Quantum Computing and Mind Simulation

At the end of a recent discussion (in the comments to this post), Allen and I started to discuss whether quantum computing theory had something to say about the potential for simulating the human mind on a computer. I then read a couple of review articles on quantum computing he referenced. Before getting to what I learned (below), I wanted to explain my prior philosophical view on the simulation question.

The Russellian Stance, Functionalism, and Simulation

I endorse a form of the Russellian approach to solving the hard problem of consciousness. Russell described the world as a causal network of events, and he noted that physical theory only describes the extrinsic or dispositional nature of these events. These events also have an intrinsic nature which ultimately grounds the qualitative and experiential character of consciousness. I think quantum mechanics provides support for this view: quantum measurements seem to fit perfectly into this Russellian picture as the base-level events which ultimately underpin both the physical and experiential facts.

Functionalism is the thesis that the mind can be described as an abstract causal system. As a practical matter, the functionalist’s description is taken at a coarse-grained level – i.e. there is some minimal scale below which the actual physical details of the brain/body system are assumed to be irrelevant to its function. It follows that such a functional model could be realized in any number of physical ways, including via computer. Computationalism is the variety of functionalism which pursues the computer modeling approach.

Now, I think the Russellian stance on functionalism and the potential for simulation is nuanced. On the one hand, functionalism is seen as misguided because it only considers extrinsic causal structure. On the other hand, unlike an old fashioned dualist, the Russellian shouldn’t rule out the possibility that the mind could be simulated. The mind, after all, is a product of a natural system – we don’t need extra immaterial stuff to explain it. Perhaps a simulation can get the functional structure right and the correct intrinsic experiential character will come along “for free.”

The problems come with the coarse-graining. In every functionalist account I’ve seen, this takes place at a scale where quantum mechanics is assumed to be safely irrelevant. But every process in the body ultimately is grounded in molecular, atomic and sub-atomic activity which must be described quantum mechanically. So, a coarse-grained, approximated simulation of the brain/body’s causal structure on some physical device would likely miss crucial details which lie at the quantum level (details I think simultaneously crucial to both extrinsic function and conscious experience)

How would a functionalist respond to the quantum question? First, many believe distinctive quantum phenomena effectively “wash out” in a macroscopic system like the human brain/body. This belief is often based on the presumed impact of environmental decoherence. I’m not going to pursue this issue in this post (I discuss this in some of my posts on quantum biology). Another response to the quantum question is an appeal to a commonly believed thesis that any physical system (including a quantum system) can be modeled by a classical computer -- so the traditional functionalist/computationalist approach wouldn’t be missing anything distinctive anyway. This is the view that I wanted to explore by reading up on quantum computing theory.

[Please note the discussion that follows may suffer even more than usual from by my ignorance of the subject matter.]

Simulation and the Church-Turing thesis

So, is it true that any physical system, including a quantum system, can be simulated by a classical computer? Well, this idea has been defended by appeals to versions of the Church-Turing thesis. The original Church-Turing thesis states (in a formulation from this article) that any effectively calculable function can be computed using a Turing machine. (For a description of a Turing machine, see here.) Now it seems that what this thesis really meant can probably only be appreciated by studying its original logical/mathematical context. In his SEP article on the C-T thesis, Jack Copeland first traces the development of the ideas associated with the thesis in the pioneering work on calculation and computing by Turing, Church and others beginning in the 1930’s. Then, Copeland spends much of the rest of the article objecting to how the thesis has been misunderstood and misused by philosophers and computing theorists. The C-T thesis did not purport to say that all physical systems, or even all machines regardless of architecture, could be simulated by a Turing machine. It certainly did not prove anything of the sort. (This discussion reminded me of similar debates over the philosophical applicability of Gödel’s incompleteness theorems beyond their original context – see old posts here and here.)

Nevertheless, as long as one is careful not to inappropriately invoke the authority of the original C-T thesis, one can explore more expansive versions and try to evaluate their validity.

Physical Versions of the C-T thesis

In her review article on Quantum Computing, Dorit Aharonov presents two versions of the thesis. First, (p.3), she presents a simple “physical” version: “A Turing machine can compute any function computable by a reasonable physical device.” She says this is something which cannot be proven, but that no known counterexamples exist. In particular, quantum computers are not believed capable of computing functions non-computable by a Turing machine.

