Editing LIGO (section)

==History==
===Background===
[[File:LIGO Hanford aerial 05.jpg|thumb|right|LIGO Hanford Observatory]]
[[File:Ligo-livingston-aerial-03 599x400.jpg|thumb|right|LIGO Livingston Observatory]]
The LIGO concept built upon early work by many scientists to test a component of [[Albert Einstein]]'s theory of [[general relativity]], the existence of gravitational waves. Starting in the 1960s, American scientists including [[Joseph Weber]], as well as Soviet scientists [[Mikhail Gertsenshtein]] and [[Vladislav Pustovoit]], conceived of basic ideas and prototypes of laser [[interferometry]],<ref name="NSF">{{cite book |publisher= National Academies Press |pages= 109–117|isbn=978-0-309-09084-1|url=http://www.nap.edu/catalog/10895/setting-priorities-for-large-research-facility-projects-supported-by-the-national-science-foundation|bibcode= 2004splr.rept.....C|doi= 10.17226/10895 |title= Setting Priorities for Large Research Facility Projects Supported by the National Science Foundation|year= 2004|journal=<!-- -->|author1=<!---->}}</ref><ref>{{cite journal |last= Gertsenshtein|first= M.E.|date= 1962|title= Wave Resonance of Light and Gravitational Waves|journal= Journal of Experimental and Theoretical Physics|volume= 14|pages= 84}}</ref> and in 1967 [[Rainer Weiss]] of [[MIT]] published an analysis of interferometer use and initiated the construction of a prototype with military funding, but it was terminated before it could become operational.<ref>{{cite journal |date= 1972 |journal= Quarterly Progress Report of the Research Laboratory of Electronics |author=Weiss, Rainer | title=Electromagnetically coupled broadband gravitational wave antenna | volume= 105| issue= 54|pages= 84| url=https://dcc.ligo.org/P720002/public|access-date=21 February 2016}}</ref> Starting in 1968, [[Kip Thorne]] initiated theoretical efforts on gravitational waves and their sources at [[Caltech]], and was convinced that gravitational wave detection would eventually succeed.<ref name="NSF"/>

Prototype interferometric gravitational wave detectors (interferometers) were built in the late 1960s by [[Robert L. Forward]] and colleagues at [[HRL Laboratories|Hughes Research Laboratories]] (with mirrors mounted on a vibration isolated plate rather than free swinging), and in the 1970s (with free swinging mirrors between which light bounced many times) by [[Rainer Weiss|Weiss]] at MIT, and then by [[Heinz Billing]] and colleagues in [[Garching bei München|Garching]] Germany, and then by [[Ronald Drever]], [[James Hough]] and colleagues in Glasgow, Scotland.<ref>{{cite web| title=A brief history of LIGO| publisher=ligo.caltech.edu| url=https://www.ligo.caltech.edu/system/media_files/binaries/313/original/LIGOHistory.pdf| access-date=21 February 2016| archive-url=https://web.archive.org/web/20170703113615/https://www.ligo.caltech.edu/system/media_files/binaries/313/original/LIGOHistory.pdf| archive-date=3 July 2017| url-status=dead}}</ref>

In 1980, the NSF funded the study of a large interferometer led by MIT (Paul Linsay, [[Peter Saulson]], Rainer Weiss), and the following year, Caltech constructed a 40-meter prototype (Ronald Drever and Stan Whitcomb). The MIT study established the feasibility of interferometers at a 1-kilometer scale with adequate sensitivity.<ref name="NSF"/><ref name="buderi">{{cite journal | last=Buderi| first=Robert |date= 19 September 1988| title= Going after gravity: How a high-risk project got funded. |url= http://www.the-scientist.com/?articles.view/articleNo/9753/title/Going-After-Gravity--How-A-High-Risk-Project-Got-Funded/| journal= The Scientist |volume=2 | issue=17 |pages=1 |access-date=18 February 2016}}</ref>

