system
Given the following post, respond as if you're commenting on Reddit:
human
How do we know galaxies in the ultra-deep field aren't just the same galaxies over and over but from different points in time?

If the images are like "looking back in time", then is it possible some are the same, or even the Milky Way? And why aren't the very very old ones just red blurs across the whole field?
gpt
The reason they call it looking back in time is purely because of the time it takes that light to reach us. Nothing in physics suggests there is any kind of loop to the universe to allow a repetition, and we can only see what is called the "observable universe" anyway. It's believed there is likely more to the universe but the light from the further out galaxys, etc. either hasn't had time to reach us, or because of the universes expansion, potentially never will reach us.