Diagram: Open / Dissipative

Open / Dissipativedefinition/feature.php

Open & dissipative systems, while 'bounded' through with primarily internal interactions,  nonetheless exchange energy with with their external environment.

why does a lobster not eat itself?


A system is considered to be open and dissipative when energy or inputs can be absorbed into the system, and 'waste' discharged. Here, system inputs like heat, energy, food, etc., can traverse the open boundaries of the system and ‘drive’ it towards order: seemingly in violation of the second law of thermodynamics.

In this case, order is achieved within the boundaries of the system because the , disorder of the system is able to dissipate into the surrounding context. Local order (within the system) is thus maintained at the expense of global disorder (within the system and its surrounding context). Were the system to be fully closed from its context, it would be unable to maintain this local order.

Example:

A basic example here is found in the example of Benard/Rayleigh convection Rolls (which is often used when examining complex system behavior). In this example,  we have a fluid in a small Petri dish, heated by a source placed under the dish. The behavior of the fluid is the system that we wish to observe, but this system is not closed: it is subject to the input of heat that traverses the boundary of the Petri dish. Further, while heat can 'get in' to the system, it can also be lost to the air above as the fluid cools. Note that the overall system clearly has a defined 'inside'  (the fluid in the Petri dish), and a defined 'outside' (the surrounding environment and the the heat acting upon the Petri dish), but there is not full closure between the inside and outside. This is what is meant when we say that complex systems are 'open'. We understand them as bounded, (with relations primarily internal to that boundary), but they nonetheless interact in some way with their surroundings. Further, because of this openness, complex systems are able to dissipate their entropy or disorder (which always increases), and export it to the outer side of their boundary. This dissipation of entropy is what allows for an increase of order within the system boundary. Were the boundary fully closed such increase in order could not occur.

Let us turn to the flows driving the system. As heat is increased, the energy of this heat is transferred to the fluid, and the temperature differential between the top and the bottom of the liquid medium causes heated molecules to be driven upwards. At the same time, the force of gravity causes the cooler, heavier molecules to be driven downwards. Finally, the drag forces acting between rising and falling molecules cause their behaviors to become coordinated, resulting in 'roll' patterns associated with Benard convection.

Rayleigh/Benard Convection (fluid of oil/ silver paint)

The roll patterns that we observe are a pattern: a global structure that emerges from the interactions of many agitated molecules without being 'coordinated' by them. What helps drive this coordination is the dynamics of the interacting forces that the molecules are subjected to (heat flows and gravity pressures), as well as how the independent molecular responses to these pressures tend to reinforce one another (through the drag forces exerted between molecules).  That said, the molecules in the fluid solution do nothing on their own, absent the input of heat. Instead, heat is the flow that drives the system behavior. Further, as the intensity of this flow is amplified (more heat added), the behavior of the fluid shifts from that of regular roll patterns to more turbulent patterns.

related terms:

 


Photo Credit and Caption: Underwater image of fish in Moofushi Kandu, Maldives, by Bruno de Giusti (via Wikimedia Commons)

Cite this page:

Wohl, S. (2019, 13 November). Open / Dissipative. Retrieved from https://kapalicarsi.wittmeyer.io/definition/open-dissipative-structures

Open / Dissipative was updated November 13th, 2019.


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