Active Matter: A fundamental theory of the living world.

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From flocking birds to swarming molecules, physicists are seeking to understand ‘active matter’

Biologists and physicists have speculated for decades about the generaprinciples of living matter, but research on cellular processes has focused on identifying the dizzying array of molecules involved, rather than on working out the principles by which they self-organize.

Active matter is now the name of a hot new subfield of soft matter physics—one that has literally exploded over the last 15–20 years, with its own journals, its own conferences, its own training programs, its own institutes.  The most extensively studied model, the Vicsek model, which we shall take a peak at below,  dates from 1995. In Vicsek’s words

“A simple model with a novel type of dynamics is introduced in order to investigate the emergence of self-ordered motion in systems of particles with biologically motivated interaction. In our model particles are driven with a constant absolute velocity and at each time step assume the average direction of motion of the particles in their neighborhood with some random perturbation (η) added.”

The term “Active matter” describes systems whose constituent elements consume energy and are thus out-of-equilibrium.   The first definition for the term ‘animate’ given by the  dating from 1398, is: ‘‘Endowed with life, living, alive; … alive and having the power of movement.’’  In this blog we will be focussing on the use of “active matter” as a concept and term for biologist and physicists working in tandem to understand life.

An influential model of active matter , Vicsek’s flocking model was being developed by Vicsek, a theoretical biophysicist in Budapest. In the early 1990s.  The group was among the first to show that complex, life-like structures could self-assemble from microtubules and a few proteins supplied with ATP

This Video from Amazing Biology is very good general review that discusses many of the issues we touch upon here in relation to each other.

Vicsek was trying to account for the collective motions of bird flocks, bacterial colonies and cytoskeleton components when he realized that no existing theory would work. Instead, Vicsek found a starting point in a model of magnetic materials developed in 1928 by German physicist Werner Heisenberg.

To explain active matter, Vicsek replaced the tiny magnets with moving ‘arrows’ symbolizing particles with velocities that aligned with the average velocity of their neighbours — albeit with a certain amount of random error.  His simulations showed that when enough arrows were packed into a small enough space, they began to move in patterns that closely resembled the familiar movements of bird flocks and fish schools

Experiments on biological systems extend over a wide range of scales, including animal groups (e.g., bird flocks, mammalian herds, fish schools and insect swarms ), bacterial colonies, cellular tissues (e.g. epithelial tissue layers, cancer growth and embryogenesis),cytoskeleton components (e.g., in vitro motility assays, actin-myosin networks and molecular-motor driven filaments[ ). Experiments on synthetic systems include self-propelled colloids (e.g., phoretically propelled particles[ ]), driven granular matter (e.g. vibrated monolayers ), swarming robots and Quinke rotators.

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However we might as well just say that “active matter’ is very much just a working model on onr level of how it is that the crucial molecule ATP and its vicissitudes determine all of our organismic life on the biological level. Saying something is “endowed with “anima” is really very much being driven and fueled by ATP in remarkably and multivaried ways. Wherever we look in our bodies in whatever tissue, and in whatever aspect of each tissue we will find ATP.

What happens to it, is what happens to us.  By virtue of their self-motion, active matter systems of all scales trace out a trajectory similar to that of a drunken person: straight, directed movements punctuated by sudden changes in direction. This drunken trajectory engenders a unique mechanical “swim pressure” that dictates the motion and collective behavior of active matter.

All known life forms are based on self-propelled entities uniting to create large-scale structures and movements. These self-propelled entities, of closure, are propelling with energy and, yes, that energy is simply a product of the back and forth between ATP and ADP and that phosphate ion.

If this didn’t happen, organisms would be limited to using much slower, passive processes such as diffusion to move DNA and proteins around inside cells or tissues, and many of life’s complex structures and functions might never have evolved.

