Monday, May 01, 2006

If entropy was the answer to everything, how do we explain heat flow?
It is an accepted fact that heat flows from the object with a higher temperature to the object with lower temperature. It is also an accepted fact that objects with a lower temperature have a lower entropy. (entropy can be thought of as a measure of randomness - a gas is more random than a solid because the molecules have less order - gases are higher temperature than their solid counterparts)
Accepting all of this, heat flow would suggest that an object with a high temperature (and therefore higher entropy) would give up its heat (an indication to the ammount of entropy of the system) to an object with a lower temperature, and lower entropy. So if objects have a tendency to become more random, as you suggest, so should they have a tendency to spontaneously increase in temperature, which we know is not the case...how can we explain this??

2 Comments:

Blogger linford86 said...

Heat flow is quite easy to explain using entropy, but you have to be very careful on how it is that you talk about such things. Entropy is a result of the second law of thermodynamics - it is a law of physics, albeit a weaker one (as Chad I'm sure would point out, the laws of thermodynamics are statistical laws, and are therefore considered "weaker" than some other laws) so every sufficiently large system in nature must obey it (as I understand it, the law only works for statistically large collections of atoms or molecules. Of course, I have yet to take statistical mechanics - so I could be wrong on a lot of this!)

One thing that's important to note about the second law of thermodynamics is how it is actually stated, namely: the entropy of a given cyclic system will either remain constant or increase with time. In order for things to go the other way, that is for things to become more ordered, work must be involved - that's why ordered structures exist in nature (energy must have gone into making them. It's highly unlikely - although not impossible - for atoms to come together to form into a highly ordered structure without some input energy.)

In any case, the cold object that you talked about had a lower entropy to begin with, and the hot object did end up with a lower entropy at the end. You might think that heat flow would imply that the two objects, collectively, ended up at a lower amount of entropy. However, this isn't the case. The whole system, taken collectively, actually would have a higher entropy than it started with when the system reached thermal equilibrium.

For more on entropy, check out one of my favorite web sites - hyperphysics:

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw.html#c4

By the way, I don't think that Chad meant that entropy was the answer to everything. However, it is the large scale trend of the universe - it is a property of the universe in which we live, and it is impossible even in principle to disobey. Unlike human laws, the laws of physics simply cannot be broken.

5:08 PM  
Blogger chad said...

Back To Entropy


I would also like to make some comments on my idea of nature and entropy. This is with respect to the concept of heat flow. Without getting into a physical explanation it should be noted that when entropy is combined with energy it becomes a different formulation all together. Heat is energy and energy always seeks the least excited stated in nature. This is why hot things give off radiation and seemingly cold things absorb radiation. However, when focused on the concept of entropy alone it serves one simple idea. For example, take a deck of cards that are arranged in perfect order, such as when you first open them. Now fling them across the room. Then pick up the cards without looking at them. The chance of ever picking them up in the same order is near impossible. But the key fact is that there is a possibility that you do pick them up in the same order.

3:30 PM  

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