Posted by: Xhyra Graf | 7 February 2007

Emergent Properties

http://plato.stanford.edu/entries/properties-emergent/

Emergence is a notorious philosophical term of art. A variety of theorists have appropriated it for their purposes ever since George Henry Lewes gave it a philosophical sense in his 1875 Problems of Life and Mind. We might roughly characterize the shared meaning thus: emergent entities (properties or substances) ‘arise’ out of more fundamental entities and yet are ‘novel’ or ‘irreducible’ with respect to them. (For example, it is sometimes said that consciousness is an emergent property of the brain.) Each of the quoted terms is slippery in its own right, and their specifications yield the varied notions of emergence that we discuss below. There has been renewed interest in emergence within discussions of the behavior of complex systems and debates over the reconcilability of mental causation, intentionality, or consciousness with physicalism.

3. Ontological Emergence

3.1 The Standard Ontology of Emergence: Supervenience Emergentism

Recall that among the British Emergentists, Mill and Broad had a more robustly ontological conception of emergence than the notions discussed immediately above. This is not always transparent in their writings, as they sometimes use epistemological criteria for identifying the metaphysical concept they have in mind. Here we offer a composite picture that captures what is implicit or explicit in a widespread understanding of ontological emergence from that era right up to much recent writing. We dub this view “supervenience emergentism.”

Ontological emergentists see the physical world as entirely constituted by physical structures, simple or composite. But composites are not (always) mere aggregates of the simples. There are layered strata, or levels, of objects, based on increasing complexity. Each new layer is a consequence of the appearance of an interacting range of ‘novel qualities.’ Their novelty is not merely temporal (such as the first instance of a particular geometric configuration), nor the first instance of a particular determinate of a familiar determinable (such as the first instance of mass 157.6819 kg in a contiguous hunk of matter). Instead, it is a novel, fundamental type of property altogether. We might say that it is ‘nonstructural,’ in that the occurrence of the property is not in any sense constituted by the occurrence of more fundamental properties and relations of the object’s parts. Further, newness of property, in this sense, entails new primitive causal powers, reflected in laws which connect complex physical structures to the emergent features. (Broad’s trans-ordinal laws are laws of this sort.)

Emergent laws are fundamental; they are irreducible to laws characterizing properties at lower levels of complexity, even given ideal information as to boundary conditions. Since emergent features have not only same-level effects, but also effects in lower levels, some speak of the view’s commitment to “downward causation” (a phrase originating in Campbell 1974).

3.2 Alternative Conceptions of Ontological Emergence

3.2.1 Emergence as a non-supervening, causal relationship

Timothy O’Connor (2000a, 2000b) contends that the standard construal of emergence as a synchronic supervenience relation is suspect. If token emergent features are metaphysically primitive, their necessary appearance in the right circumstances should admit of causal explanation. This leads him to adopt a non-supervening, dynamical conception of emergence, which relation is nonsynchronic and causal in character. (This work repudiates in part his (1994), which allowed that emergence might be thought of as a species of supervenience.) He argues that supervenience will fail given a dynamical account, once we consider the contribution that other, prior emergent properties play (alongside more fundamental properties) in determining which emergent properties are instanced at a time. As some of these antecedent factors may be indeterministic, there could be two nomological possibilities instancing the same physical properties at t while instancing different emergent properties.[7] O’Connor suggests that dynamical emergence is a promising approach to understanding the relation of mental and neural states. (For more details see O’Connor and Wong (2006), which sets up the dialectical context within which this emergentist view is situated.)

3.2.2 Emergence as ‘fusion’

Paul Humphreys also rejects the general suitability of the formal relation of supervenience of basal conditions to emergent features, and instead favors a metaphysical relation he terms “fusion”: “[Emergent properties] result from an essential interaction [i.e. fusion] between their constituent properties, an interaction that is nomologically necessary for the existence of the emergent property.” Fused entities lose certain of their causal powers and cease to exist as separate entities, and the emergents generated by fusion are characterized by novel causal powers. Humphreys emphasizes that fusion is a “real physical operation, not a mathematical or logical operation on predicative representations of properties.”

To explain the dynamics of fusion, Humphreys makes use of the notion of levels:

(L) There is a hierarchy of levels of properties L0, L1, …, Ln, … of which at least one distinct level is associated with the subject matter of each special science, and Lj cannot be reduced to Li, for any i < j.

He also assumes a Kimian event ontology, where events are property instantiations at a time. Events, so understood, are the relata of causation. (When Humphreys speaks of “property instances,” we take it that he is referring to Kimian events, not tropes.) Humphreys formally represents events as follows: Pmi(x ri) denotes an i-level entity (i.e., xr) instantiating an i-level property (i.e., Pm), for i > 0. Properties and entities are indexed to the first level at which they are instanced. Now let “*” denote the fusion operator. If Pmi(x ri)(t1) and Pni(x si)(t1) are i-level events (i.e., the event of x r‘s exemplifying Pm at t1, etc.), then the fusion of these two events, [Pmi(x ri)(t1)*P ni(xs i)(t1)], produces an i+1-level event, [Pmi*P ni][(xri)+(x si)](t2), which can also be denoted as Pli+1[(xri)+(x si)](t2). The fusion operation is not necessarily causal, but it is a diachronic, dynamic process.[8]

The key feature of a fused event [Pmi*P ni][(xri) + (xsi)](t2) is that it is a unified whole, in the sense that its causal effects cannot be correctly represented in terms of the separate causal effects of its constituents. Moreover, within the fusion the original property instances Pmi(x ri)(t1) and Pni(x si)(t1) no longer exist as separate entities and they do not have all their i-level causal powers available for use at the i+1-level. (But note that the objects themselves will often retain their separate identities, e.g., [(xri) + (xsi)] in the example of fusion above.) Properties that undergo fusion do not realize the i+1 property instance, as supervenient, realized properties would be co-present with subvenient properties. Rather, in the course of fusion the basal conditions become the i+1 property instance. For this reason, supervenience cannot obtain, as the basal conditions do not co-exist with the emergent feature.[9]

4. Possible Applications

Epistemological conceptions of emergence have clear and straightforward applications in current scientific contexts. Indeed, such notions have been carefully defined to capture macroscopic phenomena of current interest within the special sciences.

