Gravitational wave - wikipedia Gravitational wave This article is about the phenomenon of general relativity. For the movement of classical fluids, see Gravity wave. Play media Simulation of the collision of two black holes. In addition to forming deep gravity wells and coalescing into a single larger black hole, gravitational waves will propagate outwards as the black holes spin past each other. Part of a series of articles about General relativity G μ ν + Λ g μ ν = 8 π G c 4 T μ ν ( displaystyle G_ ( mu \nu ) + Lambda g_ ( mu \nu ) = ( 8 pi G over c ^ ( 4 ) ) T_ ( mu \nu ) ) Introduction History Mathematical formulation Tests Fundamental concepts Equivalence principle Special relativity World line Riemannian geometry Phenomena Kepler problem Time dilation Gravitational field Gravitational collapse Gravitational lensing Gravitational waves Gravitational redshift Gravitational time delay Gravitational time dilation Gravitational potential Gravitational compression Frame - dragging Geodetic effect Gravity well Event horizon Singularity Naked singularity Black hole White hole Spacetime Space Time Spacetime diagrams Minkowski spacetime Closed timelike curve ( CTC ) Wormhole Ellis wormhole Equations Formalisms Equations Linearized gravity Einstein field equations Friedmann Geodesics Mathisson -- Papapetrou -- Dixon Hamilton -- Jacobi -- Einstein Formalisms ADM BSSN Post-Newtonian Advanced theory Kaluza -- Klein theory Quantum gravity Solutions Schwarzschild ( interior ) Reissner -- Nordström Gödel Kerr Kerr -- Newman Kasner Lemaître -- Tolman Taub - NUT Milne Robertson -- Walker pp - wave van Stockum dust Weyl − Lewis − Papapetrou Scientists Einstein Lorentz Hilbert Poincaré Schwarzschild de Sitter Reissner Nordström Weyl Eddington Friedman Milne Zwicky Lemaître Gödel Wheeler Robertson Bardeen Walker Kerr Chandrasekhar Ehlers Penrose Hawking Raychaudhuri Taylor Hulse van Stockum Taub Newman Yau Thorne others Gravitational waves are the disturbance in the fabric ( `` curvature '' ) of spacetime generated by accelerated masses and propagate as waves outward from their source at the speed of light. They were first proposed by Henri Poincaré in 1905 and subsequently predicted in 1916 by Albert Einstein on the basis of his general theory of relativity. Gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation. Newton 's law of universal gravitation, part of classical mechanics, does not provide for their existence, since that law is predicated on the assumption that physical interactions propagate at infinite speed -- showing one of the ways the methods of classical physics are unable to explain phenomena associated with relativity. Gravitational - wave astronomy is a branch of observational astronomy that uses gravitational waves to collect observational data about sources of detectable gravitational waves such as binary star systems composed of white dwarfs, neutron stars, and black holes ; and events such as supernovae, and the formation of the early universe shortly after the Big Bang. On 11 February 2016, the LIGO and Virgo Scientific Collaboration announced they had made the first observation of gravitational waves. The observation itself was made on 14 September 2015, using the Advanced LIGO detectors. The gravitational waves originated from a pair of merging black holes. After the initial announcement the LIGO instruments detected two more confirmed, and one potential, gravitational wave events. In August 2017, the two LIGO instruments, and the Virgo instrument, observed a fourth gravitational wave from merging black holes, and a fifth gravitational wave from a binary neutron star merger. Several other gravitational - wave detectors are planned or under construction. In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry Barish for their role in the detection of gravitational waves. Contents 1 Introduction 2 History 3 Effects of passing 4 Sources 4.1 Binaries 4.1. 1 Compact binaries 4.2 Black hole binaries 4.3 Supernovae 4.4 Spinning neutron stars 4.5 Inflation 5 Properties and behaviour 5.1 Energy, momentum, and angular momentum 5.2 Redshifting and blueshifting 5.3 Quantum gravity, wave - particle aspects, and graviton 5.4 Significance for study of the early universe 5.5 Determining direction of travel 6 Gravitational wave astronomy 7 Detection 7.1 Indirect detection 7.2 Difficulties 7.3 Ground - based detectors 7.3. 1 Resonant antennae 7.3. 2 Interferometers 7.3. 3 Einstein@Home 7.4 Space - based interferometers 7.5 Using pulsar timing arrays 7.6 Primordial 7.7 LIGO and Virgo observations 8 In fiction 9 See also 10 References 11 Further reading 12 Bibliography 13 External links Introduction In Einstein 's general theory of relativity, gravity is treated as a phenomenon resulting from the curvature of spacetime. This curvature is caused by the presence of mass. Generally, the more mass that is contained within a given volume of space, the greater the curvature of spacetime will be at the boundary of its volume. As objects with mass move around in spacetime, the curvature changes to reflect the changed locations of those objects. In certain circumstances, accelerating objects generate changes in this curvature, which propagate outwards at the speed of light in a wave - like manner. These propagating phenomena are known as gravitational waves. As a gravitational wave passes an observer, that observer will find spacetime distorted by the effects of strain. Distances between objects increase and decrease rhythmically as the wave passes, at a frequency corresponding to that of the wave. This occurs despite such free objects never being subjected to an unbalanced force. The magnitude of this effect decreases in proportion to the inverse distance from the source. Inspiraling binary neutron stars are predicted to be a powerful source of gravitational waves as they coalesce, due to the very large acceleration of their masses as they orbit close to one another. However, due to the astronomical distances to these sources, the effects when measured on Earth are predicted to be very small, having strains of less than 1 part in 10. Scientists have demonstrated the existence of these waves with ever more sensitive detectors. The most sensitive detector accomplished the task possessing a sensitivity measurement of about one part in 7022499999999999999 ♠ 5 × 10 ( as of 2012 ) provided by the LIGO and VIRGO observatories. A space based observatory, the Laser Interferometer Space Antenna, is currently under development by ESA. Linearly polarised gravitational wave Gravitational waves can penetrate regions of space that electromagnetic waves can not. They are able to allow the observation of the merger of black holes and possibly other exotic objects in the distant Universe. Such systems can not be observed with more traditional means such as optical telescopes or radio telescopes, and so gravitational - wave astronomy gives new insights into the working of the Universe. In particular, gravitational waves could be of interest to cosmologists as they offer a possible way of observing the very early Universe. This is not possible with conventional astronomy, since before recombination the Universe was opaque to electromagnetic radiation. Precise measurements of gravitational waves will also allow scientists to test more thoroughly the general theory of relativity. In principle, gravitational waves could exist at any frequency. However, very low frequency waves would be impossible to detect and there is no credible source for detectable waves of very high frequency. Stephen Hawking and Werner Israel list different frequency bands for gravitational waves that could plausibly be detected, ranging from 10 Hz up to 10 Hz. History Main article : Sticky bead argument Primordial gravitational waves are hypothesized to arise from cosmic inflation, a faster - than - light expansion just after the Big Bang ( 2014 ). The possibility of gravitational waves was discussed in 1893 by Oliver Heaviside using the analogy between the inverse - square law in gravitation and electricity. In 1905, Henri Poincaré first proposed gravitational waves ( ondes gravifiques ), emanating from a body and propagating at the speed of light, as being required by the Lorentz transformations and suggested that, in analogy to an accelerating electrical charge producing electromagnetic waves, accelerated masses in a relativistic field theory of gravity should produce gravitational waves. When Einstein published his general theory of relativity in 1915, he was skeptical of Poincaré 's idea since the theory implied there were no `` gravitational dipoles ''. Nonetheless, he still pursued the idea and based on various approximations came to the conclusion there must, in fact, be three types of gravitational waves ( dubbed longitudinal - longitudinal, transverse - longitudinal, and transverse - transverse by Hermann Weyl ). However, the nature of Einstein 's approximations led many ( including Einstein himself ) to doubt the result. In 1922, Arthur Eddington showed that two of Einstein 's types of waves were artifacts of the coordinate system he used, and could be made to propagate at any speed by choosing appropriate coordinates, leading Eddington to jest that they `` propagate at the speed of thought ''. This also cast doubt on the physicality of the third ( transverse - transverse ) type ( which Eddington showed always propagate at the speed of light regardless of coordinate system ). In 1936, Einstein and Nathan Rosen submitted a paper to Physical Review in which they claimed gravitational waves could not exist in the full general theory of relativity because any such solution of the field equations would have a singularity. The journal