Has the Value of G Constant Changed Recently?

[Tony Stark]

Has there been any recent changes in the G constant value?

 

[Tony Stark]

I meant in the official value of G known to us?

 

[SteamKing]

Since G must be determined experimentally, there will be some variability in its reported value.

This article, Ref. 9, contains a report on the latest measurements of G:

https://en.wikipedia.org/wiki/Gravitational_constant

 

[D H]

The job of the CODATA Task Group on Fundamental Constants is "to periodically provide the scientific and technological communities with a self-consistent set of internationally recommended values of the basic constants and conversion factors of physics and chemistry based on all of the relevant data available at a given point in time."

Updates are released every four years. This update will be published online at http://physics.nist.gov/cuu/Constants, supposedly in May or June 2015, but that hasn't happened yet. That site still has the CODATA 2010 values. It's still June 2015, so nominally this should any day now -- or maybe not.

 

[rootone]

G cannot be a constant since the mass of the Earth is not a constant.
In fact several tonnes of micrometoric dust is accumulated every day.
Although that makes no significant difference to the measure of G over the course of a human life time, it might make a difference on geologic time scales.

 

[SteamKing]

G cannot be a constant since the mass of the Earth is not a constant.
In fact several tonnes of micrometoric dust is accumulated every day.
Although that makes no significant difference to the measure of G over the course of a human life time, it might make a difference on geologic time scales.

This just means that GM_earth varies slightly over time.

The variation in G over longer time scales has been studied using astronomical phenomena:

Under the assumption that the physics of type Ia supernovae are universal, analysis of observations of 580 type Ia supernovae has shown that the gravitational constant has varied by less than one part in ten billion per year over the last nine billion years.

from the Wiki article linked above.

 

[D H]

G cannot be a constant since the mass of the Earth is not a constant.
In fact several tonnes of micrometoric dust is accumulated every day.

You are confusing G, the Newtonian gravitational constant, with g, gravitational acceleration at the surface of the Earth. Big G is dimensional physical constant, the G in F=\frac {Gm_1m_2}{r^2} (Newton's law of gravitation). That is modern notation; Newton himself didn't express his law of gravitation that way, nor did Henry Cavendish, the first to measure G (but only after the fact). Cavendish intent was to "weigh the Earth".

Measuring G is extremely non-trivial. It is the least well known fundamental physical constant.