This question seems too simple to not have been asked, but I cannot seem to find an explanation. So apologies if this is a duplicate.
The current explanation for the expansion of the universe as I understand it, is that generally, the farther you look into space, the more redshifted galaxies tend to be, which indicate larger velocities far away from us.
As most people know, light has a finite velocity, which means the light of farther galaxies take longer to reach us than closer galaxies. So a galaxy 10 billion light years away is also looking at that galaxy 10 billion years ago.
- If you would plot the redshift of galaxies (y axis), and the time the light was emitted in billions of years since the big bang on the x axis (e.g., the light from a galaxy 10 billion light year away was emitted 10 billion years ago, therefor on the plot it would be at 13.7 - 10 = 3.7 ), you get a decreasing graph. Meaning galaxies were moving away faster in the distant past.
Point 3. is where I believe my confusion comes from.
A) Are 1. and 2. correct?
B) The part giving me the most trouble visualizing the evolution of the universe is the time aspect. In the example with two galaxies A and B, with A at distance d and B at distance 2d, all we know is that galaxy B was moving away from us at twice the speed as A twice as long ago. So the hypothetical galaxy 10 billion light years away I mentioned, how do we know it's moving away from us faster than closer galaxies now? How is this calculated to adjust for the time differences at all distances?