sent their manuscript to be reviewed by Howard P. Robertson, who ( anonymously ) reported that the singularities in question were simply the harmless coordinate singularities of the employed cylindrical coordinates. Einstein, who was unfamiliar with the concept of peer review, angrily withdrew the manuscript, never to publish in Physical Review again. Nonetheless, his assistant Leopold Infeld, who had been in contact with Robertson, convinced Einstein that the criticism was correct, and the paper was rewritten with the opposite conclusion ( and published elsewhere ). In 1956, Felix Pirani remedied the confusion caused by the use of various coordinate systems by rephrasing the gravitational waves in terms of the manifestly observable Riemann curvature tensor. At the time this work was mostly ignored because the community was focused on a different question : whether gravitational waves could transmit energy. This matter was settled by a thought experiment proposed by Richard Feynman during the first `` GR '' conference at Chapel Hill in 1957. In short, his argument ( known as the `` sticky bead argument '' ) notes that if one takes a rod with beads then the effect of a passing gravitational wave would be to move the beads along the rod ; friction would then produce heat, implying that the passing wave had done work. Shortly after, Hermann Bondi ( a former gravitational wave skeptic ) published a detailed version of the `` sticky bead argument ''. After the Chapel Hill conference, Joseph Weber started designing and building the first gravitational wave detectors now known as Weber bars. In 1969, Weber claimed to have detected the first gravitational waves, and by 1970 he was `` detecting '' signals regularly from the Galactic Center ; however, the frequency of detection soon raised doubts on the validity of his observations as the implied rate of energy loss of the Milky Way would drain our galaxy of energy on a timescale much shorter than its inferred age. These doubts were strengthened when, by the mid-1970s, repeat experiments from other groups building their own Weber bars across the globe failed to find any signals, and by the late 1970s general consensus was that Weber 's results were spurious. In the same period, the first indirect evidence for the existence of gravitational waves was discovered. In 1974, Russell Alan Hulse and Joseph Hooton Taylor, Jr. discovered the first binary pulsar ( a discovery that earned them the 1993 Nobel Prize in Physics ). In 1979, results were published detailing measurement of the gradual decay of the orbital period of the Hulse - Taylor pulsar, which fitted precisely with the loss of energy and angular momentum in gravitational radiation predicted by general relativity. This indirect detection of gravitational waves motivated further searches despite Weber 's discredited result. Some groups continued to improve Weber 's original concept, while others pursued the detection of gravitational waves using laser interferometers. The idea of using a laser interferometer to detect gravitational waves seems to have been floated by various people independently, including M.E. Gertsenshtein and V.I. Pustovoit in 1962, and Vladimir B. Braginskiĭ in 1966. The first prototypes were developed in the 1970s by Robert L. Forward and Rainer Weiss. In the decades that followed, ever more sensitive instruments were constructed, culminating in the construction of GEO600, LIGO, and Virgo. After years of producing null results, LIGO made the first direct detection of gravitational waves on 14 September 2015. It was inferred that the signal, dubbed GW150914, originated from the merger of two black holes with masses 7001360000000000000 ♠ 36 + 5 − 4 M ⊙ and 7001290000000000000 ♠ 29 + 4 − 4 M ⊙, resulting in a 7001620000000000000 ♠ 62 + 4 − 4 M ⊙ black hole. A year earlier it appeared LIGO might have been beaten to the punch when the BICEP2 claimed that they had detected the imprint of gravitational waves in the cosmic microwave background. However, they were later forced to retract their result. In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry Barish for their role in the detection of gravitational waves. Effects of passing The effect of a plus - polarized gravitational wave on a ring of particles. The effect of a cross-polarized gravitational wave on a ring of particles. Gravitational waves are constantly passing Earth ; however, even the strongest have a minuscule effect and their sources are generally at a great distance. For example, the waves given off by the cataclysmic final merger of GW150914 reached Earth after travelling over a billion light - years, as a ripple in spacetime that changed the length of a 4 - km LIGO arm by a ten thousandth of the width of a proton, proportionally equivalent to changing the distance to the nearest star outside the Solar System by one hair 's width. This tiny effect from even extreme gravitational waves makes them only detectable on Earth by the most sophisticated detectors. The effects of a passing gravitational wave, in an extremely exaggerated form, can be visualized by imagining a perfectly flat region of spacetime with a group of motionless test particles lying in a plane ( e.g., the surface of a computer screen ). As a gravitational wave passes through the particles along a line perpendicular to the plane of the particles ( i.e. following the observer 's line of vision into the screen ), the particles will follow the distortion in spacetime, oscillating in a `` cruciform '' manner, as shown in the animations. The area enclosed by the test particles does not change and there is no motion along the direction of propagation. The oscillations depicted in the animation are exaggerated for the purpose of discussion -- in reality a gravitational wave has a very small amplitude ( as formulated in linearized gravity ). However, they help illustrate the kind of oscillations associated with gravitational waves as produced by a pair of masses in a circular orbit. In this case the amplitude of the gravitational wave is constant, but its plane of polarization changes or rotates at twice the orbital rate, so the time - varying gravitational wave size, or ' periodic spacetime strain ', exhibits a variation as shown in the animation. If the orbit of the masses is elliptical then the gravitational wave 's amplitude also varies with time according to Einstein 's quadrupole formula. As with other waves, there are a number of characteristics used to describe a gravitational wave : Amplitude, h, the size of the wave -- the fraction of stretching or squeezing in the animation. The amplitude here is roughly h = 0.5 ( or 50 % ). Gravitational waves passing through the Earth show sextillion times this weakness ( 10 ). Also denoted as Wavelength, λ, the distance along the wave between points of maximum stretch or squeeze. Frequency : Usually denoted f, this is the frequency with which the wave oscillates ( 1 divided by the amount of time between two successive maximum stretches or squeezes ) Speed : This is the speed at which a point on the wave ( for example, a point of maximum stretch or squeeze ) travels. For gravitational waves with small amplitudes, this wave speed is equal to the speed of light ( c ). The speed, wavelength, and frequency of a gravitational wave are related by the equation c = λ f, just like the equation for a light wave. For example, the animations shown here oscillate roughly once every two seconds. This would correspond to a frequency of 0.5 Hz, and a wavelength of about 600 000 km, or 47 times the diameter of the Earth. In the above example, it is assumed that the wave is linearly polarized with a `` plus '' polarization, written h. Polarization of a gravitational wave is just like polarization of a light wave except that the polarizations of a gravitational wave are 45 degrees apart, as opposed to 90 degrees. In particular, in a `` cross '' - polarized gravitational wave, h, the effect on the test particles would be basically the same, but rotated by 45 degrees, as shown in the second animation. Just as with light polarization, the polarizations of gravitational waves may also be expressed in terms of circularly polarized waves. Gravitational waves are polarized because of the nature of their source. Sources The gravitational wave spectrum with sources and detectors. Credit : NASA Goddard Space Flight Center In general terms, gravitational waves are radiated by objects whose motion involves acceleration and its change, provided that the motion is not perfectly spherically symmetric ( like an expanding or contracting sphere ) or rotationally symmetric ( like a spinning disk or sphere ). A simple example of this principle is a spinning dumbbell. If the dumbbell spins around its axis of symmetry, it will not radiate gravitational waves ; if it tumbles end over end, as in the case of two planets orbiting each other, it will radiate gravitational waves. The heavier the dumbbell, and the faster it tumbles, the greater is the gravitational radiation it will give off. In an extreme case, such as when the two weights of the dumbbell are massive stars like neutron stars or black holes, orbiting each other quickly, then significant amounts of gravitational radiation would be given off. Some more detailed examples : Two objects orbiting each other, as a planet would orbit the Sun, will radiate. A spinning non-axisymmetric planetoid -- say with a large bump or dimple on the equator -- will radiate. A supernova will radiate except in the unlikely event that the explosion is perfectly symmetric. An isolated non-spinning solid object moving at a constant velocity will not radiate. This can be regarded as a consequence of the principle