Friday, March 3, 2017

Science is told by the victors and Learning to build models

A common quote about history is that "History is written by the victors". The over-simplified point is that sometimes the losers of a war are obliterated (or at least lose power) and so don't have the opportunity to tell their side of the story. In contrast, the victors want to propagate a one-sided story about their heroic win over their immoral adversaries. The origin of this quote is debatable but there is certainly a nice article where George Orwell discusses the problem in the context of World War II.

What does this have to do with teaching science?
The problem is that textbooks present nice clean discussions of successful theories and models that rarely engage with the complex and tortuous path that was taken to get to the final version.
If the goal is "efficient" learning and minimisation of confusion this is appropriate.
However, we should ask whether this is the best way for students to actually learn how to DO and understand science.

I have been thinking about this because this week I am teaching the Drude model in my solid state physics course. Because of its simplicity and success, it is an amazing and beautiful theory. But, it is worth thinking about two key steps in constructing the model; steps that are common (and highly non-trivial) in constructing any theoretical model in science.

1. Deciding which experimental observables and results one wants to describe.

2. Deciding which parameters or properties will be ingredients of the model.

For 1. it is Ohm's law, Fourier's law, Hall effect, Drude peak, UV transparency of metals, Weidemann-Franz, magnetoresistance, thermoelectric effect, specific heat, ...

For 2. one starts with only conduction electrons (not valence electrons or ions), no crystal structure or chemical detail (except valence), and focuses on averages (velocity, scattering time, density) rather than standard deviations, ...

In hindsight, it is all "obvious" and "reasonable" but spare a thought for Drude in 1900. It was only 3 years after the discovery of the electron, before people were even certain that atoms existed, and certainly before the Bohr model...

This issue is worth thinking about as we struggle to describe and understand complex systems such as society, the economy, or biological networks. One can nicely see 1. and 2. above in a modest and helpful article by William Bialek, Perspectives on theory at the interface of physics and biology.

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