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Why do we always talk of heat flow from a hotter region to a coder region? Would it be wrong to say that cold flows from one place to another?

The Cryptic Cat
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    Possible duplicate of I open the fridge - do I let the heat in or the cold out? – John Rennie Jun 12 '16 at 04:39
  • Cold means lack of heat. There is no why for definitions. You can define concepts how you like. – lucas Jun 12 '16 at 04:58
  • @lucas What about the second question? – The Cryptic Cat Jun 12 '16 at 05:16
  • @TheCrypticCat Which question? Whole of your question is about definitions of concepts. If you would like to say that cold flows from one place to another, you should define the concept of "cold" at first. – lucas Jun 12 '16 at 05:20
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    'Heat' is a form of energy. It is conserved (or created from other energy forms). Cold usually means temperature, so a quart of milk isn't four times as cold as a cup of the same milk. Cold doesn't usually mean the opposite of 'heat', but the opposite of 'hot'. – Whit3rd Jun 12 '16 at 06:40
  • @TheCrypticCat "Why can't "cold flow from an area of coldness to hotness?" Because our Universe says it can't. Honestly. Second Law of Thermodynamics. – udrv Jun 12 '16 at 07:04
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    @udrv : I think you are missing the point of the question. 'Cold' flowing from cold to hot does not violate the 2nd Law. 'Cold' flowing from hot to cold does. The OP is asking about the former, not the latter. – sammy gerbil Jun 12 '16 at 12:59

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This question is similar to the concept of electricity flowing in the same direction as electrons. If we didn't know about electrons being involved with how electricity flows, we might have never changed the historical convention of what direction electricity flows in.

In the case of your question, there is no reason why we couldn't conceptually treat entropy as "the flow of negative or lesser heat energy" instead of "the flow of [positive] energy". But the convention is to think of energy flow from higher heat energy locations to lower heat energy locations since we know that heat energy is actually a real substance (and has mass!).

Mark Ripley
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