Other galaxies observed by astronomers are almost all redshifted. This means that most galaxies are moving away from our galaxy. Since this is true in every direction, the galaxies are all moving away from each other.

Question

Suppose the galaxies in the image are moving in the directions indicated by the arrows. What would have been true at some point in the past?
A.
All the galaxies were moving in the same direction.
B.
The galaxies all had the same mass.
C.
The galaxies were closer together.
D.
All the galaxies were moving with the same velocity.

Answer 1

The correct answer is C. The galaxies were closer together.

The observation that galaxies are redshifted and moving away from each other suggests that the universe is expanding. This means that at some point in the past, the galaxies must have been closer together. The other options do not necessarily hold true based on the evidence of redshift and the expansion of the universe.