Editing Curved spacetime (section)

=== Gravitomagnetism ===
[[File:Gravity Probe B Confirms the Existence of Gravitomagnetism.jpg|330px|thumb|Figure 5–11. Gravity Probe B confirmed the existence of gravitomagnetism]]

The existence of gravitomagnetism was proven by [[Gravity Probe B]] {{nowrap|1=(GP-B)}}, a satellite-based mission which launched on 20 April 2004.<ref>
{{cite web
 |url=http://einstein.stanford.edu/content/faqs/faqs.html#launch
 |title=Gravity Probe B: FAQ
 |access-date=2 July 2017
 |archive-date=2 June 2018
 |archive-url=https://web.archive.org/web/20180602231753/http://einstein.stanford.edu/content/faqs/faqs.html#launch
 |url-status=live
}}</ref> The spaceflight phase lasted until <time>2005</time>. The mission aim was to measure spacetime curvature near Earth, with particular emphasis on [[gravitomagnetism]].

Initial results confirmed the relatively large [[geodetic effect]] (which is due to simple spacetime curvature, and is also known as de Sitter precession) to an accuracy of about 1%. The much smaller [[frame-dragging]] effect (which is due to gravitomagnetism, and is also known as [[Lense–Thirring precession]]) was difficult to measure because of unexpected charge effects causing variable drift in the gyroscopes. Nevertheless, by <time datetime="2008-08">August 2008</time>, the frame-dragging effect had been confirmed to within 15% of the expected result,<ref name="Gugliotta2009">
{{cite news
 | last = Gugliotta
 | first = G.
 | title = Perseverance Is Paying Off for a Test of Relativity in Space
 | work = [[New York Times]]
 | date = 16 February 2009
 | url = https://www.nytimes.com/2009/02/17/science/17gravity.html?_r=1
 | access-date = 2 July 2017
 | archive-date = 3 September 2018
 | archive-url = https://web.archive.org/web/20180903151359/https://www.nytimes.com/2009/02/17/science/17gravity.html?_r=1
 | url-status = live
}}</ref> while the geodetic effect was confirmed to better than 0.5%.<ref>{{cite web |last1=Everitt |first1=C. W. F. |last2=Parkinson |first2=B. W. |date=2009 |title=Gravity Probe B Science Results—NASA Final Report |url=http://einstein.stanford.edu/content/final_report/GPB_Final_NASA_Report-020509-web.pdf |url-status=live |archive-url=https://web.archive.org/web/20121023062122/http://einstein.stanford.edu/content/final_report/GPB_Final_NASA_Report-020509-web.pdf |archive-date=23 October 2012 |access-date=2 July 2017}}</ref><ref name=PRL>{{cite journal | author=Everitt | display-authors=etal | date=2011| title=Gravity Probe B: Final Results of a Space Experiment to Test General Relativity| journal=Physical Review Letters| volume = 106 | issue = 22 | page=221101 | doi = 10.1103/PhysRevLett.106.221101 |arxiv =1105.3456 | bibcode=2011PhRvL.106v1101E | pmid=21702590| s2cid=11878715 }}</ref>

Subsequent measurements of frame dragging by laser-ranging observations of the [[LARES (satellite)|LARES]], {{nowrap|1=[[LAGEOS]]-1}} and {{nowrap|1=LAGEOS-2}} satellites has improved on the {{nowrap|1=GP-B}} measurement, with results (as of 2016) demonstrating the effect to within 5% of its theoretical value,<ref>{{cite journal |last1=Ciufolini |first1=Ignazio |last2=Paolozzi |first2=Antonio Rolf Koenig |last3=Pavlis |first3=Erricos C. |last4=Koenig |first4=Rolf |date=2016 |title=A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth gravity model |journal=European Physical Journal C |volume=76 |issue=3 |page=120 |arxiv=1603.09674 |bibcode=2016EPJC...76..120C |doi=10.1140/epjc/s10052-016-3961-8 |pmc=4946852 |pmid=27471430}}</ref> although there has been some disagreement on the accuracy of this result.<ref>{{cite journal|last=Iorio|first=L.|title=A comment on "A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth gravity model. Measurement of Earth's dragging of inertial frames," by I. Ciufolini et al|journal=The European Physical Journal C|date=February 2017|volume=77|issue=2|pages=73|doi=10.1140/epjc/s10052-017-4607-1|bibcode = 2017EPJC...77...73I |arxiv = 1701.06474 |s2cid=118945777}}</ref>

Another effort, the Gyroscopes in General Relativity (GINGER) experiment, seeks to use three 6&nbsp;m [[ring lasers]] mounted at right angles to each other 1400&nbsp;m below the Earth's surface to measure this effect.<ref>{{cite web |last1=Cartlidge |first1=Edwin |title=Underground ring lasers will put general relativity to the test |url=http://physicsworld.com/cws/article/news/2016/jan/20/underground-ring-lasers-will-put-general-relativity-to-the-test |website=physicsworld.com |date=20 January 2016 |publisher=Institute of Physics |access-date=2 July 2017 |archive-date=12 July 2017 |archive-url=https://web.archive.org/web/20170712144159/http://physicsworld.com/cws/article/news/2016/jan/20/underground-ring-lasers-will-put-general-relativity-to-the-test |url-status=live }}</ref><ref>{{cite web |title=Einstein right using the most sensitive Earth rotation sensors ever made |url=https://phys.org/news/2017-05-einstein-sensitive-earth-rotation-sensors.html |website=Phys.org |publisher=Science X network |access-date=2 July 2017 |archive-date=10 May 2017 |archive-url=https://web.archive.org/web/20170510173326/https://phys.org/news/2017-05-einstein-sensitive-earth-rotation-sensors.html |url-status=live }}</ref> The first ten years of experience with a prototype ring laser gyroscope array, GINGERINO, established that the full scale experiment should be able to measure gravitomagnetism due to the Earth's rotation to within a 0.1% level or even better.<ref>{{cite book |last1=Altucci |first1=C. |last2=Bajardi |first2=F. |last3=Basti |first3=A. |last4=Beverini |first4=N. |last5=Capozziello |first5=S.  |title=The Ginger project – preliminary results. Proceedings of the MG16 Meeting on General Relativity Online; 5–10 July 2021 |date=2021 |isbn=978-981-12-6977-6 |pages=3956–3962 |doi=10.1142/9789811269776_0329 |url=https://doi.org/10.1142/9789811269776_0329 |access-date=7 September 2024}}</ref>