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LIGO

LIGO

Overview
LIGO, which stands for the Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational wave
Gravitational wave
In physics, gravitational waves are theoretical ripples in the curvature of spacetime which propagates as a wave, traveling outward from the source. Predicted to exist by Albert Einstein in 1916 on the basis of his theory of general relativity, gravitational waves theoretically transport energy as...

s. Cofounded in 1992 by Kip Thorne
Kip Thorne
Kip Stephen Thorne is an American theoretical physicist, known for his prolific contributions in gravitation physics and astrophysics and for having trained a generation of scientists...

 and Ronald Drever
Ronald Drever
Ron Drever is a Scottish physicist. He is currently a Professor Emeritus at the California Institute of Technology.Among other accomplishments he co-founded the LIGO project, and was a co-inventor of the Pound-Drever-Hall technique for laser stabilisation....

 of Caltech
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...

 and Rainer Weiss
Rainer Weiss
Rainer Weiss is professor of physics emeritus at MIT.- Early life and education :Weiss was born in Berlin, Germany, in 1932. Fleeing political unrest, his family moved first to Prague, in late 1932, and then to the United States, in 1938; his youth was spent in New York City, where he attended...

 of MIT
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...

, LIGO is a joint project between scientists at MIT, Caltech, and many other colleges and universities. It is sponsored by the National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...

 (NSF). At the cost of $365 million (in 2002 USD), it is the largest and most ambitious project ever funded by the NSF.
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Encyclopedia
LIGO, which stands for the Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational wave
Gravitational wave
In physics, gravitational waves are theoretical ripples in the curvature of spacetime which propagates as a wave, traveling outward from the source. Predicted to exist by Albert Einstein in 1916 on the basis of his theory of general relativity, gravitational waves theoretically transport energy as...

s. Cofounded in 1992 by Kip Thorne
Kip Thorne
Kip Stephen Thorne is an American theoretical physicist, known for his prolific contributions in gravitation physics and astrophysics and for having trained a generation of scientists...

 and Ronald Drever
Ronald Drever
Ron Drever is a Scottish physicist. He is currently a Professor Emeritus at the California Institute of Technology.Among other accomplishments he co-founded the LIGO project, and was a co-inventor of the Pound-Drever-Hall technique for laser stabilisation....

 of Caltech
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...

 and Rainer Weiss
Rainer Weiss
Rainer Weiss is professor of physics emeritus at MIT.- Early life and education :Weiss was born in Berlin, Germany, in 1932. Fleeing political unrest, his family moved first to Prague, in late 1932, and then to the United States, in 1938; his youth was spent in New York City, where he attended...

 of MIT
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...

, LIGO is a joint project between scientists at MIT, Caltech, and many other colleges and universities. It is sponsored by the National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...

 (NSF). At the cost of $365 million (in 2002 USD), it is the largest and most ambitious project ever funded by the NSF. The international LIGO Scientific Collaboration (LSC) is a growing group of researchers, over 800 individuals at roughly 50 institutions, working to analyze the data from LIGO and other detectors
Gravitational wave detector
A gravitational wave detector is any experiment designed to measure gravitational waves, minute distortions of spacetime that are predicted by Einstein's theory of general relativity. The existence of gravitational radiation is a prediction of Einstein's general theory of relativity. Gravitational...

, and working toward more sensitive future detectors. The current spokesperson for the LIGO Scientific Collaboration
LIGO Scientific Collaboration
The LIGO Scientific Collaboration is a collaboration by numerous physics institutes and research groups dedicated to the search for gravitational waves using the detectors LIGO and GEO 600...

, elected in March 2011, is Louisiana State University
Louisiana State University
Louisiana State University and Agricultural and Mechanical College, most often referred to as Louisiana State University, or LSU, is a public coeducational university located in Baton Rouge, Louisiana. The University was founded in 1853 in what is now known as Pineville, Louisiana, under the name...

 Professor of Physics and Astronomy, Gabriela González.

Mission


LIGO's mission is to directly observe gravitational waves of cosmic origin. These waves were first predicted by Einstein's general theory of relativity in 1916, when the technology necessary for their detection did not yet exist. Gravitational waves were indirectly suggested to exist when observations were made of the binary pulsar PSR 1913+16
PSR 1913+16
PSR B1913+16 is a pulsar which together with another neutron star is in orbit around a common center of mass, thus forming a binary star system. In 1974 it was discovered by Russell Alan Hulse and Joseph Hooton Taylor, Jr., of Princeton University...

