Thursday, December 30, 2004

Wrestling with Decoherence

In my amateur attempts to understand quantum mechanics (QM) I realize I have usually either oversimplified or misconstrued the phenomenon known as decoherence. In my mind, I had pictured decoherence as an interaction of a quantum system with the environment that brought about a collapse of superposition states essentially the same way a measurement did in the Copenhagen interpretation of QM. After renewed attempts to understand this topic, (including reading summaries like this), I should say instead that decoherence is an entanglement of the system with its environment. This entanglement involves a sharing of the degrees of freedom of the original coherent system with its environment which leads to creation of a “mixture”. From the perspective of a potential observer, decoherence takes away the interference aspect of the quantum superposition, but it still doesn’t tell the potential observer that a definite outcome of a potential measurement on the mixture has been realized. So, decoherence may account for why quantum interference effects are not seen in our macroscopic world, but it doesn’t remove the quantum measurement effect/problem from the picture at all.Also, while many believe decoherence lends support to one or another interpretation of the measurement problem, it provides no decisive evidence for any of them.

Now having said this, I have read a couple of papers by one of the leaders in the field, Wojciech H. Zurek. He (along with collaborators) seems to be trying to take the program of decoherence farther in the direction of it becoming a replacement for the concept of measurement. As explained in papers such as this and most recently this (see also this brief summary in Nature), the idea is that multiple observers can sample the environment and gain knowledge of a preferred state of a system in question without direct measurement. Decoherence leads to a dissemination of redundant copies of information about the preferred state into the environment such that an observation of any fragment will do the trick. Thus further progress is made explaining why the objective-seeming classical world arises from quantum physics.

This is very good. To understand how a classical-looking world arises from quantum reality is an important project. But it still is a quantum reality.

Despite my mistakes in understanding decoherence, I think some of the issues I’ve focused on seem relatively untouched. It is still true that quantum interactions (whether an observing system is measuring another system or a fragment of the environment or whatever) have a very different nature than classical interactions. I think the issue is sometimes obscured by terminology. Is the interaction a measurement, an observation, or an information transfer? However you put it, there is more going on in these interactions than the classical causal picture of “A” effecting “B”. One or both systems need to have an additional property in order to have a quantum event. This “ability to measure” or “ability to receive information” property is an integral part of the picture. This is in step with Gregg Rosenberg’s postulate of a receptive property in nature discussed in my recent posts. And it continues to make sense to me that incorporating this important aspect of nature into one’s toolkit will help explain consciousness and also perhaps other complex phenomena which resist a reduction to classical mechanics.

The macroscopic world may look classical, but it doesn’t follow that macroscopic phenomena can be explained classically!

Thursday, December 16, 2004

Q&A with Gregg Rosenberg

Gregg Rosenberg was nice enough to correspond with me via e-mail and gave me permission to post this Q&A exchange we had (his answer actually addresses not just my question as posed below but also the related comments I made on my last post here).

Q: My main question is: have you thought any more about the problem of time? In the book, it seemed a bit of a challenge to link the subjective time of consciousness back to the emergence of time (and space) from the causal mesh at a more primitive level (sections 10.6 and 14.3.2). Now, it's very possible I didn't comprehend some of the arguments there, but I was wondering if there is any other way to address the status of time as something which inherently accompanies (not emerges from) causality and experience?

A: I would not say that I divide time in 'subjective' and 'objective' time. Rather I divide it into 'subjective' and 'intersubjective' time, with intersubjective time being a relativistic construction from the structure of the causal mesh. That is, one must pick a node in the mesh and then back into a structure for time relative to that node, so intersubjective time is not an 'objective' view of time. FWIW, I think this view dovetails fairly well with the treatment of these things in quantum loop theory, which is a theory of physics that I find appealing.

Having two things is always less satisfying than having one, so I can understand why you might find my view a bit unsatisfying. Let me do my best to make it more digestible. The two kinds of time are really directed at answering two entirely different questions,

1) Why does experience contain an asymmetric flow?


