system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do large, orbital structures such as accretion discs, spiral galaxies, planetary rings, etc, tend to form in a 2d disc instead of a 3d sphere/cloud?
gpt
The really ELI5 answer. Everything wants to make a single ball of stuff because of gravity. But just like a centrifuge, spinning makes things want to go to the outside. Since they are only spinning in one direction, they only move to the outside in one direction. So you have a ball that is spinning and spitting out stuff in one direction, making it 2D. It is kept 2D because things attract each other, and the closes thing is in a 2D plane with it, so it keeps it in the plane.