Avignon Day 3: Reductionism

Every academic who attends conferences knows that the best parts are not the formal presentations, but the informal interactions in between. Roughly speaking, the perfect conference would consist of about 10% talks and 90% coffee breaks; an explanation for why the ratio is reversed for almost every real conference is left as an exercise for the reader.

Yesterday’s talks here in Avignon constituted a great overview of issues in cosmological structure formation. But my favorite part was the conversation at our table at the conference banquet, fueled by a pretty darn good Côtes du Rhône. After a long day of hardcore data-driven science, our attention wandered to deep issues about fundamental physics: is the entire history of the universe determined by the exact physical state at any one moment in time?

The answer, by the way, is “yes.” At least I think so. This certainly would be the case is classical Newtonian physics, and it’s also the case in the many-worlds interpretation of quantum mechanics, which is how we got onto the topic. In MWI, the entirety of dynamics is encapsulated in the Schrodinger equation, a first-order differential equation that uniquely determines the quantum state in the past and future from the state at the present time. If you believe that wave functions really collapse, determinism is obviously lost; prediction is necessarily probabilistic, and retrodiction is effectively impossible.

But there was a contingent of physicists at our table who were willing to believe in MWI, but nevertheless didn’t believe that the laws of microscopic quantum mechanics were sufficient to describe the evolution of the universe. They were taking an anti-reductionist line: complex systems like people and proteins and planets couldn’t be described simply by the Standard Model of particle physics applied to a large number of particles, but instead called for some sort of autonomous description appropriate at macroscopic scales.

No one denies that in practice we can never describe human beings as collections of electrons, protons, and neutrons obeying the Schrodinger equation. But many of us think that this is clearly an issue of practice vs. principle; the ability of our finite minds to collect the relevant data and solve the relevant equations shouldn’t be taken as evidence that the universe isn’t fully capable of doing so.

Yet, that is what they were arguing — that there was no useful sense in which something as complicated as a person could, even in principle, be described as a collection of elementary particles obeying the laws of microscopic physics. This is an extremely dramatic ontological claim, and I have almost no doubt whatsoever that it’s incorrect — but I have to admit that I can’t put my objections into a compact and persuasive form. I’m trying to rise above responding with a blank stare and “you can’t be serious.”

So, that’s a shortcoming on my part, and I need to clean up my act. Why shouldn’t we expect truly new laws of behavior at different scales? (Note: not just that we can’t derive the higher-level laws from the lower-level ones, but that the higher-level laws aren’t even necessarily consistent with the lower-level ones.) My best argument is simply that: (1) that’s an incredibly complicated and inelegant way to run a universe, and (2) there’s absolutely no evidence for it. (Either argument separately wouldn’t be that persuasive, but together they carry some weight.) Of course it’s difficult to describe people using Schrodinger’s equation, but that’s not evidence that our behavior is actually incompatible with a reductionist description. To believe otherwise you have to believe that somewhere along the progression from particles to atoms to molecules to proteins to cells to organisms, physical systems begin to violate the microscopic laws of physics. At what point is that supposed to happen? And what evidence is there supposed to be?

But I don’t think my incredulity will suffice to sway the opinion of anyone who is otherwise inclined, so I have to polish up the justification for my side of the argument. My banquet table was full of particle physicists and cosmologists — pretty much the most sympathetic audience for reductionism one can possibly imagine. If I can’t convince them, there’s not much hope for the rest of the world.

92 Comments

92 thoughts on “Avignon Day 3: Reductionism”

  1. If at a higher scale new physics occurred, it is hard to avoid concluding that all the differential equations you liked at the lower scale are now overdetermined. If biology has new rules beyond lots of Schrodinger equation solutions, this ruins the ability to solve the Schrodinger equation the way standard math rules would like to let you. That’s my main reason for supporting reductionism – emergence of unique laws is just not compatible.

  2. Matthew Saunders

    Doug (#76):

    Just to clarify, are you saying that something like my appreciation of a certain kind of music should be able to be mapped out using the Schrodinger equation, or are you saying something else?