She quickly then notes that: “However, in the theory of computation, we are interested not only in the question of which functions can be computed, but mainly in the cost of computing these functions.” [Emphasis original] The way this is evaluated is by noting whether the computational resources needed rise as a polynomial or an exponential function of input size. It is the former which form the set of tractable computations.

After also discussing the superior efficiency of a probabilistic version of the Turing machine, she presents another thesis to consider (p.4): “The modern Church thesis: A probabilistic Turing machine can simulate any reasonable physical device in polynomial cost.” We have a great deal of evidence, though not proof, that this thesis is contradicted by quantum computers.

The Advantages of Quantum Algorithms

Aharonov explains first, that quantum computers can simulate classical computers, at little loss in efficiency. On the flip side, it appears classical computers can simulate quantum computers but only at exponential cost. What we really want, though, is a positive demonstration of how far quantum computers can outperform their classical counterparts.

The a priori expectation might be that the ability to manipulate qubits, which can be in a superposition of states as opposed to just to two states, would lead to great increases in computing power. Because of the necessity for conducting a measurement to extract results (collapsing superpositions), however, the power of this idea is muted. Other, more subtle sources of limitations on quantum computing are discussed later in the paper.

Despite this, however, many investigations into quantum computing over the years have found quantum algorithms which improve efficiency. One of these algorithms, Shor’s, gives a polynomial algorithm for factoring integers where all known classical algorithms have exponential cost, thus crossing the crucial boundary. It must be pointed out that as of yet there is no proof that a classical polynomial algorithm for factoring is impossible.

Conclusions

Most of what I’ve discussed in Aharonov’s article above comes from the introduction. In the ensuing 60 pages she goes into more detail about the nature of computers and computing, various models for quantum computing algorithms, the issues of noise correction and fault tolerance, and some of her own ideas of what quantum computing theory says about the boundary between quantum and classical regimes in physics.

On the key question of what quantum computers can do better than classical ones, one is left with the impression that the question is much more subtle than might first be imagined. We have some exciting theoretical results, but perhaps fewer than might have been anticipated on a naïve expectation. At the same time, it seems we’re still in the early phase of growth in our knowledge of the field. A lot of interesting work and new developments lie ahead. (The engineering efforts underway toward building quantum computers and the challenges they face is another interesting topic).

Let me return to the question about what all this might mean for the philosophy of mind, assuming (as I do) that the quantum level grounding of biology contributes meaningfully to the mind’s function. I think a modest conclusion is called for. The fact that a classical computer can simulate a quantum computer only at an exponential cost suggests that the project of simulating a human mind is impractical, though not blocked in principle. This conclusion is broadly consistent with my philosophical stance regarding the simulation project.

[P.S: after drafting this I recalled there was a good debate (thanks to Tanasije and Mike) on the simulation topic in the comments to this May 2008 post on Russellian theory. My memory is awful.]

John Heil Gets Very Close…

…to solving the mind/body problem.

John Heil’s 2003 book From an Ontological Point of View consists of roughly three components. The first part is a thoroughgoing critique of analytic philosophy based on the central role it gives to language. The second part is his positive ontological account: this is centered on his theory of power-properties. The third section discusses the application of his ontology to philosophical problems, notably the mind/body problem.

Being a blogger, I’m only going to discuss one aspect of how his account of properties (as part of a substance/property ontology) gives him a leg up on solving the mind/body problem, although I think he ultimately falls short of the goal. For an appreciation of his overall approach to philosophy, see this paper by Ross Cameron and Elizabeth Barnes. A Notre Dame book review penned by Gary S. Rosenkrantz is here. (There is also a whole volume of collected responses to the book available -- I have not read this).

Powers and Qualities

For Heil, properties are powers (or dispositions). Properties are distinguished by their contribution to the causal powers of their possessors. There are many potential advantages for this approach in constructing a realist account of ontology and causation. One advantage as it relates to philosophy of mind is that the ubiquity of powers offers a natural home for intentionality in the world. Powers have an “aboutness” – they are always directed towards their manifestations (I discussed this at greater length in my posts on George Molnar’s powers ontology).

