In a philosophical mood at the moment, because I’m about to head to Montreal for the Philosophy of Science Association biennial meeting. Say hi if you’re in the neighborhood! I’m on a panel Thursday morning with Nick Huggett, Chris Wüthrich, and Tim Maudlin, talking about the emergence of spacetime in quantum gravity. My angle: space is obviously not fundamental, though time might be.
Here’s a Philosophy TV dialogue between John Dupré (left) and Alex Rosenberg (right). They are both physicalists — the believe that the world is described by material things (or fermions and bosons, if you want to be more specific) and nothing else. But Dupré is an anti-reductionist, which is apparently the majority view among philosophers these days. Rosenberg holds out for reductionism, and seems to me to do a pretty good job at it.
John and Alex from Philosophy TV on Vimeo.
To be honest, even though this was an interesting conversation and I can’t help but be drawn into very similar discussions, I always come away thinking this is the most boring argument in all of philosophy of science. Try as I may, I can’t come up with a non-straw-man version of what it is the anti-reductionists are actually objecting to. You could object to the claim that “the best way to understand complex systems is to analyze their component parts, ignoring higher-level structures” but only if you can find someone who actually makes that claim. You can learn something about a biological organism by studying its genome, but nobody sensible thinks that’s the only way to study it, and nobody thinks that the right approach is to break a giraffe down to quarks and leptons and start cranking out the Feynman diagrams. (If such people can be identified, I’d happily join in the condemnations.)
A sensible reductionist perspective would be something like “objects are completely defined by the states of their components.” The dialogue uses elephants as examples of complex objects, so Rosenberg imagines that we know the state (position and momentum etc.) of every single particle in an elephant. Now we consider another collection of particles, far away, in exactly the same state as the ones in the elephant. Is there any sense in which that new collection is not precisely the same kind of elephant as the original?
Dupré doesn’t give a very convincing answer, except to suggest that you would also need to know the conditions of the environment in which the elephant found itself, to know how it would react. That’s fine, just give the states of all the particles making up the environment. I’m not sure why this is really an objection.
This is purely a philosophical stance, of course; it means next to nothing for practical questions. Nor does the word “fundamental” act in this context as a synonym for
“important” or “interesting.” If I want to describe an elephant, the last thing I would imagine doing is listing the positions and momenta of all its atoms. But it’s worth getting the philosophy right. I could imagine hypothetical worlds in which reductionism failed — worlds where different substances were simply different, rather than being different combinations of the same underlying particles. It’s just not our world.
“space is obviously fundamental”
Please tell me what space is made of then. I like to make some.
Kevin said:
It’s become increasingly clear over the past few decades that any system can be derived from physics, if you have a big enough computer.
This is the position that can legitimately be opposed by anti-reductionism, I think, and also gives physicists who espouse it a bad reputation. First, the “if” is an unrealistic if. And there are some problems where the complexity or speed of the algorithm means the “big enough” computer is of extraterrestrial dimensions.
Second, biology, chemistry and physics are systems of knowledge. They happen inside people’s minds. The biological, chemical, physical phenomena are real, but the organizing principles we use to describe them are mental. In that sense, you don’t derive biology (as a system of knowledge that abstracts biological phenomena) from physics (another system of knowledge, which is compatible with but does not subsume biology). You can use a simulation of physical phenomena to predict biochemical phenomena, but you aren’t reducing laws of biology to laws of physics.
After all, even in physics, running a giant simulation doesn’t necessarily yield useful organizing principles; you need some way of abstracting the output into a simpler general principle.
Read Steven Weinberg’s Reductionism Redux, in which he distinguishes between “grand” and “petty” reductionism. Various people here (Russ Abbott, Physicalist, Ben, etc.) might benefit from this. I posted a comment yesterday that quoted Weinberg’s definition and gave a link to the essay, but apparently The Machine ate it, thinking it was yummy spam or something.
I enjoyed watching this debate and reading this post a lot!
Regarding the reducibility of the elephant to its components, I think the response that it depends on the environment is a valid response. Its more clear in the case of the protein folding- one can’t answer the question by just discussing the components, one needs the environment also.
As Dupre says around 34:40, he thinks this is the heart of the argument. Some systems are well understood with reductionism, and some are not. In particular, those that don’t depend much on their environment, can be usefully analyzed in terms of their components.
