Our sun and the Earth and all the planets and moons and dwarf planets and asteroids and comets—the solar system in short. Formed about 4.6 billion years ago. From a nebulous clouds of swirling gas and dust. Which coalesced, thanks to the irresistibly attractive force gravity.
However, this nebula started off more or less as a big shakeless blob. So, how did our solar system end up with all the planets and their moons orbiting in a flat disc? I mean we've all seen the planetary model of the atom. Which is definitely wrong when applied to atoms. But, also a kind of suggest that planets might revolve around the Sun every which way.
So, is our solar system somehow special in its flatness? The solar system compared to the planetary model of the atom is definitely wrong?
Many Galaxy and Star System are Flat
Well, our solar system definitely isn't alone. These extraterrestrial are also found orbiting or existing on a flat disc scenery.
- exoplanets and star systems are flat
- a lot of galaxies are flat
- black hole accretion disks are flat
- Saturn's rings are flat, etc.
Dimensional Model of a Flat Galaxy
So, why when there's all of 3D space to fill, does the universe have this preference for flatness?
The answer has to do with two things; [1.] collisions and [2.] the fact that we live in three dimensions.
Anytime a bunch of objects held together by gravity, or zooming and circling around. Their individual paths are nearly impossible to predict. And yet, collected together they have a single total amount that they've spin about their center of mass.
It may be hard to figure out exactly what direction that rotation is in. But the mathematics implies there must be some plane in which the cloud taken as a whole spins.
Now in two dimensions, a cloud of particles rotating in a plane is flat-wide definition—it is in two dimensions.
In three dimensions, even though the rotation at the cloud is given by one plane. Particles can whiz-around far up and down from that plane. As the particles bumped into each other all the up- and-down motion tends to cancel out. Its energy lost in crashing and clumping. Yet, the whole masses must continue spinning inexorably. Because in our universe the total amount of spinning in any isolated system always stays the same.
So, over time through collisions and crashes in the cloud loses its loaf and flattens do is spinning roughly two dimensional disc-shaped like a solar system or spiral galaxy.
However in four spatial dimensions the math works out such that there can be two separate and complimentary planes rotation. Which is both really really hard for our 3D thinking brains to picture. It also means there's no up and down direction in which particles means energy by collisions.
So, a cloud particles can continue being just that—a cloud.
It's a Matter of Spin
Lastly, only in three dimensions can a nebula o an infant galaxy start out not flat and end up flat. Which is definitely a good thing. Because we need all that matters to clump together in order for stars and planets to form and exist.