But the biggest innovation in Heil’s account compared to other treatments of power properties is his treatment of qualities. Qualitative properties are usually considered to be separate from dispositions. They are often identified with the so-called categorical properties of objects. Heil proposes that qualities and powers are the same thing. He calls this the identity theory: “If P is an intrinsic property of an object, P is simultaneously dispositional and qualitative… (p.111 – page references are to the paperback edition)” Furthermore, this is not to be seen as a dual aspect theory: P’s nature is truly and simultaneously dispositional and qualitative. (Heil gives credit to the late philosopher C.B.Martin for this idea).

Heil’s defense of this identity theory was persuasive, in my opinion. He starts by giving some homely examples (size, shape, color) of how objects can be seen as having effects by virtue of their qualities. He then notes that while physics is silent on the subject of qualities, this in no way contradicts the identity theory. If middle level objects have qualities, it makes sense that their constituents do as well. (Heil strongly objects to ontological accounts which feature distinct “levels” of reality).

Qualities in the Brain

Turning to the mind/body problem, we can see that if properties which are both dispositional and qualitative make up the world then there is no special problem with the fact that conscious experience seems to possess qualities. Still, Heil wonders, could it be that these qualities are just qualities of, say, neurological activity? He notes that the qualities we should focus on in considering this question are not the simply representational qualities of experience, but the “diaphanous” qualities associated with having an experience. The qualities of experience outstrip their representational qualities, and these residual qualities are key to the question.

P.229: “The what-it-is-likeness of conscious experience stems from the nature of the representational medium…” as well as what is being represented. Heil makes use of a thought experiment based on an actual apparatus developed for the blind whereby a camera impresses images via pressure on the skin of the back or chest. After a while, the subject using such a device mostly forgets the nature of its implementation and just processes the images. But certainly the residual, non-representational experiential qualities are different between vision and this touch-analogue of vision.

So, do these “what-it’s-like” qualities differ from material qualities, or can we say that they are no different? Can we locate them in the brain? Well, Heil asks, why not? Perhaps these qualities are just are neurological qualities.

What about the First-Person Aspect?

The remaining question relates to the different way we are acquainted with these putative neurological qualities. P.234: “…we do seem to have something like ‘direct acquaintance’ with neurological qualities.” This means there still is a distinction here between the what-it’s-like qualities and other material qualities. Heil gives us an account that deals well with the qualitative character of experience -- after all qualities are ubiquitous in the world. But what about the subjective character of experience (my term)?

One might ask: is this subjective character also ubiquitous? Alas, Heil doesn’t want to take that leap. After all: “You might be worried that a conception of this kind leads to panpsychism or worse. (p.234)” Heil wants to maintain that all of the qualities of experience are perfectly ordinary qualities of brains. He concedes that it remains to be understood how this could be the case. But he hopes we’ll know more in the future as we learn more about neuroscience.

There’s one additional passage where Heil ponders this issue of the subjective character of experience (pp.237-9). He discusses the privacy of mental states, and acknowledges the difference between being in a state and observing the state. But he objects to treating this as indicating an ontological divide between subjective and objective properties. Conscious people are, after “objective” in the sense of being natural entities in the world. But again: “What, then, distinguishes conscious states from those that are not conscious? (p.239)” Could it be that there is a different functional role? This can’t be an explanatory strategy for Heil, since causal and qualitative roles are constituted hand-in-hand. I give Heil credit for raising the issue, but for him the privacy/subjectivity issue remains unexplained.

What about Zombies?

In his Chapter 20 (pp.240-249), Heil looks at the conceivability, or “zombie” argument against materialism. The bottom line is that zombies are not conceivable given Heil’s ontology: “The zombie possibility arises only against a particular ontological background, one according to which powers and qualities are only contingently related. (p.248)” Heil is right -- IF you define the zombie problem as being about qualia, rather than being also concerned with the subjective character of experience. As an aside, this is why I personally don’t use the term qualia when discussing the mind/body problem: first-person experience possesses both qualitative character and subjective character – discussions of qualia often ignore the latter issue (on this point see also a quote from philosopher Uriah Kriegel in this old post).

