|
Emergent properties An emergent behaviour or emergent property can appear when a number of simple entities (agents) operate in an environment, forming more complex behaviours as a collective. If emergence happens over disparate size scales, then the reason is usually a causal relation across different scales. In other words there is often a form of top-down feedback in systems with emergent properties. These are two of the major reasons why emergent behaviour occurs: intricate causal relations across different scales and feedback. The property itself is often unpredictable and unprecedented, and may represent a new level of the system's evolution. The complex behaviour or properties are not a property of any single such entity, nor can they easily be predicted or deduced from behaviour in the lower-level entities: they are irreducible. No physical property of an individual molecule of air would lead one to think that a large collection of them will transmit sound. The shape and behaviour of a flock of birds or shoal of fish are also good examples. One reason why emergent behaviour is hard to predict is that the number of interactions between components of a system increases combinatorially with the number of components, thus potentially allowing for many new and subtle types of behaviour to emerge. For example, the possible interactions between groups of molecules grows enormously with the number of molecules such that it is impossible for a computer to even count the number of arrangements for a system as small as 20 molecules. On the other hand, merely having a large number of interactions is not enough by itself to guarantee emergent behaviour; many of the interactions may be negligible or irrelevant, or may cancel each other out. In some cases, a large number of interactions can in fact work against the emergence of interesting behaviour, by creating a lot of "noise" to drown out any emerging "signal"; the emergent behaviour may need to be temporarily isolated from other interactions before it reaches enough critical mass to be self-supporting. Thus it is not just the sheer number of connections between components which encourages emergence; it is also how these connections are organised. A hierarchical organisation is one example that can generate emergent behaviour (a bureaucracy may behave in a way quite different to that of the individual humans in that bureaucracy); but perhaps more interestingly, emergent behaviour can also arise from more decentralized organisational structures, such as a marketplace. In some cases, the system has to reach a combined threshold of diversity, organisation, and connectivity before emergent behaviour appears. Unintended consequences and side effects are closely related to emergent properties. Luc Steels writes about a system with "emergent functionality" in his paper Towards a Theory of Emergent Functionality: "A component has a particular functionality but this is not recognizable as a subfunction of the global functionality. Instead a component implements a behavior whose side effect contributes to the global functionality ... Each behavior has a side effect and the sum of the side effects gives the desired functionality". In other words, the global or macroscopic functionality of a system with "emergent functionality" is the sum of all "side effects", of all emergent properties and functionalities. Systems with emergent properties or emergent structures may appear to defy entropic principles and the second law of thermodynamics, because they form and increase order despite the lack of command and central control. This is possible because open systems can extract information and order out of the environment. Emergence helps to explain why the fallacy of division is a fallacy. According to an emergent perspective, intelligence emerges from the connections between neurons, and from this perspective it is not necessary to propose a "soul" to account for the fact that brains can be intelligent, even though the individual neurons of which they are made are not. Emergent structures in nature Emergent structures are patterns not created by a single event or rule. There is nothing that commands the system to form a pattern, but instead the interactions of each part to its immediate surroundings causes a complex process which leads to order. One might conclude that emergent structures are more than the sum of their parts because the emergent order will not arise if the various parts are simply coexisting; the interaction of these parts is central. Emergent structures can be found in many natural phenomena, from the physical to the biological domain. For example, the shape of weather phenomena such as hurricanes are emergent structures. Non-living, Physical Systems In physics, emergence is used to describe a property, law, or phenomenon which occurs at macroscopic scales (in space or time) but not at microscopic scales, despite the fact that a macroscopic system can be viewed as a very large ensemble of microscopic systems. Some examples include: Temperature is sometimes used as an example of an emergent macroscopic behavior. In classical dynamics, a snapshot of the instantaneous momenta of a large number of particles at equilibrium is sufficient to find the average kinetic energy per degree of freedom which is proportional to the temperature. For a small number of particles the instantaneous momenta at a given time are not statistically sufficient to determine the temperature of the system. However, using the ergodic hypothesis, the temperature can still be obtained to arbitrary precision by further averaging the momenta over a long enough time. Also, the (constant temperature) canonical distribution is perfectly well defined even for one particle. In thermodynamics, the inverse temperature is found from the change of the system entropy with its internal energy. Some care is required when applying this to finite systems, as this should only be applied in the equilibrium region where the free energy is at a minimum. For small numbers of particles the fluctuations in the internal energy are large and the system only spends some of its time at the free energy minimum. In some theories of particle physics, even such basic structures as mass, space, and time are viewed as emergent phenomena, arising from more fundamental concepts such as the Higgs boson or strings. In some interpretations of quantum mechanics, the perception of a deterministic reality, in which all objects have a definite position, momentum, and so forth, is actually an emergent phenomenon, with the true state of matter being described instead by a wavefunction which need not have a single position or momentum. In distinction from the behavioural sciences, an emergent property need not be more complicated than the underlying non-emergent properties which generate it. For instance, the laws of thermodynamics are remarkably simple, even if the laws which govern the interactions between component particles are complex. The term emergence in physics is thus used not to signify complexity, but rather to distinguish which laws and concepts apply to macroscopic