2) Why does it work when we assign numerical indexes to natural events to mark their locations relative to one another?

My answer to the first question is: because real flow is needed in the world to carry asymmetric constraint within the causal nexus. Since the carriers are experiential, the flow is a flow of experience. This is subjective time.

My answer to the second question is: because each experiencer is a node in a network, and the structure of the network is such that a temporal index is useful for cross-correlating nodes in the network. This is intersubjective time.

So the two kinds of time are really "about" two remarkably different things, though one is modeled analogically on the other. Since the initial questions are about such different things, "time" is actually a very subtly ambiguous word. That's why the final position I come to has two kinds of time.

I don't personally feel as if this is an uncomfortable answer. I think it fits together nicely within the framework and also with observation and science.

BTW, the signaling system I invoke when trying to reduce spatial direction is intended to be local.

Tuesday, December 14, 2004

Rosenberg, Consciousness & Causality (Part 2)

Clearly, I’m a fan of this book. This is no doubt partly because I was already persuaded by the panexperientialist approach to solving the mind/body problem (and I have believed Quantum Mechanics provided evidence for panexperientialism as well). But Rosenberg has added important new strength and depth to panexperientialist ideas by addressing the metaphysical problems posed by causality and showing their connection to the existence of subjective experience in the world. In particular, his system puts forth a credible way to solve the combination problem in showing how experience might participate in causal structures across all levels of nature, including our own “middle” macroscopic level.

In terms of criticism, I was first put off by the fairly complicated nature of the causal model which provided the bulk of the second half of the book. At the level of specificity Rosenberg has given, he has pretty much guaranteed that many details will prove to be wrong in describing our world. There was a part of me that thought the conceptual arguments may have been stronger with less detail (sometimes “less is more”). On the other hand, after getting through it, I thought that the effort could still pay off by showing an example of what to look for as we investigate nature.

To be more specific, it is scientists who need to explicate the receptive/experiential side of nature and find out how it really works. They won’t find anything, of course, until they know what to look for. It is my hope that the irreducible presence of subjective points of view in nature will eventually be taken seriously enough to guide science in new directions. And while it is the case that the “hiddenness” of first-person experience to third-person investigation is an obstacle to investigating this part of the natural world, if Rosenberg is right about the impact the experiential pole has on causality, then it does leave its tracks on nature. Certainly, the interpretation of QM is one area which can be rethought, and the construction of new cosmological theories which include QM will likely be influenced. But I speculate that the other great place to look for evidence of this other aspect of causality is in the area of complex systems. Non-linear dynamical systems display organizational features which are resistant to reduction to micro-physical causation. A new approach may pay dividends here.

My main question about Rosenberg’s approach relates to the concept of time. When giving his examples and diagrams explaining how the effective and receptive properties fit together to form natural individuals in chapters 9 and 10, he pictures this taking place against a fixed background of space and time. Implicitly, space and time are more fundamental entities. Then, in section 10.6, he adds a discussion of how space and time could be seen as emerging from an underlying more fundamental causal mesh.

Here, he says an ingression of an individual from possible to actual is an atemporal process. Then a series of asymmetric connections (he names this a “cascade”) among actualized entities could give rise to time. Then, another step shows how distance in space could be viewed in terms of another set of connections. To make this work, Rosenberg also has to add the ideas of non-local “signals” which propagate between cascades to keep things in sync.

Finally, in section 14.3.2, the attempt is made to link the discussion in 10.6 to the subjective flow of time experienced in human consciousness. Here, he admits the flow of time is not easy to reconcile with the “objective yet panexperientialist” model of nature. So there is a distinction between time in the fundamental picture – Rosenberg decides to call it inter-subjective time (which is derived ultimately from the causal mesh as in section 10.6) -- and subjective time. He then warms up to the existence of subjective time and proposes that this subjective flow “carries” the asymmetry of the causal process which gave rise to time in the first place.