Under pressure from the NSF, MIT and Caltech were asked to join forces to lead a LIGO project based on the MIT study and on experimental work at Caltech, MIT, Glasgow, and [[Garching bei München|Garching]]. Drever, Thorne, and Weiss formed a LIGO steering committee, though they were turned down for funding in 1984 and 1985. By 1986, they were asked to disband the steering committee and a single director, [[Rochus Eugen Vogt|Rochus E. Vogt]] (Caltech), was appointed. In 1988, a research and development proposal achieved funding.<ref name="NSF"/><ref name="buderi"/><ref name="jeffery">{{cite journal |last= Mervis| first= Jeffery|title= Funding of two science labs receives pork barrel vs beer peer review debate. |url= http://www.the-scientist.com/?articles.view/articleNo/12069/title/Funding-Of-Two-Science-Labs-Revives-Pork-Barrel-Vs--Peer-Review-Debate/ |journal= The Scientist |volume= 5|issue= 23|access-date=21 February 2016}}</ref><ref name="waldrop">{{cite journal |last= Waldrop| first= M. Mitchell|date=7 September 1990| title= Of politics, pulsars, death spirals – and LIGO |journal= Science |volume= 249|issue= 4973|pages= 1106–1108| doi=10.1126/science.249.4973.1106 | pmid= 17831979|bibcode = 1990Sci...249.1106W }}</ref><ref>{{cite web| url=http://www.ligo.org/news/detection-press-release.pdf| title=Gravitational waves detected 100 years after Einstein's prediction| date=11 February 2016| publisher=LIGO| access-date=11 February 2016}}</ref><ref>{{cite journal |last= Irion| first= Robert |date= 21 April 2000| title= LIGO's mission of gravity.|journal= Science |volume= 288|issue= 5465|pages= 420–423 |doi= 10.1126/science.288.5465.420| s2cid= 119020354 }}</ref>

From 1989 through 1994, LIGO failed to progress technically and organizationally. Only political efforts continued to acquire funding.<ref name="NSF"/><ref name="cohen">{{cite web| url=http://oralhistories.library.caltech.edu/178/1/Barish_OHO.pdf| title=Interview with Barry Barish| work=Shirley Cohen| publisher=Caltech| year=1998| access-date=21 February 2016}}</ref> Ongoing funding was routinely rejected until 1991, when the [[United States Congress|U.S. Congress]] agreed to fund LIGO for the first year for $23 million. However, requirements for receiving the funding were not met or approved, and the NSF questioned the technological and organizational basis of the project.<ref name="jeffery"/><ref name="waldrop"/> By 1992, LIGO was restructured with Drever no longer a direct participant.<ref name="NSF"/><ref name="cohen"/><ref name="Cook">{{cite conference |last= Cook|first= Victor|date= 21 September 2001|title= NSF Management and Oversight of LIGO |conference= Large Facility Projects Best Practices Workshop |publisher=NSF}}</ref><ref>{{cite journal |last= Travis|first= John|date= 18 February 2016|title= LIGO: A$250 million gamble. |journal= Science |volume= 260|issue= 5108|pages= 612–614|doi= 10.1126/science.260.5108.612|pmid= 17812204|bibcode= 1993Sci...260..612T}}</ref> Ongoing project management issues and technical concerns were revealed in NSF reviews of the project, resulting in the withholding of funds until they formally froze spending in 1993.<ref name="NSF"/><ref name="cohen"/><ref>{{cite journal |last= Anderson|first= Christopher|date= 11 March 1994 |title= LIGO director out in shakeup |journal= Science |volume= 263| issue= 5152| pages= 1366| doi= 10.1126/science.263.5152.1366|pmid= 17776497|bibcode= 1994Sci...263.1366A}}</ref><ref>{{cite news |last= Browne|first= Malcolm W.|date= 30 April 1991|title= Experts clash over project to detect gravity wave. |url= https://www.nytimes.com/1991/04/30/science/experts-clash-over-project-to-detect-gravity-wave.html?pagewanted=all |newspaper= New York Times|access-date= 21 February 2016}}</ref>

In 1994, after consultation between relevant NSF personnel, LIGO's scientific leaders, and the presidents of MIT and Caltech, Vogt stepped down and [[Barry Barish]] (Caltech) was appointed laboratory director,<ref name="NSF"/><ref name="Cook"/><ref>{{cite journal |last= Anderson|first= Christopher|date= 11 March 1994 |title= LIGO director out in shakeup |journal= Science |volume= 263|issue= 5152|pages= 1366|doi= 10.1126/science.263.5152.1366|pmid= 17776497|bibcode= 1994Sci...263.1366A}}</ref> and the NSF made clear that LIGO had one last chance for support.<ref name="cohen"/> Barish's team created a new study, budget, and project plan with a budget exceeding the previous proposals by 40%. Barish proposed to the NSF and National Science Board to build LIGO as an evolutionary detector, where detection of gravitational waves with initial LIGO would be possible, and with advanced LIGO would be probable.<ref name="Nature_2014_July_14">{{citation |title=Physics: Wave of the future|journal=Nature |volume=511 |issue=7509 |pages=278–81 |first=Alexandra |last=Witze|date=16 July 2014 |bibcode=2014Natur.511..278W |doi=10.1038/511278a |pmid=25030149 |doi-access=free }}</ref> This new proposal received NSF funding, Barish was appointed [[Principal Investigator]], and the increase was approved. In 1994, with a budget of US$395 million, LIGO stood as the largest overall funded NSF project in history. The project broke ground in Hanford, Washington in late 1994 and in Livingston, Louisiana in 1995. As construction neared completion in 1997, under Barish's leadership two organizational institutions were formed, LIGO Laboratory and LIGO Scientific Collaboration (LSC). The LIGO laboratory consists of the facilities supported by the NSF under LIGO Operation and Advanced R&D; this includes administration of the LIGO detector and test facilities. The LIGO Scientific Collaboration is a forum for organizing technical and scientific research in LIGO. It is a separate organization from LIGO Laboratory with its own oversight. Barish appointed Weiss as the first spokesperson for this scientific collaboration.<ref name="NSF"/><ref name="jeffery"/>

