Editing Gravity (section)

===Anomalies and discrepancies===
{{distinguish|Gravity anomaly}}

There are some observations that are not adequately accounted for, which may point to the need for better theories of gravity or perhaps be explained in other ways.
[[File:GalacticRotation2.svg|thumb|Rotation curve of a typical spiral galaxy: predicted ('''A''') and observed ('''B'''). The discrepancy between the curves is attributed to [[dark matter]].]]
* '''[[Galaxy rotation curve|Galaxy rotation curves]]''': Stars in galaxies follow a distribution of velocities where stars on the outskirts are moving faster than they should according to the observed distributions of luminous matter. Galaxies within [[Galaxy groups and clusters|galaxy clusters]] show a similar pattern. The pattern is considered strong evidence for [[dark matter]], which would interact through gravitation but not electromagnetically; various [[Modified Newtonian dynamics|modifications to Newtonian dynamics]] have also been proposed.<ref>{{Cite journal |last=Sofue |first=Yoshiaki |last2=Rubin |first2=Vera |date=2001-09-01 |title=Rotation Curves of Spiral Galaxies |url=https://www.annualreviews.org/content/journals/10.1146/annurev.astro.39.1.137 |journal=Annual Review of Astronomy and Astrophysics |language=en |volume=39 |pages=137–174 |doi=10.1146/annurev.astro.39.1.137 |issn=0066-4146|arxiv=astro-ph/0010594 }}</ref>
* '''[[Accelerated expansion]]''': The [[expansion of the universe]] seems to be speeding up.<ref>{{Cite web |title=The Nobel Prize in Physics 2011 : Adam G. Riess Facts |url=https://www.nobelprize.org/prizes/physics/2011/riess/facts/ |access-date=19 March 2024 |website=NobelPrize.org |language=en-US |archive-date=28 May 2020 |archive-url=https://web.archive.org/web/20200528014511/https://www.nobelprize.org/prizes/physics/2011/riess/facts/ |url-status=live }}</ref> [[Dark energy]] has been proposed to explain this.<ref>{{Cite web |title=What is Dark Energy? Inside our accelerating, expanding Universe |url=https://science.nasa.gov/universe/the-universe-is-expanding-faster-these-days-and-dark-energy-is-responsible-so-what-is-dark-energy/ |access-date=19 March 2024 |website=science.nasa.gov |date=5 February 2024 |language=en |archive-date=19 March 2024 |archive-url=https://web.archive.org/web/20240319153930/https://science.nasa.gov/universe/the-universe-is-expanding-faster-these-days-and-dark-energy-is-responsible-so-what-is-dark-energy/ |url-status=live }}</ref>
* '''[[Flyby anomaly]]''': Various spacecraft have experienced greater acceleration than expected during [[gravity assist]] maneuvers.<ref>{{Cite journal |last1=Anderson |first1=John D. |last2=Campbell |first2=James K. |last3=Ekelund |first3=John E. |last4=Ellis |first4=Jordan |last5=Jordan |first5=James F. |date=3 March 2008 |title=Anomalous Orbital-Energy Changes Observed during Spacecraft Flybys of Earth |url=https://link.aps.org/doi/10.1103/PhysRevLett.100.091102 |journal=Physical Review Letters |language=en |volume=100 |issue=9 |page=091102 |doi=10.1103/PhysRevLett.100.091102 |pmid=18352689 |bibcode=2008PhRvL.100i1102A |issn=0031-9007}}</ref> The [[Pioneer anomaly]] has been shown to be explained by thermal recoil due to the distant sun radiation on one side of the space craft.<ref>{{Cite journal |last1=Turyshev |first1=Slava G. |last2=Toth |first2=Viktor T. |last3=Kinsella |first3=Gary |last4=Lee |first4=Siu-Chun |last5=Lok |first5=Shing M. |last6=Ellis |first6=Jordan |date=12 June 2012 |title=Support for the Thermal Origin of the Pioneer Anomaly |url=https://link.aps.org/doi/10.1103/PhysRevLett.108.241101 |journal=Physical Review Letters |volume=108 |issue=24 |pages=241101 |doi=10.1103/PhysRevLett.108.241101|pmid=23004253 |arxiv=1204.2507 |bibcode=2012PhRvL.108x1101T }}</ref><ref>{{Cite journal |last=Iorio |first=Lorenzo |date=May 2015 |title=Gravitational anomalies in the solar system? |url=https://www.worldscientific.com/doi/abs/10.1142/S0218271815300153 |journal=International Journal of Modern Physics D |language=en |volume=24 |issue=6 |pages=1530015–1530343 |doi=10.1142/S0218271815300153 |issn=0218-2718|arxiv=1412.7673 |bibcode=2015IJMPD..2430015I }}</ref>