, for which the Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...

 was awarded to Hulse
Russell Alan Hulse
Russell Alan Hulse is an American physicist and winner of the Nobel Prize in Physics, shared with his thesis advisor Joseph Hooton Taylor Jr., "for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation"...

 and Taylor
Joseph Hooton Taylor, Jr.
Joseph Hooton Taylor, Jr. is an American astrophysicist and Nobel Prize in Physics laureate for his discovery with Russell Alan Hulse of a "new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation."...

 in 1993.

Direct detection of gravitational waves has long been sought. Their discovery would launch a new branch of astronomy to complement electromagnetic
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

 telescopes and neutrino
Neutrino
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...

 observatories. Joseph Weber
Joseph Weber
Joseph Weber was an American physicist. He gave the earliest public lecture on the principles behind the laser and the maser and developed the first gravitational wave detectors .-Early education:...

 pioneered the effort to detect gravitational waves in the 1960s through his work on resonant mass bar detectors
Weber bar
A Weber bar is a device used in the detection of gravitational waves first devised and constructed by physicist Joseph Weber at the University of Maryland...

. Bar detectors continue to be used at six sites worldwide. By the 1970s, scientists including Rainer Weiss
Rainer Weiss
Rainer Weiss is professor of physics emeritus at MIT.- Early life and education :Weiss was born in Berlin, Germany, in 1932. Fleeing political unrest, his family moved first to Prague, in late 1932, and then to the United States, in 1938; his youth was spent in New York City, where he attended...

 realized the applicability of laser interferometry
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...

 to gravitational wave measurements. Bob Forward operated an interferometric detector at Hughes in the early 1970s.

In August 2002, LIGO began its search for cosmic gravitational waves. Measurable emissions of gravitational waves are expected from binary systems (collisions and coalescences of neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...

s or black holes), supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...

 of massive stars (which form neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...

s and black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

s), accreting neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...

s, rotations of neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...

s with deformed crusts, and the remnants of gravitational radiation created by the birth of the universe. The observatory may in theory also observe more exotic currently hypothetical phenomena, such as gravitational waves caused by oscillating cosmic string
Cosmic string
Cosmic strings are hypothetical 1-dimensional topological defects which may have formed during a symmetry breaking phase transition in the early universe when the topology of the vacuum manifold associated to this symmetry breaking is not simply connected. It is expected that at least one string...

s or colliding domain wall
Domain wall
A domain wall is a term used in physics which can have one of two distinct but similar meanings in magnetism, optics, or string theory. These phenomena can all be generically described as topological solitons which occur whenever a discrete symmetry is spontaneously broken.-Magnetism:In magnetism,...

s. Since the early 1990s, physicists have believed that technology has evolved to the point where detection of gravitational waves—of significant astrophysical interest—is now possible.

Observatories


LIGO operates two gravitational wave observatories in unison: the LIGO Livingston Observatory (30°33′46.42"N 90°46′27.27"W) in Livingston, Louisiana
Livingston, Louisiana
Livingston is a town in and the parish seat of Livingston Parish, Louisiana, United States. The population was 1,342 at the 2000 census. It is part of the Baton Rouge Metropolitan Statistical Area....

, and the LIGO Hanford Observatory, on the Hanford Nuclear Reservation
Hanford Site
The Hanford Site is a mostly decommissioned nuclear production complex on the Columbia River in the U.S. state of Washington, operated by the United States federal government. The site has been known by many names, including Hanford Works, Hanford Engineer Works or HEW, Hanford Nuclear Reservation...

 (coordinates of central complex: 46°27′18.52"N 119°24′27.56"W), located near Richland, Washington
Richland, Washington
Richland is a city in Benton County in the southeastern part of the U.S. state of Washington, at the confluence of the Yakima and the Columbia Rivers. As of the 2010 census, the city population was 48,058. April 1, 2011 estimates from the Washington State Office of Financial Management put the...

. These sites are separated by 3,002 kilometers (1,865 miles). Since gravitational waves are expected to travel at the speed of light, this distance corresponds to a difference in gravitational wave arrival times of up to ten milliseconds. Through the use of triangulation
Triangulation
In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...

, the difference in arrival times can determine the source of the wave in the sky.

Each observatory supports an L-shaped ultra high vacuum
Ultra high vacuum
Ultra-high vacuum is the vacuum regime characterised by pressures lower than about 10−7 pascal or 100 nanopascals . UHV requires the use of unusual materials in construction and by heating the entire system to 180°C for several hours to remove water and other trace gases which adsorb on the...

 system, measuring 4 kilometers (2.5 miles) on each side. Up to five interferometers can be set up in each vacuum system.

