Editing Gravitational constant (section)

== History of measurement ==
{{further|Earth mass|Schiehallion experiment|Cavendish experiment}}

=== Early history ===

The existence of the constant is implied in [[Newton's law of universal gravitation]] as published in the 1680s (although its notation as {{math|''G''}} dates to the 1890s),<ref name=BoysG/> but is not [[Algebra#Algebra as a branch of mathematics|calculated]] in his ''[[Philosophiæ Naturalis Principia Mathematica]]'' where it postulates the [[inverse-square law]] of gravitation. In the ''Principia'', Newton considered the possibility of measuring gravity's strength by measuring the deflection of a pendulum in the vicinity of a large hill, but thought that the effect would be too small to be measurable.<ref name="Davies">{{cite journal|last=Davies|first=R.D.|title=A Commemoration of Maskelyne at Schiehallion|journal=Quarterly Journal of the Royal Astronomical Society|volume=26|issue=3|pages=289–294|bibcode=1985QJRAS..26..289D|date=1985}}</ref> Nevertheless, he had the opportunity to estimate the order of magnitude of the constant when he surmised that "the mean density of the earth might be five or six times as great as the density of water", which is equivalent to a gravitational constant of the order:<ref>"Sir Isaac Newton thought it probable, that the mean density of the earth might be five or six times as great as the density of water; and we have now found, by experiment, that it is very little less than what he had thought it to be: so much justness was even in the surmises of this wonderful man!" Hutton (1778), p. 783</ref>
: {{math|''G''}} ≈ {{val|6.7|0.6|e=-11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}}

A measurement was attempted in 1738 by [[Pierre Bouguer]] and [[Charles Marie de La Condamine]] in their "[[French Geodesic Mission|Peruvian expedition]]". Bouguer downplayed the significance of their results in 1740, suggesting that the experiment had at least proved that the Earth could not be a [[Hollow Earth|hollow shell]], as some thinkers of the day, including [[Edmond Halley]], had suggested.<ref name="Poynting_p50-56">{{cite book|last=Poynting|first=J.H.|title=The Earth: its shape, size, weight and spin|publisher=Cambridge|date=1913 |pages=50–56 |url=https://books.google.com/books?id=whA9AAAAIAAJ&pg=PA50}}</ref>

The [[Schiehallion experiment]], proposed in 1772 and completed in 1776, was the first successful measurement of the mean density of the Earth, and thus indirectly of the gravitational constant. The result reported by [[Charles Hutton]] (1778) suggested a density of {{val|4.5|u=g/cm3}} ({{sfrac|4|1|2}} times the density of water), about 20% below the modern value.<ref name="Hutton">{{cite journal|last=Hutton|first=C. |date=1778 |title=An Account of the Calculations Made from the Survey and Measures Taken at Schehallien |journal=Philosophical Transactions of the Royal Society |volume=68 |pages=689–788 |doi=10.1098/rstl.1778.0034|doi-access=free }}</ref> This immediately led to estimates on the densities and masses of the [[Sun]], [[Moon]] and [[planets]], sent by Hutton to [[Jérôme Lalande]] for inclusion in his planetary tables. As discussed above, establishing the average density of Earth is equivalent to measuring the gravitational constant, given [[Earth radius#Mean radius|Earth's mean radius]] and the [[little g|mean gravitational acceleration]] at Earth's surface, by setting<ref name=BoysG>[https://books.google.com/books?id=ZrloHemOmUEC&pg=PA353 Boys 1894], p.330 In this lecture before the Royal Society, Boys introduces ''G'' and argues for its acceptance. See:
[https://archive.org/details/meandensityeart00poyngoog/page/n26 <!-- pg=4 --> Poynting 1894], p.&nbsp;4, [https://books.google.com/books?id=O58mAAAAMAAJ&pg=PA1 MacKenzie 1900], p.vi</ref>
<!--modern values: g=9.80665 ms^-2, Re=  6.3781e+6 m
3*g/(4*pi*Re)=3.6706e-7
3.6706e-7/5.448e3=6.7375e-11
the "correct" value (for G=6.674e-11) would be 5.500 gcm^-3.
-->
<math display="block">G = g\frac{R_\oplus^2}{M_\oplus} = \frac{3g}{4\pi R_\oplus\rho_\oplus}.</math>
Based on this, Hutton's 1778 result is equivalent to {{nowrap|{{math|''G''}} ≈ {{val|8|e=-11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}}}}.

