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It is very abstract but I was asked this question recently and unfortunately I was not able to answer it decently enough.

I've seen it coming up in various forums of physics, chemistry or biology. Most of the answers I've read give examples from everyday life or approach the matter more philosophically. I'd appreciate any clarification in this matter.

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    $\begingroup$ The reason you can't answer this question is because it's a "why" question with no satisfactory answer. Why does nature favor lower energy? Why does nature anything? It just does. $\endgroup$
    – Zhe
    Jun 4, 2018 at 14:44
  • $\begingroup$ So there is absolutely no way to, at least partially, justify why? $\endgroup$ Jun 4, 2018 at 15:21
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    $\begingroup$ Well if it didn't then we would have a perpetual source of energy. Lower states of energy are more stable. $\endgroup$ Jun 4, 2018 at 15:36
  • $\begingroup$ Second Law of Thermodynamics. It is less probable that energy once distributed will again concentrate in one place. A ball will not generally get up in air on its own when kept on a table although the the heat energy in the table is enough to push it upwards. $\endgroup$ Jun 4, 2018 at 17:38
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    $\begingroup$ I'm voting to close this question as off-topic because not really about chemistry. $\endgroup$
    – Mithoron
    Jun 4, 2018 at 20:20

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It doesn't. Nature favors higher entropy, and in many situations higher entropy can be achieved by turning potential energy into heat, so it looks like the general proposition is that systems evolve to states of lower energy. In fact, that was considered as a possible general law of nature by early philosophers.

However, there are plenty of counter-examples. For example, consider the smoke from a fire. It rises spontaneously, so the atoms and molecules in it are spontaneously ascending to a higher state of gravitational potential energy. Or a steam engine, in which the flow of heat from a fire can easily do work (compress springs, move objects uphill, run a generator to charge a battery, and otherwise increase the potential energy of things). Very early philosophers rationalized these distinctions by saying that things tended to "seek their own level," with certain things seeking states of low energy and others seeking states of higher. This isn't very satisfactory, of course, because there's no way to determine ahead of time which thing seeks which state. One of the greatest triumphs of 19th century science was to discover the underlying principle of entropy, and that all spontaneous changes can be understood as tending to increase the entropy of the universe.

The question of why nature favors states of higher entropy is much harder to answer, because such a preference is not built into the laws of physics. Basic physics tells us states of higher entropy are favored only when you generally begin in states of low entropy. So far as anyone can tell, the universe generally began in a state of very low entropy, and it has been increasing ever since, and that's the only reason why we observe an evolution to state of higher entropy. Why the universe started off in a state of low entropy, nobody knows.

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  • $\begingroup$ I see. So preference of lower energy levels comes as a sequence of preference for higher entropy levels. Rearding the last part, could we say that it is the result of mere observation of nature? $\endgroup$ Jun 4, 2018 at 17:23
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    $\begingroup$ We don't know. The Second Law (that entropy always increases for spontaneous processes) is an observed fact, but we don't know if it's an "accident" having to do with the initial conditions of the universe (e.g. whether a universe could exist without the Second Law because it had different initial conditions) or whether it's required by some aspect of physical law still unknown to us. $\endgroup$ Jun 4, 2018 at 23:24

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