# How can having multiple casters for a spell create excess heat?

Magic works through transmutation circles infused with sigils that both manifest from a person's mind. The individual focuses their Anima, or life force, through these circles in order to create magical spells. Each sigil has Anima requirements, and Anima must run through them at a certain pace in order to function.

A spell that has a total cost of 1000 can be done by a spellcaster born with the same amount of anima, but another individual with 200 anima would need 4 other spellcasters to help complete the spell. Different combinations will work as long as it adds up to 1000. This presents a number of problems for the latter group, as it comes with certain requirements that must be met.

1. Each spellcaster must perform the spell accurately and in sync with each other, or the spell won't work. This makes it more difficult to perform the more casters their are.

2. These casters must be connected to each other through an object made specifically for this purpose, which links the transmutation circles together to form one large circle.

3. Anima from the casters build up a lot of heat, which can be fatal to the participants. Therefore, this object that links them together must double as a heat sink, which absorbs the excess heat from the casters, similar to a running computer.

This is the conundrum. A caster that has the exact amount or more of anima that the spell requires doesn't have to worry about heat exhaustion or burning out. However, multiple casters combining their anima to meet the requirements need a specialized heat sink to avoid burning to a crisp. Why would this be the case?

I'd go with a variation of Brooks' Law for this:

adding human resources to a late software project makes it later

The point in Brooks' book on software project management is that keeping people synchronized with each other is hidden effort that becomes greater the more people are involved.

By that logic, five casters of 200 don't really add up to 1000 because they spend a percentage on working together rather than casting, so to speak. You might go with a formula of, for example, 2% * #casters.

This is the strict interpretation of Brooks' law that replaces an individual's ability to work with their anima value. A looser interpretation might be that they can each contribute their full anima, but produce heat as a byproduct of the extra cooperation effort.

The heat is generated by magical turbulence tossing the energy away from the focus of the spell and into the ether as unproductive heat. A single skilled caster is able to predict turbulence for their own stream, but it is too chaotic to fully manage when multiple mages are involved.

Typically, when focusing their anima through a transmutation circle the energy the caster is pumping follows a laminar flow pattern, nice and smooth with no friction or energy loss.

However, when multiple casters all try to focus on a single circle, it's difficult if not impossible to predict exactly where each caster's magical flow is going to be at any given moment. Beams get crossed, magical flows turn into turbulent streams, and energy eddies cause the magic to be wasted as thermal energy.

Skilled casters are able to contain this wasted energy and channel it into the heat sinks that connects them, whereas unskilled casters either must stop the spell when it gets too hot.

1) Friction: Even synching up, their Anima is not perfectly compatible with each other. You can say, that the 1000 Anima spell doesn't require exactly 1000, when multicast but 1001, 1010, ... the extra Anima generates the heat.

2) Leakage: Similar concept as with the friction, but this time the tool is the problem. It is imperfect, so some minor Anima is leaking out as heat. If the tool wouldn't handle it (as heat sink), the heat would travel back to the casters.

3) In-built ventillator of the transmutation circle: The circle function as a ventillator for a single caster (a single core). Multiple caster is like putting multiple cores under one ventillator which wasn't designed for that. It's not the amount of output Anime which generates the extra heat, but regardless of output, the Anima usage generates constant heat. In short, low Anima casters = old CPU's. Need more of them for the same task in same time as newer versions, but only have one cooler.

If these don't work, please clarify why not and will try to come up with better ones.

Magic runs through things just like electricity. Different things have different measures of resistance or conductivity to mana (which you call anima). Mana is not electricity, though - mana resistance does not correlate with electric resistance.

Turns out most humans conduct mana very well. The ones who do have some resistance to magic are those that have, well, a lot of resistance to mana. You know them, the kind that you can hardly ever mesmerise with a spell, and who won't be polymorphed no matter how hard you try. Ever noticed that after trying to bruteforce a lot of spells onto them hoping for a critical roll, you only give them a mild fever? That's why.

Other materials may or may not conduct mana so well. When you link humans to cast magic, if you use a very conductive material the mana is distributed too fast. So the casters would need superhuman reflexes to coordinate the gestures, words and sygils. Using a material that is mana resistant means the mana flows slower, giving the time to react and coordinate so that the spell does not explode on their faces. But the greater the mana resistance, the more heat is dispersed as it flows through the material.

It arises from inconsistencies in individual transmutation circles. For instance, we can say that there is one "true" transmutation circle but that anything with a certain percent deviancy will still work fine. This results in every person who knows the spell casting it slightly differently. As a result, the source of magic has to make slight corrections to the group model as they try and combine their transmutation circles. These slight differences act as the "friction" creating heat. Thus, there is less waste heat when two people have a very similar mental transmutation circle. This would allow for highly trained groups to have very little waste heat while two random people would likely both die.