of conservation of linear momentum. A spinning disk will not radiate. This can be regarded as a consequence of the principle of conservation of angular momentum. However, it will show gravitomagnetic effects. A spherically pulsating spherical star ( non-zero monopole moment or mass, but zero quadrupole moment ) will not radiate, in agreement with Birkhoff 's theorem. More technically, the third time derivative of the quadrupole moment ( or the l - th time derivative of the l - th multipole moment ) of an isolated system 's stress -- energy tensor must be non-zero in order for it to emit gravitational radiation. This is analogous to the changing dipole moment of charge or current that is necessary for the emission of electromagnetic radiation. Binaries See also : Two - body problem in general relativity Two stars of dissimilar mass are in circular orbits. Each revolves about their common center of mass ( denoted by the small red cross ) in a circle with the larger mass having the smaller orbit. Two stars of similar mass are in circular orbits about their center of mass Two stars of similar mass are in highly elliptical orbits about their center of mass Gravitational waves carry energy away from their sources and, in the case of orbiting bodies, this is associated with an inspiral or decrease in orbit. Imagine for example a simple system of two masses -- such as the Earth -- Sun system -- moving slowly compared to the speed of light in circular orbits. Assume that these two masses orbit each other in a circular orbit in the x -- y plane. To a good approximation, the masses follow simple Keplerian orbits. However, such an orbit represents a changing quadrupole moment. That is, the system will give off gravitational waves. In theory, the loss of energy through gravitational radiation could eventually drop the Earth into the Sun. However, the total energy of the Earth orbiting the Sun ( kinetic energy + gravitational potential energy ) is about 1.14 × 10 joules of which only 200 watts ( joules per second ) is lost through gravitational radiation, leading to a decay in the orbit by about 1 × 10 meters per day or roughly the diameter of a proton. At this rate, it would take the Earth approximately 1 × 10 times more than the current age of the Universe to spiral onto the Sun. This estimate overlooks the decrease in r over time, but the majority of the time the bodies are far apart and only radiating slowly, so the difference is unimportant in this example. More generally, the rate of orbital decay can be approximated by d r d t = − 64 5 G 3 c 5 ( m 1 m 2 ) ( m 1 + m 2 ) r 3, ( displaystyle ( \frac ( mathrm ( d ) r ) ( mathrm ( d ) t ) ) = - ( \frac ( 64 ) ( 5 ) ) , ( \frac ( G ^ ( 3 ) ) ( c ^ ( 5 ) ) ) , ( \frac ( ( m_ ( 1 ) m_ ( 2 ) ) ( m_ ( 1 ) + m_ ( 2 ) ) ) ( r ^ ( 3 ) ) ) , ) where r is the separation between the bodies, t time, G the gravitational constant, c the speed of light, and m and m the masses of the bodies. This leads to an expected time to merger of t = 5 256 c 5 G 3 r 4 ( m 1 m 2 ) ( m 1 + m 2 ). ( displaystyle t = ( \frac ( 5 ) ( 256 ) ) , ( \frac ( c ^ ( 5 ) ) ( G ^ ( 3 ) ) ) , ( \frac ( r ^ ( 4 ) ) ( ( m_ ( 1 ) m_ ( 2 ) ) ( m_ ( 1 ) + m_ ( 2 ) ) ) ). ) Compact binaries Compact stars like white dwarfs and neutron stars can be constituents of binaries. For example, a pair of solar mass neutron stars in a circular orbit at a separation of 1.89 × 10 m ( 189,000 km ) has an orbital period of 1,000 seconds, and an expected lifetime of 1.30 × 10 seconds or about 414,000 years. Such a system could be observed by LISA if it were not too far away. A far greater number of white dwarf binaries exist with orbital periods in this range. White dwarf binaries have masses in the order of the Sun, and diameters in the order of the Earth. They can not get much closer together than 10,000 km before they will merge and explode in a supernova which would also end the emission of gravitational waves. Until then, their gravitational radiation would be comparable to that of a neutron star binary. Artist 's impression of merging neutron stars. This event is a source of gravitational waves. When the orbit of a neutron star binary has decayed to 1.89 × 10 m ( 1890 km ), its remaining lifetime is about 130,000 seconds or 36 hours. The orbital frequency will vary from 1 orbit per second at the start, to 918 orbits per second when the orbit has shrunk to 20 km at merger. The majority of gravitational radiation emitted will be at twice the orbital frequency. Just before merger, the inspiral could be observed by LIGO if such a binary were close enough. LIGO has only a few minutes to observe this merger out of a total orbital lifetime that may have been billions of years. ln August 2017, LIGO and Virgo observed the first binary neutron star inspiral in GW170817, and 70 observatories collaborated to detect the electromagnetic counterpart, a kilonova in the galaxy NGC 4993, 40 mega parsec away, emitting a short gamma ray burst ( GRB 170817A ) seconds after the merger, followed by a longer optical transient ( AT 2017gfo ) powered by r - process nuclei. Advanced LIGO detector should be able to detect such events up to 200 mega parsec away. Within this range of the order 40 events are expected per year. Black hole binaries Main article : Binary black hole Black hole binaries emit gravitational waves during their in - spiral, merger, and ring - down phases. The largest amplitude of emission occurs during the merger phase, which can be modeled with the techniques of numerical relativity. The first direct detection of gravitational waves, GW150914, came from the merger of two black holes. Supernovae Main article : supernova A supernova is a transient astronomical event that occurs during the last stellar evolutionary stages of a massive star 's life, whose dramatic and catastrophic destruction is marked by one final titanic explosion. This explosion can happen in one of many ways, but in all of them a significant proportion of the matter in the star is blown away into the surrounding space at extremely high velocities ( up to 10 % of the speed of light ). Unless there is perfect spherical symmetry in these explosions ( i.e., unless matter is spewed out evenly in all directions ), there will be gravitational radiation from the explosion. This is because gravitational waves are generated by a changing quadrupole moment, which can happen only when there is asymmetrical movement of masses. Since the exact mechanism by which supernovae take place is not fully understood, it is not easy to model the gravitational radiation emitted by them. Spinning neutron stars As noted above, a mass distribution will emit gravitational radiation only when there is spherically asymmetric motion among the masses. A spinning neutron star will generally emit no gravitational radiation because neutron stars are highly dense objects with a strong gravitational field that keeps them almost perfectly spherical. In some cases, however, there might be slight deformities on the surface called `` mountains '', which are bumps extending no more than 10 centimeters ( 4 inches ) above the surface, that make the spinning spherically asymmetric. This gives the star a quadrupole moment that changes with time, and it will emit gravitational waves until the deformities are smoothed out. Inflation Main article : inflation ( cosmology ) Many models of the Universe postulate that there was an inflationary epoch in the early history of the Universe when space expanded by a large factor in a very short amount of time. If this expansion was not symmetric in all directions, it may have emitted gravitational radiation detectable today as a gravitational wave background. This background signal is too weak for any currently operational gravitational wave detector to observe, and it is thought it may be decades before such an observation can be made. Properties and behaviour Energy, momentum, and angular momentum Water waves, sound waves, and electromagnetic waves are able to carry energy, momentum, and angular momentum and by doing so they carry those away from the source. Gravitational waves perform the same function. Thus, for example, a binary system loses angular momentum as the two orbiting objects spiral towards each other -- the angular momentum is radiated away by gravitational waves. The waves can also carry off linear momentum, a possibility that has some interesting implications for astrophysics. After two supermassive black holes coalesce, emission of linear momentum can produce a `` kick '' with amplitude as large as 4000 km / s. This is fast enough to eject the coalesced black hole completely from its host galaxy. Even if the kick is too small to eject the black hole completely, it can remove it temporarily from the nucleus of the galaxy, after which it will oscillate about the center, eventually coming to rest. A kicked black hole can also carry a star cluster with it, forming a hyper - compact stellar system. Or it may carry gas, allowing the recoiling black hole to appear temporarily as a `` naked quasar ''. The quasar SDSS J092712. 