science and meta-science

What is emergence, and why should we care about it?

CarbonEmergence occurs when there is a conceptual discontinuity between two descriptions targeting the same phenomenon. This does not mean that emergence is a purely subjective phenomenon — only that scientific ‘double coverage’ may be a good place to look for emergent phenomena.

For example, in the case of starling murmuration, there is an aggregate description of individual birds, and a description of the flock as a unified entity. The latter phenomenon invites description in terms of concepts from fluid dynamics, but descriptions of individual birds, however detailed, typically do not.

In the case of phase transitions in physics, the description of one phase of matter, such as gas, does not fully map onto descriptions of the other phases. Surface tension, for example, is not defined for gases, since gases do not have surfaces. In the transition from gas to liquid, a qualitatively new attribute not only emerges, it becomes a defining feature of the post-transition system. From a different perspective we can say that it is the emergent qualitative property that enables us to determine that the transition has occurred in the first place. Quantitative readings of some control variable (such as temperature or pressure) cannot themselves be used to mark out ‘events’ — they can only be used to index them.

A common type of theoretical disjunction involves mismatch between descriptions of parts and wholes. A description of micro-level constituents in terms of atomic properties does not lead in any smooth way to descriptions in terms of thermodynamics, hydrodynamics, or solid state physics. In physics, the lack of smoothness in transitioning from one theoretical domain of discourse to another is not always apparent, since the two domains are often well specified mathematically, while the (often ad hoc) linking assumptions enabling the transition are neglected in popular (and even introductory textbook-level) explanations.

Emergence and ontology

The existence of such theoretical non-smoothness is not in doubt. Why then might emergence be considered controversial? Two reasons suggest themselves. The first has to do with the ontological commitments of science in general, and the second has to do with the status of human agency.

As long as scientific theories are understood as descriptions that have restricted domains of usefulness, emergent phenomena and their accompanying theories pose no great threat to science, which in such a framework only has an instrumental goal. But subscribers to a scientific worldview often make a more ambitious claim: that the best theories are isomorphic with the fundamental nature of the universe. In such a framework, a commitment to the unity of scientific theories amounts to a commitment to the integrity and intelligibility of the universe as such. Disjunctions between theories are unpalatable in isomorphic framings of the science-nature relationship, since they seem to suggest that reality itself is not fully law-governed, and therefore contains some irrational or ineffable component. Examples of apparent emergence must then be understood as cases of incomplete theorizing or insufficient computation.

Reductionism can be understood as a combination of (1) the claim that the intelligibility of the universe depends on the unity of scientific theories, and (2) the idea that the most fundamental scientific theories describe the smallest physical parts of the universe. Reductionism can also be relativized to specific scientific disciplines, so that the parts of one discipline (say, cells in the context of organ-level biology) are the wholes of another discipline (cells in the context of molecular biology). Since reductionism has had only infrequent success as a research methodology (especially outside of physics), it must be understood primarily as a metaphysical commitment. Despite its limited usefulness as a guide to scientific practice, reductionism is a powerful cultural idea. We might call it the Lego-block conception of reality: only the Lego blocks are real, so ‘fundamental’ science involves identifying what the blocks are and how they interact, while ‘applied’ science involves discovering the right combination or permutation of blocks that accounts for the phenomenon in question. This perspective is captured in jokes that circulate in physics departments, such as Ernest Rutherford’s line “Science consists of physics and stamp-collecting.”

An emergent phenomenon can always be understood in a reductionist ontology as a situation in which the ‘true’ reductionist theory simply hasn’t been discovered yet, or (if it is understood as already existing) is too computationally intensive to be applied to macro-scale phenomena. Thus from the reductionist perspective, emergence can only ever be “weak” or “epistemic”. Emergentism as a scientific stance must then be understood as making an ontological claim that goes beyond the mere occurrence of apparent emergence: that the intelligibility of the universe does not depend on isomorphism between the universe and the (as yet undiscovered) fully reductionist theory. Emergentism instead suggests the possibility that part-whole relationships may not be fully explainable using causal chains proceeded from parts to wholes. Emergentism therefore raises a possibility that sounds radical and perhaps even meaningless from the reductionist perspective: that parts and wholes have ‘equal’ ontological priority, with the wholes constraining the parts just as much as the parts constrain the wholes. Along with this ontology that departs from strict hierarchy, emergentism may draw attention to the possibility that the universe is in some sense open to novel phenomena that cannot be perfectly anticipated using any scientific theory, but, once present, can still be studied using scientific methods. In other words, emergentism suggests that even our best quantitative theories cannot always tell us when qualitative changes will occur.

