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Microwaves work by exciting water molecules.
Put an empty bowl in and it comes out cool to the touch.
A bowl of soup and the bowl is crazy hot, because the soup warmed the bowl.
Heating a person with a microwave would make us pop as the water inside heats up faster than everything else. And blood is pretty fucking similar to water...
You could try it with an incredibly low dose, but you'd have to do it in carefully measured bursts. Even for hypothermia, warm baths are dangerous because the increase in body temp is too sudden and can fuck up the heart.
So there's a whole bunch of risks and you're still limited to what won't freak out your heart. Warming just one part warms up the blood that's there and send it through the cold parts. Like how you're not supposed to immediately add water to a radiator after a car overheats. The thermic shock can cause massive problems.
So we could...
It just wouldn't make any sense to do it
Microwaves don’t just heat water molecules, although due to density they absorb a large amount relative to many other substances. Also since humans are mostly water, the heating should be even enough to not be quite as problematic as you describe. Some sensitive areas like eyes are an issue, but otherwise it’s possible a low enough dose could warm someone a couple of degrees without causing any harm.
Bruh, it's the heart that's the issue...
The thermal stress is too great. Microwaves would heat the blood up, which within seconds would go into a cold heart
It's why they won't use a warm bath to hear someone up who's dangerously cold.
Slow and steady is how you do it. So even if you used microwaves, it would be limited to pretty much the same delta temp as other methods.
It's all risk no reward
Thanks. Your comment is the one that helped me understand the limitations the most.
But wouldn’t the microwaves also warm the heart? There’s no reason a microwave at the right power couldn’t slowly heat someone up. I don’t think the OP is asking about someone who is dangerously cold either, so the extreme care that needs to be taken when someone is in serious danger due to how cold they are might not be relevant in this case.
If it's pointed at it...
But you know what heats a cold heart faster than blood from another body part?
Direct exposure to microwave radiation...
That's what I mean, there's a safe temperature differential to warm the body, and even stuff as conventional as a warm bath or hut tub can be too much.
If we shoot microwaves at a heart, the heat increase is waaaaaaaay above the safe limits.
So if someone was in a situation where the only method was microwave radiation, it wouldn't result in an increase in heating without running serious risks.
There's just no benefit and it introduces insane risks if you tried to do it slow enough.
My point is that the heat increase of the heart doesn’t have to be so insane. If someone was designing a microwave human heater they would have to make the power level such that it would always result in a safe rate of temperature increase. Obviously using an off the shelf food microwave wouldn’t work.
Is heating someone too quickly a concern if they don’t have hypothermia? Like if I’m sitting round in my house and start to feel cold, and I get in a hot bath, it’s not going to heat me up too fast, right?