===Observations begin===
Initial LIGO operations between 2002 and 2010 did not detect any gravitational waves. In 2004, under Barish, the funding and groundwork were laid for the next phase of LIGO development (called "Enhanced LIGO"). This was followed by a multi-year shut-down while the detectors were replaced by much improved "Advanced LIGO" versions.<ref>{{cite web| title=Gravitational wave detection a step closer with Advanced LIGO| url=http://spie.org/newsroom/technical-articles/videos/ligo-hanford-spie-video| publisher=SPIE Newsroom| access-date=4 January 2016}}</ref><ref>{{cite web|title=Daniel Sigg: The Advanced LIGO Detectors in the era of First Discoveries|url=http://spie.org/x120637.xml|publisher=SPIE Newsroom|access-date=9 September 2016}}</ref> Much of the research and development work for the LIGO/aLIGO machines was based on pioneering work for the [[GEO600]] detector at Hannover, Germany.<ref name="GEO600 a precursor">{{cite news |last=Ghosh |first=Pallab |url=https://www.bbc.com/news/science-environment-35524440 |title=Einstein's gravitational waves 'seen' from black holes |work=BBC News |date=11 February 2016 |access-date=18 February 2016 }}</ref><ref name="mpg2016">{{cite web |title=Gravitational waves detected 100 years after Einstein's prediction |url=https://www.mpg.de/9953360/gravitational-waves-detected |website=www.mpg.de |publisher=Max-Planck-Gelschaft |access-date=3 September 2018 |language=en}}</ref> By February 2015, the detectors were brought into engineering mode in both locations.<ref>{{cite web |title=LIGO Hanford's H1 Achieves Two-Hour Full Lock |url=https://www.advancedligo.mit.edu/feb_2015_news.html |date=February 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150922064706/https://www.advancedligo.mit.edu/feb_2015_news.html |archive-date=22 September 2015  }}</ref>

In mid-September 2015, "the world's largest gravitational-wave facility" completed a five-year US$200-million overhaul, bringing the total cost to $620 million.<ref name="Nature_2015_Sept_15">{{citation |title=Hunt for gravitational waves to resume after massive upgrade: LIGO experiment now has better chance of detecting ripples in space-time|journal=Nature |volume=525 |issue=7569 |pages=301–302 |first=Davide |last=Castelvecchi|date=15 September 2015 |doi=10.1038/525301a |pmid=26381963 |bibcode=2015Natur.525..301C |doi-access=free }}</ref><ref>{{cite magazine |first=Sarah |last=Zhang |title=The Long Search for Elusive Ripples in Spacetime |magazine=Wired |url=https://www.wired.com/2015/09/long-search-elusive-ripples-spacetime |date=15 September 2015}}</ref> On 18 September 2015, Advanced LIGO began its first formal science observations at about four times the sensitivity of the initial LIGO interferometers.<ref>{{cite news |last=Amos |first=Jonathan |title=Advanced Ligo: Labs 'open their ears' to the cosmos |url=https://www.bbc.com/news/science-environment-34298363 |journal=BBC News |date=19 September 2015 |access-date=19 September 2015}}</ref> Its sensitivity was to be further enhanced until it was planned to reach design sensitivity {{As of|alt=around 2021|2021|01|post=.}}<ref name="LIGO_dec_2015">{{cite web| title=Planning for a bright tomorrow: prospects for gravitational-wave astronomy with Advanced LIGO and Advanced Virgo| url=http://www.ligo.org/science/Publication-ObservingScenario/index.php| publisher=[[LIGO Scientific Collaboration]] |access-date=31 December 2015 |date=23 December 2015}}</ref>

====Detections====
On 11 February 2016, the LIGO Scientific Collaboration and [[Virgo interferometer|Virgo Collaboration]] published a paper about the [[First observation of gravitational waves|detection of gravitational waves]], from a signal detected at 09.51 [[UTC]] on 14 September 2015 of two ~30 [[solar mass]] black holes merging about 1.3 billion [[light-years]] from Earth.<ref name="PhysRevLett.116.061102">{{cite journal |title=Observation of Gravitational Waves from a Binary Black Hole Merger |journal=Physical Review Letters |volume=116 |issue=6 |pages=061102 |date=11 February 2016 |last=LIGO Scientific Collaboration and Virgo Collaboration |first=B. P. Abbott|doi=10.1103/PhysRevLett.116.061102 |pmid=26918975 |arxiv = 1602.03837 |bibcode = 2016PhRvL.116f1102A |s2cid=124959784 }}</ref><ref name="Nature_11Feb16" />

