Monday, July 7, 2014

The Standard Model

I spend my time in a school of public policy, a field much dominated by social scientists such as economists. It is striking how their best theories have very weak mechanisms to account for what happens in the world, how often it is a matter of A being likely related to B, but with no idea of the size of that relationship. They do have an idea of what to do if there is a problem, and it would seem that their intuitions are helpful. They can model an economy in equilibrium, but it would be helpful to know how sensitive their models are to assumptions and to less than equilibrium, and how much they would bet on a claim they are right. There is remarkable disagreement among, them, only some of which is scientific.

I believe I understand their basic microeconomic ideas and some of the Nobel-Prize improvements. I'm less sure about their macroeconomic ideas, but the basics seem clear. I am not sure if there are any quantitative tests that are decisive.

It is almost surely the case that when we measure or theorize about society, if we know the order of magnitude of a relationship, is it say 1% or 10%, or positive or negative, we are making progress, and it is likely that we know such numbers with at most two significant figures, usually just one--0.1 is different from 0.2, but unlikely that 0.16 is different than 0.17 once we are honest about how well we can measure something taking into account confounding effects. This is not an indictment of economics or social science, for to learn that A is actually related to B, and to get that relationship roughly right with an honest sense of how good is our measurement is a major achievement. It is also a major achievement to identify significant phenomena, such as the role of information asymmetry in markets, and indicate how they work. But the next question is how much and when.

I was brought up in a different field, one that was not so precise fifty years ago.  Over the last forty years, elementary particle physicists--experimentalists and theorists--have developed a remarkably good account of the basic constituents of matter. The Standard Model, as it is called, accounts for forces between nuclei, between charged particles, and for radioactive decay--the strong, electromagnetic, and weak forces, as they are called. Gravity has not yet been incorporated in that model, but general relativity (Einstein's theory) is powerful in explaining the largest phenomena we see at the everyday to cosmic scale. Those theories have proven valuable for those studying the origin of our universe, for it tells them just what kinds of particles existed in the early hottest state of the universe, in its first few minutes, and they have used that knowledge to figure out much of what happened in those first few minutes. And what has happened after.

The experimental physicists and the observational astronomers have made unbelievably accurate measurements of the world we live in, unbelievable to anyone who was in graduate school when I was in the 1960s. Practically, we now have an origin story about our universe that is quite rich and accurate. It is surely the greatest gift from physics to religion and metaphysics. But the physicists do not pretend to have an account of our moral and personal origins, and a wide variety of explanations, from religious to anthropological are offered. Moreover, there is no conflict between the physicists' account and the moral accounts. They occupy different realms.

What is most remarkable is the accuracy of the Standard Model. It is not unusual for the theory to predict not only the rough size the effects, but to predict them to an accuracy of three decimal places. Enormous effort has been required to make that theory useful to such accuracy, but it works and it works quite well.

Any such theory will have stuff it does not explain or explains inaccurately. Sometimes we have to learn to calculate more accurately, sometimes we will need a more comprehensive theory, so-called "beyond" the Standard Model. That theory might explain some of the facts the Model does not pretend to explain, such as the mass of the electron or the values of the interaction constants.

I do not expect anything like this for public policy and social science. I am not sure there could be a standard model of society and economy. The social scientists' attempts have been very smart, but too smart by a half. Physicists do not need to account for many features of the material world, as long as they focus on the main ones as they understand them. Social scientists seem to make what they take as progress by ignoring features that most people consider important. Perhaps they should not be so imitative of the physicists. The model of economic man or political man (or woman) are notably productive of theory and Nobel Prizes, but it's hard to find out how important are parts that they leave out.

Physics is not the model science or theory. But it does suggest that there is a need for more careful consideration by social scientists of what they leave out of consideration, and the sensitivity of their theorizing to those external factors. I would think social scientists and finance theorists would be excited to incorporate the experience of the Great Recession into their theorizing, what I imagine would cause of substantial revision of their ideas. Maybe their ideas incorporated the Great Recession already. Perhaps it is not possible. To defend your theories and blame others for doing something wrong is to find yourself condemned to irrelevance.

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