At the Hanford Observatory, a second interferometer operates in parallel with the primary interferometer. This second detector is half the length at 2 kilometers (1.25 miles), and its Fabry–Pérot arm cavities have the same optical finesse and thus half the storage time. With half the storage time, the theoretical strain sensitivity is as good as
the full length interferometers above 200 Hz but only half as good at low frequencies.

The LIGO Livingston Observatory houses one laser interferometer in the primary configuration. This interferometer was successfully upgraded in 2004 with an active vibration isolation system based on hydraulic actuators providing a factor of 10 isolation in the 0.1 – 5 Hz band. Seismic vibration in this band is chiefly due to microseismic waves and anthropogenic sources (traffic, logging, etc.).

The LIGO Hanford Observatory houses one interferometer, almost identical to the one at the Livingston Observatory, as well as one half-length interferometer. Hanford has been able to retain its original passive seismic isolation system due to limited geologic activity in Southeastern Washington.

Members of the public can tour both observatories, either by special arrangement or on regular "open house" days.

Operation


The primary interferometer at each site consists of mirrors suspended at each of the corners of the L; it is known as a power-recycled Michelson interferometer
Michelson interferometer
The Michelson interferometer is the most common configuration for optical interferometry and was invented by Albert Abraham Michelson. An interference pattern is produced by splitting a beam of light into two paths, bouncing the beams back and recombining them...

 with Fabry–Pérot arms. A pre-stabilized laser emits a beam of up to 200 Watts that passes through an optical mode
Transverse mode
A transverse mode of a beam of electromagnetic radiation is a particular electromagnetic field pattern of radiation measured in a plane perpendicular to the propagation direction of the beam...

 cleaner before reaching a beam splitter at the vertex of the L. There the beam splits into two paths, one for each arm of the L; each arm contains Fabry–Pérot cavities that store the beams and increase the effective path length.

When a gravitational wave passes through the interferometer, the space-time in the local area is altered. Depending on the source of the wave and its polarization, this results in an effective change in length of one or both of the cavities. The effective length change between the beams will cause the light currently in the cavity to become very slightly out of phase with the incoming light. The cavity will therefore periodically get very slightly out of resonance and the beams which are tuned to destructively interfere at the detector, will have a very slight periodically varying detuning. This results in a measurable signal. Note that the effective length change and the resulting phase change are a subtle tidal effect that must be carefully computed because the light waves are affected by the gravitational wave just as much as the beams themselves.

After an equivalent of approximately 75 trips down the 4 km length to the far mirrors and back again, the two separate beams leave the arms and recombine at the beam splitter. The beams returning from two arms are kept out of phase so that when the arms are both in resonance (as when there is no gravitational wave passing through), their light waves subtract, and no light should arrive at the photodiode
Photodiode
A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.The common, traditional solar cell used to generateelectric solar power is a large area photodiode....

. When a gravitational wave passes through the interferometer, the distances along the arms of the interferometer are shortened and lengthened, causing the beams to become slightly less out of phase, so some light arrives at the photodiode, indicating a signal. Light that does not contain a signal is returned to the interferometer using a power recycling mirror, thus increasing the power of the light in the arms. In actual operation, noise sources can cause movement in the optics which produces similar effects to real gravitational wave signals; a great deal of the art and complexity in the instrument is in finding ways to reduce these spurious motions of the mirrors. Observers compare signals from both sites to reduce the effects of noise.

Observations



Based on current models of astronomical events, and the predictions of the general theory of relativity, gravitational waves that originate tens of millions of light years from Earth are expected to distort the 4 kilometer mirror spacing by about 10−18 m, less than one-thousandth the "diameter" of a proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

. Equivalently, this is a relative change in distance of approximately one part in 1021. A typical event which might cause a detection event would be the late stage inspiral and merger of two 10 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

 black holes, not necessarily located in the Milky Way galaxy, which is expected to result in a very specific sequence of signals often summarized by the slogan chirp, burst, quasi-normal mode ringing, exponential decay.

In their fourth Science Run at the end of 2004, the LIGO detectors demonstrated sensitivities in measuring these displacements to within a factor of 2 of their design.

During LIGO's fifth Science Run in November 2005, sensitivity reached the primary design specification of a detectable strain of one part in 1021 over a 100 Hz bandwidth. The baseline inspiral of two roughly solar-mass neutron stars is typically expected to be observable if it occurs within about 8000000 parsec, or the vicinity of our Local Group
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...

 of galaxies, averaged over all directions and polarizations. Also at this time, LIGO and GEO 600
GEO 600
GEO 600 is a gravitational wave detector located near Sarstedt, Germany. This instrument, and its sister interferometric detectors, when operational, are some of the most sensitive gravitational wave detectors ever designed...