Due to the energy consumption, these systems are intrinsically out of thermal equilibrium.. Examples of active matter are schools of fish, flocks of birds, bacteria, artificial self-propelled particles , and self-organising bio-polymers such as microtubules and actin, both of which are part of cytoskeleton of living cells

(NOTE: We have posted often and at length on the nature of the functioning of the brain as a interplay and harmony between two networks that of the astroctyes and that of the neurons and how the two of them generate waves, and then function in the context of the harmony that they have both established via interaction.

In future posts we shall see how it is precisely the interchange and production and disappearance of ATP which is extracellularly trafficked and then intracellularly used as needed.  And we will see how Ca++ ions will be implicated directly as the manner in which the regulation of ATP is conducted and assessed by the glial cells and the neurons and their jointly configured and interactive and harmoniously pulsing networks}

The primary source of cellular energy in the brain is a nutrient known as adenosine triphosphate, or ATP, which the brain requires in prodigious quantities every single minute of every single day.  ATP as the main source of chemical energy in living matter and its involve­ ment in cellular processes has long been recog nized.

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The primary mechanism whereby higher or­ ganisms, including humans, generate ATP is through mitochondrial oxidative phosphorylation. For the majority of organs, the main metabolic fuel is glucose, which in the presence of oxygen under­ goes complete combustion to CO2 and H20:ATP, or adenosine triphosphate, is critical to brain function. Indeed, it’s the second-most important molecule involved in brain function, next to oxygen

Consistently high ATP levels are needed not only for the efficient firing of neurons in the brain, but also to help keep brain tissue alive and functioning at optimal levels as we age.

The free energy ( G) liberated in this exergonic re­ action is partially trapped as ATP in two consecu­tive processes: glycolysis (cytosol) and oxidative phosphorylation (mitochondria).

The first produces 2 mol of ATP per mol of glucose, and the second 36 mol of ATP per mol of glucose. In the latter case, 6 mol of ATP are contributed from the oxidation of 2 mol of NADH generated in the cytosol during gly­ colysis and transferred into the mitochondria indi­ rectly through various “shuttle” systems. (In the a-glycerophosphate shuttle, the yield of ATP per NADH is reduced from 3 to 2 because the relevant mitochondrial dehydrogenase is a avoprotein­ linked enzyme).

Thus, oxidative phosphorylation yields 17-18 times as much useful energy in the form of ATP as can be obtained from the same amount of glucose by glycolysis alone

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Questions that need to be addressed include the following (but which cannot be dealt with here)

First, what are the true, free, concentra­ tions of the high energy phosphate compounds in brain?

Second, how is ATP compartmentalized within the brain?

Third, what are the roles of indi­ vidual reactions that provide and maintain cerebral [ATP]?

Fourth, what are the relative contributions to ATP synthesis from the various parts of the CNS?

Fifth, how is the utilization of ATP distrib­ uted among the various endergonic functions of brain?

Sixth, what are the relationships between en­ergy level and ionic gradients in neurons and glia of mammalian CNS?

Seventh, what other role(s) may ATP play in the function of the CNS?

Here we link to rather accessible but nonetheless extremely informative video about ATP.  We needn’t know everything about ATP to appreciate the current explosion in research and theorizing about ‘active matter”.  and this video certainly doesn’t give us all that.  But when and if we do know everything about ATP we will also know just about everything about “life’ and what makes it happen

We urge the reader to stick with this video and know that it will be in the background of everything else that is said and done by the active matter researchers.

When these objects interact with each other, collective behavior can emerge that is unlike anything possible with an equilibrium system. The types of behaviors and the factors that control them however, remain incompletely understood for most systems.

The domain of interest for those focussing today on Active matter is one where the system is composed of large numbers of active “agents”, each of which consumes energy in order to move or to exert  forces on its neighbors and the environment around it. Its focus is not restricted to microscopic motions—it encompasses all scales, includes schools of fish, flocks of birds, bacterial suspensions, and herds of elephants.

It is importantly not restricted to living matter: it includes the properties of colloids, liquid gels and crystals, as well as those of synthetic chemical or mechanical constructions that exhibit highly correlated collective motions and mechanical stresses like those seen in living matter. Historically, living was divided from dead, inert matter by its autonomous activity. Today, a number of materials not themselves alive are characterized as having inherent activity, and this activity has become the subject of a hot new field of physics, “Active Matter”, or “Soft matter become alive.”

