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?

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    $\begingroup$ How local is local? $\endgroup$ Aug 16, 2021 at 2:58
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    $\begingroup$ In a system with maximum entropy any perturbation at all necessarily produces increased local order. $\endgroup$
    – Peter Wone
    Aug 16, 2021 at 4:46
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    $\begingroup$ 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." $\endgroup$
    – N. Virgo
    Aug 16, 2021 at 12:13
  • $\begingroup$ Based on your comments to other answers, it looks like you are asking about global decreases rather than local decreases. $\endgroup$ Aug 16, 2021 at 13:36
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    $\begingroup$ 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: 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. $\endgroup$
    – Izzy
    Aug 16, 2021 at 15:12

3 Answers 3


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).

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    $\begingroup$ Also a lava cooling for example that does not involve life at all. $\endgroup$ Aug 16, 2021 at 3:17
  • $\begingroup$ 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. $\endgroup$
    – Peter Wone
    Aug 16, 2021 at 4:03
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    $\begingroup$ 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. $\endgroup$ Aug 16, 2021 at 6:47
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    $\begingroup$ @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. $\endgroup$ Aug 16, 2021 at 7:57
  • $\begingroup$ @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. $\endgroup$ Aug 16, 2021 at 14:35

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.

  • $\begingroup$ 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. $\endgroup$ Aug 15, 2021 at 20:51
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    $\begingroup$ @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. $\endgroup$
    – peterh
    Aug 15, 2021 at 22:09
  • $\begingroup$ 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. $\endgroup$
    – peterh
    Aug 15, 2021 at 22:48
  • $\begingroup$ 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. $\endgroup$ Aug 16, 2021 at 3:57
  • $\begingroup$ 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. $\endgroup$
    – user253751
    Aug 16, 2021 at 9:04

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).

  • $\begingroup$ 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. $\endgroup$ Aug 17, 2021 at 3:35
  • $\begingroup$ @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. $\endgroup$
    – Yakk
    Aug 17, 2021 at 13:15
  • $\begingroup$ 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). $\endgroup$
    – Yakk
    Aug 17, 2021 at 13:20
  • $\begingroup$ 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. $\endgroup$ Aug 17, 2021 at 13:49
  • $\begingroup$ @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. $\endgroup$ Aug 17, 2021 at 13:53

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