 (the German-UK interferometric detector) began a joint science run, during which they collected data for several months. Virgo
Virgo interferometer
The Virgo is a gravitational wave detector in Italy, which commenced operations in 2007. It is one of a handful of the world's major experiments working towards the observation of gravitational waves....

 (the French-Italian interferometric detector) joined in May 2007. The fifth science run ended in 2007. It is hoped that after extensive analysis, data from this run may uncover two unambiguous detection events. This would be a milestone in the history of physics. In 2004, it was reported that theorists estimated the chances of an unambiguous direct detection by 2010 at one in six.

In February 2007, GRB 070201, a short gamma-ray burst, arrived at Earth from the direction of the Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...

, a nearby galaxy. The prevailing explanation of most short gamma-ray bursts is the merger of a neutron star with either a neutron star or black hole. LIGO reported a non-detection for GRB 070201, ruling out a merger at the distance of Andromeda with high confidence. Such a constraint is predicated on LIGO eventually demonstrating a direct detection of gravitational waves.

In August 2010 the first discovery made using only home-computer collaboration through LIGO and GEO 600
GEO 600
GEO 600 is a gravitational wave detector located near Sarstedt, Germany. This instrument, and its sister interferometric detectors, when operational, are some of the most sensitive gravitational wave detectors ever designed...

 was announced in various scientific publications. This was not a detection of gravitational waves, but rather the discovery of a radio pulsar using BOINC
Berkeley Open Infrastructure for Network Computing
The Berkeley Open Infrastructure for Network Computing is an open source middleware system for volunteer and grid computing. It was originally developed to support the SETI@home project before it became useful as a platform for other distributed applications in areas as diverse as mathematics,...

-based LIGO data analysis tools on data from radio telescopes rather than data from LIGO interferometers.

Enhanced LIGO


After the completion of Science Run 5, initial LIGO was upgraded with certain Advanced LIGO technologies that resulted in an improved-performance configuration dubbed Enhanced LIGO. Its aim was a best-effort goal of achieving twice the sensitivity of initial LIGO by the end of the run, unlike the NSF-contracted sensitivity goals of the Initial and Advanced instruments. Some of the improvements in Enhanced LIGO included:
  • Increased laser power.
  • Homodyne detection
    Homodyne detection
    Homodyne detection is a method of detecting frequency-modulated radiation by non-linear mixing with radiation of a reference frequency, the same principle as for heterodyne detection....

    .
  • Output mode cleaner.
  • In-vacuum readout hardware.


Science Run 6 (S6) began in July 2009 with the enhanced configurations on the 4 km detectors. It concluded in October 2010, and the disassembling of the original detectors began. An estimated four-year long effort to install and commission the Advanced LIGO detectors is currently underway.

Advanced LIGO


The LIGO Laboratory, with support from National Science Foundation and the GEO 600
GEO 600
GEO 600 is a gravitational wave detector located near Sarstedt, Germany. This instrument, and its sister interferometric detectors, when operational, are some of the most sensitive gravitational wave detectors ever designed...

 Collaboration, and with participation by the LIGO Scientific Collaboration, is building Advanced LIGO. This new detector (formerly known as "LIGO 2") is designed to improve the sensitivity of initial LIGO by more than a factor of 10, and is currently being installed at both LIGO Observatories, replacing the original detectors. Scheduled to begin operations in 2014, the Advanced LIGO system is anticipated to transform gravitational wave science into a powerful observational tool. As of 2008, more than $200 million was planned for the upgrade over the next seven years.

LIGO scientists expect this new instrument to see gravitational wave sources possibly as often as daily, with excellent signal strengths. It should allow details of the waveforms to be read off and compared with theories of neutron stars, black holes, and other highly relativistic objects. The improvement of sensitivity will allow the one-year planned observation time of initial LIGO to be equaled in just several hours.

LIGO-Australia


LIGO-Australia was a proposed plan to install one of the three Advanced LIGO interferometers at the Australian International Gravitational Observatory (AIGO) research facility operated by the Australian Consortium for Interferometric Gravitational Astronomy (ACIGA) near Gingin in Western Australia.

