What types of corrections made and how are they the judged for the following data: positions and velocities of galaxies? This is a complex question, please see my note for further information: http://bit.ly/1nuurbz
Present data suggests that the Universe is expanding because the distance between us and galaxies is pretty much proportional to their recessional velocity (Hubble’s Law). However, all that data does not arrive at Earth representing the same time in history.
Consider the following schematic of a selection of galaxies we observe.
Data shows that galaxy A is distance, d, away from us and receding at velocity, v. Galaxy D is 4d away and receding at 4v. However, we do not observe those galaxies where they are now, but where they were in the past. The information travels at the speed of electromagnetic radiation, c. So the information from A took a time of t = d/c to reach us.¹ But information from D took a time of t’ = 4d/c = 4t. So information from D is four times older than that of A.
This would have an affect on the age of the Universe also, a factor would need to be added to account for the additional time of the position information to have reached us.