Well, if we consider the universe as a closed, isolated system, then the law of conservation of momentum should kick in.
P = MV
We know that Hubble's law states that the velocity of bodies on an astronomical scale is increasing and P is a constant, so that means M must be decreasing...
To what extent is it decreasing? If it reaches zero, wouldn't all the galaxies light eventually reach us? If so, why do astrophysicists say that some galaxies light will never reach us?