The Phenomenon of Self-Organised Criticality
Self-organised criticality is the name given to a phenomena characterised by dynamic systems that possess a critical transition point as an attractor, a state of being on the edge of a phase transition, on the edge of order and chaos, and heavily influenced by local feedback. It is considered a key mechanism by which complexity in natural systems spontaneously arises. I find it to be a beautiful and fascinating phenomena that seems to saturate the dynamics of living systems at all levels of organisation, from individual biomolecules and replication to brain function and consciousness. Wikipedia provides a starting point: https://en.wikipedia.org/wiki/Self-organized_criticality
and some fascinating examples that I’ve had bookmarked for ages and wanted to share include the following.1. Ubiquity & Adaptive Utility of Criticality in Biological SystemsInformation-based fitness and the emergence of criticality in living systems
is an excellent open-access article exploring the importance and power of self-organised criticality in living systems, particularly with regard to their evolution, adaptation, and the cooperation between a community of agents. Article here http://www.pnas.org/content/111/28/10095.full
and summary: Recently, evidence has been mounting that biological systems might operate at the borderline between order and disorder, i.e., near a critical point. A general mathematical framework for understanding this common pattern, explaining the possible origin and role of criticality in living adaptive and evolutionary systems, is still missing. We rationalize this apparently ubiquitous criticality in terms of adaptive and evolutionary functional advantages. We provide an analytical framework, which demonstrates that the optimal response to broadly different changing environments occurs in systems organizing spontaneously—through adaptation or evolution—to the vicinity of a critical point. Furthermore, criticality turns out to be the evolutionary stable outcome of a community of individuals aimed at communicating with each other to create a collective entity.2. Criticality is Crucial for Consciousness and Brain Function
A growing body of experimental evidence suggests that the phenomenon of self-organised criticality is crucial to normal effective brain function and indeed to consciousness itself. As usual Quanta Magazine provides an excellent article titled A Fundamental Theory to Model the Mind
on the history of self-organised criticality and the growing recognition of its importance in brain function here https://www.quantamagazine.org/20140403-a-fundamental-theory-to-model-the-mind/
with excerpt: There can be no phase transitions without a critical point, and without transitions, a complex system cannot adapt. That is why avalanches only show up at criticality, a “sweet spot” where a system is perfectly balanced between order and disorder. They typically occur when the brain is in its normal resting state. Avalanches are a mechanism by which a complex system avoids becoming trapped, or “phase-locked,” in one of two extreme cases. At one extreme, there is too much order, such as during an epileptic seizure; the interactions among elements are too strong and rigid, so the system cannot adapt to changing conditions. At the other, there is too much disorder; the neurons aren’t communicating as much, or aren’t as broadly interconnected throughout the brain, so information can’t spread as efficiently and, once again, the system is unable to adapt.
More recently we had an article in Science Magazine Consciousness may be the product of carefully balanced chaos
discussing how consciousness itself appears to be inherently dependent on the phenomenon of criticality in the brain. Criticality in the brain appears to maximise cortical integration to effectively combine multiple inputs from different sources simultaneously in a single moment. During wakeful consciousness, participants’ brains generated a flurry of ever-changing activity, and the fMRI showed a multitude of overlapping networks activating as the brain integrated its surroundings and generated a moment to moment “flow of consciousness.” After the propofol kicked in, brain networks had reduced connectivity and much less variability over time. The brain seemed to be stuck in a rut, using the same pathways over and over again. The results suggest that, in the brain, there is an optimal level of connectivity between neurons that creates the maximum number of possible pathways. If each neuron can be thought of as a node in the network, consciousness might result from exploring the network as thoroughly as possible.
Interestingly this also appears to provide support for Tononi’s Integrated Information Theory of consciousness. 3. Quantum Criticality, Thermodynamics, and the Inevitability of LIfeThe Origin of Life And The Hidden Role of Quantum Criticality
is another excellent article examining this phenomenon, available here https://medium.com/the-physics-arxiv-blog/the-origin-of-life-and-the-hidden-role-of-quantum-criticality-ca4707924552#.17fxh48lp
. This discusses the importance of self-organised criticality for biomolecules and proteins and the functioning of all life. The biomolecules and proteins exhibit quantum critical conduction profiles and the odds of finding one molecule that stably exhibits a quantum critical state is astronomically small; finding most here suggests an incredibly strong selection pressure for evolution to find these structures. Key excerpt: Quantum criticality describes the behaviour of electrons in large molecules when they occupy the exotic state that sits at the knife edge between conduction and insulation. Most biomolecules are quantum critical conductors; their electronic properties are precisely tuned to the transition point between a metal and an insulator. In other words, biomolecules belong to an entirely new class of conductor that is not bound by the ordinary rules of electron transport, a discovery that has profound implications for our understanding of the nature of life and its origin.
Finally, I think this other excellent article A New Physics Theory of Life
again from Quanta Magazine here https://www.quantamagazine.org/20140122-a-new-physics-theory-of-life/
discusses (what I think is) a closely related phenomena in which thermodynamic efficiency, the ever-more-effective dissipation of heat and energy, drives the inevitable birth of life and self-replicating systems that are much more effective at this than inanimate matter. Another excerpt:When a group of atoms is driven by an external source of energy (like the sun or chemical fuel) and surrounded by a heat bath (like the ocean or atmosphere), it will often gradually restructure itself in order to dissipate increasingly more energy. This could mean that under certain conditions, matter inexorably acquires the key physical attribute associated with life. Self-replication, the process that drives the evolution of life on Earth, is one such mechanism by which a system might dissipate an increasing amount of energy over time.