Interesting; are there real examples of “strongly emergent” systems? The very idea of it does not jive with my intuition.
I found a few places where water was put forth as an example of strong emergence, based on the assertion that we cannot (yet?) derive all the properties of water from the properties of hydrogen, oxygen, and individual H2O molecules. (e.g. Emergent Types – Complexity Labs ) However, no specifics are given, making it difficult to verify if the assertion is even true and to assess whether it is a statement about our current knowledge or whether there are properties of water that in principle will never be explained from a lower-level explanation.
In that same link, quantum entanglement is put forward as another example of strong emergence. I’ll let the actual quantum physicists comment on that one.
If I recall correctly, in Reinventing the Sacred, Stuart Kauffman puts forward an argument that biology is not in principle deducible from chemistry and physics. I don’t know if he called it strong emergence, but I think it might fit the criteria. I will see if I can review that part of the book and provide more specifics.
TL;DR - there are some claims about strongly emergent systems/phenomena floating around, but there doesn’t seem to be a clear consensus on any of them.
Hmm, I suppose a pair of entangled particles do behave in behaviors that is hard to justify from the properties of a couple of unentangled single particles.
There is strange distinction between strong and weak emergence that I have a hard time making sense of here:
A system is said to exhibit strong emergence when its behaviour, or the consequence of its behaviour, exceeds the limits of its constituent parts. Thus the resulting behavioural properties of the system are caused by the interaction of the different layers of that system, but they cannot be derived simply by analysing the rules and individual parts that make up the system.
Weak emergence on the other hand, differs in the sense that whilst the emergent behaviour of the system is the product of interactions between its various layers, that behaviour is entirely encapsulated by the confines of the system itself, and as such, can be fully explained simply though an analysis of interactions between its elemental units.
I’m not sure this is a valid distinction.
I agree the paper is unclear. Here are definitions I have found helpful:
Strong emergence: Higher level entities, properties, etc are governed by laws which are not determined or necessitated by the fundamental laws of physics. Using this definition, vitalism could be viewed as strong emergence from underlying chemistry.
Weak emergence: Whole systems have features which cannot be predicted from their the features of the parts in practice. Chaotic systems are mentioned in this context. Sometimes it is added that the best we can do is predict via simulation.
Downward causation: The whole has metaphysically new causal powers which can then somehow override the causal powers of the parts that interact to make the whole and from which the whole also emerges.
The ITT theory of consciousness says that consciousness emerges only if the parts are arranged in certain complex ways. Assuming consciousness exerts downward causation (eg I consciously will my arm to move), I agree with the article this is strong emergence. IIT is a version of panpsychism. Other versions of panpsychism get around arguing for strong emergence by saying consciousness is a property that a completed physics would include in its fundamental entities, and so is not emergent in the strong sense.
Downward causation can be made metaphysically compatible with physics using complexity theory. Do this by showing that the the dynamics of the parts show they can interact to create new constraints on the phase space of the system (eg bifurcations) which then limit the dynamics of the system in a novel way. So in a sense the whole determines what the parts acting together can do. But not in a strongly emergent sense because that limit depends on the causal powers of the parts.
Based on my initial reading, I agree with the blog author that the criticism of Bayesian theories based on strong emergence is incomplete or wrong. Perhaps the authors criticism is not strong emergence in the above sense, but rather that the theory is mainly mathematical and not motivated by or well-founded in neuroscience. There may be substance in that criticism.
That seems correct to me too. But I think it is different concept from emergence because what QM holism is saying is that the parts are not the the isolated entities of of pre-quantum physics. So any definition of emergence that uses QM for the parts has to allow for entangled wholes as parts.
The Wikipedia definition references computer simulation as the point of demarcation, which I found a little more helpful at least in the sense that I can tell the difference between the presence and absence of a simulation.
However, no source is given for that definition, and it’s not clear what sort of simulation qualifies. For example, we can simulate quantum entanglement, so that does that mean it is not actually an example of strong emergence? Or does it qualify because we have to include entanglement explicitly in the simulation rather than having it emerge from the simulation of individual particles?
So while this definition might be a little bit easier to understand, I’m not sure it actually resolves any of the issues.
OK, the most relevant part of the book is Chapter 4 “The Nonreducibility of Biology to Physics”. Here, Kauffman discusses “epistemological emergence” and “ontological emergence.” Epistemological emergence he defines as “an inability to deduce or infer the emergent higher-level phenomenon from underlying physics” which sounds to me like strong emergence. Ontological emergence “has to do with what constitutes a ‘real’ entity in the universe” which sounds to me like a separate issue entirely.
He goes on to argue that biology and biological organisms are both epistemologically and ontologically emergent, or at least that’s what he says he is arguing although most (all?) of the reasoning seems related to epistemological emergence.
First, he talks about biological functions. For example, the heart both pumps blood and makes thumping sounds. Which is the function of the heart? He says we cannot answer that question by looking at the heart in isolation; you will die if your heart stops pumping blood or if your heart stops making a thumping sound. Instead, we must consider the evolutionary history of the heart. The pumping of blood is what provided a selective advantage to the organism, and so that is the function of the heart. He then claims a physics-based from-the-atoms-up simulation of the heart would generate both features–pumping and thumping–but would not be able to distinguish which is the selected function.
Then he talks about trying to simulate an entire evolutionary history as a way to identify selected functions in a non-emergent way. Ultimately, his argument against this option seems to depend on the idea that spacetime is continuous and so there are uncountably many conditions to account for. I’m not sure this holds up if one takes into account things like the Bekenstein bound and the possibility of quantized spacetime.
Overall, after reviewing the chapter I think it’s possible that Kauffman is begging the question in places, and it’s not clear the concept of ontological emergence actually adds anything to the discussion (there are no examples which exhibit epistemological emergence but not ontological emergence, or vice versa). Still, I think he remains relevant to this thread as someone who is at least making a case for actual systems/phenomena exhibiting something like strong emergence. I also see he has a book coming out later this year titled The World Beyond Physics: The Emergence and Evolution of Life that addresses this topic and perhaps might have an update on his reasoning.
But physics always needs some sort of initial condition (which despite the name, doesn’t have to be prescribed at the beginning) to evolve a system. The laws of physics alone cannot show that Jupiter is going to be located so and so distance away from the Sun - that information needs to be feed (in one way or another) into the system by prescribing an initial condition.
Why is this different in this case? Of course there is no way for the laws of physics alone to identify the evolutionary history that biology on Earth would take. But with a proper initial condition (e.g. the results of evolution today), one can pin down the right evolutionary history and in principle use the laws of physics to simulate the entire evolutionary history.
Kauffman stipulates the initial conditions as part of the simulation and still thinks the end result will be incomplete. Why? Some combination of uncountable infinities and quantum indeterminism. And if we’re invoking quantum determinism – does that mean any system whose macroscopic particulars depend on measurements of quantum mechanical phenomena epistemologically emergent? If that’s the case, we have perhaps cast too wide of a net.
Hmm, so he thinks that even if the initial conditions are given, the result is still incomplete?
Yeah I agree with you, it seems that the net that was cast was too wide.
Kauffman: “The Newtonian scientific framework where we can prestate the variables, the laws among the variables, and the initial and boundary conditions, and then compute the forward behavior of the system, cannot help us predict future states of the biosphere.”