65 + 294344.0 is thought to contain a recoiling supermassive black hole. Redshifting and blueshifting Like electromagnetic waves, gravitational waves should exhibit shifting of wavelength due to the relative velocities of the source and observer, but also due to distortions of space - time, such as cosmic expansion. This is the case even though gravity itself is a cause of distortions of space - time. Redshifting of gravitational waves is different from redshifting due to gravity. Quantum gravity, wave - particle aspects, and graviton In the framework of quantum field theory, the graviton is the name given to a hypothetical elementary particle speculated to be the force carrier that mediates gravity. However the graviton is not yet proven to exist, and no scientific model yet exists that successfully reconciles general relativity which describes gravity, and the Standard Model which describes all other fundamental forces. Attempts, such as quantum gravity, have been made, but are not yet accepted. If such a particle exists, it is expected to be massless ( because the gravitational force appears to have unlimited range ) and must be a spin - 2 boson. It can be shown that any massless spin - 2 field would give rise to a force indistinguishable from gravitation, because a massless spin - 2 field must couple to ( interact with ) the stress -- energy tensor in the same way that the gravitational field does ; therefore if a massless spin - 2 particle were ever discovered, it would be likely to be the graviton without further distinction from other massless spin - 2 particles. Such a discovery would unite quantum theory with gravity. Significance for study of the early Universe Due to the weakness of the coupling of gravity to matter, gravitational waves experience very little absorption or scattering, even as they travel over astronomical distances. In particular, gravitational waves are expected to be unaffected by the opacity of the very early universe. In these early phases, space had not yet become `` transparent, '' so observations based upon light, radio waves, and other electromagnetic radiation that far back into time are limited or unavailable. Therefore, gravitational waves are expected in principle to have the potential to provide a wealth of observational data about the very early universe. Determining direction of travel The difficulty in directly detecting gravitational waves, means it is also difficult for a single detector to identify by itself the direction of a source. Therefore, multiple detectors are used, both to distinguish signals from other `` noise '' by confirming the signal is not of earthly origin, and also to determine direction by means of triangulation. This technique uses the fact that the waves travel at the speed of light and will reach different detectors at different times depending on their source direction. Although the differences in arrival time may be just a few milliseconds, this is sufficient to identify the direction of the origin of the wave with considerable precision. Only in the case of GW170814 were three detectors operating at the time of the event, therefore, the direction is precisely defined. The detection by all three instruments led to a very accurate estimate of the position of the source, with a 90 % credible region of just 60 deg, a factor 20 more accurate than before. Gravitational wave astronomy This article contains weasel words : vague phrasing that often accompanies biased or unverifiable information. Such statements should be clarified or removed. ( November 2017 ) This article 's tone or style may not reflect the encyclopedic tone used on Wikipedia. See Wikipedia 's guide to writing better articles for suggestions. ( November 2017 ) Two - dimensional representation of gravitational waves generated by two neutron stars orbiting each other. Main article : gravitational - wave astronomy During the past century, astronomy has been revolutionized by the use of new methods for observing the universe. Astronomical observations were originally made using visible light. Galileo Galilei pioneered the use of telescopes to enhance these observations. However, visible light is only a small portion of the electromagnetic spectrum, and not all objects in the distant universe shine strongly in this particular band. More useful information may be found, for example, in radio wavelengths. Using radio telescopes, astronomers have found pulsars, quasars, and made other unprecedented discoveries of objects not formerly known to scientists. Observations in the microwave band led to the detection of faint imprints of the Big Bang, a discovery Stephen Hawking called the `` greatest discovery of the century, if not all time ''. Similar advances in observations using gamma rays, x-rays, ultraviolet light, and infrared light have also brought new insights to astronomy. As each of these regions of the spectrum has opened, new discoveries have been made that could not have been made otherwise. Astronomers hope that the same holds true of gravitational waves. Gravitational waves have two important and unique properties. First, there is no need for any type of matter to be present nearby in order for the waves to be generated by a binary system of uncharged black holes, which would emit no electromagnetic radiation. Second, gravitational waves can pass through any intervening matter without being scattered significantly. Whereas light from distant stars may be blocked out by interstellar dust, for example, gravitational waves will pass through essentially unimpeded. These two features allow gravitational waves to carry information about astronomical phenomena heretofore never observed by humans, and as such represent a revolution in astrophysics. The sources of gravitational waves described above are in the low - frequency end of the gravitational - wave spectrum ( 10 to 10 Hz ). An astrophysical source at the high - frequency end of the gravitational - wave spectrum ( above 10 Hz and probably 10 Hz ) generates relic gravitational waves that are theorized to be faint imprints of the Big Bang like the cosmic microwave background. At these high frequencies it is potentially possible that the sources may be `` man made '' that is, gravitational waves generated and detected in the laboratory. A supermassive black hole, created from the merger of the black holes at the center of two merging galaxies detected by the Hubble Space Telescope, is theorized to have been ejected from the merger center by gravitational waves. Detection Main articles : Gravitational wave detection, Gravitational - wave observatory, and List of gravitational wave observations Now disproved evidence allegedly showing gravitational waves in the infant universe was found by the BICEP2 radio telescope. The microscopic examination of the focal plane of the BICEP2 detector is shown here. In 2015, however, the BICEP2 findings were confirmed to be the result of cosmic dust. Indirect detection Although the waves from the Earth -- Sun system are minuscule, astronomers can point to other sources for which the radiation should be substantial. One important example is the Hulse -- Taylor binary -- a pair of stars, one of which is a pulsar. The characteristics of their orbit can be deduced from the Doppler shifting of radio signals given off by the pulsar. Each of the stars is about 1.4 M and the size of their orbits is about 1 / 75 of the Earth -- Sun orbit, just a few times larger than the diameter of our own Sun. The combination of greater masses and smaller separation means that the energy given off by the Hulse -- Taylor binary will be far greater than the energy given off by the Earth -- Sun system -- roughly 10 times as much. The information about the orbit can be used to predict how much energy ( and angular momentum ) would be radiated in the form of gravitational waves. As the energy is carried off, the stars should draw closer to each other. This effect is called an inspiral, and it can be observed in the pulsar 's signals. The measurements on the Hulse -- Taylor system have been carried out over more than 30 years. The change in the orbital period matches the prediction from the gravitational radiation assumed by general relativity to within 0.2 percent. In 1993, Russell Hulse and Joe Taylor were awarded the Nobel Prize in Physics for this work, which was the first indirect evidence for gravitational waves. The lifetime of this binary system, from the present to merger is estimated to be a few hundred million years. Inspirals are very important sources of gravitational waves. Any time two compact objects ( white dwarfs, neutron stars, or black holes ) are in close orbits, they send out intense gravitational waves. As they spiral closer to each other, these waves become more intense. At some point they should become so intense that direct detection by their effect on objects on Earth or in space is possible. This direct detection is the goal of several large scale experiments. The only difficulty is that most systems like the Hulse -- Taylor binary are so far away. The amplitude of waves given off by the Hulse -- Taylor binary at Earth would be roughly h ≈ 10. There are some sources, however, that astrophysicists expect to find that produce much greater amplitudes of h ≈ 10. At least eight other binary pulsars have been discovered. Difficulties Gravitational waves are not easily detectable. When they reach the Earth, they have a small amplitude with strain approximates 10, meaning that an extremely sensitive detector is needed, and that other sources of noise can overwhelm the signal. Gravitational waves are expected to have frequencies 10 Hz < f < 10 Hz. Ground - based detectors A schematic diagram of a laser interferometer Though the Hulse -- Taylor observations were very important, they give only indirect evidence for gravitational waves. A more conclusive observation would be a direct measurement of the effect of a passing gravitational wave, which could also provide more information about the system that generated it. Any such direct detection is complicated by the extraordinarily small effect the waves would produce on a detector. The amplitude of a spherical wave will fall off as the inverse of the distance from the source ( the 1 / R term in the formulas for h above ). Thus, even waves