Conclusion

So, Heil comes close to solving the mind/body problem. By virtue of an ontology which places qualities in the world, the qualitative character of conscious experience is accounted for. The other dimension to experience, its subjective character, is left without an account. I think the only way to address this is to place subjective points of view into the natural world as well.

PS: My thanks go to Gualtiero Piccinini of the blog brains for his post on C.B.Martin, also suggesting Heil as a route to helping to understand Martin. This prompted me to read the Heil book, which I had been meaning to do. Martin's book is in the queue.

Montero on Russellian Physicalism

There is a lot of interesting material at the Consciousness Online conference currently underway. One paper I enjoyed reading was Barbara Montero’s entry on the Russellian theory of mind: “Russellian Physicalism”. In addition to Montero’s paper and powerpoint slides, there are links to responses by Emmett Holman and Daniel Stoljar, who have both also written on this topic in the past (see my old posts here and here).

Montero reminds us that the Russellian approach is a non-dualistic strategy for dissolving the conceivability argument against physicalism/materialism (most famously depicted as the “zombie” argument). David Chalmers' most recent paper updating the conceivability argument had as its conclusion: “materialism is false or Russellian monism is true.”

Russellian monism argues (roughly) that our knowledge of the physical world is only of its extrinsic or dispositional (causal) aspects. Physical entities also have intrinsic or categorical aspects. These hidden aspects are those responsible for consciousness. When we try to conceive of zombies, we fail because we are not conceiving of all relevant aspects of the physical world.

Montero’s paper focuses on the fact that while Russellian monism can be interpreted as a form of panpsychism (the intrinsic aspects are in some fashion mental or experiential in nature), it can also be cast as a variety of physicalism (where the intrinsic aspects are not to be seen as themselves mental).

I'll note parenthetically that both versions face further challenges. In the case of the physicalist version, it can be argued that the explanatory gap between the mental and the physical still isn’t bridged (even though the formal conceivability argument is defeated). In the panpsychist version, we arguably address the gap, but we are left with the “combination” problem: how do micro-phenomenal entities or properties combine to form macroscopic minds like ours?

The responses by Stoljar and Holman and further discussion in the comments mostly revolve around thorny issues of terminology. What do we mean by “physical”, “mental” etc. as it relates to these hidden intrinsic aspects of nature? I tend to like the approach Stoljar took in his book (finally out in paperback), where he threw out these terms and used experiential and non-experiential. Holman proposes using “subjective unity” as the key feature to distinguish things.

I enjoyed the discussion (which continues in the comments), and I hope that philosophers of mind continue to focus on this topic.

Postscript: I have a general quibble, which is that I think this all becomes clearer if you go back and read Bertrand Russell himself (Montero, taking Chalmers as her starting point, includes just one short quote from Russell). Russell’s approach, beginning in his Analysis of Matter, is distinctive for his careful critique of physical theorizing and for his use of a causal event ontology. Russell reminds us that physical theory consists of describing a causal structure connecting the experiential events which occur when we conduct empirical research. The physicists create mathematical models to allow them to generalize and extrapolate to describe events beyond our direct experience. He then argues that it is a philosophical mistake to ascribe reality to the mathematical models themselves (what Whitehead called the “fallacy of misplaced concreteness”). The causally connected events are the reality. We have no good reason to think the “physical” events which we infer have a different character from the events we experience directly. At a minimum we can be confident that an event is ontologically more than just a point in a mathematical model. Whether we think all events are experiential (leading to panpsychism) or not is something for further debate. Russell himself took the conservative option here, and was reluctant to posit panpsychism, while his former collaborator Whitehead went ahead and took the panpsychist step in formulating his process metaphysics (see also my post on Carey Carlson’s book on Russell and Whitehead).

I Heart Philpapers

David Chalmers announced here the creation of the philpapers.org site to aggregate and provide tools to explore philosophical works of all stripes. It looks stupendous. David Bourget has spearheaded this effort with Chalmers.

So, I was curious whether the site had any online papers or drafts by philosophers of science on the topic of emergent-spacetime approaches to quantum gravity research (I had not yet seen any to date). Voila, I found this nice paper by Jonathan Bain on the condensed-matter physics-based approaches.

