Is gravitational constant unchanging over age of universe?

[Gate2wire]

do we know for a fact that the gravitational constant has always been the same since the dawn of the universe? I feel like gravitational forces should slowly be decreasing as the universe ages (meaning that assuming mass of Earth doesn't change, we should weigh a bit less in a billion years) ...but I can't find any articles on a changing gravitational constant, proving or disproving.

 

[davenn]

I feel like gravitational forces should slowly be decreasing as the universe ages (meaning that assuming mass of Earth doesn't change, we should weigh a bit less in a billion years)

why do YOU think that ?

 

[Drakkith]

do we know for a fact that the gravitational constant has always been the same since the dawn of the universe?

No, but we have strong evidence suggesting that it must have been within a very small amount of its current value for most of the last 13.8 billion years or so.

I feel like gravitational forces should slowly be decreasing as the universe ages (meaning that assuming mass of Earth doesn't change, we should weigh a bit less in a billion years) ...but I can't find any articles on a changing gravitational constant, proving or disproving.

I'm sure there's at least a handful of papers out there dealing with this issue, but for the most part our observations of distant parts of the universe (corresponding to very far in the past) inherently place tight constraints on what the gravitational constant can be. Too high or too low and our universe just wouldn't look the way it does today when we view it through our telescopes.

I caution you against coming up with an idea based on how you "feel" something should be unless you are directly working in a specific field on a specific problem, and even then you should be careful. Human intuition is far from reliable.

 

[mfb]

Experimental measurements are never exact, so all we can do (in the absence of finding a change) is setting upper limits on the possible changes.

We know it changed by less than 1 part in 10 billion per year within the last 9 billion years: Measurement. In other words, it can't have been completely different billions of years ago.
More recent measurements are more precise, but limited to the last decades: In this time, the constant changed by less than 2 parts in a trillion per year: Measurement. Assuming a constant rate of change, this means the gravitational constant didn't change by more than 2% over the history of the universe. The current APOLLO measurements will improve this upper limit by a factor of about 20, constraining a linear change to less than 0.1% over the history of the universe.