Researchers hope that this work will lead them to a complete, quantitative theory of active matter. Such a theory would build on physicists’ century-old theory of statistical mechanics, which explains how the motion of atoms and molecules gives rise to everyday phenomena such as heat, temperature and pressure.

But it could go much further, providing a mathematical framework for still-mysterious biological processes such as how cells move things around, how they create and maintain their shapes and how they divide.  Over all these centuries, since Descartes isolated the living organisms except for humans as mechanical devices of sorts resident in the realm of matter and thus without any “spirit” or ‘anima” to account for their life, not much conceptual progress has been made.

One of the reasons for this, of course, is that the tacit conceptual framework for producing narratives about organisms and about humans themselves has itself stayed primitive and even barbarian in nature.

http://www.nature.com/news/scientists-print-self-assembling-living-tissue-1.12743

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Keller provides a nice historical view leading us up till the brink of today’s science, Active matter, then and now;,

“For Cartesian mechanists, matter was inert, passive, and conserved , matter is what ‘‘has mass and occupies space; physical substance as distinct from spirit, mind, qualities, actions, etc.’’ Certainly, by itself, such a notion of matter could not be expected to explain very much. As Locke put it, ‘‘Matter, then, by its own Strength, cannot produce in it self so much as Motion’’ (Locke 1690, p. 314).

 Indeed, the intrinsic inactivity of matter was for many mandated by deep theological concerns.2 For Robert Boyle, e.g., the ‘‘vulgar notion of nature’’, its personification as ‘she’ or as a goddess and hence as capable of generating activity, was to ‘‘detract from the honour of the great author and governor of the world’’ (Boyle (1685) 1744, IV,

Newton himself insisted they (sources of motion) were external. For him as for most of his followers, the activity of matter was not intrinsic to matter but induced by principles that remained external, even while their subtle spirit might be everywhere infused. Gravity, for example, can be understood in this framework.

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“Life’’ was not a special category of existence for Newton—that came a hundred years later, primarily with the writings of Jean Baptiste Lamarck. . After a hundred years or more, the living beings were natural phenomena for Lamarck, but they were clearly different from ‘‘inorganic’’ beings and he wanted to understand what accounted for that difference.He wrote,

jean-baptiste-lamarck-2-cjmadden‘‘If we wish to arrive at a real knowledge of what constitutes life, what it consists of, what are the causes and laws which control so wonderful a natural phenomenon, and how life itself can originate those numerous and astonishing phenomena exhibited by living bodies, we must above all pay very close attention to the differences existing between inorganic and living bodies; and for this purpose a comparison must be made between the essential characters of these two kinds of bodies.’’ (Philosophie zoologique, p. 191)

In the Philosophie Zoologique, he offered his definition of ‘Life’: ‘‘an order and a state of things that permit organic movement there; and these movements, which constitute active life, result from the action of a stimulating cause that excites them’’ (Philosophie zoologique, p. 403).

We still, however, see the efforts of those allegedly in the forefront of research, the state of the art work, attempting to base their conjectures on models such as computational devices….with no life anywhere to be seen either within them or in any conceptual reach from their presentations.

But, the study of ‘‘Active matter’’ initially excited attention because of its promise to unify the physical, chemical, and biological sciences—to explain what it is that makes matter come alive.  So far, biology has proven to be a rich source of questions for physicists, and at least some of the efforts of physicists in this field have proven of considerable interest to biologists.

As it happens, these non- equilibrium self-organizing phenomena have turned out to be of tremendous interest qua physics itself.  Physicists have been able to deploy a whole range of tools coming out of recent development in statistical mechanics and fluid dynamics in their analyses.  And thus innovative work in the principles of  biology has begun to inspire physics, much in contrast to the way that uninspired biological theorization was handicapped by uninspired co-option of principles of physics

“We want a theory of the mechanics and statistics of living matter with a status comparable to what’s already been done for collections of dead particles  Even the most enthusiastic proponents of this research admit that no one has yet produced a theory of active matter that describes the behaviour of everything from cell parts to birds.

