21 Aug 2015 6:40:15 UTC

Topic 198199

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From Space.com: Pulsar Proves Gravitational Constant is 'Rock-Solid'

Quote:

Through extremely high precision measurements of a pulsar orbiting a white dwarf star, astronomers have found that the gravitational constant, which dictates the force of gravity, is "reassuringly constant" throughout the universe.

Just as the speed of light in a vacuum (c) and Planck's constant (h) well-known universal constants, the gravitational constant (or simply "G") has been long assumed to be constant everywhere throughout the cosmos. But how can we be sure?

Now, through the study of one special pulsar called PSR J1713+0747, astronomers have arrived at the best, and most precise, measure of G outside the solar system.

PSR J1713+0747 is an ideal "laboratory" to study some of the most fundamental quantities of space, time and relativity. For starters, it has a uniquely wide orbit around the white dwarf, taking 68 days for the pulsar to complete one orbit. It is also extremely bright, one of the brightest pulsars known. As pair orbit one another, an extremely tiny amount of energy is lost from the system, via gravitational waves â€” a phenomenon predicted by Einstein's general theory of relativity.

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## Pulsar Proves Gravitational Constant is 'Rock-Solid'

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Hallo Who Fan!

Sorry, I canÂ´t follow this. Here and here they say, the timederivativ of G dG/dt is undistiguishable from zero : "We found that (dG/dt)/G is consistent with zero [(-0,6 +/- 1,1)x10^-12 yr^-1 , 95% confidence] and changes at least a factor of 31 (99.7% confidence) more slowly than the average expansionrate of the Universe. " They get this from observing the orbital period of about 68 days of the pulsar and the companying white dwarf for 21 years.

This measumement is from a star within our milkyway. Before such measurements were taken from laser distance measurements of the moon, with similar results.

So G ist stable over time within this scale (time and distance). Of course the distancerange of proven stability of G became now much bigger.

Kind regards and happy crunching

Martin