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
Planets are spheres because they’re full of stuff. Orbits are flat because they’re full of empty space. The orbiting stuff will stay distant in the plane of spin, but otherwise will try to get closer, until the ball compresses to something disk like. A planet can’t do this because it’s full of stuff, not space.
I may be wrong but I believe that they’re just displayed that way for comparison’s sake. It’s easier to gage relative distance between planets and their orbits if they’re displayed on the same plane
Around 2:20 to 3:10ish
They do, they’re just not as likely to stay clear of collisions if they’re not in flat same-directional orbits. The Universe has had a very long time to eliminate the orbits even slightly less likely to make it.
At least, that’s how it was explained to me when I asked the same question ~20 years ago, I don’t know how accurate it is.
[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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