October 22, 2009

The interconnectedness of science

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here.)

Even the most die-hard religious person will concede that scientific knowledge is extremely powerful. In thinking about evolution alone and the arguments presented for evolution by natural selection in Richard Dawkins's new book The Greatest Show on Earth, questions that might occur to the reader are: Why is science so powerful? What is it about its structure that has made it so successful?

This is a question that people have been grappling with for a long time and the answer is surprisingly hard to come by. The facile answer that science works so well because it produces truth is not easy to justify because great scientific theories in the past that were thought to be true have fallen by the wayside and there is little reason to think that we are better judges of the truth of theories than our predecessors were.

As long ago as 1906, Pierre Duhem in his book The Aim and Structure of Physical Theory laid out the difficulties that a scientist face in determining if a particular theory is true, by drawing an analogy between how a watchmaker and a doctor go about diagnosing the source of a malfunction in their respective areas of expertise:

People generally think that each one of the hypotheses employed in physics can be taken in isolation, checked by experiment, and then, when many varied tests have established its validity, given a definitive place in the system of physics. In reality, this is not the case. Physics is not a machine which lets itself be taken apart; we cannot try each piece in isolation and, in order to adjust it, wait until its solidity has been carefully checked. Physical science is a system that must be taken as a whole; it is an organism in which one part cannot be made to function except when the parts that are most remote from it are called into play, some more so than others, but all to some degree. If something goes wrong, if some discomfort is felt in the functioning of the organism, the physicist will have to ferret out through its effect on the entire system which organ needs to be remedied or modified without the possibility of isolating this organ and examining it apart. The watchmaker to whom you give a watch that has stopped separates all the wheelworks and examines them one by one until he finds the part that is defective or broken. The doctor to whom a patient appears cannot dissect him in order to establish his diagnosis; he has to guess the seat and cause of the ailment solely by inspecting disorders affecting the whole body. Now, the physicist concerned with remedying a limping theory resembles the doctor and not the watchmaker.

All of science is an interconnected web if theories. It is not like a set of independent modules where you can pluck one out and replace it with another. It is more like the way that the box springs in a mattress are all linked together. This is why it is so hard to replace one theory with another. All the other theories to which it is linked work to prevent the change.

This is why people who think that they can replace just evolution with some creationist idea du jour stumble badly. The theory of evolution gets its strength from that fact that it meshes well (though not perfectly because while science progresses it is never perfect) with the other theories of biology and chemistry and physics and geology and astronomy, as Dawkins so tellingly demonstrates. Creationist ideas go against all these other theories to various degrees. So when you reject the theory of evolution, you are pretty much rejecting all of science. Trying to replace evolution with the theory of intelligent design in a few cases is like (to switch analogies for the moment) trying to replace just one of the fuel injectors in a modern car with a carburetor from an older car. It just will not work.

An obvious objection to the above description is that it implies that all theories are locked in place forever, which is obviously false since we know that scientific revolutions have occurred in the past in single areas of science. How could that have happened? If you examine closely the history of how scientific revolutions occur, you see that they are preceded by extended periods of crises, when theories come under increased critical scrutiny and suspicion because of perceived weaknesses. Those correspond to the weakening, and even the slow removal, of the links connecting the theory under question to the rest of science. The other theories slowly adapt to the fact that one of their theories is suspect. This enables the suspect theory to be decoupled from the rest and replaced by the new theory.

Initially the new theory will work somewhat imperfectly because it will have few connections to the rest of the scientific theory web. But if it is a good theory that performs its own functions well and has at least some good working connections to other theories, the other areas of science will adapt to the new theory and new links will be forged, so that the end result will once again be a strong interconnected web of theories, but a different one from what existed earlier.

What religious people do not realize is that the theory of evolution is nowhere close to being in crisis and is firmly embedded in the fabric of science. In attempting to discredit it, they are taking on all of science. This is why they have failed so far and will continue to fail.

POST SCRIPT: Stephen Colbert gets ready for the end times

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I really like the part of today's post where you talk about scientific revolutions. The imagery you use regarding the web of scientific theories decoupling and relinking is evocative. Following the details in the history of science isn't easy, and it is nice to have an abstract distillation of major historical trends.


Posted by Jared on October 22, 2009 11:40 AM