[[File:Cavendish Torsion Balance Diagram.svg|thumb|Diagram of torsion balance used in the [[Cavendish experiment]] performed by [[Henry Cavendish]] in 1798, to measure G, with the help of a pulley, large balls hung from a frame were rotated into position next to the small balls.]]
The first direct measurement of gravitational attraction between two bodies in the laboratory was performed in 1798, seventy-one years after Newton's death, by Henry Cavendish.<ref>Published in ''[[Philosophical Transactions of the Royal Society]]'' (1798); reprint: Cavendish, Henry (1798). "Experiments to Determine the Density of the Earth". In MacKenzie, A. S., ''Scientific Memoirs'' Vol. 9: ''The Laws of Gravitation''. American Book Co. (1900), pp. 59–105.</ref> He determined a value for {{math|''G''}} implicitly, using a [[Torsion spring#Torsion balance|torsion balance]] invented by the geologist Rev. [[John Michell]] (1753). He used a horizontal [[torsion beam]] with lead balls whose inertia (in relation to the torsion constant) he could tell by timing the beam's oscillation. Their faint attraction to other balls placed alongside the beam was detectable by the deflection it caused. In spite of the experimental design being due to Michell, the experiment is now known as the Cavendish experiment for its first successful execution by Cavendish.

Cavendish's stated aim was the "weighing of Earth", that is, determining the average density of Earth and the [[Earth's mass]]. His result, {{nowrap|1={{math|1=''ρ''<sub>🜨</sub>}} = {{val|5.448|(33)|u=g.cm-3}}}}, corresponds to value of {{nowrap|1={{math|1=''G''}} = {{val|6.74|(4)|e=-11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}}}}. It is remarkably accurate, being about 1% above the modern [[CODATA]] recommended value {{physconst|G|round=3|ref=no}}, consistent with the claimed relative standard uncertainty of 0.6%.

=== 19th century ===
The accuracy of the measured value of {{math|''G''}} has increased only modestly since the original Cavendish experiment.<ref>
{{cite book|last1=Brush |first1=Stephen G. |last2=Holton |first2=Gerald James |title=Physics, the human adventure: from Copernicus to Einstein and beyond |url=https://archive.org/details/physicshumanadve00ghol |url-access=limited |publisher=Rutgers University Press |location=New Brunswick, NJ |date=2001 |pages= [https://archive.org/details/physicshumanadve00ghol/page/n151 137] |isbn=978-0-8135-2908-0 }}
{{cite journal |first=Jennifer Lauren |last=Lee |title=Big G Redux: Solving the Mystery of a Perplexing Result |date=16 November 2016 |journal=NIST |url=https://www.nist.gov/news-events/news/2016/11/big-g-redux-solving-mystery-perplexing-result}}</ref> {{math|''G''}} is quite difficult to measure because gravity is much weaker than other fundamental forces, and an experimental apparatus cannot be separated from the gravitational influence of other bodies.

Measurements with pendulums were made by [[Francesco Carlini]] (1821, {{val|4.39|u=g/cm3}}), [[Edward Sabine]] (1827, {{val|4.77|u=g/cm3}}), Carlo Ignazio Giulio (1841, {{val|4.95|u=g/cm3}}) and [[George Biddell Airy]] (1854, {{val|6.6|u=g/cm3}}).<ref>{{cite book | last = Poynting | first = John Henry | title = The Mean Density of the Earth | publisher = Charles Griffin | date = 1894 | location = London | pages = [https://archive.org/details/meandensityeart00poyngoog/page/n44 22]–24 | url = https://archive.org/details/meandensityeart00poyngoog }}</ref>

Cavendish's experiment was first repeated by [[Ferdinand Reich]] (1838, 1842, 1853), who found a value of {{val|5.5832|(149)|u=g.cm-3}},<ref>F. Reich, "On the Repetition of the Cavendish Experiments for Determining the mean density of the Earth, ''Philosophical Magazine''  12: 283–284.</ref> which is actually worse than Cavendish's result, differing from the modern value by 1.5%. Cornu and Baille (1873), found {{val|5.56|u=g.cm-3}}.<ref>Mackenzie (1899), p. 125.</ref>

