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etrpgb
2016-11-02, 12:01 PM
I am confused by the concept of coexistent planes. For example, about the Plane of Shadow in the Manual of Planes we read: If a wizard travels onto the Plane of Shadow from a forest, she first sees an equivalent shadow forest. If she starts underwater, she appears within a shadowy sea that behaves like a Material Plane ocean.
So the wizard arrived in the Plane of Shadows see something similar what he saw in the Material Plane, but still it is obviously another places; this brings the egg-chicken problem, what influences what? What would happen if somebody burns down the forest in one of the two planes?

I'd like to imagine some kind of symbiotic relation between the planes, but I am not sure. How do you imagine this stuff in your games?

AuraTwilight
2016-11-02, 03:20 PM
They quite literally inhabit the same 'space'. Ghosts are intangible because they exist in the Ethereal Plane, which is coexistent with the Material Plane, for example. If you went there, you could punch the Ghost, but other people might mistake you for a ghost as well.

SirBellias
2016-11-02, 04:05 PM
My first assumption would be that the Plane of Shadow would be a derivative of the Material, as shadows are dependent on other things to exist, but it would be pretty interesting to find out that the Prime was more dependent on the Shadow, or they both fed off of the others' influence equally.

Or the Plane of Shadow could just be the Prime seen through a different lens, with different rules.

Mith
2016-11-02, 04:49 PM
I would rule that the Shadow and Feywild are Negative/Positive reflection of the Prime due to the Energy Planes. So setting a fire on the Shadow forest that mirrors the one in the prime won't affect the Prime. I would even say that while the fire burns, the trees seem to only burn so far as an equilibrium is established betwern the fire and the influence of the Prime. Over time, the influence of the Prime will win out, forcing the Shadow Plane back into form. If the plane borders other planes, similar effects can be seen there as well.

If you go away from the border, things change.

Cernor
2016-11-02, 05:03 PM
Personally, I like to think that they're identical in most respects, but severe changes on one world take time to diffuse (for lack of a better word) than another. For example, while there will be a forest in the same location in all three planes, the exact location of the trees will differ. If the Shadowfell forest burns down, the other two (Prime and Feywild) forests will slowly die off as well, be that due to soil erosion, insect plagues, or so on.

Natural disasters (and magical catastrophe) will have similar effects, but not identical. A volcanic eruption on the Prime might result in the Shadowfell mountain collapsing in on itself, leaving a massive sinkhole - on the other hand, the Feywild volcano could burst with hot springs, becoming covered in jungle in only a few years.

Beneath
2016-11-02, 05:45 PM
Shadow's reflecting the Material is a special property of either Shadow or the relation between Material and Shadow (and same for Feywild), not all coexistent planes; Ethereal is coexistent and it's an empty but breathable void even in the places where Material is very much not. Coexistent means each point on one plane corresponds to a point on the other and things like direction and distance modify these correspondences in a sensible manner.

As for what this interaction means if you destroy a forest's shadow, well, that's sympathetic magic that D&D doesn't cover. Saying that either you can't because eventually the material will make it regrow, or that it will bring some effect on the material forest, are both plausible and that really depends on the DM and the needs of the plot. Personally, I lean toward that sympathetic magic would let the shadow fire affect the material, if the fire even works on Shadow, but probably in a way that appears to be coincidence.

PinkSpray
2016-11-02, 06:52 PM
The Shadow plane is both coexistent and coterminous so at key points what happens on one plane happens on another. You set fire to woods at that nexus and both burn but since shadow inhibits light/flame perhaps the damage is less on that plane. Darkness-based spells at the nexus would have more impact on the Shadow plane but still some effect on the adjacent Material plane.

If I were GM I'd let the player pick a plane he/she wanted to affect the most then describe the simultaneous effect on the adjacent plane. Certainly makes the spellcaster seem powerful, right? Players like that sense of plane-spanning power.

etrpgb
2016-11-03, 02:33 PM
It is even more problematic in cosmologies with Spirit World. The Spirit World is described as a more vibrant and extreme version of the Material Plane, but how the two planes that are coexistent and coterminous is not explained.

