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Radiation and conduction are two ways that heat is transferred. Convection isn't really a mode of transfer as the actual heat transfer really occurs through radiation/conduction and not by some other process.

What I was wondering was if this were more general; that at the atomic level, radiation is the only mode of heat transfer. So during heat conduction, do the atoms transfer heat by applying forces on each other or do they emit radiation which gets absorbed by the neighbouring atoms or is it some other way?

Thank you.

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"Convection isn't really a mode of transfer" No, convenction really is a mode of heat transfer. Yes, there is a conductive or radiative step at each end in the common examples and in most engineering applications (and there are many enginering application both forced and passive), but hot stuff moving really does move thermal energy from one placce to another. –  dmckee Jan 6 '13 at 18:14
    
@dmckee yes, but when the hot stuff moves up, heat is not being transferred to any other particles, it's essentially being transferred through space which is not really heat transfer because then a movement of an object in space could also be termed as heat transfer... right? –  Alraxite Jan 6 '13 at 18:23
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The movement of any mass to a region of different temperature is termed heat trasfer--at least by those engineers who work on forced convection systems. If you have a complex system with bits in motion and you want to understand the thermal state of the system you must take the motion of the bits into account. I think I see where you are trying to go with this, but ... see the comment I left on Ondřej Černotík's answer about usefullness. You are trying to pick useful concepts apart into less useful ones. –  dmckee Jan 6 '13 at 18:34
    
Could the downvoters please explain their downvote? I personally don't find this to be a stupid question. It's just an idea that I had that all heat transfer occurs through radiation even if the atoms are very close. I just wanted to clarify if this was really the case. Turns out that it's not which is not my fault. –  Alraxite Jan 7 '13 at 7:27
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2 Answers

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No, conduction and radiation are two different ways how to transfer heat. During radiation, an atom emits energy in form of a photon that gets absorbed by another atom and heats it up. But during conduction, the atoms exchange energy in collisions. So conduction and radiation are two completely different mechanisms.

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One could get hyperpedantic, claim that all interactions are mediated by boson exchange, itdentify that as "radiation" and say Ah, ha! I was right all along". But that would be both useless and silly because it would make it necessary to identify differnt regimes of emergent behavior cooresponding to the conventional categories "conduction" and "radiation" and end up right where you started. The conventional understandings persist because they are useful. –  dmckee Jan 6 '13 at 18:28
    
Okay... what I was wondering was how can we be certain that when we heat a rod, the atoms transfer heat to their neighbours through collisions and not by simply radiating heat right then and there. –  Alraxite Jan 6 '13 at 18:28
    
@dmckee I understand that it's practically useful to differentiate conduction and radiation, but I'm asking for what fundamentally happens during heat transfer: Is there only one kind of heat transfer between atoms which is radiation or is there another fundamental way by which heat is transferred? –  Alraxite Jan 6 '13 at 18:32
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Of course you will normally have both conduction and radiation. You can't stop atoms from emitting photons or from colliding (unless you have a very dilute gas). The only question is what prevails; and the denser the matter, the more collisions you will have. –  Ondřej Černotík Jan 6 '13 at 18:49
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I don't think this is a stupid question at all. Ultimately we don't know the answer. We have a conventional understanding of gravity but no one really knows what it is. No one really knows what electromagnetism is either, so we call both of them a "force" and pretend we've figured it all out and there is nothing left to learn. Sure we know how these forces manifest in reality and we can build things using this knowledge, but we should always question conventional understandings and real scientists do this. One can understand that "collisions" occur that transfer heat and this helps in building an oven but not in satisfying one's curiosity of what is fundamentally happening. The question asks at the atomic level, someone tell me, what is an atom and how can two of them really "touch" one another?

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Conventional understandings are challenged only when the question demands so (if it is at the boundary of physics). For the scope of @Alraxite's question, the standard definition of atom suffices. Using "ultimately we don't know the answer" for every question is too overkill. –  pcr Jan 24 at 3:20
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