system
Given the following post, respond as if you're commenting on Reddit:
human
If the universe is only 13.7 billion years old and 1 light year is how long light travels in a year, how have we seen objects farther then 13.7 billion light years away?

I have heard that the entire observable universe is 90 billion light years across. How do we know this if objects in the universe only had 13.7 billion years to send light to us?
gpt
The key here is that the universe is expanding.  When we say "how far away" we're seeing objects, we mean "how far away are they now", not "how far away were they when they emitted the light we're seeing now".

The light we're receiving that was emitted from something 13.7 billion years ago is just reaching us now... but in the meantime the universe has expanded to put that something much further away.

This is not so different than throwing a ball to a person who is running down a field.  But now imagine the field is expanding... and the ball-catcher says "man, that dude threw the ball 4000 meters!"...when they were only 40 meters away when you released the ball.