scales, and which ones apply to microscopic scales. It is useful to distinguish three forms of emergence structures. First-order emergence structures occurs as a result of shape interactions (for example, hydrogen bonds in water molecules lead to surface tension). Second-order emergence structures involves shape interactions played out sequentially over time (for example, changing atmospheric conditions as a snowflake falls to the ground build upon and alter its form). Finally, third-order emergence structures is a consequence of shape, time, and heritable instructions. For example, an organism's genetic code sets boundary conditions on the interaction of biological systems in space and time. Living, Biological Systems Emergent structures can be observed in swarms and flocks. Flocking is a well-known behavior in many animal species from swarming locusts to fish and birds. Emergent structures are a favorite strategy found in many animal groups: colonies of ants, piles of termites, swarms of bees, flocks of birds, herds of mammals, shoals/schools of fish, and packs of wolves. A more detailed biological example is an ant colony. The queen does not give direct orders and does not tell the ants what to do. Instead, each ant reacts to stimuli in the form of chemical scent from larvae, other ants, intruders, food and build up of waste, and leaves behind a chemical trail, which, in turn, provides a stimulus to other ants. Here each ant is an autonomous unit that reacts depending only on its local environment and the genetically encoded rules for its variety of ant. Despite the lack of centralized decision making, ant colonies exhibit complex behavior and have even been able to demonstrate the ability to solve geometric problems. For example, colonies routinely find the maximum distance from all colony entrances to dispose of dead bodies. Life is a major source of complexity, and evolution is the major principle or driving force behind life. In this view, evolution is the main reason for the growth of complexity in the natural world. If we speak of the emergence of complex living beings and life-forms, we refer therefore to processes of sudden changes in evolution. Biology (including biological evolution) can be viewed as an emergent property of the laws of chemistry. Chemistry (including the evolution of both elements and molecules over time) can be viewed as an emergent property of the laws of physics. Most of the laws of physics themselves as we experience them today appear to have emerged during the course of time making emergence the most fundamental principle in the universe and raising the question of what might be the most fundamental law of physics from which all others emerged. Emergence in culture and engineering Emergent processes or behaviours can be seen in many places, from any multicellular biological organism to traffic patterns, cities or organizational phenomena in computer simulations and cellular automata. The stock market is an example of emergence on a grand scale. As a whole it precisely regulates the relative prices of companies across the world, yet it has no leader; there is no one entity which controls the workings of the entire market. Agents, or investors, have knowledge of only a limited number of companies within their portfolio, and must follow the regulatory rules of the market. Through the interactions of individual investors the complexity of the stock market as a whole emerges. WWW The World Wide Web (WWW) is a popular example of a decentralized system exhibiting emergent properties. There is no central organization rationing the number of links, yet the number of links pointing to each page follows a power law in which a few pages are linked to many times and most pages are seldom linked to. A related property of the network of links in the world wide web is that almost any pair of pages can be connected to each other through a relatively short chain of links. Although relatively well known now, this property was initially unexpected in an unregulated network. It is shared with many other types of networks called small-world networks. Architecture and Cities Emergent structures appear at many different levels of organization or as spontaneous order. Emergent self-organization appears frequently in cities where no planning or zoning entity predetermined the layout of the city. The interdisciplinary study of emergent behaviours is not generally considered a field, but divided across its application or problem domains. The on-course action and vehicle progression of the 2007 Urban Challenge could possibly regarded as an example of cybernetic emergence. Patterns of road use, nondeterministic obstacle clearance times, etc. will work together to form a complex emergent pattern that can not be deterministically planned in advance. Mathematics Although the above examples of emergence are often contentious, mathematics provides a rigorous basis for defining and demonstrating emergence. In Emergence is coupled to scope, not level, Alex Ryan shows that a Möbius strip has emergent properties. The Möbius strip is a one-sided, one-edged surface. Further, a Möbius strip can be constructed from a set of two-sided, three edged, triangular surfaces. Only the complete set of triangles is one-sided and one-edged: any subset does not share these properties. Therefore, the emergent property can be said to emerge precisely when the final piece of the Möbius strip is put in place. An emergent property is a spatially or temporally extended feature – it is coupled to a definite scope, and cannot be found in any component because the components are associated with a narrower scope. Games Emergent behavior is also important in games and game design. For example, the game of poker, especially in no limit forms without a rigid betting structure, is largely driven by emergent behavior. For example, no rule requires that any player should fold, but usually many players do. Because the game is driven by emergent behavior, play at one poker table might be radically different from that at another, while the rules of the game are exactly the same. Variations of games that develop are examples of emergent metaplay, the predominant catalyst of the evolution of new games. Fads and Beliefs An emergent concept (EC) is a slight variation on consensus reality that is accepted as plausible. The hallmarks of an emergent concept, as opposed to other memes (urban myths, or viruses of the mind) are that EC are increasingly accepted as truth or possibility, based upon other empirical or anecdotal evidence in the mind of the believer or society (in its subsets) as a whole. EC can be viewed as fad, or common causal reality building. EC have no relationship to truth or fact, but are simply engines bringing individual concepts of truth into the mainstream. See also Bibliography The Evolution of Complexity' (2001) Princeton University Press Further reading discussion of emergent vs. natural phenomena and emergent vs. deterministic phenomena; as well as language and markets as examples of emergent phenomena. Specialized Wikis Robotics | |||||||||
|
| ||||||||||
 |
|
| |