There is no way someone outside a university setting like me could keep up with the work of philosophers without the internet. So, while I know I'm not the intended beneficiary of all this effort, I’m nonetheless extremely grateful to the individuals who have worked over the years to aggregate the online papers: including (in addition to Chalmers and Bourget) Brian Weatherson, Jonathan Ichikawa, and Wolfgang Schwarz.

Anathem Metaphysics

(“Metatheorics”, I should say)

Most Neal Stephenson fans probably read his book Anathem last fall, but I just finished. There are many reviews available, so I won’t add one here, but I got a big charge out of some of the philosophical ideas Stephenson put in the book.

In the course of the novel, Stephenson proposes an interesting relationship between platonic truths, the multiverse, and human rationality/consciousness, which I have enjoyed comparing to my own ideas (discussion below the fold).

The main idea is that the platonic realm is not a single transcendent world out there, but rather the source of platonic ideas is to be found in the multiverse (called the “polycosm” in the book; the overall theory is called “complex protism” where protism=Platonism and “simple protism” would be the positing of a single platonic realm).

The core of this idea is one I endorse here in the non-fictional realm, and it was very cool to see it in the novel. Modal judgments about what is possible and what is necessary play a crucial role in our reasoning. At the same time, both philosophers and theoretical physicists have proposed that our world is one member of a set of many possible worlds. If we propose that the logical possibilities we explore with our minds are identical with real possibilities present in the multiverse, then the multiverse can be seen as the source of our rationality, and of our knowledge of abstract truths. (The philosophical term for the match-up between logically possible worlds and metaphysically possible worlds is modal rationalism).

But how does a human mind access the multiverse? First, let me note that the type of multiverse being proposed in the book is inspired by the many-worlds interpretation (MWI) of quantum mechanics (QM). So the solution is to have the mind exploit the quantum realm. There’s a dialogue between the characters Orolo and Erasmus (pp. 543-548) where they discuss how the presence of the same person’s brain in multiple adjoining and interfering worlds gives the brain access to possibilities. Stephenson’s characters later make the point (which I liked) that it isn’t that the human brain is the only thing which is in contact with possibilities; one should assume everything in the world experiences some contact, but it is in our own brains that we can best see the evidence manifested (pp. 690-92).

I’ve come at this in similar spirit, with one apparent difference when it comes to interpreting QM. I believe that our world is comprised of quantum measurement “collapse” events, which each embody the actualization of one of many possibilities. The fact that we humans are ultimately grounded in quantum-level events gives us a kind of direct acquaintance with possibilia in everything we do. That makes our ability to have modal knowledge intelligible, even though we don’t yet know the manner in which our brain/body system leverages this presumably micro-level contact into macro-level knowledge.

It appears Stephenson’s idea is to try to preserve the MWI (which attempts to do away with measurement events), while allowing contact between parallel worlds to be exploited by the mind. MWI would not typically be seen as allowing any contact. Also, usually in MWI, worlds branch (what we think of as a measurement is a splitting of worlds), whereas Stephenson wants to keep worlds in parallel. Of course, positing contacts between parallel worlds is very helpful for the creating the exciting parts of the novel which involve characters and spaceships moving between worlds.

The other aspect of Stephenson’s multiverse which is interesting is that the informational contact between worlds has a flow, where some worlds are upstream or downstream from one’s own world. It seems he places a single purely platonic world at the source of the information flow (whereas I would follow the usual philosophical tradition of identifying logical and mathmatically necessary truths to be those things true in all worlds). I’m not sure this makes sense or was philosophically motivated, but it was a neat twist.

There are allusions to many other philosophical and scientific ideas in the book, and Stephenson discusses many of the sources which inspired these in this acknowledgments page on his website. There’s more to follow up on there – one philosopher he discusses who I have not read is Edward N. Zalta.

[I have a number of old posts on related topics, including
Making Abstract Truths Intelligible
Modal Realism, Modal Rationalism
Multiverses -- Physical and Metaphysical]

More on the Fundamental Status of Time

Here are two more links to arguments for why time is fundamental:

A very good talk by Lee Smolin at a Perimeter Institute conference last fall. I thought he did a very good job in explaining how physics got into the practice of viewing time in a geometric fashion (with no important role for the present moment) and why this will not work when formulating a theory of the universe as a whole.

