Overzealous reductionism, blind reification: Of hydrogen bond, introversion and Voldemort (Part 1)

Image credit: Victims of circumsolar (license)

Note: This is the first part of the series. You can read other parts here:

Part 1 |  Part 2 Part 3 (end)

Let’s talk about two interesting human tendencies, reductionism and reification, and as the title suggests (or not), the problems that arise when we overdo it.

Reductionism would be quite self-explanatory: we tend to reduce things, either down to their components, or into categories. Science itself is the epitome of this. In fact, science can be defined exactly in this context — quick Google search: Science = a systematically organized body of knowledge on a particular subject. In other words, science is a system of cataloguing knowledge (important! You will be tested later :>).

There is this xkcd strip about the purity of sciences:


One might wonder, if some fields are (debatably) purer than the others, why the less pure fields exist at all? What delineates these fields (e.g. at which point chemistry becomes biology)? One answer, among many, is that they are categorised by their level of reductionism.

If you studied chemistry in high school, you probably had this feeling that I had, that chemistry somehow has its own ‘logic’, which is especially true for organic chemistry: if one part of this molecule is nucleophilic, it should be attracted to this other part, and so on, which does not feel rigorous. Kind of hand-waving, if you will. This ‘logic’ is chemistry’s level of reductionism. Another example: when we learn the about trends in the periodic table the question will ask you to justify from first principles right? For example, atomic radius decreases across the period because the electron is added to the same shell but the increasing positive charge in the nucleus contracts the electron shell, giving decreasing radius. Notice that this explanation only goes as far as the electron shell. Can you describe the electron orbitals at quantum mechanical level and reason from there (going over to ‘purer’ physics and maths, going further in reductionism)? Yes, you can, but you don’t need to in this case. The first principles regarding proton, electron, and shell are coherent and predictive enough to give explanation.

So can you always apply reductionism level at ‘purer’ field level (like above, where we apply physics to chemistry)? It definitely works sometimes. That’s why we have such wonderful amalgamations like biochemistry, physical chemistry, and so on. My own field is biophysics, which is wonderfully at the overlap of biology, chemistry and physics. However, there are times that it is not only cumbersome, but impossible. Can we describe human altruism in terms of quantum mechanics? Probably not.

A useful concept here to know is emergence. In a complex system, the system ’emerges’ a new property that is not exhibited by any of its constituents. The emergent property is what I referred to as the field’s own ‘logic’ or ‘first principles’ to which you fall back on.

Some practitioners might feel that they are suffering from physics envy but they need not. It is not any nobler to study in one field or another, no matter the science ‘purity’ index because each field has their emergent philosophy to contend with. Since we are in Karolinska Institutet, let’s have physiology or medicine as example. Biology is messy, as you probably know already. Ask the doctors, the drug researchers, the geneticists, the researchers all over the campus. Also, since we know the different fields are not mutually exclusive and can benefit from others’ first principles, we should have more interdisciplinary interactions and exchange with each other.

But who knows if emergence is just due to our limited brain. Maybe in the future we can understand it all. Even so:

[ Ultimately, this fuzzy yet useful view of hydrogen bonding makes an important statement about the philosophy of chemistry. It tells us that chemistry has its own philosophy based on models and utility that is independent of its roots in physics. As the chemist Roald Hoffmann memorably put it, chemical concepts like aromaticity and electronegativity start to “wilt at their edges” when examined too closely, and Hoffmann could have been talking about the hydrogen bond there. The physics-based view of a hydrogen bond would involve writing down the Schrodinger equation for these bonds and rigorously solving it to obtain quantities like the energy and geometry of the bond. But that exercise is too reductionist; it does not actually help me understand the nature and variety of these bonds. It won’t tell me why water is liquid and why it flows from mountains, why it’s a universal solvent and why it’s an existential life-giver. Chemistry proclaims its own emergent language and philosophy, and while the material entities of which molecules are composed are grounded in physics, the molecules themselves belong squarely in the domain of chemistry. ]
— Ash Jogalekar, A bond by any other name…: How the simple definition of a hydrogen bond gives us a glimpse into the heart of chemistry

PS: Ash Jogalekar writes a lot about reductionism and emergence, among other things, in his wonderful blog The Curious Wavefunction.

Part 1 |  Part 2 Part 3 (end)

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