About the Planes of Existence...

[Techcaliber]

So, I've been designing a new homebrew world, and as I began working on the planes and different planets within the crystal sphere, and based on my understanding, I realized something: the entire crystal sphere is the "Prime Material". So this left me with the question, where are the other planes? Are they essentially different dimensions connected to the Prime Material, or are they somethign else entirely? I haven't been able to find this while reading, but I may just be looking in the wrong places. So, if any of you have any insights in to this, please leave it a response below!

[KillianHawkeye]

Yes, the other planes pretty much equate to alternate dimensions.

Not like one of those "everything is the same except for the Federation is evil and Spock has a goatee" alternate dimensions, but like a totally different world.

[Techcaliber]

Yes, the other planes pretty much equate to alternate dimensions.

Not like one of those "everything is the same except for the Federation is evil and Spock has a goatee" alternate dimensions, but like a totally different world.

Alright, thank you so much! I was confused mainly due to Eberron, but I also learned Eberron is unique. Again, thank you!

[Millstone85]

the entire crystal sphere is the "Prime Material".

Just to be clear, the Prime Material is made of thousands of crystal spheres and the phlogiston-filled space between them.

[Xervous]

Alright, thank you so much! I was confused mainly due to Eberron, but I also learned Eberron is unique. Again, thank you!

For the sake of understanding various D&D cosmologies and planar arrangements I feel the need to borrow from Dead Man’s Chest. ‘Unique here having the meaning broken’

But that’s intentional, Eberron works because it’s isolated in the way it is.

[Kyutaru]

Just to be clear, the Prime Material is made of thousands of crystal spheres and the phlogiston-filled space between them.

Yep. Space: The Final Frontier.

But if you're worried just about the planes for your local sphere then I'd say they pretty much overlap the prime in a sort of fourth-dimensional way. The Astral plane connects everything which means it touches everything at the same time while not containing any of them. Likewise, the Feywild and Shadow dimensions coexist with the prime while mimicking it as a copy. On top of that planar cosmology says clearly that so and so outer plane is to left of another plane while being above the inner planes while also being infinite.

Basically, all of this means it's impossible to visualize the planes. They only make sense in 4-D. Where is the plane of Fire? It could very well be inside that guy's stomach. Don't try too hard to understand where they are, they just exist to the left of reality.

[Techcaliber]

Just to be clear, the Prime Material is made of thousands of crystal spheres and the phlogiston-filled space between them.

Yeah, that's why I put it in quotes. In terms of planes connected to the sphere {and only paying attention to that sphere) I've created, the sphere is the Prime Material.

[Techcaliber]

Yep. Space: The Final Frontier.

But if you're worried just about the planes for your local sphere then I'd say they pretty much overlap the prime in a sort of fourth-dimensional way. The Astral plane connects everything which means it touches everything at the same time while not containing any of them. Likewise, the Feywild and Shadow dimensions coexist with the prime while mimicking it as a copy. On top of that planar cosmology says clearly that so and so outer plane is to left of another plane while being above the inner planes while also being infinite.

Basically, all of this means it's impossible to visualize the planes. They only make sense in 4-D. Where is the plane of Fire? It could very well be inside that guy's stomach. Don't try too hard to understand where they are, they just exist to the left of reality.

Eh, I just pictured parallel dimensions with natural and artifical connections.

[Anonymouswizard]

As has been said, they are pretty much alternate dimensions. In the pre-4e default cosmology this was most clear with the Ethereal and Shadow planes, where the 'near' portions closely resembling the material plane.

[HouseRules]

Usually, the Planes of Existence is a fantasized version of https://en.wikipedia.org/wiki/Plane_(esotericism), but we cannot discuss real esotericism because that goes too much into religion.

• Physical Plane: Material Planes
• Ethereal Plane - links the astral entity to the material entity
• Astral Plane - links the mental entity to the ethereal entity
• Mental Plane - links the causal entity to the astral entity
• Causal Plane - links the soul to the mental entity
• Soul Plane - links the sprite to the causal entity
• Spiritual Plane

At each levels, there could be multiple planes. The elemental planes are at the Physical Plane level.

[Wizard_Lizard]

Yes, the other planes pretty much equate to alternate dimensions.

Not like one of those "everything is the same except for the Federation is evil and Spock has a goatee" alternate dimensions, but like a totally different world.

Apart from the shadowfell. The shadowfell is exactly like that.

[Techcaliber]

I wanted to thank everyone for the responses, super helpful!

[Fable Wright]

Note for Eberron:

All the planes there are still alternate dimensions. It's just that said alternate dimensions can have metaphysical proximity to locations on the material and thus create manifest zones. The metaphysical proximity is often tied to the plane's respective moon, but the plane and the moon are different entities—blowing up the moon of Dal Quor did not destroy Dal Quor.