– By Byron Jennings, Theorist and Project Coordinator
Model dependent realism. I’m aware that this succinct definition sounds like an oxymoron: if it is model dependent how can it be realism? Model dependent realism comes from the book The Grand Design by Hawking and Mlodinow. The essential idea is that science is model building, but the internal aspects of the models are not significant; reality is model dependent. All our theories, laws, hypotheses are models, models for how the universe works. Nothing more and nothing less. What are the criteria for choosing a good model? There is really only one criterion: agreement with observation. Yet, as discussed in a previous blog there is also simplicity. But this is really a corollary of the first point. If the only criterion is agreement with observation, there is nothing to be gained by encumbering your model with frills that are unnecessary for making predictions for observations. Get rid of them.
A very similar idea for how knowledge is acquired goes by the name Critical Realism. (There seems to be a theorem that all approaches to science should have realism in the name.) Personally, I would just call it model building and leave the realism out. But who am I to argue with Steven Hawking (I will anyway. And the ultimate authority, Wikipedia, does say it is controversial).
Critical realism traces its roots back to a chemist, Michael Polanyi (1891 – 1976), but I first read about it in the book The New Testament and the People of God by N.T. Wright (the Anglican Bishop of Durham, written in 1992). The description given there is devoted mainly to history. It is similar to model dependent realism but puts more credence on the internals of the models. Even though Polanyi takes the stardom for this theory, Wright’s exposition is one of the best descriptions of how science works that I have read.
It will seem strange to many people that in a book that attacks the idea of God (The Grand Design) and a conservative Christian theologian propose similar models for obtaining knowledge. But it really isn’t that strange. There is a common foe: postmodernism. Postmodernism is the idea that all points of view are equally valid. This is anathema to both scientists and conservative Christians. Both scientists and Christians, want to propose a criteria that separates the sheep from the goats, the wheat from the chaff, or the valid models from the dung heap of post modernism (the reader may gather that I am not a great fan of postmodernism either).
How is the separation of sheep from goats done? Unlike the positivists’ claim that models cannot be verified, contrary to Popper, they can be not be falsified either (the dreaded Duhem-Quine Thesis) but they can be compared. Established models (the word I prefer to theory, law, or controlling narrative) are rarely abandoned because they simply disagree with observation. Rather they are abandoned because another model does a better job. To paraphrase the American gun lobby: Observations do not kill models, models do. The ether was only abandoned after Einstein proposed the special theory of relativity; the Michelson-Morley experiment was not sufficient. Michelson and Morley may have provided the ammunition, but it was Einstein that pulled the trigger. His defense lawyer would argue that the ether was not shot, but rather had it throat slit with Occam’s razor. Einstein did not prove that the ether did not exist. Rather he showed that the ether hypothesis, like the Omphalos hypothesis, has no predictive power, and in the end, it was eliminated by appeals to simplicity.
You can go through example after example and see observation deciding between or among competing models. The big bang model of the universe beat out the steady state model because it predicted the three degree microwave background, the quark model beat out rivals with the discovery of the J/Psi particle, and continental drift beat out the fixed continent model when the seabed of Atlantic was explored in detail. In every case, it is model combat and the one that was best at predicting new phenomena won. If you want to become rich and famous (or at least win a Nobel prize) come up with a model that makes a striking prediction (none of this postdiction nonsense) and have it confirmed by observation (that is the tricky part; bribing experimentalists does not count).
What do the internals of models mean? Are they really quite as meaningless as the model dependent realism implies or do they have meaning as the critical realism suggests. I take an intermediate approach and follow Poincaré. I define things to exist if all the math goes through as if they did. What’s good enough for Poincaré is good enough for me.