I thought an atom had to touch another atom in order to lose entropy.
So since space is a vacuum, shouldn’t something drifting along in space not ever touching another object retain its heat forever?
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There is another way for heat to transfer, that’s radiation. Each atoms are radiating energy away from it. The hotter the atom the lower the wavelength of the radiation. Stuff at room temperature around us are emitting infrared. That’s the reason we use infrared camera to detect the temperature of stuff. It’s the wavelength of most of the stuff we interact with.
If the matter is hotter, then the wavelength will be lower, which mean visible light. That’s the reason why the heating element of your oven is a darkish red, a fire is even more hot so it look yellow and bright red. A plasma torch will be blue, because it’s even hotter. Hotter than this and you get into ultraviolet, x-ray and gamma ray.
So most stuff in space have been radiating away most of their energy for a long time so they are cold today. That said, being hit directly by radiation from the Sun also heat things up really fast in space (no atmosphere to absorb a lot of the energy). So when we do send something in space we need to design to resist very high difference in temperature.
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