The burgeoning intellectual symbiosis between the principles of nature as defined by physics and its systems and the principles of nature as defining by biological organisms here works both ways…or at least promises to do so as it flowers.  For biologists, the idea that living matter is active “would be just so obvious as to not really contain very much information”, says Jonathon Howard, a molecular biophysicist at Yale . On the other hand that has not kept proponents from imagining applications such as self-assembling artificial tissue, self-pumping microfluidic devices and new bio-inspired materials

They don’t exactly say what they mean by alive yet, and in most places with the same interests, the term ‘‘active’’ is used instead, and that term refers to systems ‘‘composed of self-driven units, each capable of converting stored or ambient free energy into systematic movement’’ (like protein motors).

‘‘Self-driven’’ is the crucial qualifier here, but self-driven units are not restricted to protein motors: they can also be structures that arise spontaneously (in cells or in micro-fluidic chambers)—structures that are formed not by inherited ‘‘instructions’’ on the DNA, but solely by the internal dynamics of passive rod-like entities (like tubulin elements) suspended in viscous fluids and, crucially, are maintained far from equilibrium. Like the spindle, these structures are steady state (i.e., non-equilib- rium), maintained by the flow of energy through the system. For Keller,

“Where the analogy with Newton’s forces breaks down is between the formation of simple forms of life, in which the excitatory causes of organic movement remained external to the organism, and organisms sufficiently complex to incorporate the ‘‘productive form of movement’’ (and hence, the ‘power of life’) within themselves. Where the simplest forms of life (much like inorganic matter) must rely directly on their environment for the excitation of internal activity, over time, that internal activity itself gives rise to morphogenesis, i.e., to the formation of differentiated structures, and to ever-greater complexity:”

For example in this  study, published only a month or so ago, they explore the ‘ontogeny of collective behavior as revealing a “simple attraction rule”

“The striking patterns of collective animal behavior, including ant trails, bird flocks, and fish schools, can result from local interactions among animals without centralized control’, they write.

“Different interaction rules among animals can produce patterns of collective motion similar to those observed in bird flocks or fish schools. To help distinguish which rules are implemented in animal collectives, we studied the birth of the interaction rule in zebrafish during development from hatching to the juvenile stage. We used newly developed machine vision algorithms to track each animal in a group without mistakes. A weak attraction starts after hatching and gets stronger every day during development. Attraction consists in each larva moving toward one other larva chosen effectively at random and then switching to another one. This rule, simply by statistics, makes each individual move to regions of high density of individuals to produce collective motion.”

This rule makes each individual likely move to a high density of conspecifics, and moving groups naturally emerge. Development of attraction strength corresponds to an increase in the time spent in attraction behavior”

Molecular motors deployed in intra- and extra-cellular motion are interesting in part because they are so dramatic: Watch these processes unfold and you know you are watching life. The notion of ‘self driven” soon leads to the more grand notion of ‘self organization” but it leads there via a pathway that it begins to define for us.

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http://www.nature.com/news/the-tiniest-lego-a-tale-of-nanoscale-motors-rotors-switches-and-pumps-1.18262

IT is true that the proteins of which these motors are made do not themselves arise spontaneously: their amino acid sequences are encoded in the DNA; and these are generally assumed to define their structure—i.e., the transformation from linear sequence to working motor is assumed to require no further information.  This is part of the mythology of programming which has come to support the rather unthoughtful approach to delving into what may be behind life in terms of concepts that require more than arithmetic for the neuroscientists and biologists  to articulate.

In fact, as is suggested by the study quoted above,  intra- and extra-cellular dynamics involve more than genetic information: they seem also to involve many processes crucial to cell division that are induced by the physical and chemical dynamics of all the molecules that make up the cell —processes that break symmetry and form patterns in ways that are not predictable by DNA sequence alone.

