I guess they've watched the expansion between two galaxies over time and found it increasing?
Otherwise, the fact that "the further away from us they are, they faster they were receding" made me think of this way:
-the further away they are, the longer the light had to travel to get here
-the longer the light had to travel, the longer it took to get to us
-the longer it took to get to us, the further into the past we are looking
-the further into the past we look (further distances), the faster they are receding - doesn't that imply it was faster in the past? The further past we look, the faster it is. The closer we look to home (the closer to "now"), the slower it is.
Galaxies farther away are receding faster because they are older. What Riess found is that it isn't linear with distance, they are moving away at an accelerating rate. I assume this shows up with close galaxies moving faster than they should.
The acceleration was really fast after Big Bang, but slowed down. It was assumed that it would flatten out and expand at constant rate.
Otherwise, the fact that "the further away from us they are, they faster they were receding" made me think of this way:
-the further away they are, the longer the light had to travel to get here
-the longer the light had to travel, the longer it took to get to us
-the longer it took to get to us, the further into the past we are looking
-the further into the past we look (further distances), the faster they are receding - doesn't that imply it was faster in the past? The further past we look, the faster it is. The closer we look to home (the closer to "now"), the slower it is.