Everyday entropy – biomechanics


Myocin power stroke


The difference between biomechanics and industrial mechanics is pass-through entropy.  While the entropy of working fluid in an industrial machine has to be kept separate from the moving parts, entropy passes through biological machines at the molecular level, at the point where the increase in entropy actually drives biomechanics, rather than hindering its efficiency.  Every biomechanical action starts with the random motion of molecules and the probability that some portion of them will react due to higher entropy of the end product so that there is a cascade in  biological machines from food through metabolism to the distribution of action potentials.  In animals, the gut combines with the nervous system to strategically open and shut the pathways so that they both survive, while plants employ chloroplasts to start the chain reaction from sunlight to energy storage units.

While it is possible now to construct a nano-machine, it is very hard to animate it without falling back on the thermodynamic generation of force, where the action fluid is grossly distinct from the drive mechanisms.  Whether the machine is based on high pressure fluid pushing a piston in a cylinder or electromagnetic current passing through wires, the energy source is a large mass of high-momentum particles moving across a pressure or electrons passing over a potential gradient.  The fluid and the windings are grossly distinct from the piston and the drive-shaft.  What this means is that its relatively easy to replace parts in an industrial machine, but almost impossible to repair them while they are working.  The opposite is true of biomechanics, where repairs are continuously taking place, while replacing whole parts is very difficult.  This is why animals use legs while machines use wheels.

Maxwell (of the eponymous demon) and Schroedinger (of the eponymous cat), believed that life had some way of maintaining negative entropy within its skin.  Maxwell considered it a living force, separate from energy, while Schroedinger thought and that it did so through information that could be passed on down generations.  That was before the discovery of DNA, which is amazing, but beside the point.  What life does, by allowing entropy to pass through at the molecular scale, is take advantage of the fact that entropy is energy at that scale, and it generates new relationships at the same rate that old relationships are disintegrating.  By allowing motor molecules to translate DNA into proteins and enzymes, life allows high energy relationships to flow one way while low energy relationships flow another, usually outward.  Unlike Maxwell’s demon, who has to distinguish between high energy molecules that are literally too small and too fast to see, life accumulates high-energy relationships between molecules, but doesn’t separate high energy molecules from low energy molecules.  At that level, energy, entropy and information are indistinguishable, so that all of the processes are powered by the random motion of entropy, rather than the directed motion of thermodynamics.  In a biological machine, the working fluid and the moving parts are indistinguishable.  In most cases, there is no working fluid, only chemical reactions and conforming changes in the working molecules.  (The only obvious contrary example is that spiders use internal pressure to extend their legs.)  In the end, the entropy of life is no more negative locally than the entropy of crystal formation or the entropy of sand dune patterns.  Life fits neatly into the cascade of entropy.  It only appears to be negentropy because the entropy passes through life at a scale that is invisibly small.  Much like an eternally rising Shepard tone progression (or the visual barber pole), the entropy of life increase microscopically without appearing to increase macroscopically because each organism moves on from or expels each wave as it reaches maximum.

The information that makes it all work, the DNA transcription cascade, is just one example of the information side of the physical universe.  DNA is physical, but like electron spin and photon polarity, DNA has curiously non-physical attributes.  The information in DNA may be stored in a physical map, but the information itself is abstract.  Without the bio-mechanical decoders that copy the amino acid sequences and build the proteins, DNA is just a ball of twisted polymer.  Its information is similar to the spin of an electron and the polarity of a photon, which may have physical analogues in the angular momentum and wave motion of macroscopic bodies, but are fundamentally non-physical attributes.  You can’t say that an electron spins like a top or that a photon wiggles like a rope, but the physical analogies allow us to understand the concepts in terms of object that we can experience in a big and visible way.  Nevertheless, even these experiences ultimately come down to the communication of quantum information: photons and virtual photons are the only means we have of measuring physical reality.  But for life, measuring, making and deciding are the same thing, part of a cascade that started a few billion years ago and just never stopped.

With all due respect to the genius of Erwin Schroedinger, negative entropy is a macroscopic illusion created by the microscopic flow of entropy through living organisms, and it isn’t necessary to understand the persistent patterning of living organisms.  At no point does the Shepard tone stop rising, the group just lets go of the highest tone and absorbs a new low tone.  Schroedinger could not have known about the relationship between ATP and the actin-myosin cross-bridge because it was still invisible.

Curiously, pass-through entropy is also the difference between organic and artificial intelligence.  In a computer, the memory, decision and transmission circuits are grossly dissociated from one another, whereas in a living nervous system they are indistinguishable  (“brain-network structure and function form a kind of symbiosis, with cognition depending both on the precise way in which the connectome is wired and on the dynamic patterns of neuronal activity that unfold within the network” – Scientific American).  Whether a thought comes to you as a memory or an idea depends as much on its pathways as its origins, and maybe even the random distribution of calcium ions in and around the channels, which are themselves integral to the form of the information that you finally interpret as a coherent thought.   The abstract information is still binary, but there is no discrete transition from the biomechanical entropy of its core to the measurable information of the nervous outputs.  Everyday entropy – Bohr, body and mind


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