system
Given the following post, respond as if you're commenting on Reddit:
human
How is the universe ~ 78 billion light years in radius, when the universe is only 13.7 billion years old?

According to Einstein's theory of relativity, matter can not move faster than the speed of light. So, if the universe is 78 billion light years in radius, and the universe is 13.7 billion years old, wouldn't matter have to break the light barrier? If Einstein's theory of relativity was always constant, why isn't the universe a little bit less than 13.7 billion light years in diameter (to account for the matter not being able to move faster than the speed of light).Is this simply not matter (such as neutrinos) that is 78 billion light years from the "center" of the universe? Is that why it can break the so-called light barrier? 
EDIT: Why all the downvotes?
gpt
1.  Because the matter isn't moving that fast.  Space itself is expanding.  The gaps between stars and galaxies are expanding.  Some bits are moving away from us faster than the speed of light.  The important thing to note here is that matter isn't exceeding that speed, space is.

3.  There's no center, either.  Redshift increases no matter which direction you look, which implies that everything is getting farther away from everything else.

3.  Your figures are focused on the observable universe.  Those things that have had time to reach us at lightspeed within the age of the universe.  This distance is actually larger than a 13.7b ly radius, because some of the stuff we see was within that radius way back when the light was emitted, but is now much more distant due to the aforementioned expansion of space itself.