Cavendish's experiment proved to result in more reliable measurements than pendulum experiments of the "Schiehallion" (deflection) type or "Peruvian" (period as a function of altitude) type. Pendulum experiments still continued to be performed, by [[Robert von Sterneck]] (1883, results between {{val|5.0|and|6.3|u=g/cm3}}) and [[Thomas Corwin Mendenhall]] (1880, {{val|5.77|u=g/cm3}}).<ref>A.S. Mackenzie, ''The Laws of Gravitation'' (1899), [https://archive.org/stream/lawsgravitation01newtgoog#page/n140/mode/2up 127f.]</ref>

Cavendish's result was first improved upon by [[John Henry Poynting]] (1891),<ref>{{cite book |url=https://archive.org/details/meandensityofear00poynuoft |title=The mean density of the earth |last=Poynting |first=John Henry |date=1894 |publisher=London |others=Gerstein - University of Toronto }}</ref> who published a value of {{val|5.49|(3)|u=g.cm-3}}, differing from the modern value by 0.2%, but compatible with the modern value within the cited relative standard uncertainty of 0.55%. In addition to Poynting, measurements were made by [[C. V. Boys]] (1895)<ref>{{cite journal | last=Boys | first=C. V. | title=On the Newtonian Constant of Gravitation | journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | publisher=The Royal Society | volume=186 | date=1895-01-01 | issn=1364-503X | doi=10.1098/rsta.1895.0001 | bibcode=1895RSPTA.186....1B | pages=1–72| doi-access=free }}</ref> and [[Carl Braun (astronomer)|Carl Braun]]<!--[[:de:Carl Braun (Astronom)]]--> (1897),<ref>Carl Braun, ''Denkschriften der k. Akad. d. Wiss. (Wien), math. u. naturwiss. Classe'', 64 (1897).
Braun (1897) quoted an optimistic relative standard uncertainty of 0.03%, {{val|6.649|(2)|e=−11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}} but his result was significantly worse than the 0.2% feasible at the time.</ref> with compatible results suggesting {{math|''G''}} = {{val|6.66|(1)|e=−11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}}. The modern notation involving the constant {{math|''G''}} was introduced by Boys in 1894<ref name=BoysG/> and becomes standard by the end of the 1890s, with values usually cited in the [[cgs]] system. Richarz and Krigar-Menzel (1898) attempted a repetition of the Cavendish experiment using 100,000&nbsp;kg of lead for the attracting mass. The precision of their result of {{val|6.683|(11)|e=-11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}} was, however, of the same order of magnitude as the other results at the time.<ref name=Sagitov>Sagitov, M. U., "Current Status of Determinations of the Gravitational Constant and the Mass of the Earth", Soviet Astronomy, Vol. 13 (1970), 712–718, translated from ''Astronomicheskii Zhurnal'' Vol. 46, No. 4 (July–August 1969), 907–915 (table of historical experiments p. 715).</ref>

[[Arthur Stanley Mackenzie]] in ''The Laws of Gravitation'' (1899) reviews the work done in the 19th century.<ref>Mackenzie, A. Stanley, ''[https://archive.org/stream/lawsgravitation01newtgoog#page/n6/mode/2up The laws of gravitation; memoirs by Newton, Bouguer and Cavendish, together with abstracts of other important memoirs]'', American Book Company (1900 [1899]).</ref> Poynting is the author of the article "Gravitation" in the [[Encyclopædia Britannica Eleventh Edition|''Encyclopædia Britannica'' Eleventh Edition]] (1911). Here, he cites a value of {{math|''G''}} = {{val|6.66|e=−11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}} with a relative uncertainty of 0.2%.

