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I don't exactly know how to phrase the question, but it seems like most forces in the universe are governed by physical processes where entropy is constantly increasing.

Then you have Earth, where we have living organisms that expend energy to (locally) combat the forces of entropy, i.e. matter binds with itself to create structures. Although on Earth, living organisms are also subject to entropy and die and decay into smaller, more primitive constituents.

On Earth, we also have robots and technology that combat these same forces, but the work can ultimately be traced back to a life-form that initiated the process. And technically, the sun would be considered the source from whence the life-forms obtained the energy to perform the work.

I am having an extremely difficult time imagining a type of process where work is performed to create structures combatting the forces of entropy on a local scale. The obvious exception is life as it is on Earth, and it seems like the necessary antecedent.

Would all instances of processes that combat entropy in this type of scenario be considered life?

Edit: I want to tag this as entropy and universe, but I have insufficient points.

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The definition of life is not trivial and not resolved yet. If you have the opportunity, I recommend watching lecture 14 (actually, the whole series is great) of "Mysteries of Modern Physics: Time" by Sean Carroll. In it he deals with the themes of entropy, complexity and life. His book "From Eternity to Here" also seems to touch the same subject on Chapter 9, but I haven't read it yet. –  Koeng Jan 3 '13 at 6:39
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If you allow refrigerators and other entropy-combatting devices to us in order to source it to "life", why stop there? Why not trace ourselves, not to mention our evolution, to some even more grandiose and god-like entropy-combatting force? And then trace that god's existence to some yet greater non-entropic process? What motivates any particular point for curtailing the infinite regress? –  Niel de Beaudrap Jan 3 '13 at 12:06
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Well, I just wondered what makes 'life' a special thing to try to single out as a cause of non-entropic processes. This is precisely what you are trying to do, but it is not clear to me why one should. So it is related to your question, if only to ask why you would ask. –  Niel de Beaudrap Jan 3 '13 at 14:21
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Personally, I think you've made a very interesting definition of life. The immune system is precisely where I see the curtailment (historically, evolutionarily) of entropy. Even if we don't know it, our consciousness forms the adaptive immune system that continues this process (it's subtle because most things we've already found solutions to and truly novel entropic forces rarely surface). –  Mark J Jan 4 '13 at 5:20
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The canonical counterexample is a hurricane. Like a living organism, it increases the entropy of its environment (in this case by transporting heat from the warm ocean surface to the cold upper atmosphere) in order to maintain its own, localised low-entropy structure. This structure is low-entropy in part because it involves highly correlated motions of air molecules, i.e. wind.

The similarities between hurricanes and organisms do not stop there. Another important property of organisms is that their identity remains despite the continual replacement of all the atoms that make them up. Hurricanes also have this property.

Like organisms, hurricanes are subject to an analogue of death - they dissipate when they pass over land. Although the primary cause of a hurricane's motion is the prevailing wind, there is some evidence that when the prevailing wind is subtracted, hurricanes tend to move toward regions of warmer surface water, where the conditions are better for their "survival". Hurricanes thus have a rudimentary form of behaviour.

Hurricanes also possess something analogous to an organism's anatomy: the eyewall, the fast winds near the surface, and the drier air spiralling out at the top, must all be in place in order for the hurricane to persist - yet they are all generated by the processes that comprise the hurricane itself. (The anatomy of a hurricane is actually considerably more complex than how I've described it here.)

Hurricanes are not the only example. When you start looking, you realise that although they're not everywhere, they're relatively common. Sand dunes, fire and ocean waves could all be described the same way, although they're not as nicely localised as a hurricane.

If you want, you could consider all these things to be alive. Personally, I prefer not to, but it's just a question of definitions. Still, as a scientist, the existence of these counterexamples makes me happy. It means we can learn more about life by studying these simpler, yet related phenomena. This is, essentially, what I do for a living.

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I think this is brilliant –  Cayetano Gonçalves Jan 23 '13 at 20:34
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Would all anti-entropic forces be considered living?
I am having an extremely difficult time imagining a type of process where work is performed to create structures combatting the forces of entropy on a local scale. The obvious exception is life as it is on Earth, and it seems like the necessary antecedent. Would all instances of processes that combat entropy in this type of scenario be considered life?

No. Refrigerators cannot be considered life.
Some people think that life, contrary to the general tendency dictated by the Second law of thermodynamics, decreases or maintains its entropy by feeding on negative entropy. But the principle that entropy can only increase or remain constant applies only to a closed system which is adiabatically isolated, meaning no heat can enter or leave. Whenever a system can exchange either heat or matter with its environment, an entropy decrease of that system is entirely compatible with the second law. Like the refrigerators. Living organisms preserve their internal order by taking from their surroundings energy, in the form of nutrients or sunlight, and returning to their surroundings an equal amount of energy as heat and entropy. The apparent paradox between the second law of thermodynamics and the high degree of order and complexity produced by living systems has its resolution in the energy that enters the biosphere from outside sources. Entropy reduction is a general characteristic of life.

