If the universe is 13.8 billion years old, how can we see things 28 billion light-years from us? Doesn’t seem like there is enough time for the light to reach us.
In: 45
I always used to wonder what the speed of light was relative to, in terms of “what is an absolute rest?”
We can see things that are currently 28 billion light years away because they were closer than that when the light from them was emitted.
This is because the universe is expanding.
The Cosmic Microwave Background Radiation is the furthest thing we can see. The light from it has travelled 13.8 billion years (so it has travelled 13.8 billion light years) to get here. However, since that light left the universe has continued to expand and the further away that part of the universe is the faster it is expanding from us (this is the same for any two points in the universe). This means today where the CMBR was 13.8 billion years ago is now 46 billion light years away. However, when that light left it wasn’t 13.8 billion light years away, it was only millions of light years away. You really have to picture the universe as been expanding the entire time.
You can see things that is 28 billion light-years from us today.
That does not mean that it was at that distance when the light we see today was emitted, The universe is expanding so distances between galaxies get larger.
The galaxy [GN-z11](https://en.wikipedia.org/wiki/GN-z11) is 32 billion light-years for us today. The light we can see was emitted 13.4 billion years ago, so it has traveled 13.4 billion light-years.
But GN-z11 was only 2.66 billion light-years from us when the light was emitted. The universe has expanded when the light was traveling to us and its path became 13.4 billion light-years long.
So there is a difference between how far away it is today, how far the light has traveled, and how far away it was when the light was emitted. This is all a result of the expansion of the universe.
Light emitted now at 32 billion light-years will never reach us. The expansion of the universe in between is faster than the speed of light.
It is important to remember that the expansion of the universe does not mean the galaxy moving away from us, it is the space in between that gets large. that is something that happens everywhere and at a long distance, the expansion of what is in between can be faster than the speed of light.
It is hard to wrap your head around because it is not like anything that we as humans observe around us without accurate measurement of stuff very far away,
In a very generic sense: The Observable Universe is everything what we can see.
What I mean by that is: The speed of light is *whatever-it-is,* and the Universe is 13.8B years old. That means the light can only travel a maximum distance of [13.8Billion x The Speed Of Light]. Anything further away than that distance, we physically cannot see because the light (the thing that lets us see it) hasnt traveled far enough in the time since the Universe formed…
Again, not 100% accurate and correct I know, but thats the general idea…
If you can spare 30 minutes, [this video](https://youtu.be/4iC9Qi3y9q8)explains the observable universe in a very clear way. You can skip ahead to the chapter starting at 9m if you’re short on time, but the entire video is worth a watch.
If you really wanna pop a brain cell, realize that Andromeda is actually closer to us than it appears in the sky.
Smooth brain explanation: universe is expanding faster than the speed of light. Since light is slower than expansion of universe some light will never reach us thus being outside the observable universe.
From my understanding
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