Arguing With Zombies

Arguing With Zombies:
Economics, Politics, and the
Fight for a Better Future,
by Paul Krugman.

Recently I read Arguing With Zombies: Economics, Politics, and the Fight for a Better Future, by Paul Krugman. The book is a collection of editorials and blog posts Krugman wrote for the New York Times, plus a few other previously-published articles. I enjoy Krugman’s writings, but what do they have to do with biological physics or medical physics? Based on the first 390 pages of his book, the answer is: nothing. But near the end was a 1993 article that appeared in The American Economist titled “How I Work” that is relevant to Intermediate Physics for Medicine and Biology. One feature I like best about IPMB is its emphasis on deriving simple “toy models” that provide insight. Simple models aren’t in fashion in biomedical research, but I like them and so does Krugman.

“How I Work” lists Krugman’s four basic rules governing his research. You can read excerpts of his analysis below. Whenever he starts applying his rules specifically to economics, just replace all the financial talk with illustrations from physics applied to medicine and biology.

Listen to the Gentiles

What I mean by this rule is “Pay attention to what intelligent people are saying, even if they do not have your customs or speak you analytical language.”…

I am a strong believer in the importance of models, which are to our minds what spear-throwers were to stone age arms: they greatly extend the power and range of our insight. In particular, I have no sympathy for those people who criticize the unrealistic simplifications of model builders, and imagine that they achieve greater sophistication by avoiding stating their assumptions clearly. The point is to realize that economic models are metaphors, not truth.

For a physicist working in medicine and biology, the “gentiles” would be the biologists and medical doctors. They have much to tell us. For example, when I worked at the National Institutes of Health I learned a lot about magnetic stimulation of nerves from Mark Hallett and Leo Cohen, even if sometimes they mixed up their electricity and magnetism.

I like Krugman’s emphasis on using models to extend our insight. Models may not be as common in pure physics, where you can deduce things from fundamental principles, but biology is so complicated that you can rarely start from Schrödinger's equation and get anywhere. You build models to make sense of biological complexity.

Question the Question

In people in a field have bogged down on questions that seem very hard, it is a good idea to ask whether they are really working on the right questions. Often some other question is not only easier to answer but actually more interesting!

Organisms are so complex that often the right questions aren’t obvious. It’s hard to teach a student how to ask better questions, but we must try.

Dare to be Silly

If you want to publish a paper in economic theory, there is a safe approach: make a conceptually minor but mathematically difficult extension to some familiar model. Because the basic assumptions of the model are already familiar, people will not regard them as strange; because you have done something technically difficult, you will be respected for your demonstration of firepower. Unfortunately, you will not have added much to human knowledge.

What I found myself doing in the new trade theory was pretty much the opposite. I found myself using assumptions that were unfamiliar, and doing very simple things with them. Doing this requires a lot of self-confidence, because initially people (especially referees) are almost certain not simply to criticize your work but to ridicule it….

The age of creative silliness is not past. Virtue, as an economic theorist, does not consist in squeezing the last drop of blood out of assumptions that have come to seem natural because they have been used in a few hundred earlier papers. If a new set of assumptions seems to yield a valuable set of insights, then never mind if they seem strange.

Throughout my career, I have developed simple models. For example, one of my favorite publications is “How to Explain Why Unequal Anisotropy Ratios is Important Using Pictures but No Mathematics.” It consists of some almost silly hand-waving that is amazingly effective at explaining how electric fields interact with cardiac tissue. Another example is my paper “Virtual Electrodes Made Simple” in which I use a trivial little cellular automaton to explain how certain cardiac arrhythmias begin.

Biomedical engineers are doing some incredibly sophisticated calculations to simulate how our bodies work, and these studies are necessary and valuable. But I believe that for those of us who apply physics to medicine and biology, the age of creative silliness expressed through simple models is not yet over. That’s why Russ Hobbie and I stress building models in Intermediate Physics for Medicine and Biology.

Simplify, Simplify

The injunction to dare to be silly is not a license to be undisciplined. In fact, doing really innovative theory requires much more intellectual discipline than working in a well-established literature. What is really hard is to stay on course: since the terrain is unfamiliar, it is all too easy to find yourself going around in circles…. And it is also crucial to express your ideas in a way that other people, who have not spent the last few years wrestling with your problems and are not eager to spend the next few years wrestling with your answers, can understand without too much effort.

Fortunately, there is a strategy that does double duty: it both helps you keep control of your own insights, and makes those insights accessible to others. The strategy is: always try to express your ideas in the simplest possible model. The act of stripping down to this minimalist model will force you to get to the essence of what you are trying to say….

The downside of this strategy is, of course, that many of your colleagues will tend to assume that an insight that can be expressed in a cute little model must be trivial and obvious—it takes some sophistication to realize that simplicity may be the result of years of hard thinking…. There is a special delight in managing not only to boldly go where no economist has gone before, but to do so in a way that seems after the fact to be almost child’s play.

Physicists working in medicine share some of the frustrations that Krugman experiences. Reviewers of papers—and especially reviewers of grant proposals for the National Institutes of Health—often don’t appreciate simple models. My simulations of cardiac electrophysiology have always lacked the particular ion channel that the referee believed was critical, and my biomechanics models tend to use simplifications such as linear strains that trigger objections. (A referee for one of my National Science Foundation applications claimed “this proposal should never have been submitted.”😮)

I often discard biological realism in order to focus on the one or two new features of a model. I’m not asserting that the discarded behavior is unimportant. Rather, I want a simple model so I can highlight the new feature that I’m studying. I don’t want my message to be frittered away by detail. Like Thoreau, Krugman and I strive to simplify, simplify! I hope students using Intermediate Physics for Medicine and Biology learn to appreciate the value of a simple model.

Read “How I Work” online for free.

Listen to Paul Krugman explain how he revolutionized trade theory.

He and I are both big Asimov fans.

https://www.youtube.com/watch?v=pfte6Ynpe8w