Wednesday, February 28, 2007

The Limits of Computer Precision

After reading Jerome Schmitt’s article at American Thinker this morning I decide to post his excellent explanation of the roles and limits of computer models, even before Rush Limbaugh uses the story this afternoon. The Democratic Party is wagering extensive political capital on the completely wrong theory that human activity is bad for the climate. Because they are factually wrong, the collectivist big government do-gooder elitists need to lose this argument with the general public.

Numerical Models, Integrated Circuits and Global Warming Theory: Many other scientific fields besides climatology use similar models, based on the same or related laws of nature, to explain and predict what will happen in other complex systems. Most famously, the US Department of Energy's nuclear labs use supercomputer simulations to help design atomic weapons. Most of this work is secret but we know, of course, that the models are "checked" occasionally with underground test explosions. The experimental method is an essential tool.

Almost all semiconductor manufacturing processes occur in closed vessels. This permits the engineers to precisely control the input chemicals (gases) and the pressure, temperature, etc. with high degree of precision and reliability. Closed systems are also much easier to model as compared to systems open to the atmosphere (that should tell us something already). Computer models are used to inform the engineering team as the design the shape, temperature ramp, flow rates, etc, etc, (i.e. the thermodynamics) of the new reactor.

Nonetheless, despite the fact that 1) the chemical reactions are highly studied, 2) there exists extensive experience with similar reactors, much of it recorded in the open literature, 3) the input gases and materials are of high and known purity, and 4) the process is controlled with incredible precision, the predictions of the models are often wrong, requiring that the reactor be adjusted empirically to produce the desired product with quality and reliability.

The fact that these artificial "climates" are closed systems far simpler than the global climate, have the advantage of the experimental method, and are subject to precise controls, and yet are frequently wrong, should lend some humility to those who make grand predictions about the future of the earth's atmosphere.

The key point is that even with small closed limited atmospheres where all major factors are known with precision, the precision of measuring complex systems is still insufficient to guarantee computer models will produce accurate repeatable results. This is not a flaw with computers or a flaw with human intelligence. It is a product of the real world where every aspect of existence, even the smallest deviation of an outer orbital electron, contributes to the final end result. In other words, in reality, everything counts and no computer knows everything.