Shadesmar's atmosphere and temperature

[king of nowhere]

In the cognitive realm there is breathable air. This fact certainly arise from the fact that people rarely think about breathing, it's something they take for granted. So, in the cognitive, they can breath.

But what kind of air is there, exactly?

Different planets have different compositions. On Roshar there is more oxygen. On Canticle there is less pressure. And while the books, of course, don't give much exact data, I seriously doubt that most shardworlds have a pressure of exactly 1.013 bars like our planet.

So, what kind of air do you find in shadesmar? 

I can assume, from the way the place works, that each subastral has the composition of its planet. so the rosharan shadesmar has more oxygen, and so forth.

The same goes for temperature. The region corresponding to Taldain dayside is hotter and dryer than that corresponding to Roshar.

but I wonder, does that mean there should be huge winds as the air tries to naturally move from higher pressures to lower ones? Do we get tornadoes when hot dry air from taldain encounters wet cold air from roshar? or do the air just stay put?

And what about races that don't breathe out air, if there are any? would a planet with ammonia-breathing aliens have an ammonia atmosphere in shadesmar? 

Also, do atmospheric pressure change with height? or it stays constant regardless?

And what about pollution? does it happen that when a planet reaches the worst stages of industrialization, their shadesmar fills with smog? could that be a way to actually locate a planet like First of the Sun, by analysing the atmosphere and figuring out when you're reaching the right region by sensing the fine particulate in the air?

[Trusk'our he/him]

2 hours ago, king of nowhere said:

In the cognitive realm there is breathable air. This fact certainly arise from the fact that people rarely think about breathing, it's something they take for granted. So, in the cognitive, they can breath.

But what kind of air is there, exactly?

Different planets have different compositions. On Roshar there is more oxygen. On Canticle there is less pressure. And while the books, of course, don't give much exact data, I seriously doubt that most shardworlds have a pressure of exactly 1.013 bars like our planet.

So, what kind of air do you find in shadesmar? 

I can assume, from the way the place works, that each subastral has the composition of its planet. so the rosharan shadesmar has more oxygen, and so forth.

The same goes for temperature. The region corresponding to Taldain dayside is hotter and dryer than that corresponding to Roshar.

but I wonder, does that mean there should be huge winds as the air tries to naturally move from higher pressures to lower ones? Do we get tornadoes when hot dry air from taldain encounters wet cold air from roshar? or do the air just stay put?

And what about races that don't breathe out air, if there are any? would a planet with ammonia-breathing aliens have an ammonia atmosphere in shadesmar? 

Also, do atmospheric pressure change with height? or it stays constant regardless?

And what about pollution? does it happen that when a planet reaches the worst stages of industrialization, their shadesmar fills with smog? could that be a way to actually locate a planet like First of the Sun, by analysing the atmosphere and figuring out when you're reaching the right region by sensing the fine particulate in the air?

Really good questions, honestly better than the current answer we got since it is basically composed of "it has air because".

Spoiler

https://wob.coppermind.net/events/332-jordancon-2018/#e9512

Pagerunner

If you need to bring food into Shadesmar, why don't you need to bring air?

Brandon Sanderson

Y'know, we actually talked and thought about this. There are certain things I just decided for narrative reasons... I wanted Shadesmar to be travelable and I wanted it to be a real place, and so I just made air, I came up with kind of my own hacks. There are times I do this for narrative reasons. 