The ontological debate between reductionism and emergentism takes on cultural importance in the context of explaining human agency. If phenomena associated with living agents (humans and other biological entities) are ultimately to be explained in terms of their constituent parts, then can causation be attributed to an emergent agent? In other words, do humans cause their actions, or must the ultimate causes be sought at the level of molecular biology? If the latter perspective is taken then human agency becomes a kind of illusion or epiphenomenon, as it restricts causality to ‘fundamental’ entities. Emergentism in this context can therefore be understood as an attempt to create ‘ontic space’ for scientifically coherent forms of human agency.

To explore the implications of ontology on agency, we will need to make explicit our intuitions about what causality is. This challenging and, unsurprisingly, contested topic will* be dealt with in a future essay.



* Assuming my self-model of future behavior is smooth. Which is a big assumption. :P

Image: Eight different allotropes of carbon.

This post grew out of an ongoing journal club on emergence. In this post I haven’t really provided any references, but hopefully in future I’ll do short posts explaining where these ideas came from.

EDIT: the subsequent post is an annotated bibliography of the readings we covered in the journal club.



By Yohan

I'm a Research Assistant Professor at the Neural Systems Laboratory in Boston University. My PhD was in Cognitive and Neural Systems, and my work involves computational neural network modeling of cognitive-emotional interaction and psychiatric disorders. My bachelor's and master's degrees were in physics.

8 replies on “What is emergence, and why should we care about it?”

interesting observation on reductionism … honestly, in all my personal reasonings, I had never considered the scientific approach as ‘divided’, between reductionism and emergentism … before read this article I don’t really considered a division as possible, “obviously those in the sector have already noticed this”; this article, in which I happened by chance, has developed new reasonings in me.

meaning, however, that science, in its human approach (yes, because in the course of its own scientific development, the human being believes to be the only one to develop science and knowledge of the cause, as if any other animal does not develop science in its own and collective reasons), is currently relegated to an excessive importance of the time, the mental capacity of living beings, and however non-existent in space, if not as an ideological perception.

this obsessive giving importance to time in every theory, in every equation, is in my opinion reductionism, because it relegates the human-scientific approach, to one’s brain, rather than in all ‘reality’, a more complex and much wider space.

in conclusion I repeat my last sentence (without chaos of the brackets): I mean, however, that science, in its human approach is currently relegated to an excessive importance of the time.

time doesen’t exist, it’s only an perception.

and … I am not an intermediary, I am myself.

Great blog Yohan. I think I got here from a tweet by Kevin Mitchell (@WiringTheBrain), whose views on human agency seem to be related to yours. I find this topic fascinating. I understand that you’re suggesting the existence of a sort of strong emergence with downward causation, meaning not just that what happens at the emergent level cannot be predicted, even in principle, by a full understanding of the laws governing its component parts, but that the emergent phenomena can in turn affect the behavior of its parts, even at the most fundamental level of physical particles/quantum fields.

It seems that such strong emergence would be at odds with our current understanding of physics, where nothing of the sort is envisioned, as far as I know.

It is, however, an intriguing idea. Perhaps you like it because it may be seen as opening a window for free will? I for one would not see the possibility of downward causation—by consciousness, say—as a possible explanation for free will, or as support for it. For me this strong emergence would be just as “blindly mechanistic” as the laws of physics (as currently understood).

But then it’s hard to understand what the point of consciousness is… In this brief post I suggested that consciousness is just something that evolved from natural selection, not really different, say, than a body organ…:

That view would seem to suggest, however, that consciousness is capable of downward causation. Hard to accept, because I find downward causation implausible—but what purpose would it have otherwise? What does it do? Why is it necessary?