The other interesting point for me is about the difference between physics and physicalism. And the attempt of physics to call all explanations somehow a part of the science of “physics” is a kind of imperialism (43:43). You usually have to change the question a bit before its posed in the form of a physics question. When Sean says the reductionist statement is “objects are completely defined by the states of their components.” this says that we can basically only talk things that are internal to a given thing. Dupre is saying that when we talk about stuff- the concepts we apply to them are often relational qualities. An elephant may be called “friendly” for example, and that may depend on the other elephants around.
Reductionism Redux was somewhat familiar, I may have read it when it came out, back in grad school. In any case, I often disagree with Weinberg’s philosophy of science (IIRC, Weinberg does not even like Thomas Kuhn’s work), but in this case I don’t think it disagrees with what I wrote. Here Weinberg, from http://www.nybooks.com/articles/archives/1995/oct/05/reductionism-redux/ :
One of the implications of this point is not only that biology-as-theory is not necessarily reducible to physics-as-theory, but that maybe you couldn’t ever run a giant physics simulation of something as complex as a brain and hope to learn anything predictable, because of the sensitivity to initial conditions.
Sean,
you write
>A sensible reductionist perspective would be something like “objects are completely
>defined by the states of their components.”
but this makes no sense already for an atom.
There is no quantum state of each component, only a state of the whole thing.
As for the elephant, remember the no-cloning theorem.
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If Sean had an MI while arguing with a philosopher and wound up with an artificial heart, would he still be Sean, and would he still be considered a human being?
If we start replacing bits and pieces of him with prostheses and implants, at what point does he cease being Sean? Where is the Sean nature? In the fingers he types with? In the larynx he uses to speak? In his brain?
At what point does bionic-Sean stop being a human being? Suppose we give him artificial kidneys and a synthetic liver to go with his new heart. Is he still human? Should he still be treated as human under the law? What would *he* say?
What if we replace everything *but* his brain? Still Sean? Still human?
Does it matter when Sean has bits and pieces of him replaced? Is Sean’s-brain-in-plastic as human as a foetal brain transplanted into an artificial (and perhaps very non-bipedal-looking) body and grown into adulthood a human?
What about the elephant? Is a bionic elephant still an elephant? What does adult-elephant-in-artificial-body think about things? Would it find natural elephants attractive? What would a very young elephant brain raised in a non-elephantine body think about things? Would *it* find natural elephants attractive? (Cats raised by humans totally isolated from all knowledge of other cats still try to mate with other cats; likewise, cats and dogs raised in environments where they encounter all manner of other animals regularly sometimes try out a bit of forbidden dog-on-cat love. See youtube…)
We could go further and start augmenting brains, or perhaps even completely replace them: record all the memories of a person and “restore” them on compatible hardware — another brain, or a brain with electronic enhancements, or perhaps something entirely artificial. When you woke up after the procedure would you think you were less you than if it was “merely” a heart replacement surgery?
Reductionism is a useful tool in understanding how elephants and humans lay down their memories, and in understanding how to replace the various organs that feed those processes in the brain until they can be sufficiently replicated in some other medium. “What is a memory?” and “What is a personality?” are questions answerable in Sean’s “sensible reductionist perspective”.
WE JUST HAVEN’T ANSWERED THOSE QUESTIONS YET.
The lack of complete answers is not a reasonable condemnation of a reductionist approach. You would have to argue that those answers cannot — even in principle — be found in examining the components of the brain and its environment (the organism and things outside that).
“Sensible repackaging” — abstraction — is convenient both when the underlying mechanics are extremely tedious to work with and when there is actual theory choice because the underlying mechanics are not fully known. Indeed, an abstraction that is in very very close agreement with observation in some useful limit is also a powerful tool for verifying underlying theories. If your “micro-physical” theory cannot in principle reproduce “molecule”, “organelle”, “eukaryotic cell”, “organ”, “elephant”, and “herd of elephants” then it’s wrong. However, it’s reasonable that you can’t recover all of that *yet*.
Sean wrote: “nobody thinks that the right approach is to break a giraffe down to quarks and leptons and start cranking out the Feynman diagrams. (If such people can be identified, I’d happily join in the condemnations.)”
Is that a permanent objection? If at some point the ability to compute the evolution of a system of quarks and leptons of an object the size of an elephant and its immediate environment arises wouldn’t it be a useful tool for predicting the future actions of that particular elephant?
Obviously we can’t do this now and almost certainly won’t be able to in the next couple of years.
How about something that’s the scale of a prion or a small virus? Or a prokaryotic cell? Or two neurons? Do you condemn anyone looking below the level of molecules and atoms for objects of those scales?