A few thoughts about the Hubble Constant
The Hubble constant works on the basis that galaxies that are further away from us are receding away from us at speeds that seem to be proportional to their distance from us.
In my early days of studying physics at school I learned that the speed of light was the highest speed attainable. Then, later I discovered that light travelled slower in water and glass.
During the academic year 1983-1984 I attended a series of astronomy lectures given by Ian Nicholson art Hatfield Polytechnic. During the couse of those lectures I had one or two arguments with him about the Hubble Constant and other matters. I wondered if the speed of light was constant throughout the universe because it was definitely slower through glass.
He was the lecturer and I was just a mature student so the matter was never resolved to my satisfaction.
Since then some new astronomical phenomena have been discovered. The effect of gravitational lensing around galaxies has been widely observed. This means that gravity can refract light in a manner comparable to a glass lens. If the light is refracted, its speed must have been altered.
I therefore postulate that the light leaving a galaxy is slowed down by the galaxy's gravity. Light from a distant galaxy is accelerated by the gravity of our galaxy as it approaches us.
The Hubble Space Telescope has revealed that there are countless trillions of galaxies in every direction that the telescope has been pointed. I therefore ask if the combined gravities of these distant galaxies have slowed down the light leaving them sufficiently to have an effect of the preceived red shift of the light from these galaxies? If the effect is great it could mean that Hubble's constant isn't. This will then lead to a recalculation about the age of the universe.