from extreme systems like merging binary black holes die out to very small amplitudes by the time they reach the Earth. Astrophysicists expect that some gravitational waves passing the Earth may be as large as h ≈ 10, but generally no bigger. Resonant antennae Main article : Weber bar A simple device theorised to detect the expected wave motion is called a Weber bar -- a large, solid bar of metal isolated from outside vibrations. This type of instrument was the first type of gravitational wave detector. Strains in space due to an incident gravitational wave excite the bar 's resonant frequency and could thus be amplified to detectable levels. Conceivably, a nearby supernova might be strong enough to be seen without resonant amplification. With this instrument, Joseph Weber claimed to have detected daily signals of gravitational waves. His results, however, were contested in 1974 by physicists Richard Garwin and David Douglass. Modern forms of the Weber bar are still operated, cryogenically cooled, with superconducting quantum interference devices to detect vibration. Weber bars are not sensitive enough to detect anything but extremely powerful gravitational waves. MiniGRAIL is a spherical gravitational wave antenna using this principle. It is based at Leiden University, consisting of an exactingly machined 1,150 kg sphere cryogenically cooled to 20 millikelvins. The spherical configuration allows for equal sensitivity in all directions, and is somewhat experimentally simpler than larger linear devices requiring high vacuum. Events are detected by measuring deformation of the detector sphere. MiniGRAIL is highly sensitive in the 2 -- 4 kHz range, suitable for detecting gravitational waves from rotating neutron star instabilities or small black hole mergers. There are currently two detectors focused on the higher end of the gravitational wave spectrum ( 10 to 10 Hz ) : one at University of Birmingham, England, and the other at INFN Genoa, Italy. A third is under development at Chongqing University, China. The Birmingham detector measures changes in the polarization state of a microwave beam circulating in a closed loop about one meter across. Both detectors are expected to be sensitive to periodic spacetime strains of h ~ 6987200000000000000 ♠ 2 × 10 / √ Hz, given as an amplitude spectral density. The INFN Genoa detector is a resonant antenna consisting of two coupled spherical superconducting harmonic oscillators a few centimeters in diameter. The oscillators are designed to have ( when uncoupled ) almost equal resonant frequencies. The system is currently expected to have a sensitivity to periodic spacetime strains of h ~ 6983200000000000000 ♠ 2 × 10 / √ Hz, with an expectation to reach a sensitivity of h ~ 6980199999999999999 ♠ 2 × 10 / √ Hz. The Chongqing University detector is planned to detect relic high - frequency gravitational waves with the predicted typical parameters ~ 10 Hz ( 100 GHz ) and h ~ 10 to 10. Interferometers Simplified operation of a gravitational wave observatory Figure 1 : A beamsplitter ( green line ) splits coherent light ( from the white box ) into two beams which reflect off the mirrors ( cyan oblongs ) ; only one outgoing and reflected beam in each arm is shown, and separated for clarity. The reflected beams recombine and an interference pattern is detected ( purple circle ). Figure 2 : A gravitational wave passing over the left arm ( yellow ) changes its length and thus the interference pattern. A more sensitive class of detector uses laser interferometry to measure gravitational - wave induced motion between separated ' free ' masses. This allows the masses to be separated by large distances ( increasing the signal size ) ; a further advantage is that it is sensitive to a wide range of frequencies ( not just those near a resonance as is the case for Weber bars ). After years of development the first ground - based interferometers became operational in 2015. Currently, the most sensitive is LIGO -- the Laser Interferometer Gravitational Wave Observatory. LIGO has three detectors : one in Livingston, Louisiana, one at the Hanford site in Richland, Washington and a third ( formerly installed as a second detector at Hanford ) that is planned to be moved to India. Each observatory has two light storage arms that are 4 kilometers in length. These are at 90 degree angles to each other, with the light passing through 1 m diameter vacuum tubes running the entire 4 kilometers. A passing gravitational wave will slightly stretch one arm as it shortens the other. This is precisely the motion to which an interferometer is most sensitive. Even with such long arms, the strongest gravitational waves will only change the distance between the ends of the arms by at most roughly 10 m. LIGO should be able to detect gravitational waves as small as h ~ 6978500000000000000 ♠ 5 × 10. Upgrades to LIGO and Virgo should increase the sensitivity still further. Another highly sensitive interferometer, KAGRA, is under construction in the Kamiokande mine in Japan. A key point is that a tenfold increase in sensitivity ( radius of ' reach ' ) increases the volume of space accessible to the instrument by one thousand times. This increases the rate at which detectable signals might be seen from one per tens of years of observation, to tens per year. Interferometric detectors are limited at high frequencies by shot noise, which occurs because the lasers produce photons randomly ; one analogy is to rainfall -- the rate of rainfall, like the laser intensity, is measurable, but the raindrops, like photons, fall at random times, causing fluctuations around the average value. This leads to noise at the output of the detector, much like radio static. In addition, for sufficiently high laser power, the random momentum transferred to the test masses by the laser photons shakes the mirrors, masking signals of low frequencies. Thermal noise ( e.g., Brownian motion ) is another limit to sensitivity. In addition to these ' stationary ' ( constant ) noise sources, all ground - based detectors are also limited at low frequencies by seismic noise and other forms of environmental vibration, and other ' non-stationary ' noise sources ; creaks in mechanical structures, lightning or other large electrical disturbances, etc. may also create noise masking an event or may even imitate an event. All these must be taken into account and excluded by analysis before detection may be considered a true gravitational wave event. Einstein@Home Main article : Einstein@Home The simplest gravitational waves are those with constant frequency. The waves given off by a spinning, non-axisymmetric neutron star would be approximately monochromatic : a pure tone in acoustics. Unlike signals from supernovae of binary black holes, these signals evolve little in amplitude or frequency over the period it would be observed by ground - based detectors. However, there would be some change in the measured signal, because of Doppler shifting caused by the motion of the Earth. Despite the signals being simple, detection is extremely computationally expensive, because of the long stretches of data that must be analysed. The Einstein@Home project is a distributed computing project similar to SETI@home intended to detect this type of gravitational wave. By taking data from LIGO and GEO, and sending it out in little pieces to thousands of volunteers for parallel analysis on their home computers, Einstein@Home can sift through the data far more quickly than would be possible otherwise. Space - based interferometers Space - based interferometers, such as LISA and DECIGO, are also being developed. LISA 's design calls for three test masses forming an equilateral triangle, with lasers from each spacecraft to each other spacecraft forming two independent interferometers. LISA is planned to occupy a solar orbit trailing the Earth, with each arm of the triangle being five million kilometers. This puts the detector in an excellent vacuum far from Earth - based sources of noise, though it will still be susceptible to heat, shot noise, and artifacts caused by cosmic rays and solar wind. Using pulsar timing arrays Pulsars are rapidly rotating stars. A pulsar emits beams of radio waves that, like lighthouse beams, sweep through the sky as the pulsar rotates. The signal from a pulsar can be detected by radio telescopes as a series of regularly spaced pulses, essentially like the ticks of a clock. Gravitational waves affect the time it takes the pulses to travel from the pulsar to a telescope on Earth. A pulsar timing array uses millisecond pulsars to seek out perturbations due to gravitational waves in measurements of pulse arrival times at a telescope, in other words, to look for deviations in the clock ticks. In particular, pulsar timing arrays can search for a distinct pattern of correlation and anti-correlation between the signals over an array of different pulsars ( resulting in the name `` pulsar timing array '' ). Although pulsar pulses travel through space for hundreds or thousands of years to reach us, pulsar timing arrays are sensitive to perturbations in their travel time of much less than a millionth of a second. Globally there are three active pulsar timing array projects. The North American Nanohertz Gravitational Wave Observatory uses data collected by the Arecibo Radio Telescope and Green Bank Telescope. The Parkes Pulsar Timing Array at the Parkes radio - telescope has been collecting data since March 2005. The European Pulsar Timing Array uses data from the four largest telescopes in Europe : the Lovell Telescope, the Westerbork Synthesis Radio Telescope, the Effelsberg Telescope and the Nancay Radio Telescope. ( Upon completion the