While I admire the effort here, I found this two-fold nature of time somewhat unsatisfying. Rosenberg shows that experience and causality cannot exist without each other, but I would speculate that time itself is part of this relationship in an even more intimate way. There really isn’t any causality or experience except in subjective time - subjective time is the dimension of existence which co-arises with the causal process. There is no “objective” time, and this is OK – we shouldn’t expect any and the notion of true objectivity is an impossibility anyway. Now unlike Rosenberg, I’ve just presented a few bald statements and haven’t worked out anything like a complete competing picture of how this works, so for now I’ll just assert it is a topic worth further thought.

To conclude, I thought this was an excellent and thought-provoking book which really moves the discussion forward toward an improved metaphysics of the natural world. I hope the ideas in it gain circulation.

Monday, December 13, 2004

Rosenberg, Consciousness & Causality (Part 1)

Philosopher Gregg Rosenberg has written a book called A Place for Consciousness: Probing the Deep Structure of the Natural World. The book offers an ambitious new metaphysical proposal for understanding the natural world. It does this by exploring the deep connection between the philosophical problems of consciousness and causality, and then offering a thorough and detailed model for addressing both.

The outline of the book is as follows: first Rosenberg offers his take on the problem of consciousness in the context of contemporary philosophy of mind. Toward the end of this discussion he foreshadows how the issues which need to be addressed in this area connect to the challenges of understanding causality. He then shifts gears to critique past accounts of causality and present his own solution. Finally, he shows the connection between consciousness and causality and how to improve our understanding of both through a unified approach.

From the perspective of a lay reader, I would say that the more background reading you’ve done on these topics, the better you will understand the book. Between my first reading over the summer and my second try recently I read more about causality and this helped. But at the same time, I think there are so many good ideas in the book that I would recommend it to anyone, even if you end up skimming some parts.

It has been somewhat a revelation to me this year to realize the degree to which causality had still posed such a philosophical challenge. We are led to believe that the type of physical theories we have are also good objective causal explanations, but they are not. In showing how the challenges of understanding consciousness and causality are linked and making a proposal for a unified solution, Rosenberg’s book should make it extremely difficult for the reader to consider either topic in isolation from the other going forward.

Below I give a chapter by chapter summary derived from my notes on the book; please note that I can’t claim to be doing justice to the actual arguments here. I will follow this post up with another one containing some concluding thoughts and outstanding questions.
In an introductory chapter, Rosenberg outlines his agenda to provide a place for consciousness within nature. He introduces the term “liberal naturalism” to describe a perspective which looks to uncover some deeper aspects of nature which go beyond physicalism or materialism.

Chapter 2 presents a discussion of the arguments against physicalism. He presents his favorite critique, which builds on ideas which go back to Bertrand Russell and A.N. Whitehead. Physical theories describe quantitative differences and relations, but say nothing about the intrinsic, qualitative nature of being. Conscious experience is constituted by such qualities, and physicalism thus fails to explain conscious experience. As a thought experiment to support this argument, Rosenberg discusses the toy world of the 2-dimensional cellular automaton called the “game of life”. He shows how this toy world is built up from “bare differences” which do not reflect any intrinsic qualities. He then argues that the more complicated physical descriptions of our real world likewise share this shortcoming. I tend to like this argument, and agree with Rosenberg that it is stronger than the “knowledge” argument against physicalism (which, in turn, is stronger than the “conceivability” arguments).
He next spends a chapter detailing and responding to what he sees as physicalist challenges to this argument. Here, I found the discussion rather dense without much additional value-added, and I will be interested to look for responses to the arguments from other philosophers.

