Editing Gravitational constant (section)

{{Short description|Physical constant relating the gravitational force between objects to their mass and distance}}
{{Distinguish|text={{mvar|g}}, the [[gravity of Earth]]}}
{{Use dmy dates|date=August 2019}}
{|  class="wikitable floatright"
!scope="col"| Value of {{mvar|G}}
!scope="col"| Unit
|-
| {{physconst|G|unit=no}}
| [[metre|m]]{{sup|3}}⋅[[kilogram|kg]]{{sup|−1}}⋅[[second|s]]{{sup|−2}}
|-
| {{val|6.67430|(15)|e=-8}}
| [[dyne|dyn]]⋅[[centimetre|cm]]{{sup|2}}⋅[[gram|g]]{{sup|−2}}
|-
| {{val|4.3009172706|(3)|e=-3}}
| [[parsec|pc]]⋅[[Solar mass|''M''{{sub|⊙}}]]{{sup|−1}}⋅([[kilometre|km]]/[[second|s]]){{sup|2}}
|}

[[File:NewtonsLawOfUniversalGravitation.svg|thumb|right|300px|The gravitational constant {{math|''G''}} is a key quantity in [[Newton's law of universal gravitation]].]]

The '''gravitational constant''' is an [[empirical]] [[physical constant]] involved in the calculation of [[gravitational]] effects in [[Sir Isaac Newton]]'s law of universal gravitation and in [[Albert Einstein]]'s [[general relativity|theory of general relativity]]. It is also known as the '''universal gravitational constant''', the '''Newtonian constant of gravitation''', or the '''Cavendish gravitational constant''',{{efn|"Newtonian constant of gravitation" is the name introduced for ''G'' by Boys (2000). Use of the term by T.E. Stern (1928) was misquoted as "Newton's constant of gravitation" in ''Pure Science Reviewed for Profound and Unsophisticated Students'' (1930), in what is apparently the first use of that term. Use of "Newton's constant" (without specifying "gravitation" or "gravity") is more recent, as "Newton's constant" was also used for the [[heat transfer coefficient]] in [[Newton's law of cooling]], but has by now become quite common, e.g. Calmet et al, ''Quantum Black Holes'' (2013), p. 93;  P. de Aquino, ''Beyond Standard Model Phenomenology at the LHC'' (2013), p. 3.

The name "Cavendish gravitational constant", sometimes "Newton–Cavendish gravitational constant", appears to have been common in the 1970s to 1980s, especially in (translations from) Soviet-era Russian literature, e.g. Sagitov (1970 [1969]), ''Soviet Physics: Uspekhi'' 30 (1987), Issues 1–6, p. 342 [etc.].
"Cavendish constant" and "Cavendish gravitational constant" is also used in Charles W. Misner, Kip S. Thorne, John Archibald Wheeler, "Gravitation",  (1973), 1126f.

Colloquial use of "Big G", as opposed to "[[little g]]" for gravitational acceleration dates to the 1960s (R.W.  Fairbridge, ''The encyclopedia of atmospheric sciences and astrogeology'', 1967, p. 436; note use of "Big G's" vs. "little g's" as early as the 1940s of the [[Einstein tensor]] ''G''<sub>''μν''</sub> vs. the [[metric tensor]] ''g''<sub>''μν''</sub>, ''Scientific, medical, and technical books published in the United States of America: a selected list of titles in print with annotations: supplement of books published 1945–1948'', Committee on American Scientific and Technical Bibliography National Research Council, 1950, p. 26).|name=|group=}} denoted by the capital letter&nbsp;{{math|''G''}}.

In Newton's law, it is the proportionality constant connecting the [[gravitational force]] between two bodies with the product of their [[mass]]es and the [[inverse-square law|inverse square]] of their [[distance]]. In the [[Einstein field equations]], it quantifies the relation between the geometry of spacetime and the energy–momentum tensor (also referred to as the [[stress–energy tensor]]).

The measured value of the constant is known with some certainty to four significant digits. In [[SI units]], its value is approximately <!--{{math|''G''}} = -->{{physconst|G|round=4|after=.}}

The modern notation of Newton's law involving {{math|''G''}} was introduced in the 1890s by [[C. V. Boys]]. The first implicit measurement with an accuracy within about 1% is attributed to [[Henry Cavendish]] in a [[Cavendish experiment|1798 experiment]].{{efn|Cavendish determined the value of ''G'' indirectly, by reporting a value for the [[Earth's mass]], or the average density of Earth, as {{val|5.448|u=g.cm-3}}.|name=|group=}}