=== Modern value ===
[[Paul R. Heyl]] (1930) published the value of {{val|6.670|(5)|e=−11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}} (relative uncertainty 0.1%),<ref>{{cite journal |first=P. R. |last=Heyl |author-link=Paul R. Heyl |title=A redetermination of the constant of gravitation |journal= Bureau of Standards Journal of Research|volume=5 |issue=6 |year=1930 |pages=1243–1290|doi=10.6028/jres.005.074 |doi-access=free }}<!--Also  https://archive.org/details/redeterminationo56124heyl, and a shorter version at https://europepmc.org/articles/PMC1085130--></ref> improved to {{val|6.673|(3)|e=−11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}} (relative uncertainty 0.045% = 450&nbsp;ppm) in 1942.<ref>P. R. Heyl and P. Chrzanowski (1942), cited after Sagitov (1969:715).</ref>

However, Heyl used the statistical spread as his standard deviation, and he admitted himself that measurements using the same material yielded very similar results while measurements using different materials yielded vastly different results. He spent the next 12 years after his 1930 paper to do more precise measurements, hoping that the composition-dependent effect would go away, but it did not, as he noted in his final paper from the year 1942.

Published values of {{mvar|G}} derived from high-precision measurements since the 1950s have remained compatible with Heyl (1930), but within the relative uncertainty of about 0.1% (or 1000&nbsp;ppm) have varied rather broadly, and it is not entirely clear whether the uncertainty has been reduced at all since the 1942 measurement. Some measurements published in the 1980s to 2000s were, in fact, mutually exclusive.<ref name=gillies/><ref name=codata2002>{{cite journal|first1=Peter J. |last1=Mohr |first2=Barry N. |last2=Taylor |title=CODATA recommended values of the fundamental physical constants: 2002 |journal=Reviews of Modern Physics |year=2012 |volume=77 |issue=1 | pages=1–107 |url=http://www.atomwave.org/rmparticle/ao%20refs/aifm%20refs%20sorted%20by%20topic/other%20rmp%20articles/CODATA2005.pdf |access-date=1 July 2006 |doi=10.1103/RevModPhys.77.1 |bibcode=2005RvMP...77....1M |citeseerx=10.1.1.245.4554 |url-status=dead |archive-url=https://web.archive.org/web/20070306174141/http://www.atomwave.org/rmparticle/ao%20refs/aifm%20refs%20sorted%20by%20topic/other%20rmp%20articles/CODATA2005.pdf |archive-date=6 March 2007|arxiv=1203.5425 }} Section Q (pp. 42–47) describes the mutually inconsistent measurement experiments from which the CODATA value for {{mvar|G}} was derived.</ref> Establishing a standard value for {{mvar|G}} with a relative standard uncertainty better than 0.1% has therefore remained rather speculative.

By 1969, the value recommended by the [[National Institute of Standards and Technology]] (NIST) was cited with a relative standard uncertainty of 0.046% (460&nbsp;ppm), lowered to 0.012% (120&nbsp;ppm) by 1986. But the continued publication of conflicting measurements led NIST to considerably increase the standard uncertainty in the 1998 recommended value, by a factor of 12, to a standard uncertainty of 0.15%, larger than the one given by Heyl (1930).

The uncertainty was again lowered in 2002 and 2006, but once again raised, by a more conservative 20%, in 2010, matching the relative standard uncertainty of 120&nbsp;ppm published in 1986.<ref>{{Cite journal|url = http://physics.nist.gov/cuu/pdf/RevModPhysCODATA2010.pdf|title = CODATA recommended values of the fundamental physical constants: 2010|date = 13 November 2012|journal = Reviews of Modern Physics |doi = 10.1103/RevModPhys.84.1527|bibcode=2012RvMP...84.1527M|arxiv = 1203.5425 |volume=84 |issue = 4|pages=1527–1605|last1 = Mohr|first1 = Peter J.|last2 = Taylor|first2 = Barry N.|last3 = Newell|first3 = David B.|s2cid = 103378639|citeseerx = 10.1.1.150.3858}}</ref> For the 2014 update, CODATA reduced the uncertainty to 46&nbsp;ppm, less than half the 2010 value, and one order of magnitude below the 1969 recommendation.