Chapter 4 sets out the boundary problem for consciousness. Here Rosenberg discusses something we take for granted – which is the unified and bounded nature of our field of conscious experience. He argues that experience is something which need not necessarily be this well contained. What do we make of the existence of multiple personality disorders? Do sub-components of the brain have any sort of experience? (BTW, see this recent post in Desert Landscapes). This argument prepares us for the discussion of panexperientialism in the next chapters (5&6). By starting with the boundary problem, Rosenberg also wisely introduces at the outset the challenge for panexperientialists (and more modest dual-aspect physicalists) which is usually termed the combination problem. If conscious experience pervades nature, why do certain organized systems have a coherent conscious field (like us) while others appear not to (rocks, galaxies)?

Next, Rosenberg argues the case for panexperientialism while distinguishing it from panpsychism -- the slogan is that experience “outruns” cognition in nature. How can one build consciousness out of parts which lack subjective experience? It is difficult to credit that subjective experience itself could be emergent (see my previous post), although we can more easily understand that certain cognitive capabilities probably are. Anyone who argues experience is limited only to humans (or to suitably cognitive systems) needs to explain why: Rosenberg reviews the candidate explanations for tying experience uniquely to our cognitive systems (arguments from “complexity”, functional arguments, and arguments from biology) and finds them lacking. Panexperientialism is the remaining solution standing.

Still, Rosenberg realizes that adopting a panexperientialist viewpoint leaves us with some key questions and problems (reviewed in chapter 7). Again, accounting for the binding of the perceptual field in space and time remains an issue. But an even bigger problem is that experience seems epiphenomenal. If we assume physics provides a full causal explanation of nature (the causal closure assumption), then if we also conclude that conscious experience exists we necessarily find that it accompanies the physical world, but doesn’t impact it in anyway. Now we know interactionist dualist models make no sense, but a model of the world which says experience and physics somehow move in parallel fashion but never affect each other is also deeply unsatisfying. It seems at this stage we are missing something. The time has come in Rosenberg’s book to shift over to a discussion of causality with the promise of returning to the problem of epiphenomenalism better equipped.

In the second (and longer) part of the book, Rosenberg takes on causality. He starts (chapter 8) by reviewing critiques of the Humean view that what we see as causality is really just a pattern of regularities, not real causal connections based on dependency, constraint or production between events. These critiques include the fact that the Humean view undermines the existence of explanatory physical laws and the fact that the view must presuppose some kind of unity of the world, but it is the assumption of real causal closure which in practice provides the basis for the unity we assume. The Humean view also fails to objectively explain the temporal asymmetry we observe, which seems linked to “real” causality. Finally, Rosenberg asserts that the view has some epistemic problems which lead to extreme skepticism.

So, we need “real” causation (onto chapter 9). If we go back to physics, Rosenberg argues we will find part of the story, but not the whole thing. Physics underexplains causality. Rosenberg argues that association and correlation are shown by physical laws, but while we usually assume they explain causal connections, they really don’t. There is no causal dependency or production going from the state of the system at one point to the state at the next point. One can pretty easily take a Humean view of these laws, but we’ve discussed the problem with taking that route. (I would think that the fact that most laws are time-symmetric lends credence to this argument, but Rosenberg doesn’t use this point, and I infer he thinks the point would be valid even if laws weren’t time-symmetric).

Next, Rosenberg looks at philosophers’ efforts at non-Humean theories of causation, which he specifically classifies as theories of causal responsibility. He thinks these theories get off the wrong foot, because on examination they are not fully objective theories, but somehow fall back on intentional or interest-relative components. (I have thought it is interesting that the implied existence of a subjective point of view is so hard to remove from causation). To get more objective, Rosenberg moves to what he calls a theory of causal significance, which is simpler and has less baggage, compared to causal responsibility. Causal significance focuses on the constraints a thing places on how the world can be, rather than the effects it produces. He frames the difference as one between asking “Why is there something rather than everything?” instead of the usual “Why is there something rather than nothing?”

What types of properties must things possess for there to be causal significance? In a key move, Rosenberg proposes there must be two distinct (though interdependent) types of properties, called effective properties and receptive properties. Effective properties are the sort we usually picture as having the ability to impact other things (and ultimately on us as we investigate the world). It is argued that physics describes these effective properties. But effective properties alone cannot do the full job of real causation. A property of a thing can only be effective if some other thing is receptive to the property’s presence. You can’t have one without the other. And it is this necessary role for receptive properties that other theories have missed.

