# How could magic cause changes in air pressure? [closed]

I have a world in which there are two types of magic - let's call them Red and Blue, and they're much alike, but polar opposites (see Rich Burlew's worldbuilding article for a good example of this kind of idea). A side effect of using this magic is as follows: when Red magic is used, the air pressure around the user increases, while when Blue magic is used the air pressure around them decreases.

This allows for all kinds of interesting effects; heavy magic use would cause high winds, and long term constant presence of Red magic would probably make the area much more sunny, for example, while Blue magic would make the area rather wet.

The thing I'm stuck on is a reasonable explanation for why magic use would have this side effect. I'm not looking for science based answers, but I would love to have some kind of internal consistency rather than just handwaving the effect.

I've been thinking of some form of magical particles (octarons?) that are created/consumed by Red and Blue magic respectively, but that simply shifts the question of the interaction further down the line.

To clarify: I'm not interested (for the purposes of this question at least) in the source of the magic - all I'm looking for is a plausible mechanic for two types of magic to raise/lower air pressure as a side effect of magic use.

• In order to have an effect on weather, the high or low pressure cell would have to be very large - we are talking an area covering a major city. There is also the distinction between air pressure and air density. Heating air will cause it to expand, and increase pressure. Cooling air causes it to contract, and lower the pressure. But heating the air causes a lower density, and cooling it leads to a higher density. Convection winds are driven by air temperature, while air density determines if the system 'pushes' or 'pulls' other weather systems further away or closer. – Justin Thyme Sep 15 '17 at 14:08
• @JustinThyme - that's pretty much what I had in mind. A single cast of a simple spell might cause a candle to flicker, a magical duel would perhaps cause some (localised) high winds, but to have a real effect on the weather you'd need something like a portal to Hell/the Dungeon Dimensions/etc I would prefer if the magic altered specifically the pressure rather than the temperature. – walrus Sep 15 '17 at 14:22
• How is good and evil defined? By the intention of the user? (That just raises more questions.) By the "magic" itself as if "magic" is somewhat sentient? By how the air responds? For example, what is the difference between starting a forest fire to watch it burn, or starting a fire to create a barrier between a defenseless village and a group of raiding barbarians? Would the "air" react to one as "good" and the other as "evil"? Are there shade of grey in your air? (Could it ever NOT react due to something being somewhat good/somewhat evil?) – BunnyKnitter Sep 15 '17 at 16:55
• ... is it perhaps defined by "type" of magic? Necromancy, conjuring, healing, etc? What about elemental magic or telepathy type stuff - stuff that could be "used" for either good OR evil? – BunnyKnitter Sep 15 '17 at 16:55
• @SnyperBunny , I only chose 'Good' and 'Evil' because they're common reference points. I would perhaps describe them as both sides of the same coin, in a similar manner to what Rich Burlew talks about here: giantitp.com/articles/YPgbz2j3PckGjjviJU5.html – walrus Sep 15 '17 at 17:27

Let's just throw this out there. Let's say the air itself is magical, and attuned to Good magic. So, using the principle of Contagion (https://en.wikipedia.org/wiki/Law_of_contagion) air rushes toward any invocation of Good magic.

Likewise, air is repelled from Evil magic. Hmm ... is there an element attuned to Evil magic?

Hey, you could tell about how Evil magicians always are at risk of suffocating themselves... ;D

### Good magic works by taking in energy surrounding you and Evil magic works by using your inner feelings and letting them out to influence your surroundings

You can explain this behaviour by stating that Good magic is attracting all kinds of energy around you and thereby increasing the density of air in your vicinity, while the power behind Evil energy are your personal feelings, which you are trying to direct outwards to affect the world around you.

Good magic therefore is aimed at interacting which the nature surrounding you by getting accustomed to it. You have to be aware of the energy surrounding you. You have to know what you can do with what is around you and you have to make sure that you treat everything in a good way that might fuel your magical powers when you need them.

Evil magic on the other hand is about being egoistic. Fostering your own feelings for power, your hatred or other negative feelings and imposing your will on everything around you. You need to want to rule everyone and everything to effectively control Evil magic.