The following table shows the NIST recommended values published since 1969:
[[File:Gravitational constant historical.png|thumb|350px|Timeline of measurements and recommended values for ''G'' since 1900: values recommended based on a literature review are shown in red, individual torsion balance experiments in blue, other types of experiments in green.]]
{|class=wikitable
|+Recommended values for ''G''
!scope="col"| Year
!scope="col"| ''G'' <br />{{bracket|10{{sup|−11}}&nbsp;m{{sup|3}}⋅kg{{sup|−1}}⋅s{{sup|−2}}}}
! scope="col"|Relative standard uncertainty
!scope="col"| Ref.
|-
!scope="row"|1969
| {{val|6.6732|(31)}}  || 460&nbsp;ppm || <ref>{{cite journal | last1=Taylor | first1=B. N. | last2=Parker | first2=W. H. | last3=Langenberg | first3=D. N. | title=Determination of ''e''/''h'', Using Macroscopic Quantum Phase Coherence in Superconductors: Implications for Quantum Electrodynamics and the Fundamental Physical Constants | journal=Reviews of Modern Physics | publisher=American Physical Society (APS) | volume=41 | issue=3 | date=1969-07-01 | issn=0034-6861 | doi=10.1103/revmodphys.41.375 | bibcode=1969RvMP...41..375T | pages=375–496}}</ref>
|-
!scope="row"|1973
| {{val|6.6720|(49)}}  || 730&nbsp;ppm || <ref>{{cite journal | last1=Cohen | first1=E. Richard | last2=Taylor | first2=B. N. | title=The 1973 Least-Squares Adjustment of the Fundamental Constants | journal=Journal of Physical and Chemical Reference Data | publisher=AIP Publishing | volume=2 | issue=4 | year=1973 | issn=0047-2689 | doi=10.1063/1.3253130 | bibcode=1973JPCRD...2..663C | pages=663–734| hdl=2027/pst.000029951949 | hdl-access=free }}</ref>
|-
!scope="row"|1986
| {{val|6.67449|(81)}} || 120&nbsp;ppm || <ref>{{cite journal | last1=Cohen | first1=E. Richard | last2=Taylor | first2=Barry N. | title=The 1986 adjustment of the fundamental physical constants | journal=Reviews of Modern Physics | publisher=American Physical Society (APS) | volume=59 | issue=4 | date=1987-10-01 | issn=0034-6861 | doi=10.1103/revmodphys.59.1121 | bibcode=1987RvMP...59.1121C | pages=1121–1148}}</ref>
|-
!scope="row"|1998
| {{val|6.673|(10)}} || 1500&nbsp;ppm || <ref>{{cite journal | last1=Mohr | first1=Peter J. | last2=Taylor | first2=Barry N. | title=CODATA recommended values of the fundamental physical constants: 1998 | journal=Reviews of Modern Physics | volume=72 | issue=2 | year=2012 | issn=0034-6861 | doi=10.1103/revmodphys.72.351 | bibcode=2000RvMP...72..351M | pages=351–495| arxiv=1203.5425 }}</ref>
|-
!scope="row"|2002
| {{val|6.6742|(10)}} || 150&nbsp;ppm || <ref>{{cite journal | last1=Mohr | first1=Peter J. | last2=Taylor | first2=Barry N. | title=CODATA recommended values of the fundamental physical constants: 2002 | journal=Reviews of Modern Physics | volume=77 | issue=1 | year=2012 | issn=0034-6861 | doi=10.1103/revmodphys.77.1 | bibcode=2005RvMP...77....1M | pages=1–107| arxiv=1203.5425 }}</ref>
|-
!scope="row"|2006
| {{val|6.67428|(67)}} || 100&nbsp;ppm || <ref>{{cite journal | last1=Mohr | first1=Peter J. | last2=Taylor | first2=Barry N. | last3=Newell | first3=David B. | title=CODATA recommended values of the fundamental physical constants: 2006 | journal=Journal of Physical and Chemical Reference Data | volume=37 | issue=3 | year=2012 | issn=0047-2689 | doi=10.1063/1.2844785 | bibcode=2008JPCRD..37.1187M | pages=1187–1284| arxiv=1203.5425 }}</ref>
|-
!scope="row"|2010
| {{val|6.67384|(80)}} || 120&nbsp;ppm || <ref>{{cite journal | last1=Mohr | first1=Peter J. | last2=Taylor | first2=Barry N. | last3=Newell | first3=David B. | title=CODATA Recommended Values of the Fundamental Physical Constants: 2010 | journal=Journal of Physical and Chemical Reference Data | volume=41 | issue=4 | year=2012 | pages=1527–1605 | issn=0047-2689 | doi=10.1063/1.4724320 | bibcode=2012JPCRD..41d3109M | arxiv=1203.5425 }}</ref>
|-
!scope="row"|2014
