# The pros and cons of thermokinesis

I am currently working on a magic system that involves Thermokinesis, which is the ability to manipulate temperature. This power involves controlling the rate of movement of molecules, which is involved in the definition of thermal energy. This means the user could manipulate the wind, the density of water and to some extent, the earth.

The question is can the human body withstand instantaneous temperature changes, if for example you wished to become extremely dense to withstand a punch to the face, or gut? What are the potential consequences of withstanding kinetic blows?

• Hi Austin, You seem to be mixing two different concepts here. Heat involves how much the molecules move and bounce of each other, while becoming extremely dense would have to involve you squishing molecules very close together (sort of like Ant-Man). Solid things are already bonded in a pretty fixed form, so the only way would be to reduce the distance between bonded molecules which is different from heat. Please choose either Heat change or Density change because they are different. (Its like saying, how fast can you travel a meter vs how many people you can fit in a meter) – Shadowzee Oct 29 '18 at 6:54
• Hmm... I was under the impression that the lower the temperature, the higher density an object could be. Could you elaborate on the difference between density and temperature? – Austin Trigloff Oct 29 '18 at 7:00
• Density is basically a measurement of "how much of x in y amount of space." Temperature is basically a measurement of "how fast is x moving in y amount of space." (AKA measurement of heat.) It's not that they have no connection, but it's an irrelevant connection. Density doesn't substantially change from temperature though unless you were to heat something up to the point the molecules go everywhere in an explosion or you compact the molecules in a tighter arrangement than they should be able to fit normally. – Sora Tamashii Oct 29 '18 at 7:08
• Generally, thermokinesis works in a much more limited spectrum like heating something up a few degrees or cooling it down a little. It doesn't tend to come with extra powers like aerokinesis, hydrokinesis, or geokinesis, even in a limited capacity. It's usually considered a lesser version of pyrokinesis or could be seen as a weakened blend of pyro- and cryokinesis without the outright control properties they possess. You may be better off just selecting one of the other kinetic abilities if you truly desire that degree of control. – Sora Tamashii Oct 29 '18 at 7:10
• NK Jemesin uses a sort of similar idea in the Broken Earth Trilogy. Much that you've received some criticism for the idea, it could be developed – but it may not be the sort of 'superpower' that you would wish it to be. Eg, stopping bullets wouldn't work. – Konchog Oct 29 '18 at 12:18

Honestly, your premise is flawed as was pointed out in comments and the other answer. What you're describing is less thermokinesis. While I made a comment breaking down the issue with how you seem to be using thermokinesis, I'll include some of it in this as well.

First: Thermokinesis is temperature manipulation. Usually it's a primer ability before giving a character pyro/cryokinesis. In some cases, it's the only power a person has, but is then commented as being useless in battle, even if it's amazing for domestic uses. (Drying clothes, keeping food/drinks warm/cool, killing off viruses to keep from getting sick, etc.) It rarely comes with those extras you listed, but if it does, they're treated as separate powers to avoid confusion: aerokinesis, hydrokinesis, and geokinesis. That said, I'll explain how you COULD make it work in those regards while still being thermokinesis, but it'd be extremely limited.

• Aerokinesis: You could change the temperature of the air causing it to heat up or cool down. This would allow basic weather-manipulation like with Nami's climatack from One Piece. Again, it'd be very, VERY basic at best. You couldn't expect the type of control Nami's weapon has unless you take liberties with science... which wouldn't be unusual seeing as this is a magic system anyways. You could heat up parts of the ground to cause heat to rise creating weak updrafts. This wouldn't be useful aside from flying a paper airplane, but you could still do it. That said, wherever you're heating the ground, it'd likely have to be heated to such a point that it would burn to walk across. If you have a limitation of needing to touch the object, it'd likely get too hot for your hero to handle without injury. You couldn't cause the opposite reaction to occur by doing that, though. You'd have to seriously cool the air higher in the sky without cooling the surrounding air, and that wouldn't make sense for pure thermokinesis.

• Hydrokinesis: You could heat the water to the point it boils and steams or you could cool the water to the point it freezes. You could even cool the moisture in the air that it condenses and precipitates. You wouldn't be able to control it beyond that. You couldn't shape water. You couldn't create water shields. All you'd be able to do is take what you have and use it how it wants to act naturally. The closest exception to this would be if you had a creature like a slime with a high regeneration factor and used it as a meat shield by having it jump in front of attacks for you, but it'd shatter with enough force put into it. Furthermore, that slime will die if it takes too much damage or if its core breaks, so you'd be forced to take care of it if you want it to serve you well. You cannot make water freely more dense, though. It would just become ice from having its temperature dropped past 32F (0C). Since you're not hydrokinetic, you couldn't freely change its shape either, so you can't do more than maybe use the frozen water as a temporary running hazard.

• Geokinesis: Quite simply, you can't. You may be able to heat up the earth to cause an updraft from the heat. Maybe you could heat it up enough it turns to magma for a short period. You could even freeze it, not that it would help you any to do so aside from killing some plants. It would just go back to normal very shortly after, and it'd likely take more mana/energy than it'd be worth. Doing this to the earth serves no purpose other than being a mana sink, unless you're a gardener/farmer/glassblower/potter.

