this post was submitted on 08 Jul 2025
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Humans don't explode in vacuum.
We do, however, swell up quite a bit.
i mean after you're dead, sure, but that happens on earth too
afaik surface-dwelling mammals exposed to a vacuum just get some terrible damage to things like the lungs and eyes, and the more sensitive blood vessels, and if left in the vacuum and exposed to the sun they'd go kinda crispy..
Thanks! I was about to ask if there is time for the pressure differences to act upon our biology, or if the freezing bit happens before everything has a chance to go pop!
Freezing would happen very slowly, and not at all if the human was relatively near the Sun (around Earth's orbit or closer).
That makes sense, I mean we're already melting over here with the atmospheric buffer, I imagine it'd be the same or maybe even hotter straight on.
Feel dumb for not thinking about it this way, to be honest, thank you!
The Earth is actually warmer than an object in space would be due to the greenhouse effect. But even without the effect, a spherical blackbody human won't freeze. Since humans aren't spheres, you could probaby get one to partially freeze by pointing its head or feet at the Sun, minimizing the surface area it receives sunlight from. This is definitely something that needs experimental testing.
If it'd get me to space, I'd happily volunteer!:)) With a sensor-laden space suit, of course, not looking to lose any toes:))
There are no cool breezes in space
For gases, volume is inversely proportional to pressure, which means as pressure approaches zero, very slight changes in pressure will make a big difference to the behavior of the gases.
But for solids and liquids, the absence of pressure doesn't make that big of a difference. Yes, vapor pressure means that water will boil at lower temperatures in a vacuum, but the way the actual liquids stay together, especially when enclosed in in a way that limits vapor pressure, remains the same in low pressure environments as they are in medium pressure environments.
So when you go scuba diving, the doubling of pressure when you hit a depth of 10 meters is simply accommodated by you breathing denser air out of your tank. But nothing else about your body feels any different under that pressure. Go even deeper, and some things might start getting affected by the dissolved gases in your blood and other bodily fluids, but we're talking about huge pressure differences from the surface, basically 1 atmosphere of pressure for each 10 meters you descend.
In contrast, the difference between sea level atmospheric pressure and the vacuum of space is only one atmosphere of pressure. The liquid and solid parts of your body will be fine. Your reliance on breathing might not fare so well, but see how militaries deal with it: pressurizing the cabin to some degree but making sure that the actual breathing mask is delivering the right amount of oxygen even when the cabin pressure is the equivalent of a high altitude.
So when that blobfish gets yanked out from 900 meters deep up to the surface, that's a sudden loss of pressure from 91 atms to 1 atm, a 90 atm swing. But for a human going from 1 to 0 atms, that's just a 1-atm difference. If you open your mouth and exhale while it's happening, maybe relax your eustachian tubes if you know how to do that, you probably won't have any issues from the decompression, until you start to try to breathe.
Oh, wow, so not all of that sci-fi was purely -fi! This makes so much sense, yet I've never conceptualised it as such. Like, I knew the concrete pressure differences, but never had them set in a big picture view:-?
Jesus, now I wish I would've taken up more physics, would've happily soldiered through the math for this amount of interesting!
You don't really freeze because in a vacuum you lose heat very slowly. You'd suffocate long before that. Or, as previously mentioned, go pop
Hmm, is it because vacuum acts essentially like an insulator? I'm thinking this because, from what I remember about high-school thermodynamics, heat needs to "jump" from matter to matter, and there's not a relevant quantity of matter in a vacuum to act as a heat absorber, like air does over here, right?:-?
I'm genuinely asking, I'm sure I have brain rot from watching too many sci-fi movies...
I'm not sure that I'll get the English terms wrong but basically heat can move in three ways:
Thank you, this makes a lot of sense!
Also, guess I missed my mark, would've been the ideal astronaut based on this! Does being dumb also help help? I mean, less going on up in the ol' noggin, thinking energy is transferred slower that way:))) Or that I use less, which would make me fuel-efficient!=))))
Radiation will still transfer heat. But that will be relatively slow. This image gives a quick overview of the ways heat may be transfered.
Yep, this is very clear, thank you! Visual aides are OP, I swear!
It's exactly what the other commenter said, to transfer heat efficiently you need something else to transfer it to. In a vacuum, you only lose energy by radiation. Therefore on a spaceship you're actually in greater danger of overheating than freezing to death.
Another counterintuitive thing that stems from this is that space vacuum isn't even, strictly speaking, cold. The few and far between particles of space dust and gas can have very high energy flying by, at least until they hit something. It's only cold when you average out over all the empty space.
Huh, that's really interesting! Yeah, given all of these factors, I would imagine that absolute vacuum would be... well, nothing in terms of cold or hot:-? Wow, that's a huge paradigm shift, I shoud dare to be stupid online more often, I'm learning more from this thread than I would have expected!
Thank you!
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Doesn’t all the water in us boil. Like instant Bends.
Also aliens who evolved on planets without magnetospheres: “these earthlings are interesting but they seem to get stressed and lumpy in space.”
It boils, but because of the pressure drop, not because of the temperature change
No, that doesn’t happen. The bends is worse because you can go from multiple atmospheres of pressure to just 1. The worst space can get is from 1 atm to 0 atm.