Alternatively, it could be something superfluous (like an evolutionary byproduct that doesn’t really cause anything—equally hard to accept, because consciousness seems to have been exquisitely “designed” by evolution to serve very specific purposes).

Or maybe it’s just an emergent property that “seems” to cause our behavior only at the level suitable for describing human psychology and actions, but not at all at the fundamental level of physics, where everything is “mechanistic”, and where a consideration of consciousness is not at all necessary to predict the trajectory of particles, whether they happen to be in a human body or not. It would be analogous to the mechanism that regulates the constriction or dilation of our pupils according to the light intensity reaching them: we could say that there’s a sort of sensor in our eyes that causes our pupils to behave that way, yet at the fundamental level of physics the knowledge of such sensory mechanism is not needed to predict (in principle) the behavior of all the particles composing the eye as they interact among themselves and with all the external particles affecting them. This is still my preferred view.

My background is actually physics, and it was a physics professor who got me interested in emergence when I was doing my master’s degree. Based on everything I have read, physics does not contradict the idea of downward causation. You just need to use some imagination to get out of the reductionist dead-end. In other words, if you assume reductionist notions of causality to begin with, then obviously downward causation is ruled out. But reductionism is a metaphysical rather than physical theory — no theory or experiment in physics proves (or disproves) reductionism.

I recommend reading the physics citations in my emergence reading list (which is linked here), particularly PW Anderson’s ‘More is Different’ and Robert Batterman’s ‘The Devil in the Details’. In addition, check out Robert Laughlin’s book ‘A Different Universe’, as well as his PNAS paper with David Pines. ‘The Theory of Everything’.

The key physics concept that I think is conducive to a non-reductionist metaphysics is ‘asymptotic freedom’. Robert Batterman’s book goes into this in detail. This paper by him also summarizes the idea:

Click to access found-phys-emerge.pdf

Very broadly, I would disagree with the very claim that micro-level physics is more fundamental than biology. As PW Anderson argues, at each level or scale, symmetries are broken and new laws of science emerge. If we get over our bias that the small is more fundamental than the big, then we can explore some very interesting ontological speculations.

The philosopher Jenann Ismael also has some relevant theorizing, but it focuses more on clarifying what we mean by causality. Most people are unaware that there are several different ways to think about what causality is — I myself only began exploring causality in detail in the last year or so. Here’s a review of her book:

Thanks for the reading recommendations. Lots more to explore here. At present I’m very inclined to agree with Sean Carroll’s skeptical views on strong emergence and downward causation, but I’m open to the possibility that such phenomena exist.

So far I’ve resisted the idea that consciousness is a mere byproduct that doesn’t really cause anything, as it seems so counterintuitive and illogical (especially given, as I stated above, how fine-tuned it seems to be by evolution to work precisely the way it does). Of course believing in downward causation and free will would clear up this conundrum, but so far I find downward causation unpersuasive, and free will incoherent—even if downward causation existed.

I recently came across these lines by Thomas Henry Huxley:

[QUOTE] It may be assumed, then, that molecular changes in the brain are the causes of all the states of consciousness of brutes. Is there any evidence that these states of consciousness may, conversely, cause those molecular changes which give rise to muscular motion? I see no such evidence. The frog walks, hops, swims, and goes through his gymnastic performances quite as well without consciousness, and consequently without volition, as with it; and, if a frog, in his natural state, possesses anything corresponding with what we call volition, there is no reason to think that it is anything but a concomitant of the molecular changes in the brain which form part of the series involved in the production of motion.
The consciousness of brutes would appear to be related to the mechanism of their body simply as a collateral product of its working, and to be as completely without any power of modifying that working as the steam-whistle which accompanies the work of a locomotive engine is without influence upon its machinery. Their volition, if they have any, is an emotion indicative of physical changes, not a cause of such changes.
It is quite true that, to the best of my judgment, the argumentation which applies to brutes holds equally good of men; and, therefore, that all states of consciousness in us, as in them, are immediately caused by molecular changes of the brain-substance. It seems to me that in men, as in brutes, there is no proof that any state of consciousness is the cause of change in the motion of the matter of the organism. [UNQUOTE]

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