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Universal entropy can decrease only locally at the expense of bigger increase elsewhere.

Can this occur in a lifeless environment or does it necessarily require living organisms to do it?

Can this occur spontaneously or does it have to be an intentionally arranged process, like building a refrigerator?

My assumption is that you need to spend purposeful effort to decrease entropy locally. You need to spend energy to create differences in energy density and you need to have a reason why you do it. Living organisms use energy to create and maintain their internal order for the reason of survival. Inanimate matter has no reason to do anything. Causal uncontrolled processes always go towards higher entropy.

This question seems to enter the grey zone between physics and philosophy. Does a local decrease of entropy require intentional control over the course of events?

Pertti Ruismäki
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    How local is local? – Charles Hudgins Aug 16 '21 at 02:58
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    In a system with maximum entropy any perturbation at all necessarily produces increased local order. – Peter Wone Aug 16 '21 at 04:46
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    This is a very good question IMHO. I don't have time to write a good answer, but a relevant search term is "dissipative structures." – N. Virgo Aug 16 '21 at 12:13
  • Based on your comments to other answers, it looks like you are asking about global decreases rather than local decreases. – BioPhysicist Aug 16 '21 at 13:36
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    The first assumption that may be challenged in the question is that life decreases entropy.

    Here's is an answer to that very issue I find particularly compelling: https://physics.stackexchange.com/a/450742/311469

    A better question might be "What systems are capable of internally decreasing entropy?" of which I doubt life would be one. As work necessitates an increase in entropy my guess would be a system that is capable of producing negative work.

     – Izzy Aug 16 '21 at 15:12
  • The term "local", "expend energy" and "entropy" and "globally" seem to be used in fuzzy ways by this question. Do you mean the physics definition of "local" and "entropy"? "Spend energy" clearly can't use physics meaning, unless you are referring to converting energy to rest mass, or are talking about raising the entropy of energy. You use "energy density", which ... might be an attempt to talk about low entropy? – Yakk Aug 17 '21 at 15:23
  • There is nothing fuzzy about my question. Causal processes always increase entropy. Random noise is inserted in the system in every single quantum event. So I have been told. If this is true, then only non-causal processes can decrease entropy. I am not aware of any other non-causal processes besides life. - This is parallel to Shannon entropy, where noise increases entropy and signal decreases it. I am looking for the "signal" of thermodynamic entropy. – Pertti Ruismäki Aug 18 '21 at 06:51
  • I have a different thought on this from most, here: https://physics.stackexchange.com/questions/758499/is-this-an-existing-interpretation-of-the-measurement-problem?noredirect=1#comment1699096_758499 – scl Apr 07 '23 at 02:09
  • To answer your question directly: I think you need to add the qualifier "sustained" .. so "sustained local decrease of entropy, does it require life?"... and then you'd have to define "sustained"

    There are definitely people who believe so though, and propose that as the definition of life.

     – scl Apr 07 '23 at 02:24

3 Answers3

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No life needed for this. All you need is for heat to flow away from the local region. It will carry entropy with it. Example: make yourself a cup of coffee. Put the cup on a table and wait while it cools. The entropy of the cup of coffee falls (and the entropy of the surrounding air increases).

Andrew Steane
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    Also a lava cooling for example that does not involve life at all. – Maja Piechotka Aug 16 '21 at 03:17
  • The prerequisite is that there be a local entropy be higher than surrounds. Entropy is an emergent quality of systems with uneven excitation, parallel to buoyancy. – Peter Wone Aug 16 '21 at 04:03
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    I am asking about the situation where local entropy is lower than surrounds, further away from equilibrium. Spontaneous cooling increases entropy by distributing energy more evenly. – Pertti Ruismäki Aug 16 '21 at 06:47
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    @PerttiRuismäki ok but could you be more precise? It is temperature not entropy (nor entropy density) which is equalized in equilibrium. Temperature can be lowered by e.g. evaporation or chemical reaction. – Andrew Steane Aug 16 '21 at 07:57
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    @PerttiRuismäki - well, what about the lava cooling example Maciej Piechotka mentioned? Consider a small (imaginary) local region centered around a growing crystal (lava crystalizes into rock); this region has lower entropy than the surroundings (which is a hot soup of melted rock), and its entropy decreases as the crystal grows. It's just that the chosen local region is not an isolated system; life is just another (although vastly more complicated) example of a localized system that's not isolated. – Filip Milovanović Aug 16 '21 at 14:35
  • @FilipMilovanović Entropy is extensive, so any small enough thing must have lower entropy than other bigger things. So I guess you mean entropy per unit volume or per unit mass or something like that. – Andrew Steane Aug 16 '21 at 15:25
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    @AndrewSteane I suppose so (I was trying to address OP's requirement of "local entropy is lower than surround[ing]s", so entropy per unit volume fits that) - but that's more an aside, my point was about the local decrease. – Filip Milovanović Aug 16 '21 at 16:53
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It happens about 50 times in a second in any internal combustion engine, including cars. Without life. Life has no specific meaning in thermodynamical sense.