A 2010 developmental roadmap issued by the Gravitational Wave International Committee (GWIC)
Gravitational Wave International Committee
The Gravitational Wave International Committee is a panel of experts and senior members from the gravitational wave detection community that promotes cooperation and collaboration between the gravitational wave detector projects and provides direction and advice on the future development of the...

 for the field of gravitational-wave astronomy recommended that an expansion of the global array of interferometric detectors be pursued as a highest priority. Such a network would afford astrophysicists with more robust search capabilities and higher scientific yields. In its roadmap, GWIC identified the Southern Hemisphere as one of the key locations in which a gravitational-wave interferometer could most effectively complement existing detectors. The AIGO facility in Western Australia was well-located to work with the existing and planned components of the global network, and already possessed an active gravitational-wave community.

In October 2010, the LIGO interferometers concluded their sixth data-taking science run, and the initial instruments began to be disassembled prior to a four-year effort to install and commission the Advanced LIGO detectors with their tenfold increase in sensitivity. This operational hiatus offers LIGO scientists and engineers an ideal opportunity to transfer all the components of one of their advanced detectors to a new location, such as the AIGO site, to be assembled and operated there. The LIGO Hanford Observatory would provide one of its two detectors, leaving a pair to remain on a continental baseline in North America.

The LIGO-Australia plan was approved by LIGO's US funding agency, the National Science Foundation, contingent on the understanding that it involved no increase in LIGO's total budget. The cost of building, operating and staffing the interferometer would have rested entirely with the Australian government. The decision had to be made before installation of the Advanced LIGO interferometers is scheduled to begin and the window of opportunity for relocation has closed.

After a year-long effort, the LIGO Laboratory reluctantly acknowledged that the proposed relocation of an Advanced LIGO detector to Australia was not to occur. The Australian government had committed itself to a balanced budget and this precluded any new starts in science. The deadline for a response from Australia passed on October 1, 2011.

LISA


LISA, the Laser Interferometer Space Antenna
Laser Interferometer Space Antenna
The Laser Interferometer Space Antenna is a planned space mission to detect and accurately measure gravitational waves from astronomical sources. LISA was originally conceived as a joint effort between the United States space agency NASA and the European Space Agency...

, is a proposed gravitational-wave detection project to build a laser interferometer consisting of three spacecraft in solar orbit. As initially conceived, LISA would be sensitive to gravitational waves in a different frequency band from that of the LIGO detectors, making the two experiments complementary of each other. LISA began as a joint project of NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 and the European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...

 (ESA), but in April 2011 NASA announced that it would be unlikely to continue its LISA partnership with the ESA, due to funding limitations. The ESA is planning to begin a full revision of the mission's concept commencing in February 2012.

See also

  • Einstein Telescope
    Einstein Telescope
    Einstein Telescope or Einstein Observatory, is a future third generation gravitational wave detector, currently being designed by different institutions in the European Union...

    , for a European third-generation gravitational wave detector.
  • Einstein@Home
    Einstein@Home
    Einstein@Home is a volunteer distributed computing project hosted by the University of Wisconsin–Milwaukee and the Max Planck Institute for Gravitational Physics . The project is directed by Bruce Allen...

    , for a volunteer distributed computing program one can download in order to help the LIGO/GEO teams analyze their data.
  • GEO 600
    GEO 600
    GEO 600 is a gravitational wave detector located near Sarstedt, Germany. This instrument, and its sister interferometric detectors, when operational, are some of the most sensitive gravitational wave detectors ever designed...

    , for a gravitational wave detector located in Hannover, Germany.
  • Fermilab Holometer
  • Tests of general relativity
    Tests of general relativity
    At its introduction in 1915, the general theory of relativity did not have a solid empirical foundation. It was known that it correctly accounted for the "anomalous" precession of the perihelion of Mercury and on philosophical grounds it was considered satisfying that it was able to unify Newton's...

  • Virgo interferometer
    Virgo interferometer
    The Virgo is a gravitational wave detector in Italy, which commenced operations in 2007. It is one of a handful of the world's major experiments working towards the observation of gravitational waves....

    , an interferometer similar to LIGO, located close to Pisa
    Pisa
    Pisa is a city in Tuscany, Central Italy, on the right bank of the mouth of the River Arno on the Tyrrhenian Sea. It is the capital city of the Province of Pisa...

    , Italy.

Further reading

  • Einstein's Unfinished Symphony by Marcia Bartusiak, ISBN 0425186202.
  • Fundamentals of Interferometric Gravitational Wave Detectors by Peter R. Saulson, ISBN 9810218206.
  • Gravity's Shadow: The Search for Gravitational Waves by Harry Collins, ISBN 0226113787.
  • Traveling at the Speed of Thought by Daniel Kennefick, ISBN 9780691117270

External links