Editing Graviton (section)

== Experimental observation ==
Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, has been thought to be impossible with any physically reasonable detector.<ref name="Rothman">
{{cite journal
 |last1=Rothman |first1=T.
 |last2=Boughn |first2=S.
 |date=2006
 |title=Can Gravitons be Detected?
 |journal=[[Foundations of Physics]]
 |volume=36 |issue=12 |pages=1801–1825
 |arxiv=gr-qc/0601043
 |bibcode=2006FoPh...36.1801R
 |doi=10.1007/s10701-006-9081-9
|s2cid=14008778
 }}</ref> The reason is the extremely low [[cross section (physics)|cross section]] for the interaction of gravitons with matter. For example, a detector with the mass of [[Jupiter]] and 100% efficiency, placed in close orbit around a [[neutron star]], would only be expected to observe one graviton every 10 years, even under the most favorable conditions. It would be impossible to discriminate these events from the background of [[neutrino]]s, since the dimensions of the required neutrino shield would ensure collapse into a [[black hole]].<ref name="Rothman" /> It has been proposed that detecting single gravitons would be possible by quantum sensing.<ref name="Tobar">{{Cite journal |last=Tobar |first=Germain |display-authors=etal |date=22 August 2024|title=Detecting single gravitons with quantum sensing|journal=Nat Commun|volume=15 |issue=1 |page=7229 |language=en |arxiv=2308.15440|doi=10.1038/s41467-024-51420-8 |pmid=39174544 |pmc=11341900 |bibcode=2024NatCo..15.7229T }}</ref> Even quantum events may not indicate quantization of gravitational radiation.<ref>{{Cite journal |last1=Carney |first1=Daniel |last2=Domcke |first2=Valerie |last3=Rodd |first3=Nicholas L. |date=2024-02-05 |title=Graviton detection and the quantization of gravity |url=https://journals.aps.org/prd/abstract/10.1103/PhysRevD.109.044009 |journal=Physical Review D |volume=109 |issue=4 |pages=044009 |doi=10.1103/PhysRevD.109.044009|arxiv=2308.12988 |bibcode=2024PhRvD.109d4009C }}</ref>

