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Life appears to not follow the second law which states that (approximately speaking) physical systems tend towards more disorder (higher entropy).

This appears to be not true with life which actively manipulates its surroundings. For instance, I spent time every day making my room more orderly. If you consider my room to be a closed system, then my behavior seems to make it more orderly. This, at least at the face level, seems to be a violation of the second law.

Can we reconcile this apparent discrepancy?

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  • Please add details and argument to this question. This question can generate a lot of discussion. – Mark Andrews Sep 3 '20 at 0:38
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    That's because most people get their second law from sloppy formulations in pop-literature. Entropy is supposed to grow in closed systems, i.e. those with no influx of energy. Living systems are open, constantly receiving energy from outside through food or photosynthesis, so the second law does not apply to them in that form. – Conifold Sep 3 '20 at 0:45
  • @MarkAndrews just did. – J Li Sep 3 '20 at 1:47
  • As Conifold said, the key is that life is getting energy from outside. Life dissipates the entropy generated by its internal processes into the environment (thermal radiation for example), and it depends on a steady supply of low-entropy matter or energy to consume. So if you take into account the organism and its environment, the entropy of the whole increases over time, but the organism can maintain a low-entropy state. – Hypnosifl Sep 3 '20 at 3:57
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    (cont.) This feature is not unique to life, see the theory of dissipative structures like the Belousov–Zhabotinsky reaction. – Hypnosifl Sep 3 '20 at 3:59
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Entropy can decrease locally. What the second law requires is that it increase in the system as a whole -- which includes the sun, and all the earth.

Furthermore, the chemical reactions that mediate life must result a decrease in the enthalpy or an increase in the entropy to work, just as with all reactions.

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    Must decrease enthalpy? – Cell Sep 3 '20 at 1:39
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Ill-formed question. There's some misunderstandings that result in wrong conclusions. Please read.

Entropy is a property of a system; remark this, remember this, do not forget this: entropy is related to a specific system; when assessing the entropy of a system, the entropies of its subsystems, neighbouring systems or the supra system are irrelevant.

Now, high entropy means high energy propagation (check the formulae!), a configuration that implies disorder in classical thermodynamical systems, but not in all systems. Some systems could get order after energy is propagated. For example, magnets will align in order in space, metronomes can synchronize at maximum entropy [1], or Benard cells might raise in a boiling fluid.

As you've seen, high entropy might produce order, which means new systems [2]. Let's focus on a single Benard cell. At a large entropy of the container, a new system has been born! (the Benard cell). New systems usually born with low entropy. Now, forget the large entropy of the container and focus on the low entropy of the Benard cell. With time, this cell will increase its internal entropy and get dissipated. In the initial case, a system with a large entropy produces small systems with low entropy. In the second case, the cell, the larger the entropy, the lower the probability of persistence of the cell.

In the previous example, a system generated order with large entropy, and a second system generated disorder with large entropy.

Now, imagine a set of systems that produce order with large entropy. Examples of those are the molecules of a rock, or the cells of a living body. We can even generate artificial systems like those: a commercial organization is an example of a system that generates order when entropy grows (e.g. for some form of energy propagation, the organization tends to get more order and growth).

As you see, nothing new here. Only misunderstandings. High entropy does not mean disorder. It might imply order, and order implies the emergence of new systems with low entropy. A perspective absolutely coherent with normal biological life or just plain existence.

[1] https://youtu.be/T58lGKREubo

[2] Always consider that a system is a subjective perception, not a fact of nature which is independent of an observer.

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The thermodynamic law of increasing entropy applies to any closed system. And only to closed systems.

A living organism is not a closed system, as it interacts with its environment. Because of this, it can decrease its own entropy at the cost of increasing that of its environment even more.

Even when you consider the whole biosphere, or Gaia, in these terms, it receives energy from the Sun which is forever increasing its own entropy, allowing Gaia to decrease hers a little less.

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