Sardinia Radio Telescope will be added to the EPTA also. ) These three projects have begun collaborating under the title of the International Pulsar Timing Array project. Primordial Main article : Primordial gravitational wave Primordial gravitational waves are gravitational waves observed in the cosmic microwave background. They were allegedly detected by the BICEP2 instrument, an announcement made on 17 March 2014, which was withdrawn on 30 January 2015 ( `` the signal can be entirely attributed to dust in the Milky Way '' ). LIGO and Virgo observations Main articles : First observation of gravitational waves and List of gravitational wave observations LIGO measurement of the gravitational waves at the Hanford ( left ) and Livingston ( right ) detectors, compared to the theoretical predicted values. On 11 February 2016, the LIGO collaboration announced the first observation of gravitational waves, from a signal detected at 09 : 50 : 45 GMT on 14 September 2015 of two black holes with masses of 29 and 36 solar masses merging about 1.3 billion light - years away. During the final fraction of a second of the merger, it released more than 50 times the power of all the stars in the observable universe combined. The signal increased in frequency from 35 to 250 Hz over 10 cycles ( 5 orbits ) as it rose in strength for a period of 0.2 second. The mass of the new merged black hole was 62 solar masses. Energy equivalent to three solar masses was emitted as gravitational waves. The signal was seen by both LIGO detectors in Livingston and Hanford, with a time difference of 7 milliseconds due to the angle between the two detectors and the source. The signal came from the Southern Celestial Hemisphere, in the rough direction of ( but much further away than ) the Magellanic Clouds. The confidence level of this being an observation of gravitational waves was 99.99994 %. Since then LIGO and Virgo have reported more gravitational wave observations from merging black hole binaries. On 16 October 2017 the LIGO and Virgo collaborations announced the first ever detection of gravitational waves originating from the coalescence of a binary neutron star system. The observation of this GW170817 transient, which occurred on 17 August 2017, allowed for constraining the masses of the neutron stars involved between 0.86 and 2.26 solar masses. Further analysis allowed a greater restriction of the mass values to the interval, to 1.17 -- 1.60 solar masses, with the total system mass measured to be 2.73 -- 2.78 solar masses. The inclusion of the Virgo detector in the observation effort allowed for an improvement of the localization of the source by a factor of 10. This in turn facilitated the electromagnetic follow - up of the event. In contrast to the case of binary black hole mergers, binary neutron star mergers were expected to yield an electromagnetic counterpart, that is, a light signal associated with the event. A gamma - ray burst ( GRB 170817A ) was detected by the Fermi Gamma - ray Space Telescope, occurring 1.7 seconds after the gravitational wave transient. The signal, originating near the galaxy NGC 4993, was associated with the neutron star merger. This was corroborated by the electromagnetic follow - up of the event ( AT 2017gfo ), involving 70 telescopes and observatories and yielding observations over a large region of the electromagnetic spectrum which further confirmed the neutron star nature of the merged objects and the associated kilonova. In fiction An episode of the Russian science - fiction novel Space Apprentice by Arkady and Boris Strugatsky shows the experiment monitoring the propagation of gravitational waves at the expense of annihilating a chunk of asteroid 15 Eunomia the size of Mount Everest. In Stanislaw Lem 's Fiasco, a `` gravity gun '' or `` gracer '' ( gravity amplification by collimated emission of resonance ) is used to reshape a collapsar, so that the protagonists can exploit the extreme relativistic effects and make an interstellar journey. In Greg Egan 's Diaspora, the analysis of a gravitational wave signal from the inspiral of a nearby binary neutron star reveals that its collision and merger is imminent, implying a large gamma - ray burst is going to impact the Earth. See also 2017 Nobel Prize in Physics, which was awarded to three individual physicists for their role in the discovery of and testing for the waves Anti-gravity First observation of gravitational waves Gravitational field Gravitational - wave astronomy Gravitational wave background Gravitational - wave observatory Gravitomagnetism Graviton ( and Gravitational wave observation # Gravitons ) Hawking radiation, for gravitationally induced electromagnetic radiation from black holes HM Cancri LISA, DECIGO and BBO -- Proposed space - based detectors LIGO, Virgo interferometer, GEO600, KAGRA, and TAMA 300 -- Ground - based gravitational - wave detectors Linearised Einstein field equations Peres metric pp - wave spacetime, for an important class of exact solutions modelling gravitational radiation PSR B1913 + 16, the first binary pulsar discovered and the first experimental evidence for the existence of gravitational waves. Spin - flip, a consequence of gravitational wave emission from binary supermassive black holes Sticky bead argument, for a physical way to see that gravitational radiation should carry energy Tidal force References Jump up ^ http://www.academie-sciences.fr/pdf/dossiers/Poincare/Poincare_pdf/Poincare_CR1905.pdf Jump up ^ Einstein, A ( June 1916 ). `` Näherungsweise Integration der Feldgleichungen der Gravitation ''. Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften Berlin. part 1 : 688 -- 696. Bibcode : 1916SPAW... 688E. ^ Jump up to : Einstein, A ( 1918 ). `` Über Gravitationswellen ''. Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften Berlin. part 1 : 154 -- 167. Jump up ^ Finley, Dave. `` Einstein 's gravity theory passes toughest test yet : Bizarre binary star system pushes study of relativity to new limits ''. Phys.Org. Jump up ^ The Detection of Gravitational Waves using LIGO, B. Barish Archived 2016 - 03 - 03 at the Wayback Machine. Jump up ^ Einstein, Albert ; Rosen, Nathan ( January 1937 ). `` On gravitational waves ''. Journal of the Franklin Institute. 223 ( 1 ) : 43 -- 54. Bibcode : 1937FrInJ. 223... 43E. doi : 10.1016 / S0016 - 0032 ( 37 ) 90583 - 0. Retrieved 2016 - 05 - 13. ^ Jump up to : Castelvecchi, Davide ; Witze, Witze ( 11 February 2016 ). `` Einstein 's gravitational waves found at last ''. Nature News. doi : 10.1038 / nature. 2016.19361. Retrieved 2016 - 02 - 11. ^ Jump up to : B. P. Abbott ( LIGO Scientific Collaboration and Virgo Collaboration ) et al. ( 2016 ). `` Observation of Gravitational Waves from a Binary Black Hole Merger ''. Physical Review Letters. 116 ( 6 ) : 061102. arXiv : 1602.03837. Bibcode : 2016PhRvL. 116f1102A. doi : 10.1103 / PhysRevLett. 116.061102. PMID 26918975. CS1 maint : Uses authors parameter ( link ) ^ Jump up to : `` Gravitational waves detected 100 years after Einstein 's prediction NSF - National Science Foundation ''. www.nsf.gov. Retrieved 2016 - 02 - 11. Jump up ^ LIGO Scientific Collaboration and Virgo Collaboration ; Abbott, B. P. ; Abbott, R. ; Abbott, T. D. ; Abernathy, M. R. ; Acernese, F. ; Ackley, K. ; Adams, C. ; Adams, T. ( 2016 - 06 - 15 ). `` GW151226 : Observation of Gravitational Waves from a 22 - Solar - Mass Binary Black Hole Coalescence ''. Physical Review Letters. 116 ( 24 ) : 241103. arXiv : 1606.04855. Bibcode : 2016PhRvL. 116x1103A. doi : 10.1103 / PhysRevLett. 116.241103. PMID 27367379. Jump up ^ Abbott, B.P. ; Abbott, R. ; Abbott, T.D. ; Acernese, F. ; Ackley, K. ; Adams, C. ; Adams, T. ; Addesso, P. ; Adhikari, R.X. ( 2017 - 06 - 01 ). `` GW170104 : Observation of a 50 - Solar - Mass Binary Black Hole Coalescence at Redshift 0.2 ''. Physical Review Letters. 118 ( 22 ) : 221101. arXiv : 1706.01812. Bibcode : 2017PhRvL. 118v1101A. doi : 10.1103 / physrevlett. 118.221101. PMID 28621973. Jump up ^ `` European detector spots its first gravitational wave ''. 27 September 2017. Retrieved 27 September 2017. ^ Jump up to : Abbott, B. P. ; et al. ( LIGO Scientific Collaboration & Virgo Collaboration ) ( 16 October 2017 ). `` GW170817 : Observation of Gravitational Waves from a Binary Neutron Star Inspiral ''. Physical Review Letters. 119 ( 16 ). arXiv : 1710.05832. Bibcode : 2017PhRvL. 119p1101A. doi : 10.1103 / PhysRevLett. 119.161101. CS1 maint : Explicit use of et al. ( link ) Jump up ^ `` The Newest Search for Gravitational Waves has Begun ''. LIGO Caltech. LIGO. 18 September 2015. Retrieved 29 November 2015. ^ Jump up to : Rincon, Paul ; Amos, Jonathan ( 3 October 2017 ). `` Einstein 's waves win Nobel Prize ''. BBC News. Retrieved 3 October 2017. ^ Jump up to : Overbye, Dennis ( 3 October 2017 ). `` 2017 Nobel Prize in Physics Awarded to LIGO Black Hole Researchers ''. The New York Times. Retrieved 3 October 2017. ^ Jump up to : Kaiser, David ( 3 October 2017 ). `` Learning from Gravitational Waves ''. The New York Times. Retrieved 3 October 2017. Jump up ^ `` First Second of the Big Bang ''. How The Universe Works 3. 2014. Discovery Science. Jump up ^ Bernard Schutz ( 14 May 2009 ). A First Course in General Relativity. Cambridge University Press. ISBN 978 - 0 - 521 - 88705 - 2. Jump up ^ LIGO Scientific Collaboration ; Virgo Collaboration ( 2012 ). `` Search for Gravitational Waves from Low Mass Compact Binary Coalescence in LIGO 's Sixth Science Run and Virgo 's Science Runs 2 and 3 ''. Physical Review D. 85 ( 8 ) : 082002. arXiv : 1111.7314. Bibcode : 2012PhRvD... 85h2002A. doi : 10.1103 / PhysRevD. 85.082002. Jump up ^ Krauss, LM ; Dodelson, S ; Meyer, S ( 2010 ). `` Primordial Gravitational Waves and Cosmology ''. Science. 