• While I like this idea, the only reference to the question being asked is attracting all kinds of energy around you and thereby increasing the density of air in your vicinity, which seems like just as much of a handwave as before. – walrus Sep 15 '17 at 13:10
• Well, in any scientific sense, if you're pumping energy into the air around you it would be more likely to disperse than gather at that location. – person27 Sep 15 '17 at 17:41
• As far as weather is concerned, cool air (air with energy removed) creates high pressure zones. This is because cool air is denser, thus heavier, and heavier air creates a local high pressure zone. And exactly the opposite case for higher energy less dense air. So, you've pushed the question back to why are the physics backwards? – Samuel Sep 15 '17 at 19:13

Terry Goodkind, in his books has "additive and subtractive" magic. Something like that could be used to explain things. The "good" magic could be adding to things, and the "evil" could be banishing/destroying/sending things away.

Building on that, the "good" could be pulling in forces while the "evil" could have sources requiring sacrifice, thus actually sending something to the source of the magic which would cause an decrease in the air pressure.

You've mentioned a possible explanation in your question, The Sun.

A few natural causes of Atmospheric pressure changes are elevation, solar radiation, and migrating weather patterns. Uneven heating of the atmosphere and planet surface is a significant factor in the generation of atmospheric pressure differentials. You also got the science correct, that low pressure can bring rain, high pressure is hot & tends to be sunny. Wind is air moving from high to low pressure areas.

The fantasy pseudoscience-

Magic could have an effect on solar radiation which causes changes in pressure and therefore weather. The dampening effect on sun light caused by evil magic causes cooling, darkening, winds and possibly precipitation. Good magic bolsters the sun's intensity creating heat, humidity, and increases brightness.

Something in the magic either compresses or expands the space between the air molecules. With compression, a vacuum is created which sucks more air molecules into the immediate area, and increases the pressure. Expansion pushes the molecules away, lowering the pressure.

Incidentally, these changes would produce that ear popping experience of take off and landing while aboard a plane. That might be useful as a painful/annoying indication of a successful casting.

My approach to this is that some magic is Endothermic, and some of it is Exothermic.

Magic (like everything in our universe) has to be explainable to a mind of sufficient knowledge and intelligence; if we accept this assumption, then magic is just a form of science that has yet to be fully understood.

In science, we have endothermic reactions, like photosynthesis. These reactions USE energy to create a specific outcome. In photosynthesis, the power of the sun is used to take water and carbon-dioxide and convert them into oxygen and carbo-hydrates. The rest state of the output molecules has a higher energy level than the rest state of the input molecules, and the solar energy is harnessed by the plant to make up the shortfall.

We also have exothermic reactions. When we breathe in oxygen or eat a plant, we convert those molecules into carbon-dioxide and water, thus releasing the energy difference in the rest states and therefore sustaining us. This is how food gives us energy. It's also how most explosives (especially hydrocarbons like petrol) work.

So; let's call blue magic endothermic. It will draw energy from the atmosphere around it making it slightly colder which in turn will make it a little less dense. The red magic though is exothermic, so it heats up the atmosphere around it slightly, increasing the air pressure slightly by heating it up.

This would mean that Red magic used consistently in the same place would lead to slightly higher air pressure in that area (at least temporarily) and would also cause thermal currents etc. You'd probably see birds circling above Red magic hotspots, giving an indication of where the practitioners are.

Blue magic on the other hand would indeed be a little colder and by extension would cause some water vapor to condense. If practiced in the early morning or dusk, you might find practitioners just by seeking out fog.

It should be noted that the amount of energy consumed / released would have to be significant, and the effect would be temporary. The Coriolis effect would eventually reset things in the atmosphere once the magic ceased.

Magic can be seen as manipulating the fabric of reality subtly (or bluntly). These two types of magic (Red and Blue) are two fundamentally different ways of manipulating the world around us. One could channel from a positive plane, bringing extra air along with it, whereas the other could be channeled from a negative plane, and suck in air from around the user whilst the rift is open. It's a little messy, but it also adds the potential for magic inadvertently summoning extraplanar entities, which could be an interesting plot point.

