No, this is not about a cat, dead or alive.
Yes, I am a quantum mechanic by training and possibly a quantum astrologer. And yes, there are many strange and interesting features of the quantum world, but Schrodinger’s contributions to thinking conceptually about thermodynamics might, in the long run, make a larger impact on the riddle of life.
Schrodinger’s famous little green book – What is Life? – was borne out of three lectures he delivered at Trinity College, Dublin, in 1943. Some might consider him a dabbler, a theoretical physicist trying to discuss questions of biology that were out of his league. Schrodinger’s name is not typically associated with the greats of biology, and his best-known connection to a living system has to do with a cat. A philosophical cat, mind you, not a biological or physical one.
But if we peer a little deeper at Schrodinger’s thoughts and written words, we might sense that he’s on to something. A deeper something. I’ve only just begun to appreciate Schrodinger’s foray into the physical and material basis of living systems through the work of Robert Rosen in Life Itself. It’s a pleasure to see Dorion Sagan and Eric Schneider use the same starting point in their book Into the Cool.
Schrodinger’s question, posed in his third lecture: “How does an organism concentrate a stream of order on itself and thus escape the decay of atomic chaos mandated by the Second Law of Thermodynamics?” There’s a lot to unpack here, and Sagan & Schneider, will discuss the many shades of words such as order and chaos. But fundamentally, life seems like an enigma – fighting against the inexorable decay ruled by thermodynamics. Paradoxical beings are we, no?
There is much popular punditry waxing poetically (and confusingly) about the seeming paradox, and I used to think these ideas strange, but I don’t any longer. At least not conceptually. I still don’t understand how it all works, but I generally agree with the explanation provided by Sagan & Schneider. They state it better than I do, so I’ll just quote them.
Organisms continue to exist and grow by importing high-quality energy from outside their bodies. They feed on what Schrodinger termed “negative entropy” – the higher organization of light quanta from the sun. Because they are not isolated, or even closed systems, organisms – like sugar crystals forming in a supersaturated solution – increase their organization at the expense of the rise in entropy around them. The basic answer to the paradox has to do with context and hierarchy. Material and energy are transferred from one hierarchical level to another. To understand the growth of natural complex systems such as life, we have to look at what they are part of – the energy and environment around them. In the case of ecosystems and the biosphere, increasing organization and evolution on Earth requires disorganization and degradation elsewhere. You don’t get something from nothing.
There’s even more to unpack. And Sagan & Schneider will do this. But other thoughts swirl in my head in connection to what my students are learning in my G-Chem 2 class that focuses mainly on thermodynamics and equilibria. Therein lies the limitation. The model of equilibrium thermodynamics we teach to students is a reduced system. A simpler system. Easier to understand. Easier to apply. Useful in many instances. But like all models, it has its limitations.
This semester I’ve been experimenting with asynchronous discussion board prompts to nudge students to explore concepts outside the simple model. Last week’s prompt was: “We've seen that Energy is nebulous and hard to define. The same applies to Entropy. In class we've talked about entropy in several different ways (order/disorder, available motion, probability + perception, heat dissipation) but there are others (such as a measure of information, e.g., Shannon entropy has a formula very similar to Boltzmann's). And Life has been expressed as a negentropy ("negative" entropy) machine. What do you think about this?”
I might have over-reached. While I think the students might have found the prompt interesting, their musings reflected many confusing ways of applying the terminology. There were some good examples based on what I emphasized in class (available motion and counting arrangements), peppered with speculative ideas that don’t make sense on closer examination. I should not have been surprised at the way Shannon-like information entropy was conflated with chemical thermodynamic entropy, nor at the way negentropy was bandied. My fault for not being precise with the terms. But I’ve learned a useful lesson in how to use open-ended vagueness as an engagement tool. The riddle of life is not an easy one to answer, and I think students got a gist of this.
In Chapter 2 of Into the Cool, the authors choose to use the term exergy, the equivalent of chemistry’s free energy. This year, I opted to engage my G-Chem students in a longer in-class discussion (by which I mean forty minutes, as opposed to a quick two-minute definition) of why free energy is “free”. Because I’ve been stressing the uses and limitations of models, I used the simple diagram below (but with more arrows and scribblings) to show the evolution of what we’ve been learning. We start with the tripartite thermodynamic universe (on the left), then dissolve one of the distinctions (dotted line, middle) when we introduce enthalpy, and finally add a new box (right) when we introduce free energy. Entropy is a big part of the discussion, as is the “quality” of energy and its eventual dissipation into the large pool of the thermal surroundings. This is finally illustrated with ratios of delta-G/delta-H for a variety of fuels.
What is exergy and why haven’t you heard of it? I’ll quote Sagan & Schneider once more.
Exergy is not really a new word, as it is widely used in energy engineering, especially in Europe. Engineers are interested in wringing the mist work out of a given parcel of energy. All energy is not equal. Some energy may be embodied in high-energy electricity that can run motors, boil water, or run a computer. Another form of energy is low-grade heat, infrared radiation that can do little or no work… Exergy measure the quality of energy. It measures the maximum capacity of an energy system to perform useful work as it proceeds to a state of equilibrium. When energy does work, its quality, its exergy, diminishes. This is another statement of the second law. Not only is exergy a measure of the quality of the energy, but also it tells you how much the system is out of equilibrium, and how big the gradients are and the potential of doing something useful with that energy.
I say something roughly similar in class without using the term exergy. And I use high-energy photons as my example rather than electricity. But I wish I had known of the pithy quote that the authors provide (a personal communication to them from James Kay): “Exergy is about the potential to do something with energy and entropy tells you what happened to the energy.” I’ll have to remember this one!
That brings me to the end of today’s post. Hopefully you’ve gotten a sense of why the book is titled Into the Cool. We’re heat-producing organisms, eating higher quality energy and dissipating lower quality heat. To live we’re constantly trying to go into the cool.
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