Further, receptivity is a connective property (and it can be non-local, such as in the case of entangled particles in a coherent quantum system). Importantly, in this model the existence of the receptive pole of causality seems to offer what I would call an extra “degree of freedom” which allows connections to exist at multiple levels of nature, which becomes very important in this overall system. Rosenberg argues that not all causation needs to be at the micro-level of nature, as physicalism assumes. (But the model is not in my view simply asserting some sort of “downward causation”; rather it is a more of a simultaneous multi-level causation). Receptivity can be a shared attribute among multiple systems. This leads to a higher-level causal nexus. In a sense, I interpret receptivity to be something which can provide qualities of organization or participation to a higher level system.

Rosenberg spends several pages detailing this model with notation and diagrams. A few important themes from the later part of the chapter:
When effective and receptive properties are bound together, it creates a natural individual in the world;
The ontology of this model can be considered an event ontology, where the actualization of the natural individual is the event (determination is an actualization);
Individuals seek completion (the filling of their receptive “slots” with effective properties) – this adds a bit of teleology to the model.

Chapter 10 goes over the model again with a toy universe where charge (+ or -) is the only effective property. Importantly, Rosenberg shows how at higher levels of the model, new kinds of laws emerge. He calls these strongly emergent laws, but I’m not sure why—I usually associate the modifier “strongly” with ontological emergence, which I don’t think is what is happening here.

Important ideas from the chapter:
The world as described by the causal significance model is a causal mesh. Causal significance is a system of constraint, and thus implies that an actual world is emerging from a possibility space which itself exists. It is a type of realism with two modes of existence, the possible and the actual; “…causation has no work to do unless there exist real alternatives to actuality.” This metaphysical perspective is compared to the world of quantum mechanics, and to Whitehead. An ingression is a (atemporal) movement from possible to actual.
Late in chapter 10, Rosenberg takes a stab at showing how space and time themselves could emerge from an underlying causal mesh which featured these ingressions. I plan to come back to this topic in my next post.

In chapter 11, Rosenberg returns to the theme that physics underexplains causality. He uses the example of quantum entanglement to show evidence of receptive binding: the system cannot be captured simply from the particles’ physical (effective) properties of mass, spin, charge. He also revisits the game of life world to make the point that physics designates the nature and the regular behaviors of effective properties, but the receptive structure of the world does not ontologically supervene on the facts about low-level effective properties. It is shown by the fact that different sorts of receptive connections could dovetail with the same physical facts. The physical facts suggest the structure of receptive facts, but don’t explain them.

Now it is time to start connecting back to consciousness. In Ch. 12, Rosenberg takes the next key step in his story by introducing the “carrier theory of causation”. Returning to themes from his anti-physicalism arguments in chapter 2, he discusses how physical systems need to be instantiated in the real world; an example is the instantiation of the game of life on a checkerboard or computer. The qualities of the checkerboard or computer “outrun” or are “extrinsic” to the system. If you look at physics, the same thing is true. Physical concepts are circular- they are difference relations which don’t “sit on” anything else. There must be a wider system of properties on which these differences and relations are instantiated. These properties are called carriers. He then argues that phenomenal properties are perfect candidates to be carriers. Phenomenal properties are differentiated yet qualitative and are extrinsic within a system (their nature is not exhausted by the difference relations in the system). So, it is postulated that phenomenal properties are the carriers of the effective properties described by physics.

So what carries receptive properties? An experiential property. Experiencing carries receptivity. Putting it together, a natural individual is one which experiences phenomenal properties. Each event is an individual experience of phenomenal properties. This is a panexperientialist model, where each event in the world is proto-conscious, by virtue of having some sort of experience.