That's a tough one. Magic by its very nature is a bit handwavy. I am not sure what kind of magic good and evil do so I'm just going to assume both use same spells.

So if both versions of the magic have access to a general range of spells then you could go with how the magic itself is created. Magic could be a bit a system where the spells are read and the energy stored to be released at a later time. In such a system you could have good magic practitioners take just enough energy to create the effect and maybe just use their own internal life force to give it shape. It could also mean those good practitioners are leaner in appearance and maybe get white hair sooner than their evil counterparts. The effect of radiating their own life force means that their areas are warmer and the air blows away from them as they channel their magic.

The evil practitioners would rather use someone else's life force. They syphon the energy from their environments and generate the spells that they need. Since they don't feel the effects of draining someone else's energy they get greedy and take more than they need and their spells tend to be flashier and more destructive. Maybe they are sloppier about the use of their magic. The main effect of this is that the air is cold and dense. Plants and life around them are wilted and withered. A cold hard rain or fog may be common around those that draw too much energy. Dark practitioners may be healthier looking if not fatter or bloated looking. It depends on what you want to convey with their look.

Maybe neutral practitioners use a mix of personal and syphoned energy they take from particular areas since they may know the effects of taking energy and want to spread out the effect or target particular areas.

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If you have them generate the magic on the spot rather than before hand then it is likely to cause local weather effects. battles could cause huge thunder storms and lightning to clash as battles happen. You'll be able to tell what kind of wizard used magic near by because of the weather.

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If it is that these wizards know how to draw that energy and turn them into spells you may have untrained wizards just pull and push energy without realizing it causing minor weather effects.

Druid type wizards may just manipulate the energy to create the weather effects to use rather than just powering spells.

I think the more instant use of energy would be more dramatic visually than doing it all back at home before they go out.

I still think that the definition and method of "measuring" good/evil is absolutely fundamental to describing the mechanism of how the magic affects the air pressure, but... perhaps if you assume that MAGIC itself has a fundamental understanding of good/evil. Then it could be an affinity thing:

Good magic attracts magic-energy-stuff or particles or something. evil magic repels them. Call them sentient particles or invisible sprites or something.

Pulling my example from the comments: in the case of a magician using fire magic to burn someone alive, the evil act repells the "stuff" in the air thus also having a slight effect on the air as it all is pushed away. In the case of a magician using fire magic to light a campfire, perhaps nothing happens as it is roughly a neutral act. A magician using fire magic to prevent someone from freezing to death attracts more of the "stuff" in the air which pulls air molecules with it as it comes nearer.

Well, I cannot see any particular argument for good and evil magic. As far as I can see magic exists in some fundamental way, and there may be different types, but it is difficult to see how magic can properly understand purpose. To consider good and evil as defining magic seems rather limiting to me. Magic can be used with good or evil intent (and that is subjective anyway), but the nature of the magic, and the final result of using it is not necessarily the same: evil intent does not necessarily do evil.

However, for magic to work it must be directed from the mage and, in the process, charges the air between the mage and the subject magically. The nature of this charge is unclear but, assuming the presence of magic, it is not unreasonable to assume that some kind of conduit must be formed for its release, so the air between the mage and the subject forms this conduit, magic flows, and the air is affected by this.

The emission of the magic has to be driven by the mage, so it is the focus and will of the mage that forms and directs the conduit. Typically, this conduit is formed of low-pressure air, because this offers less resistance to magic flow. The magic itself, once flowing, decreases air pressure further, as air is pushed away by it. This area of low pressure, though, is held by the magic flow, so it is not noticeable, except perhaps by the target.

The formation of the low pressure conduit, though, causes the air pressure to rise elsewhere around the user, and this effect is noticeable and can affect the weather.

Now, my problem is understanding the differences between your two types of magic. If one type of magic required a high pressure conduit, rather than a low pressure one, the above could be made to work for you, but I find it difficult to see how the two types of magic could be that different.

However, I have given an explanation of how magic use might cause changes in air pressure. Maybe you can modify it to your purposes.