coming years, a wide range of experiments provided additional support for the idea of general relativity. Today, Einstein's theory of relativity is used for all gravitational calculations where absolute precision is desired, although Newton's inverse-square law is accurate enough for virtually all ordinary calculations. In modern physics , general relativity remains

7221-437: Was able to measure the most important components of the neutrino spectrum from the Sun, as well as antineutrinos from Earth and nuclear reactors. The SNO+ experiment uses linear alkylbenzene as a liquid scintillator, in contrast to its predecessor Sudbury Neutrino Observatory which used heavy water and detected Cherenkov light (see below). Chlorine detectors, based on the method suggested by Bruno Pontecorvo , consist of

7308-410: Was measured on 14 September 2015 by the LIGO detectors. The gravitational waves emitted during the collision of two black holes 1.3 billion light years from Earth were measured. This observation confirms the theoretical predictions of Einstein and others that such waves exist. It also opens the way for practical observation and understanding of the nature of gravity and events in the Universe including

7395-700: Was never completed, DUMAND was in a sense a precursor of the Antarctic Muon And Neutrino Detector Array (AMANDA), and the water Cherenkov neutrino telescopes in the Mediterranean ( ANTARES , NEMO and the NESTOR Project ). The DUMAND hardware was also donated to NESTOR, to reduce costs and cut on development and construction time. DUMAND experiment record on INSPIRE-HEP Neutrino telescope Various detection methods have been used. Super Kamiokande

7482-543: Was through measurements of the Hulse–Taylor binary in 1973. This system consists of a pulsar and neutron star in orbit around one another. Its orbital period has decreased since its initial discovery due to a loss of energy, which is consistent for the amount of energy loss due to gravitational radiation. This research was awarded the Nobel Prize in Physics in 1993. The first direct evidence for gravitational radiation

7569-540: Was well received by the scientific community, and his law of gravitation quickly spread across the European world. More than a century later, in 1821, his theory of gravitation rose to even greater prominence when it was used to predict the existence of Neptune . In that year, the French astronomer Alexis Bouvard used this theory to create a table modeling the orbit of Uranus , which was shown to differ significantly from

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