peterh
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  • But you need life to build the engine. Besides, does an engine decrease local entropy? I understand that a refrigerator does, but I am not sure about the engine. – Pertti Ruismäki Aug 15 '21 at 20:51
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    @PerttiRuismäki Yes, in a 4-phase engine, in at least 1 phases, the local entropy decreases. Yes, life was required to create an ICE engine. – peterh Aug 15 '21 at 22:09
  • Afaik local entropy decrease is not an uncommon thing, it happens always if a medium cools without other significant processes. It can happen any time. – peterh Aug 15 '21 at 22:48
  • Afaik, spontaneous cooling is an entropy increasing process as energy is distributed more evenly towards equilibrium. A refrigerator is the opposite, it uses energy to transfer energy from the cooler inside to the warmer outside, increasing the temperature difference. – Pertti Ruismäki Aug 16 '21 at 03:57
  • If the universe is truly infinite and mostly random, then somewhere out there, space rocks coalesced into a planet-sized internal combustion engine purely by chance. Heck, under those conditions, somewhere out there, a 1965 Ford Mustang materialized out of quantum fluctuations. – user253751 Aug 16 '21 at 09:04
  • @PerttiRuismäki The count of the microstates decreases by the temperature. – peterh Aug 16 '21 at 09:19
  • @user253751 This is a random micro-fluctuation around the equilibric state. Thermodynamics is about the macro-state of the system. There are border-phylosophy thought experiments about that the Universe might be a big quantum fluctuation, and there are even yet more hard ideas around. – peterh Aug 16 '21 at 09:22
  • @peterh As the total energy decreases by the temperature, also the amount of energy available for work decreases. This fact is in conflict with another fact that a decrease in entropy requires insertion of energy. What am I missing here? – Pertti Ruismäki Aug 16 '21 at 09:52
  • @PerttiRuismäki I think enthalpy and similars are only complicating things here. But probably you can calculate it, by substituting things into formulas. I think it is better if you think in the statistical thermodynamical formulation. – peterh Aug 16 '21 at 10:31
  • an internal combustion engine is made and maintained by humans.. for all practical purposes it is part of our living system . – scl Apr 07 '23 at 02:07
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When something hot cools off it loses entropy locally, and its environment gains it.

When an animal eats food and emits heat and waste products, it loses entropy locally, and its environment gains it. The food is converted into higher entropy waste products, and the extracted low entropy is used to maintain the animal.

When an internal combustion engine burns fuel, it loses entropy locally, and its environment gains it. The low-entropy fuel is converted into useful low entropy work, and the higher entropy byproducts are emitted.

All forms of "entropy lowering" require emitting high entropy "waste". To locally reduce entropy, you need to add in low entropy and convert it to waste.

Lava flowing into an ocean. It has lots of heat (entropy), which it loses to the water producing steam (cold water is low entropy input, steam is high entropy waste).

Initial  <-- low entropy input
System   --> high entropy waste
 \/        
Lower entropy system

I suspect the above is what you are getting at. Life tends to do the above a lot.

The trick is that the transfer of entropy from the low entropy input to the higher entropy waste is greater than the lowering of entropy of the system itself.

The game then becomes assigning what is the input, what is the waste and what the system is.

Life, and our inventions, tends to have a clear macro-state "system" you can talk about. But the same thing can happen on molecular scales.

If you have any chemical reaction with two components A and B and two outputs C and D, such that C is lower in entropy then A, it would qualify. To be recognizable, the reaction would also have to cause C and D to separate (like one becomes a gas, the other does not).

Yakk
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  • My understanding of entropy is that in high entropy energy is distributed evenly and in low entropy energy is in lumps of different densities. Therefore lava flowing in ocean seems like a process towards higher entropy. Energy is distributed more evenly, lava cools and the ocean warms up. – Pertti Ruismäki Aug 17 '21 at 03:35
  • @pertti In all processes, entroy becomes higher. There is, in practice, no process where entropy does not increase. If you combine the lava and water systems, entroy goes up; if you just look at the lava locally, entroy goes down; the cold water is low entropy "food", the steam is higher entropy "waste". When I eat, I eat food, then expell heat and higher entropy poop. If you take the system (me+food)->(me+poop+waste heat), entropy went up. Just like lava. – Yakk Aug 17 '21 at 13:15
  • Plants, via photosynthesis, take low entropy light, and co2 and water, and produce lower entropy carbon sugars and waste heat. The system gains entropy; but one of the byproducts (carbon sugars) is lower entroy than one of the inputs (co2 and water). This is counter balanced by the food (low entropy sunlight) vs waste (heat). – Yakk Aug 17 '21 at 13:20
  • In lava cooling the amount of energy available for work does not increase. Temperature differences are not increased, heat is only dispersed and none of it is converted to other forms of energy. In photosynthesis some of the solar energy is converted into chemical energy. – Pertti Ruismäki Aug 17 '21 at 13:49
  • @PerttiRuismäki As I stated in my comment to your question, it looks like you are actually asking about global entropy changes rather than local ones. – BioPhysicist Aug 17 '21 at 13:53
  • @PerttiRuismäki No, the total energy available for work is decreased by photosynthesis? Total entropy goes up. Total entropy always goes up. Life doesn't change that. Lots of heat is converted to other forms of energy -- it breaks water into steam, which isn't heat. The lava becomes solid: again, not heat. By assigning "food", "waste" and "system" to arbitrary before/after subsets, you can have some subsystem have less entropy afterwards; but total entropy went up. – Yakk Aug 17 '21 at 15:19
  • @Yakk Of course total entropy always goes up. I am talking about the entropy of a local subsystem. Hot lava in cool ocean is a low entropy system. There are temperature differences, energy available for work. Cool lava in slightly warmer ocean is a higher entropy system. No temperature differences, no energy available for work. - A plant grows. More and more atoms are organized to build the plant. Energy is converted to chemical energy that is available for work later. The entropy of the plant-surroundings-system is decreased. – Pertti Ruismäki Aug 18 '21 at 03:46