| {{val|6.67408|(31)}} ||  46&nbsp;ppm || <ref>{{cite journal | last1=Mohr | first1=Peter J. | last2=Newell | first2=David B. | last3=Taylor | first3=Barry N. | title=CODATA Recommended Values of the Fundamental Physical Constants: 2014 | journal=Journal of Physical and Chemical Reference Data | volume=45 | issue=4 | year=2016 | pages=1527–1605 | issn=0047-2689 | doi=10.1063/1.4954402 | bibcode=2016JPCRD..45d3102M | arxiv=1203.5425 }}</ref>
|-
!scope="row"|2018
| {{val|6.67430|(15)}} ||  22&nbsp;ppm || <ref>Eite Tiesinga, Peter J. Mohr, David B. Newell, and Barry N. Taylor (2019), "[http://physics.nist.gov/constants The 2018 CODATA Recommended Values of the Fundamental Physical Constants]" (Web Version 8.0). Database developed by J. Baker, M. Douma, and [[Svetlana Kotochigova|S. Kotochigova]]. National Institute of Standards and Technology, Gaithersburg, MD 20899.</ref>
|-
!scope="row"|2022
| {{val|6.67430|(15)}} ||  22 ppm || <ref>{{citation |author1=Mohr, P. |author2=Tiesinga, E. |author3=Newell, D. |author4=Taylor, B. |date=2024-05-08 |title=Codata Internationally Recommended 2022 Values of the Fundamental Physical Constants |work=NIST |url=https://www.nist.gov/publications/codata-internationally-reconmmended-2022-values-fundamental-physical-constants |access-date=2024-05-15 }}</ref>
|-
|}
In the January 2007 issue of ''[[Science (journal)|Science]]'', Fixler et al. described a measurement of the gravitational constant by a new technique, [[atom interferometry]], reporting a value of {{nowrap|1={{math|''G''}} = {{val|6.693|(34)|e=−11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}}}}, 0.28% (2800&nbsp;ppm) higher than the 2006 CODATA value.<ref>{{cite journal |first1=J. B. |last1=Fixler |first2=G. T. |last2=Foster |first3=J. M. |last3=McGuirk |first4=M. A. |last4=Kasevich |s2cid=6271411 |title=Atom Interferometer Measurement of the Newtonian Constant of Gravity |date=5 January 2007 |volume=315 |issue=5808 |pages=74–77 |doi=10.1126/science.1135459 |journal=Science |pmid=17204644 |bibcode=2007Sci...315...74F }}</ref> An improved cold atom measurement by Rosi et al. was published in 2014 of {{nowrap|1={{math|''G''}} = {{val|6.67191|(99)|e=−11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}}}}.<ref>
{{cite journal
 |last1=Rosi |first1=G.
 |last2=Sorrentino |first2=F.
 |last3=Cacciapuoti |first3=L.
 |last4=Prevedelli |first4=M.
 |last5=Tino |first5=G. M.
 |title=Precision measurement of the Newtonian gravitational constant using cold atoms
 |journal=Nature |volume=510 |issue=7506  |date=26 June 2014 |pages=518–521
 |url=http://www2.fisica.unlp.edu.ar/materias/FisGral2semestre2/Rosi.pdf |url-status=live
 |archive-url=https://ghostarchive.org/archive/20221009/http://www2.fisica.unlp.edu.ar/materias/FisGral2semestre2/Rosi.pdf
 |archive-date=2022-10-09
 |doi=10.1038/nature13433 |pmid=24965653  |arxiv=1412.7954
 |s2cid=4469248
 |bibcode=2014Natur.510..518R
}}</ref><ref>
{{cite journal
 |last1=Schlamminger |first1=Stephan
 |title=Fundamental constants: A cool way to measure big G
 |journal=Nature |volume=510 |issue=7506 |pages=478–480
 |date=18 June 2014
 |url=https://www.nature.com/articles/nature13507.pdf
 |archive-url=https://ghostarchive.org/archive/20221009/https://www.nature.com/articles/nature13507.pdf
 |archive-date=2022-10-09
 |url-status=live
 |doi=10.1038/nature13507 |doi-access=free
 |bibcode=2014Natur.510..478S |pmid=24965646
}}</ref> Although much closer to the accepted value (suggesting that the Fixler ''et al.'' measurement was erroneous), this result was 325&nbsp;ppm below the recommended 2014 CODATA value, with non-overlapping [[standard uncertainty]] intervals.
<!-- 6.67191(99) vs. 6.67408(31) [2014], a difference of 0.00217(104). Also *barely* not overlapping with the
2010 interval, 6.67384(80) [2010] (differences 0.00193(127) and 0.00024(86)).
This doesn't mean anything beyond "2-sigma effect" until the experiment is repeated.
-->

