492
The sun is a deadly laser...
(thelemmy.club)
cross-posted from: https://feddit.uk/post/44126927
Goldilocks
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this post was submitted on 12 Feb 2026
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But you will if you sit in a vacuum for a while without a radiation source nearby, and it will be quite low.
Are you dissipating heat in a vacuum, though? Pressure shenanigans aside, would someone's body heat slowly, continually build up, or would they freeze?
If you could somehow prevent yourself from dying due to lack of pressure, without blocking heat, you would radiate about 650W more than you generate.
That's using the Stefan Boltzmann law, at normal body temp, perfect blackbody and 1.5m2 of skin. (~ 750 Watt) And then assuming 2000kcal a day (~100W)
You'd cool down pretty quickly.
So how long do I have? Also, if you guys could hurry with the answer...?
RIP
I can't really find a good number for how cold you can get and not die, so let's say 20 degrees. That gives 16 degrees to lose.
Meat has a specific heat of about 3.5kJ per kilo per degree, so say you weigh 70kg, that's about 4 million joules to lose before you die.
At 650 joules per second, you've got slightly over 10 minutes. Of course, shivering will burn more calories and stuff, and the panic of impending death will likely stretch it a few more.
I didn't include clothes, because then the maths would make me cry.
Your skin isn't at core temp tho, so the loss rate should be lower I think
At that point, you'll have to calculate the heat transport of the human body, and answer questions like "how long can a person live with frozen skin" and other fun questions I'm not equipped to answer.
4,000,000/650/60=102.57 minutes
But that's for a resting body, a shivering one would lose only like 200j/s
Also, you forgot one important aspect, if you're getting bathed by the sun and spinning, you're constantly getting heated up.
Good to know! I didn't realize humans would radiate heat so much, I wrongly assumed it was more convective and relied on atmosphere
https://en.wikipedia.org/wiki/Black-body_radiation
You constantly radiate heat. The warmer you are, the faster you radiate it away. In space this is the primary way you lose heat.
In your living room you are constantly bombarded by radiated heat from all the objects that surround you, even if they're just at room temperature, which lessens the effect. In space, not so much.
Someone who knows better might chime in, but as far as I know the trope of rapidly freezing out in space is exaggerated. You would definitely freeze eventually, but perhaps not as dramatically fast as portrayed in The Guardians of The Galaxy for example.
Have you ever looked up at a clear summer night sky? Your face will feel cold. Colder than when looking at the ground. That's because there's not as much stuff radiating heat at you up there.
Heat doesn't work quite like that. In order for heat to transfer efficiently, there has to be "stuff" for it to transfer to. Vacuums are famous for lacking "stuff".
You're talking about conduction. I'm talking about radiation.
Sure, but radiation acts extremely slowly in the scenario of a person in the vacuum of space.
Yes it is. But it is the main way by which things cool down in space.
That's how satellite electronics are cooled down. They have large heat sinks that slowly radiate heat away.
And those heat sinks are large because at the low temperatures involved, radiation is not an efficient way to shed heat.
I thought we were talking about a person in the vacuum of space.
A human body will also eventually freeze in space. The same physics apply. It's just not going to happen fast.
I just did the maths in another post. It's surprisingly fast! 10 minutes till you die, under 20 till you freeze. Assuming perfect heat conduction and no increased energy generation from shivering or panicking, which probably won't make much of a difference.
I presume a person would curl up into a ball to preserve heat which would reduce the effective skin surface area. But that is still quite fast
I did the maths three times, because I was sure I got it wrong, but on Earth you get a LOT of energy from the radiation of stuff around you. I never really thought about that.
Infrared
Bonus: Making Infrared Cooling Paint From Grocery Store Items
It would be pretty warm at earth if the planet didn't radiate some of the heat away