Do economists have physics envy? (Part 2)

Last year I wrote a post called "Do economists have physics envy?". Historian Philip Mirowski (who I notice also got his econ PhD from Michigan!), who literally wrote the book on the interplay between economics and physics, is not too happy with my post. In a recent interview, he explains why:

Let’s take a recent example of a popular contemporary economist blogger, insisting that economists don’t suffer from physics envy. Instead of looking at the history, or the technical issues involved, he just blurts out some random impressions: economists make more money than physicists (I cannot make this stuff up); an economist can talk about how much progress physicists are likely to make, and get taken seriously, but not vice versa (ditto); economic theorists, traditionally, have been free from the constraints of empirical validation (note the total innocence of the history of empiricism in economics); and that equilibrium means something different in economics than in physics.The level of arrogance combined with parochial ignorance is pretty stunning, but not unusual. He has no conception of the historical track record of the disciplines of economics and physics evolving through time, with earlier points of interaction being masked by later developments, and further waves of strange action at a distance. The result would therefore never appear to contemporaries as strict identity.  

Economists with a tad more sophistication may admit something happened in the 1870s, but they go on to insist that a century and a half of further development has produced a set of doctrines that doesn’t necessarily have anything to do with that heritage. So in a weird sort of way, the more sophisticated modern line is that intellectual origins don’t matter to contemporary doctrines. Your average modern economist thinks history has entirely been banished by the activities of subsequent generations. Actually, I would argue against that; it is more plausible to think that it’s a path-dependent process. Neoclassical economists can’t entirely wish away their origins, and there are a number of times where I try to point that out in the book: for example, the eccentric ways in which the early neoclassicals are totally confused about how to deal with production. Moreover, I think the physics origins really instantiates the central metaphor of a market as if it were a kind of machine that takes stuff from a place it’s not supposed to be and puts it in a place that it deserves to be. That leads to this whole idea of allocation as a special phenomenon, which captures the essence of economics. That’s the way the first three generations of neoclassical economists think, in terms of movement in a commodity space. So for them, trade (exchange) is motion in a commodity space. All of these points comprise a deep inheritance of the early appropriation from physics that is really hard to get away from.

A couple of observations here. First, responses that rely on phrases like "I cannot make this stuff up" and "the level of arrogance combined with parochial ignorance", but fail to substantively address the argument in question, are indicative of a degraded discourse. Sputtering disdain is no substitute for an honest attempt to address someone's points. Of course, there's no reason at all that Mirowski should spend time and effort addressing or rebutting my points...but if he's not going to, at least he might consider ignoring my post completely instead of lobbing some sputtering disdain in my direction and moving on!

But anyway. 

Mirowski's work seems to attempt to answer two questions:

1. "How are physics and economics related historically?"

2. "How do current economic methods reflect the legacy of this historical relation?"

But my post was an attempt to answer a different question:

3. "How do economists currently view the discipline of physics?"

Which was related to a fourth question I didn't directly address, namely:

4. "To what extent do economists look to physics for new ideas nowadays?"

Those aren't the same thing. Regarding question 2, it's obvious to anyone who's studied both econ and physics that there are mathematical similarities between the two (e.g. calculus of variations). As for question 1, it's common knowledge that many economists in the past tried to apply physics ideas to econ. So I would never try to dispute those points. For more specifics on exactly how ideas crossed from physics to econ, and on which of those ideas remain to this day, one should probably check out Mirowski's book (though I hope it's written in a different tone than this interview).

But OK, just because economists did get inspiration from physicists in the past doesn't mean they do now. I've never met or heard of a currently working economist who reads physics papers. I'm sure some are out there, but it would seem to be a rarity. In the past, economists probably got lots of inspiration from physics, but I don't think that seems true anymore. Maybe I'm wrong about that, but I don't think so. That still leaves econ models with a legacy of physics influence (as I notice every time I see a Hamiltonian), but the phenomenon of economists looking to physicists for new ideas doesn't seem very pronounced or significant these days.

Now if that's true - and I'm happy to look at any evidence to the contrary - it leads to the question of "Why?" Why would economists draw less inspiration from physics than they used to?

Some reasons might be sociological. That's what my initial post was about. 

First, if economists don't see physicists as having higher status than themselves, they're less likely to look to physics for ideas about how to make models. And my impression is that modern economists, in general, don't see physicists as anyone that they need to emulate or look up to. In my initial post, I cited 1) money, and 2) popular respect as reasons economists probably no longer see physicists as being higher on the academic food chain than themselves.

Second, if economists value different things in their models than physicists do, there will probably be less impetus to emulate physics. In my initial post, I cited 1) empirical predictive power, and 2) symmetry as two things physicists care a lot about and economists value less (though (1) is changing). Econ and physics are just two different epistemic communities

In addition to sociological reasons for economists to take less inspiration from physics than in days of yore, there are also probably methodological reasons. A lot of modern econ theory is based on game theory. Game theory is not very similar to anything in physics - only a few tentative attempts have been made to connect the two, and generally from the physics side. Nash Equilibrium, as Von Neumann pointed out, is not really the same thing as an equilibrium in a physical system. In fact, some people argue that game theory isn't even part of "neoclassical economics," which is the historical strain of thought that Mirowski studies. 

So what does this all have to do with "physics envy"? The term "physics envy" gets tossed around a lot in public discussions of economics. Some people use it to mean that econ just isn't as good at describing reality as physics. Others use it to imply that economists have a pride and confidence in their discipline that only physicists really deserve. Still others use it in a historical sense, to refer to the links that Mirowski and others have written about. And some use it to imply that economists are just failed physicists. 

But I think most people use it as a simple emotive term, a stock phrase that carries an implication of "econ bad, physics good". Obviously most economists would disagree. Some of that is pure chauvinism, of course, but a lot has to do with the diverging methodologies of the two disciplines. And diverging methodologies come partly from sociology, and partly from the fact that these are just two different sciences attempting to answer two different sets of questions.