328 ( 5981 ) : 989 -- 992. arXiv : 1004.2504. Bibcode : 2010Sci... 328... 989K. doi : 10.1126 / science. 1179541. PMID 20489015. ^ Jump up to : Hawking, S.W. ; Israel, W. ( 1979 ). General Relativity : An Einstein Centenary Survey. Cambridge : Cambridge University Press. p. 98. ISBN 0 - 521 - 22285 - 0. ^ Jump up to : Staff ( 17 March 2014 ). `` BICEP2 2014 Results Release ''. National Science Foundation. Retrieved 18 March 2014. CS1 maint : Uses authors parameter ( link ) ^ Jump up to : Clavin, Whitney ( 17 March 2014 ). `` NASA Technology Views Birth of the Universe ''. NASA. Retrieved 17 March 2014. Jump up ^ Overbye, Dennis ( 17 March 2014 ). `` Detection of Waves in Space Buttresses Landmark Theory of Big Bang ''. New York Times. Retrieved 17 March 2014. Jump up ^ Heaviside O. A gravitational and electromagnetic analogy, Electromagnetic Theory, 1893, vol. 1 455 -- 466 Appendix B Jump up ^ ( PDF ) Membres de l'Académie des sciences depuis sa création : Henri Poincare. Sur la dynamique de l ' electron. Note de H. Poincaré. C.R.T. 140 ( 1905 ) 1504 -- 1508. Jump up ^ http://www.academie-sciences.fr/pdf/dossiers/Poincare/Poincare_pdf/Poincare_CR1905.pdf page 1507 ^ Jump up to : Cervantes - Cota, J.L. ; Galindo - Uribarri, S. ; Smoot, G.F. ( 2016 ). `` A Brief History of Gravitational Waves ''. Universe. 2 ( 3 ) : 22. arXiv : 1609.09400. Bibcode : 2016Univ... 2... 22C. doi : 10.3390 / universe2030022. ^ Jump up to : Daniel Kennefick ( 29 March 2016 ). Traveling at the Speed of Thought : Einstein and the Quest for Gravitational Waves. Princeton University Press. ISBN 978 - 1 - 4008 - 8274 - 8. Jump up ^ Gertsenshtein, M.E. ; Pustovoit, V.I. ( 1962 ). `` On the detection of low frequency gravitational waves ''. JETP. 43 : 605 -- 607. Jump up ^ Clara Moskowitz ( 17 March 2014 ). `` Gravity Waves from Big Bang Detected ''. Scientific American. Retrieved 21 March 2016. Jump up ^ Ian Sample. `` Gravitational waves turn to dust after claims of flawed analysis ''. the Guardian. Jump up ^ LIGO press conference 11 February 2016 Jump up ^ Landau, L.D. ; Lifshitz, E.M. ( 1975 ). The Classical Theory of Fields ( Fourth Revised English ed. ). Pergamon Press. pp. 356 -- 357. ISBN 0 - 08 - 025072 - 6. Jump up ^ `` Gravitational Astrophysics Laboratory ''. science. gsfc / nasa. gov. Retrieved 20 September 2016. Jump up ^ Peters, P. ; Mathews, J. ( 1963 ). `` Gravitational Radiation from Point Masses in a Keplerian Orbit ''. Physical Review. 131 ( 1 ) : 435 -- 440. Bibcode : 1963PhRv... 131... 435P. doi : 10.1103 / PhysRev. 131.435. Jump up ^ Peters, P. ( 1964 ). `` Gravitational Radiation and the Motion of Two Point Masses ''. Physical Review. 136 ( 4B ) : B1224 -- B1232. Bibcode : 1964PhRv... 136.1224 P. doi : 10.1103 / PhysRev. 136. B1224. ^ Jump up to : Gravitational Radiation Jump up ^ `` ESO Telescopes Observe First Light from Gravitational Wave Source - Merging neutron stars scatter gold and platinum into space ''. www.eso.org. Retrieved 18 October 2017. Jump up ^ LIGO Scientific Collaboration -- FAQ ; section : `` Do we expect LIGO 's advanced detectors to make a discovery, then ? '' and `` What 's so different about LIGO 's advanced detectors ? '', retrieved 14 February 2016 Jump up ^ Pretorius, Frans ( 2005 ). `` Evolution of Binary Black - Hole Spacetimes ''. Physical Review Letters. 95 ( 12 ) : 121101. arXiv : gr - qc / 0507014. Bibcode : 2005PhRvL... 95l1101P. doi : 10.1103 / PhysRevLett. 95.121101. ISSN 0031 - 9007. PMID 16197061. Jump up ^ Campanelli, M. ; Lousto, C.O. ; Marronetti, P. ; Zlochower, Y. ( 2006 ). `` Accurate Evolutions of Orbiting Black - Hole Binaries without Excision ''. Physical Review Letters. 96 ( 11 ) : 111101. arXiv : gr - qc / 0511048. Bibcode : 2006PhRvL... 96k1101C. doi : 10.1103 / PhysRevLett. 96.111101. ISSN 0031 - 9007. PMID 16605808. Jump up ^ Baker, John G. ; Centrella, Joan ; Choi, Dae - Il ; Koppitz, Michael ; van Meter, James ( 2006 ). `` Gravitational - Wave Extraction from an Inspiraling Configuration of Merging Black Holes ''. Physical Review Letters. 96 ( 11 ) : 111102. arXiv : gr - qc / 0511103. Bibcode : 2006PhRvL... 96k1102B. doi : 10.1103 / PhysRevLett. 96.111102. ISSN 0031 - 9007. PMID 16605809. Jump up ^ `` Neutron Star Crust Is Stronger than Steel ''. Retrieved 2016 - 07 - 01. Jump up ^ Merritt, D. ; et al. ( May 2004 ). `` Consequences of Gravitational Wave Recoil ''. The Astrophysical Journal Letters. 607 ( 1 ) : L9 -- L12. arXiv : astro - ph / 0402057. Bibcode : 2004ApJ... 607L... 9M. doi : 10.1086 / 421551. Jump up ^ Gualandris, A. ; Merritt, D. ; et al. ( May 2008 ). `` Ejection of Supermassive Black Holes from Galaxy Cores ''. The Astrophysical Journal. 678 ( 2 ) : 780 -- 797. arXiv : 0708.0771. Bibcode : 2008ApJ... 678... 780G. doi : 10.1086 / 586877. CS1 maint : Explicit use of et al. ( link ) Jump up ^ Merritt, D. ; Schnittman, J.D. ; Komossa, S. ( 2009 ). `` Hypercompact Stellar Systems Around Recoiling Supermassive Black Holes ''. The Astrophysical Journal. 699 ( 2 ) : 1690 -- 1710. arXiv : 0809.5046. Bibcode : 2009ApJ... 699.1690 M. doi : 10.1088 / 0004 - 637X / 699 / 2 / 1690. Jump up ^ Komossa, S. ; Zhou, H. ; Lu, H. ( May 2008 ). `` A Recoiling Supermassive Black Hole in the Quasar SDSS J092712. 65 + 294344.0 ? ''. The Astrophysical Journal. 678 ( 2 ) : L81 -- L84. arXiv : 0804.4585. Bibcode : 2008ApJ... 678L... 81K. doi : 10.1086 / 588656. Jump up ^ For a comparison of the geometric derivation and the ( non-geometric ) spin - 2 field derivation of general relativity, refer to box 18.1 ( and also 17.2. 5 ) of Misner, C.W. ; Thorne, K.S. ; Wheeler, J.A. ( 1973 ). Gravitation. W.H. Freeman. ISBN 0 - 7167 - 0344 - 0. Jump up ^ Lightman, A.P. ; Press, W.H. ; Price, R.H. ; Teukolsky, S.A. ( 1975 ). `` Problem 12.16 ''. Problem book in Relativity and Gravitation. Princeton University Press. ISBN 0 - 691 - 08162 - X. Jump up ^ Update on Gravitational Wave Science from the LIGO - Virgo Scientific Collaborations ( Video of the press conference ), retrieved 27 September 2017 Jump up ^ Berry, Christopher ( 14 May 2015 ). `` Listening to the gravitational universe : what ca n't we see ? ''. University of Birmingham. University of Birmingham. Retrieved 29 November 2015. Jump up ^ Mack, Katie ( 2017 - 06 - 12 ). `` Black Holes, Cosmic Collisions and the Rippling of Spacetime ''. The Atlantic. Jump up ^ L.P. Grishchuk ( 1976 ), `` Primordial Gravitons and the Possibility of Their Observation '', Sov. Phys. JETP Lett. 23, p. 293. Jump up ^ Braginsky, V.B., Rudenko and Valentin, N. Section 7 : `` Generation of gravitational waves in the laboratory '', Physics Report ( Review section of Physics Letters ), 46, No. 5. 165 -- 200, ( 1978 ). Jump up ^ Li, Fangyu, Baker, R. ML, Jr., and Woods, R.C., `` Piezoelectric - Crystal - Resonator High - Frequency Gravitational Wave Generation and Synchro - Resonance Detection '', in the proceedings of Space Technology and Applications International Forum ( STAIF - 2006 ), edited by M.S. El - Genk, AIP Conference Proceedings, Melville NY 813 : 2006. Jump up ^ Wall, SPACE.com, Mike. `` Gravitational Waves Send Supermassive Black Hole Flying ''. Scientific American. Retrieved 2017 - 03 - 27. Jump up ^ Chiaberge, M. ; Ely, J.C. ; Meyer, E.T. ; Georganopoulos, M. ; Marinucci, A. ; Bianchi, S. ; Tremblay, G.R. ; Hilbert, B. ; Kotyla, J.P. ( 2016 - 11 - 16 ). `` The puzzling case of the radio - loud QSO 3C 186 : a gravitational wave recoiling black hole in a young radio source ? ''. Astronomy & Astrophysics. 600 : A57. arXiv : 1611.05501 ( astro - ph ). Bibcode : 2017A&A... 600A... 57C. doi : 10.1051 / 0004 - 6361 / 201629522. ^ Jump up to : Cowen, Ron ( 2015 - 01 - 30 ). `` Gravitational waves discovery now officially dead ''. nature. doi : 10.1038 / nature. 2015.16830. Jump up ^ Relativistic Binary Pulsar B1913 + 16 : Thirty Years of Observations and Analysis Jump up ^ Damour, Thibault ( 2015 ). `` 1974 : the discovery of the first binary pulsar ''. Classical and Quantum Gravity. 32 ( 12 ) : 124009. arXiv : 1411.3930. Bibcode : 2015CQGra... 32l4009D. doi : 10.1088 / 0264 - 9381 / 32 / 12 / 124009. Jump up ^ Crashing Black Holes Jump up ^ Binary and Millisecond Pulsars Archived 2012 - 03 - 01 at the Wayback Machine. Jump up ^ `` Noise and Sensitivity ''. gwoptics : Gravitational wave E-book. University of Birmingham. Retrieved 10 December 2015. Jump up ^ Thorne, Kip S. ( 1995 ). `` Gravitational Waves ''. Particle and Nuclear Astrophysics and Cosmology in the Next Millenium : 160. arXiv : gr - qc / 9506086. Bibcode : 1995pnac. conf... 160T. Jump up ^ David G. Blair ( Ed. ) ( 1991 ). The detection of gravitational waves. Cambridge University Press. CS1 maint : Extra text : authors list ( link ) Jump up ^ For a review of early experiments using Weber bars, see Levine, J. ( April 2004 ). `` Early Gravity - Wave Detection Experiments, 1960 -- 1975 ''. Physics in Perspective. 6 ( 1 ) : 42 -- 75. Bibcode : 2004PhP... 6... 42L. doi : 10.1007 / s00016 - 003 - 0179 - 6. Jump up ^ `` MiniGRAIL, the first spherical gravitational wave detector ''. Jump up ^ de Waard, Arlette ; Luciano Gottardi ; Giorgio Frossati ( July 2000 ). Spherical Gravitational Wave Detectors : cooling and quality factor of a small CuAl6 % sphere ( PDF ). Marcel Grossmann meeting on General Relativity. Rome, Italy : World Scientific Publishing Co. Pte. Ltd. ( published December 2002 ). pp. 1899 -- 1901. Bibcode : 2002nmgm. meet. 1899D. doi : 10.1142 / 9789812777386_0420. ISBN 9789812777386. Jump up ^ Cruise, Mike. `` Research Interests ''. Astrophysics & Space Research Group. University of Birmingham. Retrieved 29 November 2015. Jump up ^ High Frequency Relic Gravitational Waves Archived 2016 - 02 - 16 at the Wayback Machine... page 12 Jump up ^ The idea of using laser interferometry for gravitational wave detection was first mentioned by Gerstenstein and Pustovoit 1963 Sov. Phys. -- JETP 16 433. Weber mentioned it in an unpublished laboratory notebook. Rainer Weiss first described in detail a practical solution with an analysis of realistic limitations to the technique in R. Weiss ( 1972 ). `` Electromagetically Coupled Broadband Gravitational Antenna ''. Quarterly Progress Report, Research Laboratory of Electronics, MIT 105 : 54. Jump up ^ LIGO Scientific Collaboration ; Virgo Collaboration ( 2010 ). `` Predictions for the rates of compact binary coalescences observable by ground - based gravitational - wave detectors ''. Classical and Quantum Gravity. 