As of 2018, efforts to re-evaluate the conflicting results of measurements are underway, coordinated by NIST, notably a repetition of the experiments reported by Quinn et al. (2013).<ref>{{cite journal |author1=C. Rothleitner |author2=S. Schlamminger |title=Invited Review Article: Measurements of the Newtonian constant of gravitation, G |journal=Review of Scientific Instruments |volume=88 |issue=11 |pages=111101 |id=111101 |year=2017 |doi=10.1063/1.4994619 |pmid=29195410 |pmc=8195032 |quote=However, re-evaluating or repeating experiments that have already been performed may provide insights into hidden biases or dark uncertainty. NIST has the unique opportunity to repeat the experiment of Quinn et al. [2013] with an almost identical setup. By mid-2018, NIST researchers will publish their results and assign a number as well as an uncertainty to their value.|bibcode=2017RScI...88k1101R |doi-access=free }} Referencing:
* {{cite journal |author1=T. Quinn |author2=H. Parks |author3=C. Speake |author4=R. Davis |title=Improved determination of G using two methods |journal=Phys. Rev. Lett. |volume=111 |issue=10 |pages=101102 |id=101102 |year=2013 |doi=10.1103/PhysRevLett.111.101102 |pmid=25166649 |bibcode=2013PhRvL.111j1102Q |url=https://www.bipm.org/utils/en/pdf/PhysRevLett.111.101102.pdf |access-date=4 August 2019 |archive-date=4 December 2020 |archive-url=https://web.archive.org/web/20201204172116/https://www.bipm.org/utils/en/pdf/PhysRevLett.111.101102.pdf |url-status=dead }}
The 2018 experiment was described by {{cite conference |author=C. Rothleitner |url=https://www.bipm.org/cc/CODATA-TGFC/Allowed/2015-02/Rothleitner.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.bipm.org/cc/CODATA-TGFC/Allowed/2015-02/Rothleitner.pdf |archive-date=2022-10-09 |url-status=live |title=Newton's Gravitational Constant 'Big' G – A proposed Free-fall Measurement |conference=CODATA Fundamental Constants Meeting, Eltville – 5 February 2015 }}</ref>

In August 2018, a Chinese research group announced new measurements based on torsion balances, {{val|6.674184|(78)|e=−11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}} and {{val|6.674484|(78)|e=−11|u=m<sup>3</sup>⋅kg<sup>−1</sup>⋅s<sup>−2</sup>}} based on two different methods.<ref>{{cite journal|first=Qing |last=Li |s2cid=52121922 |display-authors=etal |title=Measurements of the gravitational constant using two independent methods |journal=Nature |volume=560 |issue=7720 |pages=582–588 |year=2018 |doi=10.1038/s41586-018-0431-5|pmid=30158607 |bibcode=2018Natur.560..582L }}.
See also: {{cite news|url=https://www.techexplorist.com/physicists-precise-measurement-ever-gravitys-strength/16643/ |title=Physicists just made the most precise measurement ever of Gravity's strength |date=31 August 2018 |access-date=13 October 2018 }}</ref> These are claimed as the most accurate measurements ever made, with standard uncertainties cited as low as 12&nbsp;ppm. The difference of 2.7{{px1}}[[standard deviation|''σ'']] between the two results suggests there could be sources of error unaccounted for.