Another way to look at dark energy is to see it as the red shifting of gravitons. If two bodies are in mutually departing motion their gravitons are mutually seen as red shifted. Hubble found that as a general rule all distant objects are in receeding motion, with velocity proportional to their distance from us. Since the red shiting of gravitons (as well as photons) is proportional to the velocity, there appears to be a repelling force that is proportional to distance, a kind of dark energy from the vacuum, which it is not. It is merely the diminution of gravity.
Regards, Horace Heffner