There is obviously some connections, quoting the manual: [i]where a citadel stands on the Material Plane, a similar citadel (though greater and stronger) may stand in the Spirit World[i], but it's unclear why and how...

Thanks for the input anyhow.

Jay R
2016-11-03, 03:10 PM
What kind of evolutionary path would lead to several very different intelligent species?
How do scientific laws like gravity or conservation of momentum "turn off" magically? Where does the momentum go?
Why is there so much lost treasure that wandering the wilderness is the best way to get rich?
Why does a fireball blast have full power 19 feet from the source, but no power 21 feet from it?

The correct answer to all of these questions, and yours, is to not ask them. Any answer you invent would only lead to more unanswerable questions, and wouldn't make the game any more fun.

If you're wondering how he eats and breathes. And other science facts,
Just repeat to yourself "It's just a show, I should really just relax."

Mystery Science Theater 3000

Mastikator
2016-11-03, 04:33 PM
There are two ways to think about it that makes a little bit of sense (IMO)
1 "the hyperdimensional Ω particle" version

Both planes exist on the same x,y,z,t axis but not the same Ω axis. (let's use omega to describe the coordinate of which plane you're on)
Mundane particles can not move on the Ω axis the same way they travel in the x,y,z and t axis.
Certain hyper dimensional particles (we can call them Ω particles) do travel back and forth between planes and they influence the wave function of particles on both side, creating certain bias in the probability distribution on particles on both sides.

Without knowing about the Ω particles the outcome of events on either side seem fully random and natural but looking at both sides you see a clear pattern.

But when you go to the shadow world you see houses, trees rocks etc but not people? That's because the soul repels Ω particles making living sentient creatures immune to the shadow world (and vice versa). If you destroy a building or tree on one side it won't instantly affect the other but it will start to decay rapidly, which would appear like natural "bad luck".
If you build a thing on one side the other side would generate a "natural formation" that over time resembles it more and more.

2 "the reflection of our world" version

The shadow world doesn't really exist in a true state when nobody is there, it's all in a state of flux. When you enter the shadow world you cause it to take shape, it takes shape according to the real world and with certain rules. (the rules might be instead of people you have monsters)
Whatever happens in the shadow world can not affect the real world unless someone is in the shadow world making it real, when you change the real world you change the shadow world- given that that part of the shadow world is real at the moment, making changes in the shadow world requires that it is real and being altered by someone from the real world. That would change the real world directly. Any real world alterations is direct evidence that someone is in the shadow world and doing stuff.

When nobody goes to the shadow world it might as well not exist.

Edit- the easy answer is "it doesn't make sense and the people who thought it up haven't thought it through and didn't expect you to either", but if you do want coexistent interacting planes to make sense you will have to change the rules so that they are consistent.

GorinichSerpant
2016-11-03, 04:52 PM
What kind of evolutionary path would lead to several very different intelligent species?
How do scientific laws like gravity or conservation of momentum "turn off" magically? Where does the momentum go?
Why is there so much lost treasure that wandering the wilderness is the best way to get rich?
Why does a fireball blast have full power 19 feet from the source, but no power 21 feet from it?

The correct answer to all of these questions, and yours, is to not ask them. Any answer you invent would only lead to more unanswerable questions, and wouldn't make the game any more fun.

If you're wondering how he eats and breathes. And other science facts,
Just repeat to yourself "It's just a show, I should really just relax."

Mystery Science Theater 3000

For a second I thought you were going to say that the moment and such goes in and out of the Feywild and Shadow Plane. Like when you cast featherfall a lot of your mass is floating in the Shadow plane and when you cast a fireball the sudden energy comes from the Feywilds instead of nowhere.

Mith
2016-11-03, 04:59 PM
There are two ways to think about it that makes a little bit of sense (IMO)
1 "the hyperdimensional Ω particle" version

Both planes exist on the same x,y,z,t axis but not the same Ω axis. (let's use omega to describe the coordinate of which plane you're on)
Mundane particles can not move on the Ω axis the same way they travel in the x,y,z and t axis.
Certain hyper dimensional particles (we can call them Ω particles) do travel back and forth between planes and they influence the wave function of particles on both side, creating certain bias in the probability distribution on particles on both sides.

