I am aware that Hubble discovered that the further away a galaxy is the greater its redshift. What I don't understand is how astronomers can be sure that distant objects are still moving at greater velocities than nearer objects, as the redshifts light is also much older than the light from the nearer object. In other words, the galaxies billions of light years away may be moving fast away from us billions of years ago (when the light was emitted), but how do we know they haven't slowed down or even sped up more since?
For example, Galaxy A is 3 million light years away and has a slight redshift. Galaxy B is 3 billion light years away and has a much greater red shift and so it is assumed Galaxy B is moving away at a much greater velocity than Galaxy A even though Galaxy B's light is older.
I'm not an astronomer so please go easy on your explanation to me
I'm aware that this question may have been asked before, but I could not understand the answers given to them.