Finally, how do we build up from this to explain human consciousness? Well, each consciousness is a cognitively structured high-level individual with an experiential receptive field.

In Ch. 13, this model is tested for how it addresses problems from recent work in the philosophy of mind. The status of knowledge is discussed: here it is argued that the binding of causal connections provides a kind of direct acquaintance with the world. It is argued that the consciousness model addresses both the binding and epiphenomenon issues from chapter 7.

Other applications of the model to commonly discussed problems follow in chapter 14, including additional discussion of emergence, and the relationship between this model and functionalism. While most forms of functionalism are false, there is a consistency with a more modest sort of non-reductive functionalism. Additional sections address the subjective flow of time and possible contributions to cognitive neuroscience. These sections are brief pointers toward possible future work.

But the real substance of the book is metaphysics, and this is where it makes such a valuable contribution. Chapter 15 is a brief summary of what the theory means for how we should view the natural world and the individuals in it.

Thursday, December 09, 2004

Purpose, but not "Higher Purpose"

I want to briefly clarify what I mean when I speculate that first-person purposeful experience is a part of the natural world. Using the word purpose can lead to misunderstanding because it is so often part of the construction “higher purpose”. Because I subscribe to philosophical (or metaphysical) naturalism, I do not believe the world includes supernatural entities or interventions. Thus in investigating the world there is no appealing to “higher purpose” (or “intelligent design”, for that matter).

But I believe naturalism can and should include first-person experience as an ingredient in the fabric of the world (the philosophical position known as panexperientialism). I have further speculated that this experiential element does some work in the world, and this work consists of the modification of natural events to serve the purpose of the participating experiencing system. This happens within a limited scope consistent with our observations of physical phenomena. Further out on a limb, I speculate that it is at the subtle level of quantum events (measurements) that this modification takes place in nature.

Now, I may be wrong about all this, but it won’t be because it is inconsistent with the methods or prior findings of science. The room for my speculations is opened up due to the fact that the prevailing materialist or physicalist versions of naturalism fail to account for first-person experience. And modifying or expanding naturalism to include experience need not lead to any slippery slopes to irrational or supernatural beliefs.

Wednesday, December 08, 2004

Morals Predate Religion

I haven’t read much lately on evolutionary psychology or game theory, but enjoyed reading this talk by Karl Sigmund on Those who have followed this area even casually know that researchers have offered compelling reasons to think that diverse impulses such as generosity, altruism, cooperation, forgiveness, a sense of fairness, care for reputation and a desire to punish defectors are all grounded in natural selection. The combination of enlightened self-interest and our development as inherently social animals provided the basis for these impulses, which formed the backdrop for the later cultural evolution of moral codes and precepts in oral and written form.

Now, many have written eloquently on the topic of having why it is possible to have morality without religion. See for example this post from AnalPhilosopher. I think it seals the arguments to also note that morality predates religion (unless you are a “young-earth” creationist!)

Many are now studying the origins of religion itself from an evolutionary standpoint, but my impression is that this is a complex subject and there is no consensus yet on key points. However, it is pretty easy to speculate on the advantageous roles religion could have played in strengthening a pre-existing moral system among a social group (it seems obvious to anyone who is a parent): Religion adds both putative authority and a promise of punishment/reward to moral instructions, thereby giving them some extra oomph.

Friday, December 03, 2004

Do Quantum Effects Explain Consciousness?

There is a new posting on the Stanford Encyclopedia of Philosophy on “Quantum Approaches to Consciousness”. The summary is written by Harald Atmanspacher.

It seems natural that the intriguing features of quantum mechnanics (QM), such as the duality of observing and observed systems and the notion of a collapse of superposition states, would over time get pressed into service to try to shed light on the problem of consciousness. Atmanspacher gives a brief taxonomy of several such efforts.

The aspect of this I’m commenting on is the attempts by several philosophers and physicists to postulate that it is macroscopic-size components of the human brain which implement quantum effects thereby helping explain the mysterious nature of human consciousness as it relates to phenomenal experience and/or free will, etc. I think these efforts are looking in the wrong place to find the connection between QM and consciousness.

