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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The primary mode of heat transfer in space is radiative – the atom emits a photon that carries energy off into the abyss.
This is how the sun’s energy reaches earth across the vacuum, and this is how a rock lost in deep space will eventually cool down to cryogenic levels.
Far from any stars or galaxies the only incoming energy you’ll receive the same way is the feeble heat still echoing from the big bang itself, a feeble 3 kelvin.
Oddly enough, one of the problems we have in space is not keeping things warm, but keeping them cool! The various space stations we put into orbit frequently have large radiators to get rid of excess heat, because when they’re exposed to the sun they absorb a lot of heat, but they have a hard time getting rid of it- vacuum and near-vacuum is a great insulator (consider thermos bottles).
When objects are further away from sources of light and heat like our sun or in the shadow of something, they will cool down over time. But the vacuum of space is actually a quite effective insulator.
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.
Your question is good enough. There are some notable physicists that for teaching issues prefer to actively differentiate heat by contact with the other kind of heat that doesn’t requieres touching.
And also a good question as covers different fields of physics
First electromagnetism. There are certain important and accurate equations called Maxwell’s equations that give us a very deep and accurate understanding of things like, electricity, magnetism, electromagnetic waves etc…, within this equations one of the multiple results we get is that electrical charges that are accelerated emit an electromagnetic wave.
On the other hand we define “cold” or “hot” according to temperature which is a concept of thermodynamics. In simple words we can say that the more speed the particles of a body have the more hot it is.
Now with both things in mind. Bodies are composed by atoms or molecules and both have electrons and protons which are electric charges. Inside a body atoms move randomly at certain speed, so the body has certain temperature. When an atom collide with another it changes it’s speed and that means acceleration. Because the charges were accelerated they emit an electromagnetic wave. As result part of the moving energy of that atom is converted to an electromagnetic wave and so then now it’s moving slower. So then gradually and randomly all particles are loosing moving energy, therefore the temperature of the body is getting lower therefore colder. And at the same time emits electromagnetic radiation.
All bodies emit that radiation all around, and they can do in vacuum. And if some other body separated from the original received that’s radiation and absorbs it the second body can increase it’s temperature. That’s a way of heat transfer that can be done in complete vacuum and at a distance without touching.
The complete understanding of that radiation was an issue on the latest 19th century, and it was one of the first reasons that quantum mechanics started to become a thing. But that’s another history…
There are three primary means of heat transfer:
1) Conduction — This is caused by energetic molecules bumping into nearby molecules and transferring some of their energy to them. This is how heat will travel down a metal bar.
2) Convection — This is when a mass of higher temperature physically moves to an area of lower temperature. As you can probably guess this is NOT a primary means of heat transfer in a solid. This is what happens in the atmosphere as hot air rises and cold air falls.
3) Radiation — This is where a hot object generates electromagnetic radiation that carries some of the heat energy away. Black body radiation is an example of this.
In space #3 is the primary means of heat transfer for a solid object although there is a negligible amount of #1 and #2 going on since space is NOT a complete vacuum.
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