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Lots of games have a type of "freeze" or "ice" element effect to their weapons, like for instance cryo weapons in Borderlands, but I'm trying to work out how that might be physically plausible.

Apparently thermodynamics is extremely complicated, but there are some crude approximations with specific heat. I've tried investigating different masses and materials in simplified scenarios, different specific heats and so on and I was stumped, because realistically, the mass contained inside a bullet, or a very then film of an sword, is generally not enough to greatly cool an entire character from my preliminary research, not even if you had beyond-physically-possible conditions like below-absolute-zero temperature and 10000 specific heat outside of conditions so extreme that you'd have a difficult time explaining them.

This is generally because you need a lot of mass to cool another massive body like a character, or lot of motion like a lot of flow of a pre-chilled material to carry heat away and coming up with that energy and circumstance is also difficult to explain.

But there's one explanation I didn't explore, which is the adiabatic expansion of hyper-compressed coolant gas.

Could you pressurize enough gas with a low enough heat capacity, inside a bullet so much so that when it expanded and contacted with a character, it spread and cooled a lot of their surface in a short time to explain a cryogenic effect?

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  • $\begingroup$ I think you are going to have fall back, on not everything being scientifically possible. Your intuition is correct. Anything passive you will be limited by the amount of mass. You can get a bigger effect with a phase transition, but it will still be limited plus probably less directed. Any active system refrigerator or heat engine or something will also have a hot side. $\endgroup$
    – UVphoton
    Commented May 8, 2022 at 20:13
  • $\begingroup$ I don't know that your vague statement addresses the creative plausibility of extremely pressurized gas. It's certainly not proportional to the hours of studying of heating and cooling I've done. $\endgroup$
    – StackQuest
    Commented May 8, 2022 at 22:00
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    $\begingroup$ I'd have thought that the expansion/explosion effect would predominate. Not saying you wouldn't get something, but it would be minimal in comparison. $\endgroup$ Commented May 8, 2022 at 23:15
  • $\begingroup$ Well, if you can turn an "explosion" into super-cooling, perhaps you'd be onto something. $\endgroup$
    – StackQuest
    Commented May 9, 2022 at 0:14
  • $\begingroup$ @StackQuest Under a lot of pressure your gas would become a liquid or even a solid. If you release the pressure suddenly you will get a big change in volume. If this was in the form of a bullet and the pressure was suddenly released that change in volume would likely look something like an explosion. A rapid expansion of gas does result in cooling, you can make dry ice from a cylinder of compressed CO2 and a nozzle, but it is very loud and inefficient. $\endgroup$
    – UVphoton
    Commented May 9, 2022 at 5:09

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Dineutrinos

Note: I was making this up, but doing a web search, I see that dineutrinos actually exist. Whether they can be used this way ... well, the first ArXiv paper I looked at seemed quite hard to understand in practical terms. If anyone has ideas please comment!

Your gun manages to perturb an atomic nucleus in a particular way (perhaps some weak collision) that would almost cause it to decay. A true decay might create a positron + electron neutrino, or an electron + electron antineutrino. But here we just whack the nucleus with some energy and out pops a pair of neutrino + antineutrino, and no other radiation. We've done "pair production" and made them out of nothing.

Now it turned out (total BS here, sorry) that these two particles, at a small separation from each other, but not so close as to annihilate, have some kind of force attracting them, and act as some sort of antenna that can interact with other matter much more than normal neutrinos. I mean, you could reach age 10 before any of the trillions of neutrinos passing through your body each second interacts with a single atom of it. But here, it's a pair, a "dineutrino", and we're going to disperse the two from each other without otherwise reacting them, so that's different.

Now you see where I'm going with this? We're going to blast the victim with this pure neutrino/antineutrino radiation we made out of the kinetic energy given to neutrons in our gun before collision, ideally releasing no radioactivity at all (beyond ordinary neutron decay), and when the pairs hit his flesh, they will interact with electrons, equipartitioning the heat energy between them and the electrons, meaning that everything they touch gets way colder. They go on their merry way, separated and warmed up. Entropy wins by separating them and by evening out the heat, so no complaints there.

Apart from the lack of any evidence I know of the needed interactive forces, this should otherwise make sense. There are enough new quasiparticles being discovered every day that one for neutrinos, if we could see it, doesn't seem outrageous. For a freeze ray, that seems better than average.

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  • $\begingroup$ Ionizing radiation generally "heats" a substance, and the scatters are often random. How do you ensure anti-pair reactions always take away heat from the subject but obey the thernodynamic increase in entropy? $\endgroup$
    – StackQuest
    Commented May 9, 2022 at 15:37
  • $\begingroup$ The gun generating the neutrino pairs can be capped with lead shielding to block the ionizing radiation. The neutrino pairs I will fudge, and say they can make it through "a short distance of shielding" with little interaction, but "mostly get absorbed" within the thickness of a human victim. I'm supposing they are made quite cold (the neutrons have little unplanned random motion, and the neutrino pairs move very slowly increasing their chance of interaction) and any interaction with an electron scatters them apart, at the cost of thermal energy. $\endgroup$ Commented May 9, 2022 at 21:35
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Basically, no.

The problem is not just that the bullet has to act like a heat sink of nearly infinite capacity. The real problem is that the target body has a finite thermal conductivity, and ice in particular has a very low thermal conductivity (which is what makes igloos possible).

So your bullet hits, and the target area gets deep frozen - and then the process starts going really, really slow because the heat from outside the frozen area can't travel to the absorption point fast enough, no matter how cold the absorption point is.

You need magic - i.e. a technology sufficiently advanced to target and lock individual atoms within a certain distance and (waves hands quickly) entangle their momentum to particles in the central cooling unit. Heat is not absorbed but, in effect, teleported away. The bullet therefore creates a certain number of freezing entangled volumes inside sufficiently dense matter within a certain radius.

The problem now being where the heat gets transferred to.

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Interesting question.

As I see it you limit yourself by only thinking in terms of currently viable freezing techniques.

We know from thermodynamics that temperature is based on the movement of particles. Eg. low movement = cold, high movement = hot

What if you could fire "something" (could be a ray or a projectile or somehing else) that caused the particles in a body to slow down or instantly stop? That would cause the body to try to even out the temperature and thus lowering the temperature in the nearby parts as well. If the duration of the effect is long enough (and/or the slow down of particles are big enough) it would chain react and cause the entire body to freeze.

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