27 ( 17 ) : 17300. arXiv : 1003.2480. Bibcode : 2010CQGra... 27q3001A. doi : 10.1088 / 0264 - 9381 / 27 / 17 / 173001. Jump up ^ `` Einstein@Home ''. Jump up ^ `` Gravitational waves from black holes detected ''. BBC News. 11 February 2016. Jump up ^ This collision was 50 times more powerful than all the stars in the universe combined ^ Jump up to : LIGO 's First - Ever Detection of Gravitational Waves Opens a New Window on the Universe Jump up ^ `` GW170817 Press Release ''. LIGO Lab Caltech. Retrieved 2017 - 10 - 17. Jump up ^ ME Gerstenstein ; VI Pustovoit ( 1962 ). `` On the Detection of Low - Frequency Gravitational Waves ''. ZhETF ( in Russian ). 16 ( 8 ) : 605 -- 607. Bibcode : 1963JETP... 16... 433G. Further Reading Bartusiak, Marcia. Einstein 's Unfinished Symphony. Washington, DC : Joseph Henry Press, 2000. Chakrabarty, Indrajit ( 1999 ). `` Gravitational Waves : An Introduction ''. arXiv : physics / 9908041. Landau, L.D. and Lifshitz, E.M., The Classical Theory of Fields ( Pergamon Press ), 1987. Will, Clifford M. ( 2014 ). `` The Confrontation between General Relativity and Experiment ''. Living Reviews in Relativity. 17 ( 1 ) : 4. arXiv : 1403.7377. Bibcode : 2014LRR... 17... 4W. doi : 10.12942 / lrr - 2014 - 4. Peter Saulson, Fundamentals of Interferometric Gravitational Wave Detectors, World Scientific, 1994. Barish, Barry C. ; Weiss, Rainer ( 1999 ). `` LIGO and the Detection of Gravitational Waves ''. Physics Today. 54 ( 10 ) : 44. Bibcode : 1999PhT... 52j... 44B. doi : 10.1063 / 1.882861. Bibliography Berry, Michael, Principles of Сosmology and Gravitation ( Adam Hilger, Philadelphia, 1989 ). ISBN 0 - 85274 - 037 - 9 Collins, Harry, Gravity 's Shadow : The Search for Gravitational Waves, University of Chicago Press, 2004. ISBN 0 - 226 - 11378 - 7 P.J.E. Peebles, Principles of Physical Cosmology ( Princeton University Press, Princeton, 1993 ). ISBN 0 - 691 - 01933 - 9. Wheeler, John Archibald and Ciufolini, Ignazio, Gravitation and Inertia ( Princeton University Press, Princeton, 1995 ). ISBN 0 - 691 - 03323 - 4. Woolf, Harry, ed., Some Strangeness in the Proportion ( Addison -- Wesley, Reading, Massachusetts, 1980 ). ISBN 0 - 201 - 09924 - 1. Collins, Harry, Gravity 's Kiss : The Detection of Gravitational Waves ( The MIT Press, Cambridge Massachuetts, 2017 ). ISBN 978 - 0 - 262 - 03618 - 4. External links Wikimedia Commons has media related to Gravitational waves. Look up gravitational wave in Wiktionary, the free dictionary. Laser Interferometer Gravitational Wave Observatory. LIGO Laboratory, operated by the California Institute of Technology and the Massachusetts Institute of Technology Gravitational Waves -- Collected articles at Nature Journal Gravitational Waves -- Collected articles Scientific American Video ( 94 : 34 ) -- Scientific Talk on Discovery, Barry Barish, CERN ( 11 February 2016 ) Gravitational - wave astronomy Gravitational wave Gravitational - wave observatory Detectors Resonant mass antennas Active AURIGA Mario Schenberg MiniGRAIL Past ALLEGRO Weber bar Proposed TOBA Ground - based Interferometers Active AIGO Advanced LIGO ( LIGO Scientific Collaboration ) Advanced Virgo ( European Gravitational Observatory ) CLIO GEO600 Past TAMA 300 Planned INDIGO ( LIGO - India ) KAGRA Proposed AIGO ( LIGO - Australia ) Cosmic Explorer Einstein Telescope Space - based interferometers Past LISA Pathfinder Proposed Big Bang Observer DECIGO LISA TianQin Pulsar timing arrays EPTA IPTA NANOGrav PPTA Data analysis Einstein@Home PyCBC Zooniverse : Gravity Spy Observations Events List of observations First observation ( GW150914 ) GW151226 GW170104 GW170608 GW170814 GW170817 ( first neutron star merger ) Methods Direct detection Laser interferometers Resonant mass detectors Proposed : Atom interferometers Indirect detection B - modes of CMB Pulsar timing array Binary pulsar Theory General relativity Tests of general relativity Metric theories Graviton Effects / properties Polarization Spin - flip Redshift Travel with speed of light h strain Chirp signal ( chirp mass ) Carried energy Types / sources Stochastic Cosmic inflation - quantum fluctuation Phase transition Binary inspiral Supermassive black holes Stellar black holes Neutron stars Continuous Rotating neutron star Burst Supernova or from unknown sources Hypothesis Colliding cosmic string and other unknown sources Relativity Special relativity Background Principle of relativity Special relativity Foundations Frame of reference Speed of light Hyperbolic orthogonality Rapidity Maxwell 's equations Formulation Galilean relativity Galilean transformation Lorentz transformation Consequences Time dilation Relativistic mass Mass -- energy equivalence Length contraction Relativity of simultaneity Relativistic Doppler effect Thomas precession Relativistic disks Spacetime Light cone World line Spacetime diagram Biquaternions Minkowski space General relativity Background Introduction Mathematical formulation Fundamental concepts Special relativity Equivalence principle World line Riemannian geometry Minkowski diagram Penrose diagram Phenomena Black hole Event horizon Frame - dragging Geodetic effect Lenses Singularity Waves Ladder paradox Twin paradox Two - body problem BKL singularity Equations ADM formalism BSSN formalism Einstein field equations Geodesic equation Friedmann equations Linearized gravity Post-Newtonian formalism Raychaudhuri equation Hamilton -- Jacobi -- Einstein equation Ernst equation Tolman -- Oppenheimer -- Volkoff equation Advanced theories Brans -- Dicke theory Kaluza -- Klein Mach 's principle Quantum gravity Solutions Schwarzschild ( interior ) Reissner -- Nordström Gödel Kerr Kerr -- Newman Kasner Friedmann -- Lemaître -- Robertson -- Walker Taub -- NUT Milne pp - wave van Stockum dust Weyl − Lewis − Papapetrou Scientists Einstein Lorentz Hilbert Poincaré Schwarzschild de Sitter Reissner Nordström Weyl Eddington Friedmann Milne Zwicky Lemaître Gödel Wheeler Robertson Bardeen Walker Kerr Chandrasekhar Ehlers Penrose Hawking Taylor Hulse Stockum Taub Newman Yau Thorne Weiss Bondi Misner others The fundamental interactions of physics Physical forces Strong interaction Weak interaction Electromagnetism Gravitation Radiations Electromagnetic radiation Gravitational radiation Hypothetical forces Quintessence Weak gravity conjecture Glossary of physics Particle physics Philosophy of physics Universe Weakless Universe Breakthrough of the Year Science journal 1996 : HIV understanding 1997 : Dolly the sheep 1998 : Accelerating universe 1999 : Stem cell 2000 : Whole genome sequencing 2001 : Nanocircuits or Molecular circuit 2002 : RNA interference 2003 : Dark energy 2004 : Spirit rover 2005 : Evolution in action 2006 : Poincaré conjecture proof 2007 : Human genetic variation 2008 : Cellular reprogramming 2009 : Ardipithecus ramidus 2010 : First quantum machine 2011 : HPTN 052 clinical trial 2012 : Higgs boson discovery 2013 : Cancer immunotherapy 2014 : Rosetta comet mission 2015 : CRISPR genome - editing method 2016 : First observation of gravitational waves 2017 : GW170817 ( neutron star merger ) LCCN : sh85056562 GND : 4158119 - 2 NDL : 00575135 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Gravitational_wave&oldid=826444772 '' Categories : Binary stars Black holes Effects of gravitation Gravitational waves Unsolved problems in physics Hidden categories : Webarchive template wayback links CS1 maint : Uses authors parameter CS1 maint : Explicit use of et al. CS1 maint : Extra text : authors list CS1 Russian - language sources ( ru ) Articles containing potentially dated statements from 2012 All articles containing potentially dated statements All articles with unsourced statements Articles with unsourced statements from March 2016 Articles with unsourced statements from September 2017 Articles with unsourced statements from February 2016 Articles with weasel words from November 2017 Wikipedia articles needing style editing from November 2017 All articles needing style editing Wikipedia articles needing clarification from May 2009 Pages using div col with deprecated parameters Wikipedia articles with LCCN identifiers Wikipedia articles with GND identifiers Talk Contents About Wikipedia Wikiquote Afrikaans বাংলা Bân - lâm - gú Беларуская Български Bosanski Català Čeština Cymraeg Dansk Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Gaeilge Galego 한국어 Հայերեն हिन्दी Hrvatski Bahasa Indonesia Italiano עברית Қазақша Latviešu Lietuvių Magyar Македонски മലയാളം मराठी Bahasa Melayu မြန်မာဘာသာ Nederlands 日本 語 Norsk Norsk nynorsk Occitan ਪੰਜਾਬੀ Polski Português Română Русский Scots Sicilianu Simple English Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska Tagalog தமிழ் Татарча / tatarça ไทย Türkçe Українська اردو Tiếng Việt 中文 Edit links This page was last edited on 19 February 2018, at 03 : 48. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: what is the wavelength of a gravity wave
Answer: the distance along the wave between points of maximum stretch or squeeze