“From flocking birds to swarming molecules, physicists are seeking to understand ‘active matter’ — and looking for a fundamental theory of the living world”.  The notion of ‘programming” is a quick and easy sleight of hand to avoid confronting the issues of life, just as the ancillary sidekick to the “programming ” dogma’ that of “information, information everywhere” As it is now clear that gene products function in multiple pathways and the pathways themselves are interconnected in networks, it is obvious that there are many more possible outcomes than there are genes. The genotype, however deeply we analyze it,  and how deeply we believe in the dogma of its ‘program” replacing the Aristotelian essences of olden days, cannot be predictive of the actual phenotype,

Information talk and the chatter of those who believe devoutly in it (and we say “devoutly” because there is no firm foundation for using it as a style of talking than anything else is nothing more than yet another easy way out not much different from “emergence” were the same lackadaisical intellectual approach simply waves its hands at times and says…oh well…phenomena on one level, that we observe with our instruments and eyes…somehow from events on another level.  Poooofff. They just “emerge” LOL  You know like “wetness” emerges from water molecules in interaction?   We can only laugh at this..as we do about the “information” peddlers…

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For these” information integration” peddlers  (such as Tononi et al) while “information” ios just about everywhere they look  yet the concept is  nowhere able to up any sort of narrative  cogent enough to quench any thirst of understanding  of what life might be. “Information, information everywhere “, but alas, there is ” not a drop to drink”. And the DNA of the genes and any kind of “programming “metaphor certainly does not solve that problem

Biological systems have evolved to restrict these phenotypes, and in self-organizing systems the phenotype might depend as much on external conditions and random events as the genome-encoded structure of the molecular components… Yet out of such a potentially nondeterministic world, the organism has fashioned a very stable physiology and embryology. It is this robustness that suggested ‘‘vital forces’’, and it is this robustness that we wish ultimately to understand in terms of chemistry. We will have such an opportunity in this new century.’’ (Kirschner et al. 2000, p. 79).

The common ancestor of life-forms may be now readily assumed to not to be a “modern cell”  This motivates minimal-cell models and protocell models in mathematics nd chemistry Simple embodied non-genetic cell-like structures exhibit behavior, interaction in vicinity, and even duplication3In relation to other protocell models that mimic certain properties of living cells, especially droplet systems share many characteristics with our primordial particle system.

Yet another recent publication  How a life-like system emerges from a simplistic particle motion law. makes this point directly (so the reader need not be diverted by suspicions that this is yet another social media exaggeration(

Self-structuring patterns can be observed all over the universe, from galaxies to molecules to living matter, yet their emergence is waiting for full understanding.

We discovered a simple motion law for moving and interacting self-propelled particles leading to a self-structuring, self-reproducing and self-sustaining life-like system. The patterns emerging within this system resemble patterns found in living organisms. The emergent cells we found show a distinct life cycle and even create their own ecosystem from scratch. These structures grow and reproduce on their own, show self-driven behavior and interact with each other.

Here we analyze the macroscopic properties of the emerging ecology, as well as the microscopic properties of the mechanism that leads to it. Basic properties of the emerging structures (size distributions, longevity) are analyzed as well as their resilience against sensor or actuation noise. Finally, we explore parameter space for potential other candidates of life.

The generality and simplicity of the motion law provokes the thought that one fundamental rule, described by one simple equation yields various structures in nature: it may work on different time- and size scales, ranging from the self-structuring universe, to emergence of living beings, down to the emergent subatomic formation of matter.

We were led to explore this brave new world of “active matter’ where matter proceeds bravely on its own into a new universe where what we know as ‘life” seems to be emerging and coming onto our observational stage for the very first time, via a review aptly entitled “The physics of life”

They report on the coming of age of the pursuit of the active principle in “active matter” in that piece, that in 2012,

“Zvonimir Dogic, a physicist at Brandeis created a new kind of liquid crystal. Unlike the molecules in standard liquid-crystal displays, which passively form patterns in response to electric fields, Dogic’s components were active.