Here's George Ellis in another entry from the FQXi essay contest explaining why it is a mistake to try to describe the universe without time asymmetry.

Review of Quantum Aspects of Life

Quantum Aspects of Life is a collection of papers edited by Derek Abbott, Paul Davies, and Arun K. Pati which was recently published by the Imperial College Press (this review refers to the paperback edition). The target topic of the book is the role played by quantum mechanics (QM) in living things. Actually, we need to be more specific than that, since it’s accepted that all biology is based on chemistry, and chemistry is inherently based on quantum physics. In the book, the key distinction is described in a couple of different ways: in the foreword, Sir Roger Penrose distinguishes between “strongly” and “weakly” quantum mechanical features utilized by living things; the editors’ preface says the intent is to address the question of “whether quantum mechanics plays a non-trivial role in biology” (p.xiii). In each case the phenomena in question are those which are distinctively quantum mechanical: superposition, entanglement, tunneling, etc.

The volume is very welcome, since the topic seems to demand more focus than it has received. Confirming a significant quantum role could have a huge impact – both on the practical pursuit of biology and the philosophical perspective we take on the nature of life and mind.

There has long been a good circumstantial case to be made that the remarkable nature of non-trivial QM effects may serve to help explain the remarkable capabilities of biological systems. The foreword, preface, and Davies’ opening chapter all invoke Schrödinger’s 1944 book What is Life? as the ur-text exploring this idea. However, experimental confirmation of QM’s role in life didn’t follow, and molecular biology experienced huge growth and success nonetheless. Again repeating themselves a bit, the editors, Penrose and Davies each lament that the science of the intervening decades has been dominated by the “ball-and-stick” model of chemistry. They seem to be implying that scientists (for institutional reasons perhaps) haven’t been bothering to look for quantum effects. Of course, a hurdle for the idea, not as explicitly evident in Schrödinger’s time, is the phenomena of environmental decoherence. An issue running through the book is the challenge posed by the fact that maintaining quantum coherence is very difficult even in carefully controlled experimental settings.

While experimental confirmation of non-trivial QM effects in biology has indeed been elusive, it has not been absent, and a recent result strikes me as not only important, but possibly seminal. I’m referring to the 2007 Engel, et.al. paper in Nature which showed the utilization of quantum coherence in photosynthesis (please see the post “Quantum Biology Goes Mainstream” for links). The timing of this result’s publication was such that it either barely pre-dated or else post-dated the submission of papers to Quantum Aspects of Life. As I read the book, I was often thinking about how this result might change the debate as we move forward: it not only showed the utilization of QM in one of the core processes in biology, it also showed the engineering challenge (and attendant resource demands) which are involved in confirming the presence of such a phenomenon. There are quite a number of papers out there which present theoretical models which postulate QM effects to answer outstanding questions in biology -- here’s a good example of this sort of paper I saw recently – but confirming a theoretical result is another story.

Quantum Aspects of Life begins with a nice foreword by Penrose, whose perspective will be familiar to those who have read his books. He thinks the human mind will demand a quantum-derived explanatory account (which he thinks will be linked to a future theory of quantum gravity). Now, environmental decoherence becomes an increasingly strong obstacle as distances lengthen, so quantum computing in the human brain seems unlikely to be a result of quantum coherence extending across neuronal assemblies. Penrose, and his collaborator Stuart Hameroff (who also contributes a paper to the volume), think, however, that quantum effects may be effected through intra-cellular structures (microtubules) thereby creating an avenue for large-scale computation. Penrose has the following thoughtful observation: “Indeed, there is no question that if the brain does make use of such “strongly” quantum-mechanical phenomena, it must do so through the agency of some very sophisticated organization. (p.viii)” Life and mind might combine small-scale quantum effects with (classically describable) organizational structure.

Chapter one, by Paul Davies, and Chapter three, by Jim Al-Khalili and Johnjoe McFadden both focus on the possible role QM may have played in the origin of life on earth (OOL). Life may have learned to exploit QM phenomena via natural selection after a classically explainable beginning, but it seems plausible that QM may have been key to life from the start. The complexity of the building blocks of life (as we know it) make it statistically very unlikely that the components randomly came together in a primordial soup as was once suspected. Davies explores a model of a quantum replicator as a precursor; both he and Al-Khalili/McFadden discuss the possibility of a quantum-coherent search algorithm which helped lead to an early replicator. These are interesting ideas, although probably a long way from being confirmed or falsified (I have prior posts on work by Davies and McFadden here and here, respectively).

