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I understand why entropy tends to a maximum; it is the tendency of a system to spend most of its time in the macroscopic state that corresponds to the largest number of phase cell configurations. How does entropy increase with age in humans?

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    $\begingroup$ Wouldn't that presuppose that a human is a closed system? Is that really a valid assumption to make? $\endgroup$
    – Alex Nelson
    Apr 1, 2014 at 2:28

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The law states that entropy increases in isolated systems.

Let us take a cell, as an example of a live organism.

If you isolate a cell, it will die, and the entropy of the isolated system will increase , as an isolated cell cannot live.

All organisms live by continuously decreasing their own entropy and increasing the entropy of the surroundings, considering the earth as the isolated system.

It is simpler to contemplate a crystal coming out of a solution. The crystal forms by decreasing the entropy its equivalent mass has in the liquid but the whole system can be isolated and the entropy increases overall.

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  • $\begingroup$ Thank you for that. Is it through solar radiation (I'm excluding geothermal energy) that most organisms on Earth keep their entropy down? Am I correct in thinking that the photons that reach Earth are of lower entropy than the longer wavelength photons that leave it? i.e. assuming a steady state, more photons leave than enter via Eph = hf $\endgroup$
    – Seanosapien
    Apr 1, 2014 at 13:05
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    $\begingroup$ We have to take in counting entropy as closed system the whole solar system, if we want to count all photons supplying energy to the earth. Then we have to add the positive change in the number of microstates because the system ( in this example) cell + surroundings, through the process of life, i.e. exchange of nutrients etc , increase the number of microstates and thus entropy. For a cell to be alive, it needs, like a crystal, to have symmetries and order, i.e. a smaller number of microstates than the chemicals that give it mass. but cell + suroundings have larger entropy .. $\endgroup$
    – anna v
    Apr 1, 2014 at 13:31

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