Current executive director [[David Reitze]] announced the findings at a media event in Washington D.C., while executive director emeritus Barry Barish presented the first scientific paper of the findings at CERN to the physics community.<ref>{{Cite book | url=https://cds.cern.ch/record/2131411 | title=New results on the Search for Gravitational Waves| year=2016| series=CERN Colloquium}}</ref>

On 2 May 2016, members of the [[LIGO Scientific Collaboration]] and other contributors were awarded a [[Fundamental Physics Prize|Special Breakthrough Prize in Fundamental Physics]] for contributing to the direct detection of gravitational waves.<ref name=FPP-May2016>{{cite web|title=Fundamental Physics Prize – News|url=https://breakthroughprize.org/News/32|publisher=Fundamental Physics Prize (2016)|access-date=4 May 2016}}</ref>

On 16 June 2016 LIGO announced a [[GW151226|second signal]] was detected from the merging of two black holes with 14.2 and 7.5 times the mass of the Sun. The signal was picked up on 26 December 2015, at 3:38 UTC.<ref name="chu"/>

The detection of a third black hole merger, between objects of 31.2 and 19.4 solar masses, occurred on 4 January 2017 and was announced on 1 June 2017.<ref name = "Abbott2017">{{cite journal |doi=10.1103/PhysRevLett.118.221101 |pmid= 28621973 |title= GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2 |journal= [[Physical Review Letters]] |date= 1 June 2017 |author=B. P. Abbott |display-authors=etal |collaboration=[[LIGO Scientific Collaboration]] and [[Virgo interferometer|Virgo Collaboration]] |volume=118 |issue= 22 |pages=221101|arxiv=1706.01812 |bibcode=2017PhRvL.118v1101A |s2cid= 206291714 }}</ref><ref name = SciNews2017.06.01>{{cite journal | last = Conover | first = E. | title = LIGO snags another set of gravitational waves | journal = [[Science News]] | date = 1 June 2017 | url = https://www.sciencenews.org/article/ligo-snags-another-set-gravitational-waves | access-date = 3 June 2017}}</ref> [[Laura Cadonati]] was appointed the first deputy spokesperson.<ref>{{cite web | url=https://news.gatech.edu/news/2017/04/20/college-sciences-professor-appointed-top-role-search-gravitational-waves | title=College of Sciences Professor Appointed to Top Role in Search for Gravitational Waves &#124; News Center }}</ref>

A fourth detection of a black hole merger, between objects of 30.5 and 25.3 solar masses, was observed on 14 August 2017 and was announced on 27 September 2017.<ref>{{cite web|title=GW170814 : A three-detector observation of gravitational waves from a binary black hole coalescence|url=https://dcc.ligo.org/LIGO-P170814/public/main|access-date=29 September 2017}}</ref>

In 2017, Weiss, Barish, and Thorne received the [[Nobel Prize in Physics]] "for decisive contributions to the LIGO detector and the observation of gravitational waves." Weiss was awarded one-half of the total prize money, and Barish and Thorne each received a one-quarter prize.<ref>{{cite web|title=The Nobel Prize in Physics 2017|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/press.html|website=Nobelprize.org|access-date=4 October 2017}}</ref><ref name="BBC-20171003">{{cite news |last1=Rincon |first1=Paul |last2=Amos |first2=Jonathan |url=https://www.bbc.co.uk/news/science-environment-41476648|title=Einstein's waves win Nobel Prize |work=[[BBC News]] |date=3 October 2017 |access-date=3 October 2017}}</ref><ref name="NYT-20171003">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=2017 Nobel Prize in Physics Awarded to LIGO Black Hole Researchers |url=https://www.nytimes.com/2017/10/03/science/nobel-prize-physics.html |date=3 October 2017 |work=[[The New York Times]] |access-date=3 October 2017 }}</ref>

After shutting down for improvements, LIGO resumed operation on 26 March 2019, with Virgo joining the network of gravitational-wave detectors on 1 April 2019.<ref>{{Cite web | url= https://www.ligo.org/news/pr-O3resumes.pdf| title=LSC News}}</ref> Both ran until 27 March 2020, when the [[COVID-19 pandemic]] halted operations.<ref name="O3suspended" /> During the COVID shutdown, LIGO underwent a further upgrade in sensitivity, and observing run O4 with the new sensitivity began on 24 May 2023.<ref name=":1" />