Answer:
Because light takes time to travel from one place to another, we see objects not as they are now but as they were at the time when they released the light that has traveled across the universe to us. Astronomers can therefore look farther back through time by studying progressively more-distant objects.
Step-by-step explanation:
Given the vastness of the universe, studying its earliest days is like looking back in time. Faint light from the oldest galaxies is still traveling across the universe to reach Earth, so the farthest reaches of the universe visible to scientists is light from the past.