Chapter 2 is from Seth Lloyd, who stays at 40,000 feet by discussing generally how complexity should be expected to arise in a universe which is inherently quantum-mechanical (see my several posts on Lloyd’s “universe as quantum computer” thesis here).

Models of how photosynthesis likely exploits coherence is the subject of Chapter 4 (with the Engel paper validating broadly the idea); the authors of Chapter 5 present models to help quantify the impact of environmental decoherence in biological contexts. This work seems to sharply delimit the potential for coherence; however other authors argue that dynamic systems can foster insulated sub-spaces larger than what would otherwise seem likely.

A quantum role in DNA mutation and replication is a topic which is discussed in several chapters (6,9,10). It seems accepted that tunneling is one avenue to DNA mutation; possibly QM has a more meaningful role to play. The capabilities of artificial quantum systems are explored in chapters 11-14. To the extent QM systems are good at mimicking features of living things, this offers more circumstantial evidence.

One of my favorite parts of the book is the inclusion (as chapters 15 and 16) of the transcripts of two staged debates which took place at conferences: one is on the future of quantum computing (from 2003), and one specifically on the topic of whether life utilizes non-trivial quantum effects (2004). Both debates featured good insights and a good deal of wit. At one point in the latter debate, one of the participants, Howard Wiseman, offered his definition of a non-trivial quantum effect as “something that will make a biologist want to go out and, you know, take a second year quantum mechanics course and learn about Hilbert spaces and operators, so that they understand what’s going on. (p.358)” Again, I thought about how something like the Engel, et.al. result would change the debate if it were held again today. Wiseman and Jens Eisert --another debate participant -- contributed a thoughtful paper (Ch. 17) explaining in a more organized format why they were on the skeptics’ side of the discussion.

Stuart Hameroff gets the last word in the book, offering his positive proposals for how it all might work (Ch.18). He sees in the structure of cells, both cytoskeleton and protoplasm, features which could lead to a larger scale participatory quantum biology. As a layperson, I’m not a good one to offer judgment; my feeling is that Hameroff presents a string of plausible ideas which nonetheless link together to form a very speculative edifice. On the other hand, as far as I know he could be right! Until we have more attention on the topic we will be slow to sort through and find out which quantum biological ideas are fanciful and which are on target.

So, I second the editors of this volume in their hope that its publication will provoke further debate and help motivate experimental research into this fascinating subject.

Markopoulou: Time is Fundamental, Space is Not

The Foundational Questions Institute has run an essay contest on "The Nature of Time" and received a wide variety of responses. These come from well known physicists, other academics, and amateurs alike. Because of time contraints I've only read a few, beginning with authors I recognized (there are likely some "diamonds in the rough" if one plows through all the contributions).

Fotini Markopoulou of the Perimeter Institute, whose work I mentioned in the last post (and several older ones), wrote: "Space does not exist, so time can." She has a talent for writing clearly about these deep concepts, and I find her arguments persuasive (even if her work toward a full theory of quantum gravity still has a long road ahead). So I highly recommend the essay.

Kudos also to cosmologist and blogger Sean Carroll for his nice essay: "What if Time Really Exists" (here is the Cosmic Variance post introducing it). While I don't like some of his specific suggestions (associating time's arrow with macroscopic entropy considerations), I liked the stance he takes in the essay.

For countervailing views you can read the contributions of Carlo Rovelli and Julian Barbour.

UPDATE (7 January 2009): I just found this interesting post by Scott Aaronson - "Time: Different from space" which includes his computer science-derived insight on why time (causal structure)is fundamental.