  3. If every time something happened and we didn’t know the reason we said “Well, it’s a miracle”, then science would never have gotten anywhere.

    This has gone way off topic from reductionism, though.

  4. Sean,
    If you’re wrong (and I’m certain you are), a lot of your thoughts is about something that can’t exist. Therefore it’s important for you to figure out that you’re wrong (or right if you prefer to believe that 🙂 ).

  5. It is rather amusing that League-Two scientists, like astro-cosmologists, still discuss reductionism vividly.

    Most Leauge-One scientists, i.e. string theorists, have already settled the issue in favour of holism by virtue of Holography. Every time you scratch deeper into an explanation, you end up with a more complicated and rich structure (much to the contrary of the “dream of a final theory” which advocated the explanation of nature by some “elementary particle/string or other simple theory”). String theory, M-theory and further still to be discovered more complicated structures are *necessary* to explain such different phenomena from superconductivity, chaos and confinement. Moreover, the Landscape put the final nail in the coffin of predictability. Hence, we are more and more confident that we cannot explain physical reality even in principle.

    So, even if “in principle” we cannot disprove reductionism (but we cannot prove it as well), there is currently a strong intuition to think more in terms of a holistic approach. People who still debate reductionism are not current research frontliners. Those who are in negation, are relegated to League-Two and become astro-cosmologists.

  6. 81. tasos,

    It’s rather amusing that that someone who probably fancies him or her self as a League-One Scientist has such a hard time spelling League. 🙂

  7. This has devolved really quickly, and tasos what you just wrote down sounds like a bunch of malakias (im assuming you’re greek, if not, that means bullshit). Braden,getting back to your point, you definitely are correct that we use infinite limits and other such things in physics, but this does not mean that we automatically have to support a non-reductionist line of thinking. The fact is that some things are uncomputable or unprovable in certain formal systems, but this does not mean in any way shape or form that the dynamics of the system is not fully determined by lesser parts, it simply means that we need to further add axioms or attempt to prove those other propositions in metalanguages that are more expressive if you will. This goes back to Godel; just because some things are not provable in an axiomatic system does not mean that there are consistent mathematical truths that are beyond our reach, it means we simply have to find the right axioms to further express those truths. In this way we get closer and closer to absolute truth. For an infinitely rich system (which mathematics is) there are likely an unbounded number of axioms, but to relate it back to reductionism, this only occurs in an system or universe with infinite information content. Our universe has finite information, and thus can be expressible with simple equations. You will find a neat example here: http://www.math.com/students/wonders/life/life.html

  8. Pete,
    That’s a neat example, I agree. It shows that we live in a real world and that we can make theories. The game of life is not a real world.

  9. I’m wondering if there is a way to split the difference between reductionism and the other what-have-you points of view. For instance, what if there were a mechanism at work in the universe that fades out “forces” over time? This is in analogy (or maybe more than an analogy) to the idea that we need ever higher energies to probe the energies at which the forces are unified.

    What I mean is say there were lots more quantum-like forces in the early universe, much more than just the electoweak and strong forces. These rapidly became unmeasurable via an uncertainty principle based on frequency, except for the forces that we can measure today. That is, these ur-forces went dark after only a short time and the only thing that remains of them is their gravity (gravity being the nonquantum residue of these faded forces; goodbye graviton).

    Detection of their faded quanta would be extremely infrequent so as to lie below a Planck Frequency that determines the difference between what can be statistically meaningful and what cannot be statistically meaningful. That is, were they ever to be detected now or in the future it would be in principle impossible to separate the event from detector noise.

    This faded forces theory would explain gravity in a new way. Gravity would not be quantum and have some aspects of an effective field theory. Dark matter would be gravitationally observable but not associated with a particle. And although you can make a reductionist statement about the beginning of the universe, since forces fade out, what remains forms essentially a new universe with fewer rules than the previous one, and fewer rules working together would be like new rules emerging.

  10. Aleksandar Mikovic

    Goedel’s theorems in logic prove that reductionism is impossible even in principle.

