Is the gravitational constant actually a variable?

[Luis Ochoa]

Hi, as an engineer i don't have much formal training in theoretical physics so bare with me.
As most of you know, we can only understand 4% of our universe with the current models we have. The rest of the 96% is dark matter and dark energy (23% and 73%, respectively). Could these unexplained phenomena be a consequence of G, gravitational constant, not being a constant at all, but a variable dependent on a scalar field that it itself is dependent on the amount of matter surrounding a certain point?
As mentioned, this variable would increase if there is a large matter density surrounding it, thus in the context of a galaxy it would explain dark matter. And become negative in the space between galaxies where the matter density surrounding it is extremely low, thusly explaining dark energy.
I know the math behind this might be very simplistic and that in theory dark energy actually expands space itself, but i would very much appreciate it if someone with deeper knowledge on this issue gave it a thought!
Thanks before hand to all of you!

 

[PeterDonis]

Could these unexplained phenomena be a consequence of G, gravitational constant, not being a constant at all, but a variable dependent on a scalar field that it itself is dependent on the amount of matter surrounding a certain point?

There is a theory of gravity in which G is a scalar field variable: it's called Brans-Dicke theory. This theory has not been ruled out, but experiments have shown that, if it is true, the variation of the scalar field in space and time must be extremely small--much too small for effective variation in G to explain the phenomena we associate with dark matter and dark energy.