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An idea struck me as I was walking to class today. According to Wikipedia, entropy is defined as the number of specific ways in which a thermodynamic system may be arranged, commonly understood as a measure of disorder. I believe this is because the more ways you have of arranging an object, the more chance there is of it being completely disordered and random than being ordered and symmetrical and nice looking, though I could be wrong.

So, if this follows, to me the body seems pretty orderly when you are first born and growing up. The perfection of your heart, your brain, blood vessels, muscles, everything seems to fit together, to work together, in perfect harmony. As you grow older though, things start falling apart, diseases riddle your body, muscles atrophy, your brain was no longer the powerhouse it was when you were younger. And I drew up an analogy, perhaps due to the second law of thermodynamics that entropy would always be increasing, perhaps it is simply the entropy of your body that is steadily increasing through time, and that it is not "old age" that kills you but rather entropy.

This all seems pretty logical, but lets take it a step further. According to Boltzmann's entropy formula $S = k_b ln w$ where $k_b$ is the boltzmann constant and $w$ is the number of ways of being arranged, it seems as if to me if we could somehow know the number of ways our bodies could be arranged, that the entropy at a certain time would come out to a number, say 671. It states in wikipedia that this equation is for ideal gases, so I'm not sure if it is very applicable to human beings, there might be another equation generalizing?

If so, and the entropy really does come out to just a number, does that mean that there could be some entropy limit, say if we hit 3771 entropy, we would die? Of all the things I have said today, this seems pretty far-fetched, as we all die at different ages. But the thing is that different circumstances occur to us. Perhaps I broke my leg, and my entropy jumps up by 50 (though I'm not too sure how that works, it didn't really increase the number of states in my body did it).

So, does anything I've written today work? If so I might write a dystopic story about it for fun, where people have entropy clocks in the future.

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  • $\begingroup$ Some insight into this (silly) question four years on; my conception of 'entropy' was incredibly flawed. Entropy is a quantity defined for a closed system, which our body is not. Even if one could define some sensible notion of entropy, one would have to be incredibly careful with associating to formal mathematics (entropy) with informal human ideas (such as 'disorder'); and that even though we can explain entropy in certain simplistic circumstances as 'disorder' that it should not be taken to be a formalism of disorder. $\endgroup$
    – QCD_IS_GOOD
    Sep 25, 2018 at 4:55
  • $\begingroup$ The author of "Death by entropy?" (yes, a question mark could be addes) relatively clearly asks if "entropy really does come out to just a number, does that mean that there could be some entropy limit, say if we hit 3771 entropy, we would die?". In other words, if the body reaches a certain level of entropy, would we die? With a little fantasy, one could interpret the question as: "Is entropy the cause of our death, or is there something else important? Would holding entropy under certain level hold us alive?". There are opposing answers and I think the question should be reopened. $\endgroup$
    – wondering
    Feb 11, 2019 at 14:35

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The aging of the body has nothing to do with entropy. As has been pointed out, the body is not a closed system. It takes in energy all during its life and the overall thermodynamic state of 2 bodies of different ages but identical everything else (such as fat content, state of hydration, and so on) are equivalent. Aging is caused by many factors such as accumulation of lipofuscin in cells making molecular transport less efficient, shortening of telomeres making genetic errors and unrestrained growth more likely, and so on. It is a sort of built-in time-bomb to encourage renewal of the species and evolution. It also prevents overpopulation and the resulting scarcity of resources. Aging occurs, in short, so that the species can adapt to its surroundings in increasingly better ways. The exchange of energy with the environment does not change in kind throughout life.

The universe is another story. Disorder (entropy) increases until eventually time will end when events cease to occur due to the homogeneity of space.

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    $\begingroup$ When you say time will end, do you mean there won't be anyone there to see the progression of time or that the dimension of time will end? $\endgroup$
    – Peter R
    Dec 4, 2015 at 20:56
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    $\begingroup$ Very late. But I mean that there will be no time. Time is not a "thing" but an emergent of our perceptions of motion. Time only "passes" when events occur. In a homogeneous universe, events cease, nothing ever occurs, and time, therefore, no longer exists, nothing ever changes, and because there is no change, there can be no end or beginning. (Time is only a "dimension" in a figurative sort of way - its variables behave like those of the normal 3 dimensions in many equations. But it is only a dimension in that sense and not a real dimension beyond the 3 that we can see.) $\endgroup$
    – Abraxas
    Oct 10, 2016 at 3:40
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    $\begingroup$ How do you define "event" without invoking the concept of time? In other words, how do you have an event following a prior event without time someplace in there? $\endgroup$
    – Peter R
    Oct 11, 2016 at 18:20
  • $\begingroup$ "Aging is caused by many factors such as accumulation of lipofuscin in cells making molecular transport less efficient, shortening of telomeres making genetic errors and unrestrained growth more likely, and so on." Entropy is always towards the most "probable" state, and unorganized systems are much more probable than unorganized ones. Our body fights all the external factors to keep its internal order, until it cant, and dies. All these factors you mention are just examples of increased "disorder" in the system. $\endgroup$
    – PedroD
    May 26, 2020 at 18:56
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Interestingly, I have found an answer to your question in Geoffery West's book, Scale, that seems to contradict Abraxas' statement that the "aging of the body has nothing to do with entropy.

In his discussion on aging and death, G.W. states the following:

All the evidence points to the origins of aging and mortality as being the result of the "wear and tear" processes that unavoidably arise simply from being alive. Like all organisms, we metabolize energy and resources in a highly efficient way in order to combat the continuous fight against the inevitable >production of entropy in the form of waste products and dissipative forces that cause physical damage. As we begin to lose the multiple localized battles against entropy we age, ultimately losing the war and succumbing to death. Entropy kills.

So, there you have it. In case you were wondering, the professor explains that damage from entropy mainly occurs through two mechanisms: viscous drag in blood flow and chemical damage from free radicals.

I recommend you read the entire book of course - it is amazing!

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A trivial proof that this is not so would be to consider a particular human, who has embedded in them a large number of flash drives. The number of flash drives is specifically chosen to have an an amount of entropy greater than the number you choose for the amount of entropy for the living/dead transition. Said person then has a heart attack and dies. It is trivial to see that, thanks to those flash drives, they never cross your particular threshold for the amount of entropy, and yet they died, by our normal definitions.

Likewise, consider how little it takes to render someone brain dead versus the effects of amputating all limbs. Clearly the amputation changes entropy far more, and yet the smallest change in state in the brain is sufficient to render someone brain dead.

In both of these cases, we see that it is necessary to consider more than just entropy in a definition of death.

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