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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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…
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