Guided by other critiques (like this one), I’m very skeptical that macroscopic quantum coherence can be maintained in the brain sufficient to, say, orchestrate collapses of quantum superposition states which affect whole neuronal assemblies. The evidence I’ve seen from experimental accounts suggests that coherence is very fragile, and that while progress is being made at preserving coherence for larger molecules in the laboratory, the likelihood of the warm, wet brain supporting macroscopic coherence seems the longest of long shots.

Nevertheless, I think quantum effects do provide evidence for the existence of a proto-experiential element within nature (see my previous post). But it seems it must be the case that this is instantiated at the microscopic level where decoherence typically occurs. Then, the question becomes whether and how macroscopic systems are able to leverage this part of nature into something robustly experiential. The answer to this must come from the systems’ functional organization and complexity.

Now, the brain is a compelling unique object in our world – it is the most complex system there is. Furthermore the living cells within our brain have an extremely intricate structure themselves. And therefore I think we can expect that this incredibly complex functional organization forms the basis for the remarkable features of our mind up to and including our reflective stream of self-consciousness.

So, going back to David Chalmer’s separation of consciousness studies into the “easy problems” (explaining the workings of various cognitive sub-systems like sensory perception, memory, etc.) and the “hard problem” (explaining the existence of subjective experience itself): I think QM provides evidence for the existence of a panexperientialist solution to the hard problem at a micro-level in nature. Therefore I think it follows that analyzing the functional organization of the brain and its cells will eventually provide explanations for the easy problems, including what I might call the “hardest easy problem”: the way the brain leverages the proto-experiential nature of its very small parts into the robust consciousness which we humans uniquely enjoy in the world.

I admit I have no idea at this point how this works, but I think the functional coordination of the quantum interactions we know to be occurring at the microscopic level is the place to look for consciousness.

Wednesday, December 01, 2004

Methodological vs. Metaphysical Naturalism

Recently there was this post on The Panda’s Thumb (the group evolution blog) introducing a new contributor, Henry Neufeld, whose professional field is biblical scholarship. He is both a theist as well as a defender of evolution. This led to some discussion on the blog about the compatibility of these stances. Also on the relationship between the creationism/evolution divide and the theism/atheism divide see this blog entry from Dispatches from the Culture Wars.

I listened to a talk by philosopher Paul Draper awhile back on the topic of “God, Science and Naturalism”. Part of his talk highlighted a distinction between methodological naturalism and metaphysical naturalism. Now, not everyone agrees on the definitions of these terms, so let me give the impression I got from Prof. Draper. Accepting methodological naturalism means that one accepts that in our collective efforts we should look exclusively for natural explanations for phenomena when investigating the world. One accepts this stance based on the established pattern of the success of this approach, but not because of a pre-commitment to a belief regarding the existence or non-existence of supernatural entities. Some theists are comfortable with this stance. Others feel their personal beliefs are threatened by this stance and advocate a search for signs of God’s interventions when examining the world (unfortunately some of them try to subvert the public education system to try to include this approach). Subscribing to metaphysical naturalism goes the extra step in explicitly adopting a philosophical worldview which rules out the possibility of supernatural intervention. A traditional theist could not take this step and retain a belief in a deity which is transcendent, omnipotent, supremely good, etc.

I think this distinction is helpful in parsing these kinds of discussions. So, if someone supports and defends evolution and the other products of science, but is also a traditional theist, I would think you could assume they support methodological naturalism, but do not subscribe to metaphysical naturalism.
On the other hand, when I’ve said I subscribe to naturalism, I did mean metaphysical naturalism. I’m therefore someone willing to take the step from the success of the methodology to a claim about the truth about the world. Finally, I have explained why such a naturalistic worldview can be consistent with some (admittedly less traditional) forms of theism (see this post).