They propelled themselves, taking energy from their environment — in this case, from ATP. And they formed patterns spontaneously, thanks to the collective behaviour of thousands of units moving independently.

 Dogic cand his students took microtubules microtubules — threadlike proteins that make up part of the cell’s internal ‘cytoskeleton’ — and mixed them with kinesins, motor proteins that travel along these threads like trains on a track. Then the researchers suspended droplets of this cocktail in oil and supplied it with the molecular fuel known as adenosine triphosphate (ATP).

To the team’s surprise and delight, the molecules organized themselves into large-scale patterns that swirled on each droplet’s surface. Bundles of microtubules linked by the proteins moved together “like a person crowd-surfing at a concert”

Increasingly, as see these systems are now being made in the laboratory: investigators have synthesized active matter using both biological building blocks such as microtubules, and synthetic components including micrometre-scale, light-sensitive plastic ‘swimmers’ that form structures when someone turns on a lamp.:

Only in the late 2000s did the theoretical and experimental pieces begin coming together. Bausc and his colleagues mixed actin, a filament that forms most of the cytoskeleton of complex cells, with myosin, a molecular motor that ‘walks’ on actin and makes muscles contract.

The researchers added myosin’s natural fuel, ATP, then put the mixture on a microscope slide and watched. “We didn’t do anything; we just added the stuff,” Bausch says. At low concentrations, the actin filaments swam around without recognizable order. But at higher densities, they formed pulsating clusters, swirls and bands.

The resulting patterns were much more complex and dynamic than the ones Bausch saw: the flowing microtubules looked like fingerprint whorls in motion.

Dogic and his team also noticed that the orderly alignment of this flow would occasionally break down and produce ‘defects’: discontinuities in the pattern that resemble converging longitude lines at the North and South poles. These defects were dynamic, moving around like self-propelled particles.

In 2011, Dogic and his colleagues reported that microtubule bundles anchored at one end to air bubbles on a microscope slide beat in synchronized, wave-like patterns eerily reminiscent of the hair-like cilia and flagella that protrude from the surfaces of some cells. And in his 2012 paper he noted a striking similarity between his microtubule flows and cytoplasmic streaming, a process in which cytoskeletal filaments team up to whisk a cell’s contents around like “a giant washing machine”, he says.

No theory at the time could account for this behaviour. But in 2014, Dogic teamed up with Bausch to describe the behaviour of active liquid crystals swirling on spherical vesicles in terms of the movement of defects rather than of individual crystal elements . Furthermore, the group found that it could tune the defects’ motion by adjusting the vesicle’s diameter and surface tension, suggesting a possible way to control an active crystal.

“We’re still kind of astonished at what can happen.”

Lab-made materials remain primitive, however, compared with those produced in cells by billion years of evolution. but Dogic notes that the kinesins he uses are much more efficient than any human-made motors at converting energy to motion

“Whenever videos of spherical microtubule–kinesin systems are present these to cell biologists in particular, they are always fooled,”they think they are seeing a real cell.

But something can look and act like a living organism without actually following the same rules, caution biologist sceptics. They pointout that Dogic’s group created something that looks and acts very much like a cilium or flagellum with its multitude of proteins — but that may, in fact, work very differently.

“There’s something in there about the underlying mechanism, but it’s extremely abstract,” he says.

To probe whether active-matter theory can reveal biological mechanisms, Daniel Needleman, a biophysicist at Harvard studied the spindle: a microtubule-based structure that controls the separation of chromosomes during cell division. He wanted to test the idea, suggested by earlier theories and experiments, that short-range microtubule–kinesin interactions by themselves were sufficient to yield spindle-like structures.

The interactions they observed among closely spaced microtubules are enough to produce the spindle and keep it stable . “People have argued that you need more complex processes,” says Needleman. “But the fact that one can understand so much of the spindle without invoking any of that shows that it’s certainly not necessary.”