Aether Makes a Comeback

The nineteenth century version of the ancient concept of the aether (or ether) was killed by the Michelson-Morley experiment and the success of Einstein’s theory of special relativity. Electro-magnetic radiation needed no substance to support wave propagation. Of course we did not revert to a view of space as an void sprinkled with a few solid objects. In modern particle theory, space-time is pictured as filled with matter fields. And in general relativity, space-time is revealed as a dynamic actor, not just a backdrop. Still, space-time remains distinct from matter/energy, and is geometric, rather than substantive. It thus retains a bit of the conceptual flavor of an empty container (a related discussion on the blog is here).

I was surprised to see the number of physics papers on arxiv which invoke the concept of aether (or ether) in the context of theoretical proposals to solving outstanding problems (e.g. dark energy). For me, aether was brought to mind by certain quantum gravity research programs.These propose that the space-time of general relativity is not fundamental: it emerges (along with the matter fields of the standard model) from something more basic – an underlying network of elementary quantum systems. This underlying network is not itself defined against a spatial backdrop and lacks the usual notions of distance or locality. Both space-time geometry and matter as we know them are constituted by the quantum systems: they arise from the aether.

For an example of this kind of work, here’s the second “quantum graphity” paper from Fotini Markopoulou and colleagues (the authors do not invoke the term aether, so don’t blame them!*). The introduction does a good job of discussing the stance they are taking toward the space-time of general relativity, and places this in the context of how other quantum gravity research programs approach the issue.

* Although they do link their work to the model described in this paper: “Quantum ether: photons and electrons from a rotor model” by Levin and Wen.

{UPDATED 19 November, 2008: Minor edits; 8 December 2008: Sean Carroll at Cosmic Variance just posted about his collaboration on aether field models.}

Ruminating on Theism and Personhood

As I’ve discussed in previous posts (see list below), one can try to put a theistic spin on my concept of the necessarily existing metaphysical “megaverse”: one can identify the megaverse with “God”. To be sure, it would be a non-traditional concept of God compared with that of our Western religious traditions – it would be a variety of panentheism (or perhaps panendeism). But perhaps this is simply stretching things too far, and using the label “God” is simply incongruous. Certainly there may be less room for confusion in communicating the ideas if one leaves “God” out of it (I think the historical reception given to Whitehead’s process metaphysics is a cautionary tale in this respect). While there are several considerations here, I think this decision of labeling should be driven in part by the question of personhood, which seems to be an important component of most conceptions of God.

I have a longstanding skepticism about the attribution of personhood to God -- if personhood means something similar to what it means in the human context. In the context of traditional religions, I always suspected anthropomorphism was at the root of this attribution. In outlining my version of the cosmological argument for a necessarily existing entity, I disliked even using the term “necessary being”, because it has the flavor of “human being”, and thus too readily invokes personhood.

Despite this skepticism, the panentheistic version of my view would say that human characteristics arise from the same raw materials which also constitute God, so there must be some essential affinity. Given my specific opinion that first-person experience is rooted in the most fundamental level of reality, I suspect that God might well be a subject of experience – a key aspect of human personhood.

On the other hand, when discussing Timothy O’Connor’s book (here and here), I disagreed with him on whether the necessary being (NB) needed to be considered an agent (and agency seems to be another key aspect of personhood). It seemed sufficient for the NB to be an impersonal font of creation without need of intentions, purposes, or discrete top-down decision-making. My thought here is that a human being moves within a sea of other beings or systems, and his/her agency arises in this context. The NB is the source and sum of all being, and does not operate in a larger context. This seems to me to be an important difference. To use an analogy: if a human being is an actor, then God is the theater, not another actor.

So, at this point I have a mixed verdict – our human essence is derived from the NB, but our status as a finite subset of the NB’s totality makes our nature very different. Whether the concept of personhood can be stretched to cover both situations is unclear, and I think the better option is to decline to consider the NB to be a person. And this may be a good reason to resist using the label God for what I have in mind.

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Note: I’m even less well-read in relevant literature in this area than in other subjects I discuss: any reading suggestions in philosophy of religion are welcome.
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Post Series (in chronological order): A Philosophical Path to Theism?

Modal Realism and the Cosmological Argument
Exploring the Borderlands
Panentheism
Whitehead's Philosophical Theism
Logos vs. Chaos, Part One
Logos vs. Chaos, Part Two
A Necessary Being or Just a Collection?
Why the Megaverse is a Unified Entity
Is the Megaverse a Subject of Experience?