Emergence
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In philosophy, systems theory, science, and art, emergence occurs when a complex entity has properties or behaviors that its parts do not have on their own, and emerge only when they interact in a wider whole.
Emergence plays a central role in theories of integrative levels and of complex systems. For instance, the phenomenon of life as studied in biology is an emergent property of chemistry and physics.
In philosophy, theories that emphasize emergent properties have been called emergentism.[1]
In philosophy
[edit]Philosophers often understand emergence as a claim about the etiology of a system's properties. An emergent property of a system, in this context, is one that is not a property of any component of that system, but is still a feature of the system as a whole. Nicolai Hartmann (1882–1950), one of the first modern philosophers to write on emergence, termed this a categorial novum (new category).[2]
Definitions
[edit]This concept of emergence dates from at least the time of Aristotle.[3] In Heideggerian thought, the notion of emergence is derived from the Greek word poiein, meaning "to make", and refers to a bringing-forth that encompasses not just a process of crafting (techne) but also the broader sense of something coming into being or revealing itself. Heidegger used emerging blossoms and butterflies as examples to illustrate poiêsis as a threshold event where something moves from one state to another.[4] Many scientists and philosophers[5] have written on the concept, including John Stuart Mill (Composition of Causes, 1843)[6] and Julian Huxley[7] (1887–1975).
The philosopher G. H. Lewes coined the term "emergent" in 1875, distinguishing it from the merely "resultant":
Every resultant is either a sum or a difference of the co-operant forces; their sum, when their directions are the same – their difference, when their directions are contrary. Further, every resultant is clearly traceable in its components, because these are homogeneous and commensurable. It is otherwise with emergents, when, instead of adding measurable motion to measurable motion, or things of one kind to other individuals of their kind, there is a co-operation of things of unlike kinds. The emergent is unlike its components insofar as these are incommensurable, and it cannot be reduced to their sum or their difference.[8][9]
Strong and weak emergence
[edit]Usage of the notion "emergence" may generally be subdivided into two perspectives, that of "weak emergence" and "strong emergence". One paper discussing this division is Weak Emergence, by philosopher Mark Bedau. In terms of physical systems, weak emergence is a type of emergence in which the emergent property is amenable to computer simulation or similar forms of after-the-fact analysis (for example, the formation of a traffic jam, the structure of a flock of starlings in flight or a school of fish, or the formation of galaxies). Crucial in these simulations is that the interacting members retain their independence. If not, a new entity is formed with new, emergent properties: this is called strong emergence, which it is argued cannot be simulated, analysed or reduced.[10]
David Chalmers writes that emergence often causes confusion in philosophy and science due to a failure to demarcate strong and weak emergence, which are "quite different concepts".[11]
Some common points between the two notions are that emergence concerns new properties produced as the system grows, which is to say ones which are not shared with its components or prior states. Also, it is assumed that the properties are supervenient rather than metaphysically primitive.[10]
Weak emergence describes new properties arising in systems as a result of the interactions at a fundamental level. However, Bedau stipulates that the properties can be determined only by observing or simulating the system, and not by any process of a reductionist analysis. As a consequence the emerging properties are scale dependent: they are only observable if the system is large enough to exhibit the phenomenon. Chaotic, unpredictable behaviour can be seen as an emergent phenomenon, while at a microscopic scale the behaviour of the constituent parts can be fully deterministic.[citation needed]
Bedau notes that weak emergence is not a universal metaphysical solvent, as the hypothesis that consciousness is weakly emergent would not resolve the traditional philosophical questions about the physicality of consciousness. However, Bedau concludes that adopting this view would provide a precise notion that emergence is involved in consciousness, and second, the notion of weak emergence is metaphysically benign.[10]
Strong emergence describes the direct causal action of a high-level system on its components; qualities produced this way are irreducible to the system's constituent parts.[12] The whole is other than the sum of its parts. It is argued then that no simulation of the system can exist, for such a simulation would itself constitute a reduction of the system to its constituent parts.[10] Physics lacks well-established examples of strong emergence, unless it is interpreted as the impossibility in practice to explain the whole in terms of the parts. Practical impossibility may be a more useful distinction than one in principle, since it is easier to determine and quantify, and does not imply the use of mysterious forces, but simply reflects the limits of our capability.[13]
Viability of strong emergence
[edit]One of the reasons for the importance of distinguishing these two concepts with respect to their difference concerns the relationship of purported emergent properties to science. Some thinkers question the plausibility of strong emergence as contravening our usual understanding of physics. Mark A. Bedau observes:
Although strong emergence is logically possible, it is uncomfortably like magic. How does an irreducible but supervenient downward causal power arise, since by definition it cannot be due to the aggregation of the micro-level potentialities? Such causal powers would be quite unlike anything within our scientific ken. This not only indicates how they will discomfort reasonable forms of materialism. Their mysteriousness will only heighten the traditional worry that emergence entails illegitimately getting something from nothing.[10]
The concern that strong emergence does so entail is that such a consequence must be incompatible with metaphysical principles such as the principle of sufficient reason or the Latin dictum ex nihilo nihil fit, often translated as "nothing comes from nothing".[14]
Strong emergence can be criticized for leading to causal overdetermination. The canonical example concerns emergent mental states (M and M∗) that supervene on physical states (P and P∗) respectively. Let M and M∗ be emergent properties. Let M∗ supervene on base property P∗. What happens when M causes M∗? Jaegwon Kim says:
In our schematic example above, we concluded that M causes M∗ by causing P∗. So M causes P∗. Now, M, as an emergent, must itself have an emergence base property, say P. Now we face a critical question: if an emergent, M, emerges from basal condition P, why cannot P displace M as a cause of any putative effect of M? Why cannot P do all the work in explaining why any alleged effect of M occurred? If causation is understood as nomological (law-based) sufficiency, P, as M's emergence base, is nomologically sufficient for it, and M, as P∗'s cause, is nomologically sufficient for P∗. It follows that P is nomologically sufficient for P∗ and hence qualifies as its cause...If M is somehow retained as a cause, we are faced with the highly implausible consequence that every case of downward causation involves overdetermination (since P remains a cause of P∗ as well). Moreover, this goes against the spirit of emergentism in any case: emergents are supposed to make distinctive and novel causal contributions.[15]
If M is the cause of M∗, then M∗ is overdetermined because M∗ can also be thought of as being determined by P. One escape-route that a strong emergentist could take would be to deny downward causation. However, this would remove the proposed reason that emergent mental states must supervene on physical states, which in turn would call physicalism into question, and thus be unpalatable for some philosophers and physicists.
Carroll and Parola propose a taxonomy that classifies emergent phenomena by how the macro-description relates to the underlying micro-dynamics.[16]
- Type‑0 (Featureless) Emergence
- A coarse-graining map Φ from a micro state space A to a macro state space B that commutes with time evolution, without requiring any further decomposition into subsystems.
- Type‑1 (Local) Emergence
- Emergence where the macro theory is defined in terms of localized collections of micro-subsystems. This category is subdivided into:
- Type‑1a (Direct) Emergence: When the emergence map Φ is algorithmically simple (i.e. compressible), so that the macro behavior is easily deduced from the micro-states.
- Type‑1b (Incompressible) Emergence: When Φ is algorithmically complex (i.e. incompressible), making the macro behavior appear more novel despite being determined by the micro-dynamics.
- Type‑2 (Nonlocal) Emergence
- Cases in which both the micro and macro theories admit subsystem decompositions, yet the macro entities are defined nonlocally with respect to the micro-structure, meaning that macro behavior depends on widely distributed micro information.
- Type‑3 (Augmented) Emergence