01-29-2017, 04:15 PM
Quote:Yes it is. Correlations and models are analogies of reality. For example, what do we measure when air is assayed for CO2 content. What is measured is an electrical signal, the output of a photomultiplier that converts light intensity to an electrical signal. According to the Beer-Lambert theory: the negative log of the fraction of light of a particular wavelength that is not absorbed by a colored species (i.e. one that is not transparent at this wavelength) is directly proportional to the molar concentration of the species.
The idea is based on an observation. If you make up a suspension, it will look almost clear, hazy, translucent, or opaque depending the concentration of the suspension. This leads to an analogy for what might be going on. Place the suspension in a square tube (cuvette). When you shine a light on it, some of the light rays will hit a particle and not pass through the cuvette. Other rays will miss the particles and pass right though. The percentage of the rays that get through is the percent transmission or T. Concentration of the particles is proportional to -logT. THe log relationship comes from an imagined slicing the mixture into thin layers perpendicular to the light path that is one particle thick. Each slice either contains a particle (which blocks the light ray) or it doesn't, which transmits the light. Each layer adds another chance at blocking the light. The effect of additional layers is not additive. This is because particles in one layer can be behind the location of particles in the layers in front of it, in which case the light was already blocked. If you use a little math it is clear that that the transmission and concentration have a log-dependence on the fraction of the locations of a layer than contain a particle (concentration) and the number of layers contained in the cuvette (path length) which gives the Beer-Lambert Law .
The Beer-Lambert Law is the basis for the utility of spectroscopic analytical methods. When a theory becomes well accepted it is sometimes called a Law. If one wishes to analyze something one measures absorbance (-logT) of the species in the sample and established they absence of interference and linearity of method. One then has a validated assay. The output of a validated assay is a fact. It is a fact derived from a model/theory based on some analogy obtained by conjecture, from observations. Basic observations are facts. But so are assays, which are analogies. That is, analogies can be facts, and ARE facts--if the analogy is valid.
This is how science works. We advance not because we know more, but because we have more facts to contemplate, most of which are derived from a theory/analogy. Issac Newton was one of the greatest physcists of all time, but he knew far less than a run of the mill physicist today.
What a ridiculous response. The level of CO2 in the atmosphere is something that has a definite answer independent of the observer. Issues in measurement (the precise method used, whether the sample being tested is truly representative of the larger whole, etc.) clearly affect the degree of certainty we have in knowing that answer, but the answer itself is a real thing. Arguing whether a doctor is or isn't like a mechanic, in what ways (it can't be in all ways otherwise it wouldn't be an analogy, but an identity), and how that relates to the question of public policy, is a wholly different kind of question, one that does indeed depend on one's "underlying philosophical assumptions" in a way that the other really doesn't.
So please, spare me the sophistry.