Recent papers have claimed that gravity is "different" on the galactic scale, as observed from the motions of distant galaxies. Since the light from those galaxies is billions of years older than today, if analysis shows that gravity was stronger in the past than now, isn't it possible that the force of gravity is changing and becoming weaker as the universe expands? The "stronger" ancient gravity which some attribute to dark matter for an explanation, may be simply stronger than today because it has decreased with the continued expansion of the universe. Since the amount of matter and energy in the universe must remain constant, an expanding universe would cause the overall concentration of mass to be lower now than in the past, and I postulate that the force of gravity is proportional to the density of mass in the expanding universe, so that we should expect the force of gravity to decrease over time. Might this explain why "dark matter" is not required to explain the movements of distant galaxies?
In that case, how do you explain the demonstrated time lag in radio frequency communication over distances from here to the Moon, to Mars, to Jupiter, and Pluto which in every case demonstrate a time lag for propagation of the radio waves at the speed of light? Laser measurements of the distance to the Moon using the reflectors left there by the Apollo missions also demonstrate a lack of "instantaneous" action at a distance.
There is an observable delay between the origin and the perception of reflection of a laser beam using the reflectors on the Moon. This experiment is reproducible by anyone with the proper equipment. Spectral analysis of light shows that the doppler effect applies. Commands sent to spacecraft from Earth must consider the delay in transmission which occurs, and is measurable, and is real. This is all done using the same clock at the origin of the signal on Earth. The positional accuracy of the space-based GPS system to determine one's location on Earth is testimony to the fact that there is a measurable delay in the transmission of electromagnetic waves.
I find no reason to question that which is easily observed, based upon fancy mathematics that claim to demonstrate otherwise.
If these claims that transmission of light is instantaneous were true, then the red-shift data easily observed during observation of distant objects would not be perceptible.
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