Perspectives on theory at the interface of physics and biology

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William Bialek has just posted on the arxiv a thoughtful piece exploring the role of theory in biology. He argues that theory has played a more important role in the development of biology than it is given credit for, and also that there is cause for optimism regarding the role that theory will play in the future. For example, he wrote “What is emerging from our community goes beyond the “application” of physics to the problems of biology. We are asking physicists’ questions about the phenomena of life, looking for the kinds of compelling answers that we expect in the traditional core of physics.” I also liked the introduction to Bialek’s Biophysics textbook, which explores some of the same issues.

One of the topics that Bialek addresses in the arxiv article is the explosion of parameters in biological models. I particularly appreciated his historical discussion of the Hodgkin-Huxley model of action potentials in neurons, and how progress can be made by analyzing the class of behaviors that can be achieved and to consider how the cell can adapt to remain in the proper regime. He summarizes his thoughts on the role of parameters with the following:

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Students don’t always understand what you think that they understand

Below is a figure that had a tremendous impact on me when I saw it ten years ago in a paper written by Carl Wieman and Kathy Perkins (figure adapted from work done by Eric Mazur at Harvard). The figure shows two  problems designed to test the same basic physics concept, namely how current flows in circuits. Determining the current through the various resistors in part (a) requires solving a pair of equations, and as a teacher a reasonable assumption is that if students can do the question correctly then they understand the concepts. However, what Mazur found is that many students could solve this challenging problem but were unable to solve the (apparently) much simpler conceptual problem in part (b) asking about how the brightness of the light bulbs will change when the switch S is closed.

The students were simply using a “recipe” to solve the problem given in (a), indicating that they would quickly become confused when attempting to apply their knowledge outside of the artificial realm of the problems that they had practiced. This realization played a significant role in my decision to spend three months as a Christine Mirzayan Fellow at the National Academics with the Board on Science Education , where I became convinced that active learning approaches could help students with these conceptually challenging topics.

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