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A biology textbook I once read described humans and other organisms as "moving zones of low entropy", referring to the fact that our bodies display a high level of organization and complexity among the relatively disordered natural environment (of course, all biological processes increase entropy at the scale of the universe, so the 2nd law of thermodynamics is not being violated). I believe this would also apply to things built by intelligent life.

Just as our eyes enable light perception or as birds' beaks enable magnetic field perception, is there any physical mechanism which evolution could use as the basis of an organ for perceiving entropy itself? This seems like it would be extremely evolutionarily adaptive, for example in hunting by enabling the sensing of animals very effectively, or in foraging since plants which produce edible structures are usually more complex than plants that don't. (The organ could just as well be used to detect high entropy entities in a uniformly low entropy environment, such as a rock within a highly complex spacecraft.)

For reference, here is an imagined entry in an encyclopedia for such a creature:

Entropy hunters: creatures that perceive entropy itself. They are feared by biological and cybernetic species alike. However, they are countered by species of which individual members are simple and whose capabilities arise from emergent complexity (e.g. creatures whose intelligence is manifest mostly as a hive mind). More generally, their abilities are rendered useless when the complexity of their target does not substantially differ from that of the environment.

If such an organ is not feasible, or it would be too energetically costly for evolution to possibly implement in a creature, what might be the next most reasonable mechanism by which one could detect entropy or some close proxy of it?

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    $\begingroup$ Aren't those creatures called "teenager's moms"? $\endgroup$
    – L.Dutch
    Jan 24, 2023 at 15:33
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    $\begingroup$ You're treating entropy (a word that identifies the process of order reducing into chaos) as if it's a measurable and objective something. Decay is an expression of entropy. Cooling is an expression of entropy. When scientists describe how much "entropy" a system has, they're simulating a complex system. Having said that, my nose can smell decay. My fingers can feel things colder than I am. My eyes can perceive disorder. In other words, we already have organs that sense entropy. VTC:Needs More Details as you need to describe what manifestation of entropy we're to detect. $\endgroup$
    – JBH
    Jan 24, 2023 at 15:43
  • $\begingroup$ physics.stackexchange.com/questions/129158/… may be useful given the science-based tag. $\endgroup$
    – Jon Custer
    Jan 24, 2023 at 16:24
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    $\begingroup$ My suspicion is that such an organ would not be useful. I assume it's detecting "high degrees of order" aka low entropy but that would mean lots of things set off its sensors: rocks, tree branches, bushes, etc. "Moving areas of low entropy" would be everywhere when it's windy. The best evidence against it being feasible (or useful) is that we don't have examples of it already. $\endgroup$
    – JamieB
    Jan 24, 2023 at 16:24
  • $\begingroup$ @JBH Thanks, I was worried I might be using the term entropy improperly. So when one writes $S=k_b \ln \Omega$, where $\Omega$ is the number of microstates and $k_b$ is the Boltzmann constant, would this not be a singular measure that we can apply to a single entity? Why do we have to think only of processes that result in changes in entropy (e.g. your example of fingers feeling cold which happens when the finger is losing heat to a surface)? $\endgroup$
    – xojfqa
    Jan 24, 2023 at 16:27

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Think smarter, not harder.

While I don't plan on press the same key again, this feel like a pointless thing given what it'd take. For starters, entropy itself is not something that can be observed, only calculated. Add to that how the effects of entropy themselves generate signals many animals can and do detect and we have a situation where the cool organ proves as a waste.

Entropy itself, if I understand correctly, manifests in our world on a macroscopic scale mainly through 3 ways: changes in temperature, changes in appearance and decomposition, and we already have examples of animal senses for all of those. Hell, in the case of changes in appearance you have at least 3 or 4 different types of eyes in the animal world to choose from.

Not long ago I answered a question about a potential new organ capable of detecting water, and my answer to that question was "they already exist in elephants, and they're called trunks". This is a similar scenario, except you want a single organ that does the job of many, and that will not only be impossible, but be potentially worse overall in a scenario where it wasn't, since forcing a single organ to detect many things means it cannot be specialized, and thus can't be as effective as a specialized one (a universal price to be paid in the animal kindgom, Jack of all trades, master of none will be more flexible than the master of one, but they sure as hell won't beat the master in their specialty). The eyes of birds let them see shades of color we never will, shades which make them able to detect what to us would've been a perfectly camouflaged rabbit. Hammerhead sharks have potent electroreceptors in their heads, which allow them to detect basically anything that uses some form of electric signal to function while it's underwater and close enough. Fun fact: those are basically present in basically every form of multicellular animal life on earth. Foxes, as far as we know, use earth's magnetic field to help them hunt prey hidden in the snow, and owls do the thing, but instead relying on asymmetrical ears and potent hearing to be able to detect the exact distance of prey from it with frightening accuracy in 3 dimensions, all that without movable ears, all while bats and dolphins simply use sound to perceive the ambient around them and move around expertly even in absolute darkness, while also be able to tell a lot about what's nearby simply based on how sound bounces off it.

In your example scenario, the goal is to forage for edible fruits. Sure, a magical entropy detector might be able to tell a more complex plant from a less complex one, but will it be able to tell which of the more complex plants is currently producing fruits? Or even if the fruits have nothing poisonous to it in them? While it struggles to figure that out, a monkey with good eyes and a better nose has already found the fruits and could tell both whether they were edible and which were the most fresh. Your entropy organ might be able to allow the creature to sense fish hidden underwater in a river... Only for an electric eel to also come along, be equally able to identify basically everything nearby with a nervous system and zap the ones it liked so it could eat them.

Summing up: could it exist? Probably not, since entropy itself cannot be measured, and even if it could, there's a pretty high chance that it would not be as effective as simply having a large number of already existing sensory organs made to identify different things, many of which are already direct effects of entropy. I get the reasoning, it sounds much cooler to say "we're being hunted by something that can sense entropy itself" in a story than "the thing hunting us has a crazy sense of smell", but the truth is that nature already provides a large array of examples on how you don't need to be able to detect every little aspect of reality to be a good hunter.

To put one last thing in perspective on what makes a good hunter: unless my memory is failing me, the most successful predator in the world is the not-so-humble dragonfly, which can basically catch what it's after 97% of the time. How does it do this? Pristine eyesight and motion detection helps a lot, but being able to use said eyesight to predict where its prey will go helps even more. What it can perceive is only a portion of what makes something successful. How it uses that available information is arguably much more important, especially since koalas are here to demonstrate just that.

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