[[LIGO]] and [[Virgo interferometer|Virgo]] collaborations' observations have [[First observation of gravitational waves|directly detected]] gravitational waves.<ref name="Abbot">{{Cite journal |last=Abbott |first=B. P. |display-authors=etal |date=2016-02-11 |others=LIGO Scientific Collaboration and Virgo Collaboration |title=Observation of Gravitational Waves from a Binary Black Hole Merger |url=https://link.aps.org/doi/10.1103/PhysRevLett.116.061102 |journal=Physical Review Letters |language=en |volume=116 |issue=6 |page=061102 |arxiv=1602.03837 |bibcode=2016PhRvL.116f1102A |doi=10.1103/PhysRevLett.116.061102 |issn=0031-9007 |pmid=26918975 |s2cid=124959784}}</ref><ref name="Discovery 2016">{{cite journal |title=Einstein's gravitational waves found at last |journal=Nature News|date=February 11, 2016 |last1=Castelvecchi |first1=Davide |last2=Witze |first2=Witze |doi=10.1038/nature.2016.19361 |s2cid=182916902}}</ref><ref name="NSF">{{cite web |title=Gravitational waves detected 100 years after Einstein's prediction |url=https://www.nsf.gov/news/news_summ.jsp?cntn_id=137628 |access-date=2016-02-11 |website=NSF – National Science Foundation}}</ref> Others have postulated that graviton scattering yields gravitational waves as particle interactions yield [[coherent state]]s.<ref>{{cite journal | last1 = Senatore | first1 = L. | last2 = Silverstein | first2 = E. | last3 = Zaldarriaga | first3 = M. | year = 2014 | title = New sources of gravitational waves during inflation | journal = Journal of Cosmology and Astroparticle Physics | volume = 2014 | issue = 8| page = 016 | doi=10.1088/1475-7516/2014/08/016| arxiv = 1109.0542 | bibcode = 2014JCAP...08..016S | s2cid = 118619414 }}</ref> Although these experiments cannot detect individual gravitons, they might provide information about certain properties of the graviton.<ref name="detecting graviton">{{cite journal|first=Freeman |last= Dyson|date=8 October 2013|journal=[[International Journal of Modern Physics A]]|volume=28|issue=25|pages=1330041–1–1330035–14|title=Is a Graviton Detectable?|doi=10.1142/S0217751X1330041X|bibcode = 2013IJMPA..2830041D }}</ref> For example, if gravitational waves were observed to propagate slower than ''c'' (the [[speed of light]] in vacuum), that would imply that the graviton has mass (however, gravitational waves must propagate slower than ''c'' in a region with non-zero mass density if they are to be detectable).<ref>
{{cite journal
 |last=Will |first=C. M.
 |date=1998
 |title=Bounding the mass of the graviton using gravitational-wave observations of inspiralling compact binaries
 |journal=[[Physical Review D]]
 |volume=57 |issue=4 |pages=2061–2068
 |arxiv=gr-qc/9709011
 |bibcode=1998PhRvD..57.2061W
 |doi=10.1103/PhysRevD.57.2061
 |s2cid=41690760
 |url=https://cds.cern.ch/record/333219/files/9709011.pdf
 |archive-url=https://web.archive.org/web/20180724135835/https://cds.cern.ch/record/333219/files/9709011.pdf
 |archive-date=2018-07-24
 |url-status=live
}}</ref> Observations of gravitational waves put an upper bound of {{val|1.76|e=-23|u=eV/c2}} on the graviton's mass.<ref name="Abbot2">{{cite journal|doi=10.1103/PhysRevD.103.122002|title= Tests of General Relativity with Binary Black Holes from the second LIGO-Virgo Gravitational-Wave Transient Catalog|journal= [[Physical Review Letters]]|date= 15 June 2021|author=R Abbot|display-authors=etal|volume=103|issue=12|pages=122022|arxiv=2010.14529|bibcode= 2021PhRvD.103l2002A}}</ref> Solar system planetary trajectory measurements by space missions such as [[Cassini–Huygens|Cassini]] and [[MESSENGER]] give a comparable upper bound of {{val|3.16|e=-23|u=eV/c2}}.<ref name="Bernus2020">{{cite journal|doi=10.1103/PhysRevD.102.021501|title= Constraint on the Yukawa suppression of the Newtonian potential from the planetary ephemeris INPOP19a|journal= [[Physical Review Letters]]|date= 15 July 2020|author=L. Bernus|display-authors=etal|volume=102|issue=2|pages=021501(R)|arxiv=2006.12304|bibcode= 2020PhRvD.102b1501B}}</ref> The gravitational wave and planetary ephemeris need not agree: they test different aspects of a potential graviton-based theory.<ref>{{Cite journal |last1=Fienga |first1=Agnès |last2=Minazzoli |first2=Olivier |date=2024-01-29 |title=Testing theories of gravity with planetary ephemerides |journal=Living Reviews in Relativity |language=en |volume=27 |issue=1 |pages=1 |doi=10.1007/s41114-023-00047-0 |issn=1433-8351|doi-access=free |arxiv=2303.01821 |bibcode=2024LRR....27....1F }}</ref>{{rp|71}}

Astronomical observations of the kinematics of galaxies, especially the [[galaxy rotation curve|galaxy rotation problem]] and [[modified Newtonian dynamics]], might point toward gravitons having non-zero mass.<ref>{{Cite journal|arxiv = 1211.4692|doi = 10.5303/JKAS.2013.46.1.41|last1 = Trippe|first1 = Sascha|title = A Simplified Treatment of Gravitational Interaction on Galactic Scales|year = 2012|journal=Journal of the Korean Astronomical Society |volume=46 |issue=1 |pages=41–47 |bibcode=2013JKAS...46...41T}}</ref><ref>{{cite journal |title=Long range effects in gravity theories with Vainshtein screening |year=2018 |last1=Platscher |first1=Moritz |last2=Smirnov |first2=Juri |last3=Meyer |first3=Sven |last4=Bartelmann |first4=Matthias|journal=Journal of Cosmology and Astroparticle Physics |volume=2018 |issue=12 |page=009 |doi=10.1088/1475-7516/2018/12/009|arxiv=1809.05318 |bibcode=2018JCAP...12..009P|s2cid=86859475}}</ref>