Recently I came across some things written on emergent phenomena. While I was searching for “emergence” as a theme and thus was not enlightened about emergence itself, I did come across something interesting in the same domain. This is called downward causation.
Downward causation is when the higher order phenomenon exerts influence on its constituents. This effect, if it can be inferred from the structure of the system is called weak downward causation and if not, strong downward causation. The weak downward causation is relatively simple idea – the parts make the whole and the whole in turn affects the parts; and that the effects of whole on parts are integral to the coming together of parts. The strong downward causation is a much more powerful idea – since in this case the parts do make the whole but it starts to influence parts in ways not foreseeable from the parts alone. A set of new phenomena hence emerges at the level of the whole.
Let us work with an example. If a lot of people walking on a rope bridge decide for some reason to move towards its one side, the rope bridge will tilt to that side and could potentially trip. The whole in this case is influenced by its parts and influences the parts in turn. The fact that the rope bridge turns over is neither unpredictable nor surprising. On the other hand, in equity markets, the stocks constituting an index start to move in a similar direction, they make the index move in that direction. Now some market participants start to get influenced by the overall movement of the index in one direction and that guides their actions regarding the constituents of the index. In this case, the parts move the whole, the whole starts to influence the parts in unpredictable ways.
Another example is the economy. Let us specifically refer to what is called the paradox of thrift. While individually saving is considered a virtue, if everyone starts to save more in an economy, the total and per capita income is bound to fall. In a mathematical identity sense, this is weak form of downward causation since the behavior of the system can be predicted from the parts and their interconnections. Where it may start to become strong form downward causation is if the very act of falling incomes prompts people to save even more thus creating a vicious circle of greater savings and lesser incomes.
The presence of downward causation raises a fundamental epistemological question as regard our methods of enquiry in sciences hard and soft. The reductionist and analytical approach is likely to hit its bounds when dealing with real life due to presence of emergence and downward causation. Stated simply, knowing how electrons and molecules behave will still not tell us how systems like whether evolve and knowing how individuals react to economic incentives will not tell us how the economy will evolve. Granted that the study of parts is a crucial first step in most enquiries. The almost exclusive focus on reductionist methods is quite a limiting feature of our knowledge building endeavour though. In general the reductionist conclusions are aggregated clumsily into larger wholes (as in economics) or left to statistical techniques (e.g. thermodynamics and gas theory) or simply left alone (particle physics vs real objects).
Fritjof Capra draws attention to this in his emphasis on synthetic thinking besides analytical thinking in the pursuit of knowledge. As we grapple with the complexities of real life and real system, and armed with the computational power unheard of just 20 years ago, I suppose we can start to build models of emergent phenomena and downward causation.