Comment on Why is space 2 dimensional?
neidu2@feddit.nl 16 hours ago
It’s not. But orbits do tend to coalesce around the same plane, this is true. Planets pull on each other, and over time this results in orbits being on a similar plane. However, it’s not perfectly flat - there is some variation, just look at Pluto as a good example.
And if you were to go what one would consider “up” from this plane, then you’d be going in that direction. There’s nothing special, there’s just less stuff there.
magiccupcake@lemmy.world 15 hours ago
I hate to be that guy, but this is wrong.
The solar system is mostly in one plane because it formed from a cloud of gas. The cloud of a gas has some total non zero rotation and interactions flatten the cloud into a disk, where all of the planets formed.
This same principle applies to galaxies.
cynar@lemmy.world 14 hours ago
It’s a combination of both, I believe.
The initial conditions had a definite rotational bias. This is preserved in the current orbital plane and direction.
On top of that, anything massively off that plane is liable to hit or interact with the material in the plane, given enough time. It will be flung around, eventually either out of the system or into the plane.
Stuff orbiting relatively close to the plane will have a biased pull towards the “average” plane. This will slowly flatten the orbits out.
All these processes take a lot of time. The solar system, in general, has had enough time to settle. The ort cloud and other outer bodies are still quite chaotic. We see a lot more off plane than within the traditional solar system. They experience the latter effects far less, and so take longer to equalise. They still have a bias towards the initial spin however.
neidu2@feddit.nl 15 hours ago
I was explaining why the orbits are similar, not why orbits exist. You’re arguing a different topic.
magiccupcake@lemmy.world 14 hours ago
The original question was why solar systems and galaxies are in planes, and your explanation is wrong.
What do you even mean by similar orbits? Most orbits are circular for a totally different reason, and that is tidal interactions.
tunetardis@lemmy.ca 14 hours ago
It’s been a long time since I got my astronomy degree, but your version is what I recall also. Whatever small rotational perturbation in the initial gas becomes more pronounced as it coalesces in on itself and defines the plane of the star system. Planets form within this plane after it is defined, and they all travel in the same direction around the star.
Regarding galaxies, the most common spiral ones like our own Milky Way follow the same principle at a larger scale. But there are also elliptical galaxies, not to mention irregular ones. In an elliptical galaxy, there is a more random movement of stars in a cloud around its core. So they look more 3D I guess, to go back to what the OP was asking about. I seem to recall the most accepted explanation for how these form is from the aftermath of a collision between 2 spirals? So presumably, when our galaxy collides with Andromeda in several billion years time, the resulting combined galaxy may emerge as an elliptical?