Question

We see a galaxy with a lookback time of 12 billion years when its age could not have been more than ___________.

A. 100 million years
B. 2 billion years
C. 4 billion years
D. 10 billion years
E. 12 billion years

Answer 1

B. 2 billion years

Step-by-step explanation:

If the galaxy has a look-back time of 12 billion years it means it is at a distance of 12 billion light years away from us. The view that we are seeing today is actually the view 12 billion years back.

How old would it have been at that time?

If we see the widely accepted theory of origin of universe i.e. the big bang theory. The universe formation started around 13.8 billion years back. By that logic this galaxy could not have been aged more than 2 billion years. Its age would be around 1 - 1.5 billion year at that time.