Let me give you an easier example. In the Mistborn books, and I've told people this before, I was working on speed bubbles. Slowing down time, speeding up time in a small little bubble around you, right? I went to Peter and I'm like, "This is what I'm going to do, what are the problems with this?" And he's like, "Well, redshift." Which means that basically you would be irradiating everyone with the light coming from inside the speed bubble. I'm like, "alright, we're just going to say that doesn't happen." This is where the line between for me science fiction and fantasy exists. When I'm building my story, I do try to have one foot in science with things like this. But I tend to work backward... A lot of science fiction starts with what we have now and extrapolates forward to [an] interesting, plausible premise. For my fantasy works, I start with some cool idea. And then I work backward in plausibility, trying to justify it. And we kind of meet in the center, but at the end of the day I am breaking the laws of thermodynamics, right? Just straight-up breaking laws-- I mean, we have our whole Realmatic Theory and stuff like that, but at the end of the day, I am trying to tell stories where certain extreme situations exist. Like, I bent over backwards to make the science of Roshar work with the greatshells, but at the end of the day, we still have to have a magical solution, right. To get beasties as big as we want to do, it doesn't matter how high your oxygen content is, if you've got .7 gravity or not, all these concessions we've made: the square-cube law says those things crush themselves. You just can't have things this big. And so we built in a magical solution. The spren creating this symbiotic bond is making it so these things don't crush themselves. 

And when I was looking at Shadesmar, there are a couple things-- what I want for the narrative is this place. I am going to work backward and try to make as many concessions and nods toward science as I can. But the air one, I just said "You know what? There's just gonna be air in Shadesmar. I am just gonna make it so that you can." I want you to be able to walk between the planets on Shadesmar, I don't want people to have to worry about bringing a Windrunner with them and plants or whatever to get oxygen. I'm just gonna make that the case. Your in-world answers, I'm like "Well, air kind of permeates and has escaped through and things," but really do we have an oxygen cycle there? We've got plants, but are they really--

The answer is, there is air in Shadesmar because I want there to be air in Shadesmar. 

I'd assume the air quality would be filtered by those nearby in the PR perceiving the world around them. Got Ashmounts? Probably also have pollution. 

Though, it may be adjustable in some ways, so since Rosharans aren't actively thinking about having higher oxygenated air than Scadrial, Scadrian worldhoppers in the CR might not feel a difference. 

Edited October 17, 2025 by Trusk'our

[Returned he/him]

It is an interesting question!

I doubt the answers will be too satisfying, especially given the explanation we already have. It's a fundamentally magical place and, most importantly, is specifically distinct from the physical realm in its basic composition and philosophical orientation. We should maybe be mildly surprised when there are similarities to the physical realm, not assume that it's basically the same as a totally different plane of existence. Expecting fundamentally physical interactions and relationships seems like the wrong basis.

I would think that there's something like an observer effect involved. Like, when Dalinar and co. went to the spiritual realm they experienced (variably) things like position and time even though we have been told that neither of those concepts exist there. Maybe a thinking being's presence there is enough to sustain themselves by manifesting not just air but your air when you draw breath, temperature and pressure appropriate to you but not physically imposed outside of yourself.

I wish Shallan or Jasnah had narrated their perceptions more clearly, as I'm sure their training and inquisitiveness would have led them to think about questions like these. We don't hear Shallan note that the air pressure is different at different elevations, for example, but that doesn't mean that they aren't, just that she wasn't described as noticing them.

[Duxredux he/him]

Yeah... we're gonna have rampant speculation at best I suspect. Considering space within Shadesmar is directly tied to perception with geography not mapping directly to the Physical Realm, I want to say that some people have been wondering what will happen to Shadesmar when people actually begin space travel and physically see how far apart everything actually is. Because people have a hard time actually grasping astrological scale, Shadesmar doesn't have the matching scale and this probably relates to aspects of the environment. Like... maybe breathing isn't a problem because the vacuum of space wasn't an understood concept. Gravity doesn't make sense either when it comes to walking from planet to planet. Now for hundreds if not thousands of years people just take it for granted that you can walk and breathe in Shadesmar - and so it probably has cognitively been cemented that way.

So why does it look so weird? Because not everything was imagined by humanity according to Syl.

[Nitpicking]

Hmm ... if I were sent to the Cosmere, I'd invent gliders and powered aircraft, and sell them to Shadesmar explorers, since they'd work far better than the sailing ships. I wonder how far you can get above the Reverse Map of Roshar in a sailplane ....