Value Of G over time

[colin lowing]

TL;DR Summary

Looking for published experimental material

Hi folks, a question regarding the value of G, has there been an experimental data collected on the value of G over time, what I'm interested in, is if the value of G in the observable universe, is decreasing or increasing (by a small amount) over time, thanks.

 

[berkeman]

What reading have you been doing on this question so far? If you could posts links to your reading, that would help us a lot to answer your question. Thanks.

 

[berkeman]

Summary:: Looking for published experimental material

value of G over time

I did a Google search on value of G over time and got lots of good hits. Check out the hit list to see if it helps you:

https://www.google.com/search?client=firefox-b-1-d&q=value+of+G+over+time

 

[colin lowing]

Other than the basic material re the constant etc. Mostly I do lectures and TED talks etc from you tube, most of my information these days comes from video. Having said that, I don't watch regular T.V., my evenings are spent with various lectures and science interviews digests and fairly hefty in depth stuff, way beyond the "popular science" programming. I've never seen any info over the years on whether experimental evidence has been gathered to verify the Gravitational constant, or for that matter whether there has been a observation of over time to determine whether there is a decrease or increase in G. Most sources I can find suggest there should be a decrease over time but the opposite would be most interesting.

 

[davenn]

Most sources I can find suggest there should be a decrease over time but the opposite would be most interesting.

Did you follow Berkeman's link ?

 

[hutchphd]

Start here. There are plenty of references.

 

[Vanadium 50]

While that does have references (including to Newton), I don't think it's a very good argument for the time-variation of G:

1. Many of the data points lie very far off the curve they are supposed to be on.
2. The data points have no time uncertainty, but the measurements they correspond to surely do.
3. The product GM is known to be very, very stable for most celestial bodies (the authors mention this but go into less detail than I would have liked), and for this to be a real oscillation in G, there needs to be a corresponding oscillation in M that is ~100,000x larger than observed for the sun, ~10,000x larger than observed for the earth, ~1000x larger than observed for the moon and Jupiter, all in mysterious lockstep with this oscillation in G.

 

[hutchphd]

All true. I was really responding to the question of whether measurements have been made. I will also restate my frequent admonition that to see if the gravity force is changing, one must compare it to another force, which also might be changing. So the even the question is tricky.

 

[colin lowing]

All true. I was really responding to the question of whether measurements have been made. I will also restate my frequent admonition that to see if the gravity force is changing, one must compare it to another force, which also might be changing. So the even the question is tricky.

I'm actually looking for a variance in G in the observable universe, not on earth, as Earth's gravity gradually increases due to the accumulation of debris from space.

 

[colin lowing]

I'm guessing there has been no measurement over time to detect a variance however small, I'm hoping it increases over time by a miniscule amount but all the searches I've done so far seem to be nothing more than postulation, rather than firm experimental evidence, just wondered if anyone had some info.

 

[hutchphd]

This is not a new question, and plenty of folks have looked at it. I reiterate my caution: all you can do is compare it to another force somehow and test the ratio for stability..

 

[colin lowing]

Unfortunately measurements on Earth won't be accurate, due to the accumulation of mass from dust, meteors etc. the value should increase albeit by a tiny amount, I was wondering if there had been any universal measurements of the constant, repeated every x number of years to find out if G is decreasing perhaps due to expansion, or as I hope there will be a small increase over time, if it's the latter I'll be a very happy chap, i can tell you ;)

 

[colin lowing]

It also relates to a recent paper (2012) now published regarding Jamie Farnes's hypothesis regarding dark matter, my question is related to his hypothesis. tx for the help appreciated ;)

 

[Vanadium 50]

as Earth's gravity gradually increases due to the accumulation of debris from space.

You should put some numbers in that. G is known to something like a part in 10⁵. If the Earth's radius (and thus g) were to grow by one part in 10⁵ per year, that works out to about half a foot per day. It would be snowing meteors.

 

[Keith_McClary]

if the value of G in the observable universe, is decreasing or increasing (by a small amount) over time

If you mean over cosmological timescales, it has only been measured on Earth for 222 years using torsion balances. So even if it was changing fast on cosmological scale we would not see it.

"40,000 metric tons of interplanetary matter strike Earth's atmosphere every year." which is an insignificant change to the Earth's mass (6x10^21 tons).

 

[Motore]

Overall Earth is actually losing mass by about 55,000 metric tons a year, because the gases (most notably Hydrogen) are escaping the atmosphere.
https://en.wikipedia.org/wiki/Earth_mass#Variation

 

[colin lowing]

You should put some numbers in that. G is known to something like a part in 10⁵. If the Earth's radius (and thus g) were to grow by one part in 10⁵ per year, that works out to about half a foot per day. It would be snowing meteors.

The effect would be tiny on Earth's gravity but it is increasing in mass over time, just from the normal material it picks up, I think it would be virtually impossible to measure an increase or decrease in the constant here on Earth, as it's impossible to accurately measure how much mass the Earth gains over a period of time.

 

[colin lowing]

Overall Earth is actually losing mass by about 55,000 metric tons a year, because the gases (most notably Hydrogen) are escaping the atmosphere.
https://en.wikipedia.org/wiki/Earth_mass#Variation

I never thought of atmospheric loss, thanks.

 

[colin lowing]

I think my question has been answered, as far as I can tell, there has not been any accurate survey on the G constant over time on the scale of the observable universe, there is no information I can find from links etc. So whether the constant increases or decreases over time is as much a mystery as the mystery of why it bends spacetime, we have a calculated G constant and we know spacetime bends in the presence of mass but we still have no confirmation of any fluctuation in the G constant or indeed why spacetime bends. As far as I can see anyway.

 

[phyzguy]

The why question is basically the question of , "Why is the universe the way it is?" These questions are inherently unanswerable, since each response can just be met with, "But why is that?"

 

[colin lowing]

The why question is basically the question of , "Why is the universe the way it is?" These questions are inherently unanswerable, since each response can just be met with, "But why is that?"

I think they will eventually understand why spacetime bends in the presence of mass, I actually think there's serious problems in our understanding of time and gravity itself, I think it probably relates to the way we understand spacetime personally but I think one day we'll be able to answer it.

 

[Vanadium 50]

I'm guessing there has been no measurement over time to detect a variance however small,

How can you say that after this'?

Start here. There are plenty of references.

 

[colin lowing]

How can you say that after this'?

? This particular paper appears to be in relation to a gravitational variance on the Earth, which was not my question, I will read it through.