Recent discoveries in chemical systems show that, under certain autocatalytic reactions, non-living molecules (such as RNA) compete for resources chemical (nucleotides). Small differences in the configuration of these molecules may result in higher or lower reaction efficiency. Since resources are finite, the variant leads to less reactive to extinction. The process of Darwinian selection begins even before the emergence of life. In fact, this type of system, unlike the more common chemical reactions, is only stable when it reaches a stage of continuous changes. This is the dynamic kinetic stability, or DKS. Since the system receive power, the second law of thermodynamics is not violated, and biology becomes a particular case of chemistry. ( See What is Life?: How Chemistry becomes Biology, Addy Pross )

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Great answer! So, are the only structures in the universe where an apparent negentropy can be observed considered life-like (RNA, virus, spider) or a consequence of life (spiderweb, laser, refrigerator)? Because to battle entropy, structures would have to be built from the microscopic level to deal with even the smallest entropy. –  Cayetano Gonçalves Jan 3 '13 at 16:29
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@CayetanoGonçalves - No, not even close. Crystal growth reduces the entropy of the molecules in the crystal. Freezing water reduces the entropy in the water molecules. Draw your boundaries right and entropy goes up and down all over the place. –  Rex Kerr Jan 4 '13 at 16:20
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Chemistry is anti-entropic.

Whether a reaction will occur or not depends on what is called Gibbs Free Energy. The fundamental equation is

∆G = ∆H - T∆S

where H is the stored energy and S is the entropy. Any reaction where ∆G is negative will proceed--which could occur because entropy goes up, or could because energy is released (heating up the surroundings). If there is no way to vent the heat, then overall entropy will go up (because of the temperature term T increasing, which will also increase S; the direct dependence of S on T is not shown in this equation which assumes T is held constant), but any system that can lose heat to the outside--and that's basically any chemical reaction--can power its way to lower entropy by expending enough energy.

A canonical example of an exothermic (∆H > 0) entropy-reducing reaction is crystallization. Solids essentially always have lower entropy than liquids. (This goes for phase changes from gas to liquid and liquid to solid, also.) But there are plenty of other examples; any reaction which reduces the number of molecules also tends to be entropy-reducing (even burning hydrogen: 2H2 + O2 -> 2H2O converts three molecules to two).

Bottom line: local reduction in entropy is not in the least exclusive to life; it is a general property of chemical systems which do not trap all heat that they produce.

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You have answered my question entirely. But it just opened more up! So, living organisms employ metabolic processes where ∆G<0 to generate Gibbs free energy and then apply the work to non-spontaneous processes that are vital to life, where ∆G>0. Right? –  Cayetano Gonçalves Jan 4 '13 at 22:54
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@CayetanoGonçalves - All chemical reactions that move forward have ∆G<0. But in a sense, yes, living organisms have found ways to couple processes where ∆G>0 to ones with ∆G<0 so that the overall free energy decreases (this is much of the point of metabolism--sugar wants to burn, but organisms make sure that it only can when something else useful happens at the same time). Living organisms are also special in having quite a few different reactions where ∆S<0 (burning energy and dumping waste heat to the outside). It's no secret that life exploits chemistry to survive! –  Rex Kerr Jan 4 '13 at 23:00
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Well, personally doubt what you already think about entropy. For a while we were told in schools and universities that the second law of thermodynamics is among the most fundamental laws of Nature. I even saw a book titled "arrow of time" which was trying to define the arrow of time by entropy increasing (or negentropy decreasing) processes toward a maximum entropy content of the whole universe: negative entropy gradient depicts the arrow of time, in the sense that a negative pressure gradient locally depicts the forward flow of a fluid, and a negative voltage gradient guarantees an electrical current and etc. But more that I read and thought about it the more I doubt about the whole issue (in the sense it is usually put forward) and finally I found out that entropy is just a measure of OUR lack of knowledge about the reality, the true order. Increasing entropy is a statistical observation (coarse graining, see here for example), not a real happening. A good question can be to ask how our epistemic knowledge can be such closely related to the real laws of Nature, so that the processes USUALLY happen in a way to reduce our knowledge about the instantaneous phase of a system? That "USUALLY" can then explain why it is not always the case and you can (though not always obviously) find a good number of events that at least locally contradict with this USUAL conclusion. Now you are asking about if local contradictions can be viewed as a definition of "life" (consciousness?) and the other guys have already answered you.

Godspeed

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