Changes
Jump to navigation
Jump to search
Line 1:
Line 1: − + Line 28:
Line 28: + +
Second Law of Thermodynamics (view source)
Revision as of 13:49, September 9, 2016
, 13:49, September 9, 2016Added some more detail explaining the law
The '''Second Law of Thermodynamics''' is a statistical law of nature about the tendency of an isolated system towards disorder in the absence of intelligent intervention. This principle correctly predicts that heat will tend not to flow from a cold body to a warmer one without work being done, e.g. by a [[refrigerator]]. It also predicts that "[t]he universe is constantly getting more disorderly!"<ref>The quotation is from Isaac Asimov, who continued to say "[v]iewed that way, we can see the second law all about us. We have to [[work]] hard to straighten a room, but left to itself it becomes a mess again very quickly and very easily. Even if we never enter it, it becomes dusty and musty. How difficult to maintain houses, and machinery, and our bodies in perfect working order: how easy to let them deteriorate. In fact, all we have to do is nothing, and everything deteriorates, collapses, breaks down, wears out, all by itself -- and that is what the second law is all about.” Isaac Asimov, Smithsonian Institute Journal, June 1970, p. 6. Put in physics terminology, the Second Law states that the [[entropy]] of an [[closed system|isolated system]] never decreases.</ref>
The '''Second Law of Thermodynamics''' is a statistical law of nature about the tendency of an [[closed system|isolated system]] towards disorder in the absence of intelligent intervention. This principle correctly predicts that heat will tend not to flow from a cold body to a warmer one without work being done, e.g. by a [[refrigerator]]. It also predicts that "[t]he universe is constantly getting more disorderly!"<ref>The quotation is from Isaac Asimov, who continued to say "[v]iewed that way, we can see the second law all about us. We have to [[work]] hard to straighten a room, but left to itself it becomes a mess again very quickly and very easily. Even if we never enter it, it becomes dusty and musty. How difficult to maintain houses, and machinery, and our bodies in perfect working order: how easy to let them deteriorate. In fact, all we have to do is nothing, and everything deteriorates, collapses, breaks down, wears out, all by itself -- and that is what the second law is all about.” Isaac Asimov, Smithsonian Institute Journal, June 1970, p. 6. Put in physics terminology, the Second Law states that the [[entropy]] of an [[closed system|isolated system]] never decreases.</ref>
The Second Law of Thermodynamics is the result of the intrinsic uncertainty in nature, manifest in [[quantum mechanics]], which is overcome only by intelligent intervention.
The Second Law of Thermodynamics is the result of the intrinsic uncertainty in nature, manifest in [[quantum mechanics]], which is overcome only by intelligent intervention.
The often heard argument that this law disproves an eternal universe is true, since in that case maximum entropy would have been reached already. A counter-argument to this would be to suggest that the universe is still in the process of approaching maximum entropy.
The often heard argument that this law disproves an eternal universe is true, since in that case maximum entropy would have been reached already. A counter-argument to this would be to suggest that the universe is still in the process of approaching maximum entropy.
It should be stressed that the second law is statistical. To see this, consider adding a drop of red dye to a glass of water. What we see is the drop spread out and after a long time, the water is coloured uniformly red. It is more "disordered" now (a mixture of dye and water) than it was at the start (a glass containing only water and a single, concentrated drop of dye.) So the second law holds. However, it is possible by chance for all the molecules to just happen to move such that the red dye molecules all group together to form a single, concentrated drop. This appears to contradict the second law that "disorder" is always increasing. However the second law says that "disorder" increases as there are more microstates (ways of rearranging the molecules such that they look the same to macroscopic observer, i.e. a human) corresponding to "disorder" than "order". Hence it is more likely that the system will become more "disorderly" but not '''imposible''' for the system to become more "orderly".
==Reversibility and Irreversibility==
==Reversibility and Irreversibility==
(username removed)