  11. I’m not sure if this thread has already fallen apart, but I thought I’d add my 2 cents. Here’s the problem I have with complete reductionism.

    On most weekdays, the particles that make up me bounce back and forth between the Ravenswood and Hyde Park neighborhoods of Chicago. Why do my particles do this? My answer would be that I live in Ravenswood and I work in Hyde Park: So this happens because of my job. However, to the reductionist, my “job” seems not exist. It’s not part of the physical stuff of the universe. The building where I do my job is real, but my job is merely a set of immaterial tasks–not ontologically real. So it can’t be the real reason for my particles to bounce between the two neighborhoods. There must be a physical reason for it.

    If that’s true, it renders my job, and by extension the industry in which I work, and indeed the entire world economy a mere illusion. Each must be constructed post-hoc, mere reflections of the physical workings of the universe. Any causal powers they may seem to have are illusions. This scenario is troubling to me, and doesn’t pass the parsimony test. Can someone from the reductionist camp show me where I’ve gone wrong?

    (Having just re-read this, I will accept “You’re crazy” as an answer.)

  12. Not sure where you’ve gone, wrong or otherwise 🙂

    But I agree completely with your second paragraph, and that was exactly the point Deutsch was making in my quote above @9. Emergent explanations are often more important than reductionist ones, but reality ultimately consists of both — as long as they’re good explanations. See @16.

  13. Matthew Saunders

    Yes, I don’t think this thread is ‘falling apart’ — curiosity is part of being a genuine, alive, human being. To have a long life, one has to learn how to live with embarassment and to avoid the silly little tribal pulls that can cause one to love something not because it is true but because your fellow tribe members practice it/believe in it. Life is a riff.

    The game of life demonstrates how simple rules can result in other rules that weren’t in the original rules. How one thinks of it depends, I think, on how one thinks of the rules; are they descriptors of the behaviors observed or are they, in a very real sense, actual inherent rules that limit behavior.

    Maybe, they are both 😉

    Baby Jones,

    I think that Niels Bohr’s Principle of Complementarity can apply to ways of knowing as well; if you get analytic, you can’t pay attention to the synthetic, and vice-versa. But both are complementary and needed to get the ‘whole picture’.

    Ric,

    good job 🙂

    I think part of the ‘issue’ is that, and I think this is a left-over from supernatural theism, that people in Western culture grow up thinking that these laws/habits are more ‘real’/important if they exist independently of us than if they are, at least a bit, created by us (like the various ways we have of harnessing the economy or justice).

    I think also a big problem is just translation — when these scientists do their discoveries, they do it (hopefully) in a precise epistemology (eg. we observed this at such and such a time under such and such conditions in this location), but when they then talk about it to the public, they have to then use a language that isn’t quite up to snuff for discussion of the experiment — a lot of the precise nuance is lost and we get things like ‘the G_d particle’ being discussed.

    Or so it is perhaps.

  14. In his new book, David Deutsch says that reductionism does not work even in principle since the laws of thermodynamics, and more specifically entropy and the irreversible arrow of time, do not follow from the microscopic laws of physics which are reversible.

  15. Curious Wavefunction,

    I read that too and I think your take is basically right, but I think Deutsch’s view is a bit more nuanced.

    As he said in the Fabric of Reality: “The fabric of reality does not consist only of reductionist ingredients like space, time and subatomic particles, but also of life, thought, computation and the other things to which those explanations refer.”

    Also, as I quoted previously in this thread, he said “In the reductionist world-view, the laws governing subatomic particle interactions are of paramount importance, as they are the base of the hierarchy of all knowledge. But in the real structure of scientific knowledge, and in the structure of our knowledge generally, such laws have a much more humble role.”

    So, in his view they have “role” (though often a very humble one). The examples you quote point out how humble that can be at times.

  16. Scientific theory gives me the decision of what I’m going to do in the next. The laws governing subatomic particle interactions are of paramount importance, as they are the base of the hierarchy of all knowledge. But in the real world such laws have a bad sense among us.

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