Could someone explain how orbits are so flat? For example, why do most of the planets orbit on the same plane instead of randomly? Why are galaxies flat instead of spherical? Gravity forms matter into a ball (planets, stars, etc..) so why not orbits?
In: Physics
[Why is the Milky Way flat and the Earth Round?](https://www.youtube.com/watch?v=Aj6Kc1mvsdo) this is a great PBS spacetime video that answers your exact question.
Essentially masses like planets are pulled in all directions under their own gravity forming spheres. It’s true that they do get slightly pulled apart from spinning so the earth IS a little bit wider at the equator.*
All of the spinning dust and gas that forms galaxies would do this too if they were big solid balls (like stars). ALl that spinning dust and gas has an overall angular momentum (more dust and gas spinning in one direction than another). Collisions cancel eachother out, so over very long periods of time, you are left with one predominant direction.
Finally, this isn’t perfect. There *are* smaller objects in our own solar system that don’t follow the same orbital plane because they haven’t hit anything yet. [Here] {https://www.universetoday.com/wp-content/uploads/2015/02/Scholzs-and-the-OortCloud.jpg) is a picture demonstrating this.
*Not the equator per se, because the earth is tilted on its axis. But you get what I am saying here 🙂
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