As I said earlier: Thermokinesis is a generally worthless power for in battle. Give your character either the more common pyrokinesis or less common but still known cryokinesis if you want him to have more combat-based usefulness for his abilities. Otherwise, this character would be functionally powerless in a fight, having to rely on raw fighting ability, knowledge/wisdom, and ability to deescalate a situation if he wants to win, which can work out quite well if you know how to handle physically weaker protagonists.

• I appreciate the insight. I'll work on remodeling this concept with this revelation. – Austin Trigloff Oct 29 '18 at 10:38
• If you ever need assistance, feel free to talk with me. I'll try to run through what I can to help you out since you seem to be retreading a lot of the same ground I have, both with the snake riders and this. I'll do what I can to help. – Sora Tamashii Oct 29 '18 at 16:24
• As I said, the power itself isn't a bad one. It's just not useful in the manner proposed. A fight is never reliant on who is physically stronger. It relies on who has the greatest understanding of their opponent and their abilities. Your character could use their thermokinesis in a manner reminiscent of other powers, which could be used to trick opponents into thinking he's more dangerous than he is or into being cautious due to not having enough information on his powers. You could even take it a step further and have one opponent with access to all the powers he emulates or a way to counter – Sora Tamashii Oct 29 '18 at 17:03
• the powers he emulates. In the first case, they could serve as a foil where they are always better than your hero and is a hurdle he needs to overcome. In the second, you could have them questioning why they can't counter your character's abilities and why they can't seem to beat him no matter what they do, possibly coming to the realization later down the line. – Sora Tamashii Oct 29 '18 at 17:04

What you are describing isn't really consistent. First of all, the random movement of molecules is heat, not temperature. To manipulate wind you'd have to create some sort of temperature gradient, in other words transfer energy from one volume of air to another, which is not a bad idea (assuming you don't care about the second law of thermodynamics), but it would take some time for airflow to start after you transfer the heat. Don't expect to create quick puffs of wind.

Changing the density of water is a whole different question. Sure, water density changes with temperature, but the coefficient is $$0.0002/^\circ C$$, which won't get you very far. Using that to counter a punch to the gut—no, not really. But then, why would you need to? If you can instantaneously transfer heat from one place to another, simply shift it away from the opponent's arm and freeze him.

• Another info is that there is also the minimum temperature of 0° Kelvin. Whatever variance in potential density you could achieve by changing temperature, there is quite a close limit to it. Meaning you can go ~300°C downwards, but you could go up millions, billions or more upwards. That is the scale in which changing temperature for altering density works. As of beings in living conditions, we are already quite close to the bottom - relatively speaking. – Battle Oct 29 '18 at 7:25
• I see. This concept definitely needs some work. Thanks – Austin Trigloff Oct 29 '18 at 7:26
• Another thing to point out is when you change the temperature of something, it will constantly try returning to the temperature of its environment by releasing or absorbing heat. Increase the room's temperature by 50 degrees, and it will try releasing that heat outwards and into any objects of the room. Increase a cup's temperature by 50 degrees, if it doesn't shatter first, it will then release that heat into the room. Oversimplified? Sure. But it gets the idea across. The more you change the temperature, the harder it will be to do so and it will immediately try to return. – Sora Tamashii Oct 29 '18 at 8:09

NK Jemesin uses a very similar idea to yours in the Broken Earth Trilogy; I recommend you read it.

Much that you've received some criticism for the idea, it could be developed – but it may not be the sort of 'superpower' that you would wish it to be. In general, you want to keep the temperature changes far away from your own body (again, read the Broken Earth Trilogy - it's great).

So stopping bullets by making your body wouldn't work. But freezing the gun could prevent the gun from working, or even shatter it. In fact, Jemesin thinks up all sorts of things that can be done with it.

However, it may be better to work out what you really want to achieve - magic is a huge subject, and all too often it's used as a backdrop for an otherwise flat story.

(Dare I mention Hogwarts? Take the magic out and you have famous five go to a posh school).

LeGuin begins to explore magic (Earthsea), as does Pullman (His Dark Materials), Stross (Laundry Series), and Aaronovitch (Rivers of London series). But very rarely does anyone do much than scratch the surface of what magic really is, and how it works...

Also it's worth remembering Clarke's third law...

Any sufficiently advanced technology is indistinguishable from magic

• Insightful advice, I'll keep that in mind. – Austin Trigloff Oct 29 '18 at 12:39

The human body is made mostly of water, so let's use it for analysis and extrapolate from there.

Water at normal conditions (~300K, 1 atm) has a density of $$1g/cm^3$$. At the same pressure and close to 0K, the density of water hasn't varied by even 10% in either direction (more on that here). Not really impressive for a superpower.

Supposing a marvelesque hero could increase their density to resist, say, a point blank assault rifle shot. They would either reduce in size considerably or potentially break the floor or sink into the ground.

Don't try to explain superpowers with science. Whenever I remember that Banner would have died of radiation poisoning within minutes or that Lois can't breath when Clark takes her to a flight it just ruins all the fun.