Others are using ideas from active matter to probe how large numbers of cells organize in processes such as tissue growth, wound healing and the spread of tumours. Theorists have modelled tissues and tumours as flowing cells that self-organize through short-range cell-to-cell interactions rather than chemical signals.

Importantly, When scientists study crowd movement, they often model people as moving particles that repel each other, similarly to electrostatic charges of the same sign. Skinner and his colleagues expected that the ‘repulsive force’ would depend on the separation in space between the pedestrians, making them change trajectory when they get too close, so as to avoid collisions.

If the electrostatic analogy were correct, the strength of the force would be proportional to the inverse square of the mutual distance, with the repulsion becoming rapidly stronger as two people approach each other. Instead the team found that the force is proportional to the inverse square of the anticipated time to the next collision. In particular, the researchers point out, if two people walk side-by-side — and therefore do not anticipate bumping together — they can do so at very close distance without feeling the need to put more distance in between.

What they point out is a fascinating “aspect”. The behavior of these systems seems to not be ONLY dependent on chemical interactions between neighbors..but merely propinquity counts in some way as well. The question therefore arises of how distance…can include some ‘action at a distance”.

This has always been a philosophical obstacle to physics progress. But there must be a further aspect which is simply an inverse function of distance between two element or ‘individuals”..beyond the chemistry of interaction. That means to me that flocks and swarms should serve as the model for these microcosmic vicissitudes.

Precision formation flight astounds scientists (video)

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This may mean that there is likely some other mode of ‘communication” between the participants is ongoing and allow for the coordination..when the density rises and/or the distance is smaller so that the effects of the “nearness’ interaction overrides the obvious other factors in the space.

We have come across yet more progress in this heretofore uncharted direction to a heretofore unsuspected universe, Flocking ferromagnetic colloids.  As we have noted, Active matter has a strong propensity toward the onset of large-scale collective behavior stemming from a simple alignment interaction between the self-propelled agents. In living systems, collective behavior is exemplified by bacterial swarms, bird flocks, fish schools  Many aspects of collective behavior, at least on a qualitative level, are captured by a paradigmatic Vicsek model for the interacting self-propelled point particles.

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Here the  e authors, who have worked with magnetic colloids bring home the observations the laboratory systems and what they “now see” happening in the lab to the flocking of populations, whether human walkers or flocking birds,  They write,

“We have established that the flocking is an outcome of mostly collisional and magnetic interactions between the particles, whereas the long-range hydrodynamic forces do not have a qualitative effect on the collective behavior….. We have also observed a strong correlation between the onset of flocking and the synchronization of particle motion by the applied ac magnetic field

 Like in living systems, they point out,  flocking behavior is characterized by a spontaneous onset of coherently moving groups of many particles with “assemblies of self-propelled particles: which  are capable of transducing energy stored in the environment into mechanical motion.

However, the flocks do not keep their identity; they often change their direction, break up, and reassemble. Our discrete particle simulations have provided insight into the behavior of our experimental system.

Our work in “control and prediction of collective behavior in out-of-equilibrium colloidal systems”, they write, ” provides fundamental insights into a broad class of active systems, both synthetic and living, where collective motion is caused by a subtle interplay of long- and short-range interactions.

Some biologists hope that such studies will reveal the fundamental principles that govern how cells divide, take shape or move. “It’s like Linnaean classification before Darwin came along,” says biologist Tony Hyman. “We’ve got all these molecules, just like they had all those species, and we need to put some kind of order, some kind of reason behind it all.”

Active matter, Hyman thinks, could provide that reason.

But even enthusiasts admit that mainstream biologists may need convincing. “We used to get a lot of papers rejected at the beginning,” says Hyman — in part because the manuscripts’ heavy use of mathematics made it hard to find reviewers. Even the phrase ‘active matter’ may hinder communication, adds Howard.

“It’s kind of a physics-y term.”

However, happily,  we might add, it is today muchmore of a biological term as well.

More on ATP  and the “Minding” Brain to come.

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