Without knowing about the Ω particles the outcome of events on either side seem fully random and natural but looking at both sides you see a clear pattern.

But when you go to the shadow world you see houses, trees rocks etc but not people? That's because the soul repels Ω particles making living sentient creatures immune to the shadow world (and vice versa). If you destroy a building or tree on one side it won't instantly affect the other but it will start to decay rapidly, which would appear like natural "bad luck".
If you build a thing on one side the other side would generate a "natural formation" that over time resembles it more and more.

2 "the reflection of our world" version

The shadow world doesn't really exist in a true state when nobody is there, it's all in a state of flux. When you enter the shadow world you cause it to take shape, it takes shape according to the real world and with certain rules. (the rules might be instead of people you have monsters)
Whatever happens in the shadow world can not affect the real world unless someone is in the shadow world making it real, when you change the real world you change the shadow world- given that that part of the shadow world is real at the moment, making changes in the shadow world requires that it is real and being altered by someone from the real world. That would change the real world directly. Any real world alterations is direct evidence that someone is in the shadow world and doing stuff.

When nobody goes to the shadow world it might as well not exist.

Edit- the easy answer is "it doesn't make sense and the people who thought it up haven't thought it through and didn't expect you to either", but if you do want coexistent interacting planes to make sense you will have to change the rules so that they are consistent.

Good summary. I think my personal setting would probably go with the second more then the first, but that's because I am taking some ideas from Garth Nix's Old Kingdom (https://en.wikipedia.org/wiki/Old_Kingdom_(book_series)), where Death is a spiritual river running away to the Final Destination. I can write the Shadow Plane as the "Valley" of the Negative Plane "River". So stuff can influence from the Shadow Plane through to the Material, but that would be more of a deliberate working to weaken the barrier, rather than a more natural occurrence.

This is a good thread. I've fleshed out some parts of my setting's cosmology.

Frozen_Feet
2016-11-03, 05:02 PM
The way I treat these concepts is that the Otherworld is an expansion of the material world. If something drastic happens to the interface where two terrains meet, the path between them is discontinued as if it never was there.

Example: if you walk deep into a forest, you may cross over to Faerie woods. The Faerie woods are connected to, but not the same, as the forest. If someone hacks down the forest while you are in Faerie Woods, then nothing immediately tangible happens to your surroundings, but you cannot return to the mundane world the way you came; attempting to trace your steps will just lead you to some other part of Faerie woods. Likewise, if you hack down Faerie woods, the forest will be fine, but no-one can follow you into Faerie woods anymore.

This applies to the Spirit World example as well. If there's a fortress in the mundane world, chances are there is a similar but bigger one in the Spirit World. If the mundane one is destroyed, the spiritual one will keep existing, but can no longer be reached from that spot; and vice versa. In practice, this means the Spirit World tends to be much larger than the mundane world, with extra space between landmarks corresponding to mundane ones. It may contain several versions or "echoes" of the same place at various points in time, some of which can only be reached by entering the Spirit World from another point of the mundane world and traversing the distance. It also contains many fractured, isolated "mini-worlds" due to places where all the paths to it through the Spirit World were destroyed. Such spots can only be entered from a particular spot of the mundane world.

The Legend of Zelda video games make frequent and great use of the concept.

etrpgb
2016-11-03, 05:20 PM
To anyone who answers "don't ask, you won't know" I want to underline that I am aware everything here has only one common fact: it is 100% false.

Still, I am curious to know what other people think and imagine about this and how they'd DM the situation. If you do not care, and it is a perfectly valid position, this thread is not for you.

I really like the Frozen_Feet idea; I think I will go for something like that in my adventure.

Kelb_Panthera
2016-11-03, 08:06 PM
I'd run it that the shadow is dependent on the material but I lean that way because of the deep shadow region of the plane of shadow that is neither coexistent nor dependent on a paralell material area.

BTW, which version of the Manual of the Planes were you looking at?

etrpgb
2016-11-04, 03:49 AM
The '91 version authored by Jeff Grubb, Bruce R. Cordell, and David Noonan.

But I am looking for ideas, if you know something interesting from elsewhere is still very welcome. Just like Frozen_Feet got some ideas from videogames.