Whether there are any instances of ontological emergence is highly controversial. Some metaphysicians and philosophers of mind contend that there are strong first-person, introspective grounds for supposing that consciousness, intentionality, and/or human agency are ontologically emergent. The intrinsic qualitative and intentional properties of our experience, they suggest, appear to be of a fundamentally distinct character from the properties described by the physical and biological sciences.[12] And our experience of our own deliberate agency suggests a form of ‘direct’, macroscopic control over the general parameters of our behavior that cannot be reduced to the summation of individual causal interchanges of relevant portions of the cerebral and motor cortex.[13]

Other philosophers reject such appeals to introspection. Some of these grant the appearance but dismiss it as of little evidential value and likely, on indirect grounds, to be illusory.[14] Others deny the emergentist claims about the character of our experience on one of the following grounds: there is no qualitative aspect to conscious experience beyond its intentional or representational content[15]; there is a qualitative aspect to conscious experience that we are able reliably to discriminate but we are not aware of its true, underlying nature (which is neurophysiological)[16]; intentional quality is not an intrinsic and immediately apprehendable feature of experience[17]; in our experience of agency we are not aware of a primitive form of direct, macroscopic control but are simply unaware of the underlying microscopic activities which in fact constitute our control.[18] Note that, if one grants the phenomenological claims of the mind-emergentist while denying their veridicality, one is doing something very different from twentieth-century scientists who debunked vitalist and strong emergentist views about life by uncovering life’s physico-chemical basis. In the latter case, one accepts a challenge to provide a reductionist story of a seemingly unique sort of phenomenon, and meets it by developing better experimental and analytical tools. In the former case, on the other hand, one accepts the claims about how experience and agency seem to us but simply dismisses such seemings as illusory. Here, one is not simply overcoming an argument from ignorance with new, powerful theories; instead, one is doing something rather more like denying the data. (Further, classic empiricist accounts of the justification of our empirical beliefs assume that beliefs about the character of experience are veridical. Rejecting this assumption, it seems, entails a radical overhaul of one’s epistemology, and it may be that this can be accomplished only by giving an implausible, deflationary conception of epistemic justification.)

Adjudicating the case for or against ontological emergence outside the mental realm is equally difficult. The Nobel laureate chemist, Ilya Prigogine, has long suggested that the ‘dissipative structures’ of non-equilibrium thermodynamics involve properties and dynamical principles irreducible to basic physics.[19] More recently, Nobel laureate physicist R.B. Laughlin and others have focused attention on a rich range of “protected” properties — properties that are insensitive to microscopics — of various kinds of macroscopic matter, such as the crystalline state. They argue that the behavior of these properties is well-understood through high-level principles while inexplicable in fundamental physical terms. Laughlin freely used the term “emergent” to describe such states.[20]

With both Prigogine and Laughlin, it is very difficult to tell whether they conceive the phenomena that concern them to be not only epistemologically, but also ontologically, emergent. Consider these assertions in Laughlin and Pine’s manifesto against “reductionism”:

… the generic low-energy properties [of the crystalline state] are determined by a higher organizing principle and nothing else. (p. 29)

The belief on the part of many that the renormalizability of the universe is a constraint on an underlying microscopic Theory of Everything rather than an emergent property is nothing but an unfalsifiable article of faith (p. 29).

And, discussing the quantum Hall effect and the Josephson quantum:

Neither of these things can be deduced from microscopics, and both are transcendent, in that they would continue to be true and to lead to exact results even if the Theory of Everything were changed. Thus the existence of these effects is profoundly important, for it shows us that for at least some fundamental things in nature the Theory of Everything is irrelevant. (pp. 28-29)

The first two assertions can easily be read in context as suggesting a type of ontological emergence. But they stand alongside other claims about the practical impossibility of directly deriving predictions from quantum mechanics for systems containing more than ten particles. So it is also possible to understand Laughlin and Pine as arguing only that science must, as a practical matter, work with high-level principles in dealing with complex systems, and that these principles are confirmed independently of the nature of, or evidence for, our best fundamental theories. (That’s a natural way of reading the third quoted statement.) Finally, one might argue that even if Laughlin and Pine are advancing a stronger, ontological claim, the evidence they adduce clearly supports only an epistemological conception, while being neutral on the question of ontological emergence.

A similarly uncertain verdict, we believe, must be given to Prigogine’s claims in the context of thermodynamics. Still, the apparent independence of various confirmed high-level principles and the practical impossibility of deriving them from fundamental principles suggest that Brian McLaughlin’s (1992) claim that there is ‘not a scintilla of evidence’ in favor of any sort of ontological emergence is overstated or at least highly misleading. The practical difficulties that prevent one from putting the ontological reductionist’s vision to the test can hardly be counted as a strike against the emergentist.

______________________________________

O’Connor, Timothy, Wong, Hong Yu, “Emergent Properties”, The Stanford Encyclopedia of Philosophy (Winter 2006 Edition), Edward N. Zalta (ed.), URL = http://plato.stanford.edu/entries/properties-emergent/

Advertisements

Categories

%d bloggers like this: