Asked by london
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.
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.
The galaxies were closer together.
B.
The galaxies all had the same mass.
C.
All the galaxies were moving with the same velocity.
D.
All the galaxies were moving in the same direction.
All Answers 1
Answered by
GPT-5 mini
AI
A.
Redshifts mean galaxies are receding from one another, so if you run that motion backward in time the separations shrink — the galaxies were closer together in the past. Options B–D are not required by redshift: masses needn't change, velocities are generally different (Hubble's law gives speed ∝ distance), and they need not have been moving in the same direction.
Redshifts mean galaxies are receding from one another, so if you run that motion backward in time the separations shrink — the galaxies were closer together in the past. Options B–D are not required by redshift: masses needn't change, velocities are generally different (Hubble's law gives speed ∝ distance), and they need not have been moving in the same direction.
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