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“Observational Science” and the Limits of Certainty: The Case of Chemical Mechanisms | Righting America

by Mark Masthay

Continuing from his earlier post examining observational science and certitude, this week Dr. Mark Masthay clarifies the epistemic differences between observational science and his own chemistry lab for achieving scientific certainty. 

Because I do not study the past, Ken Ham’s bifurcation of science into “observational” and “historical” categories places no constraints upon my research enterprise; according to Ham’s criteria, my research is pure “observational science.”  Much of my research focuses on the elucidation of chemical reaction mechanisms, which—though they are characterized by experimentation—can nevertheless be known only with reasonable certainty, as explained below.  

When writing research articles and reports, my research group uses the mantra:  

The description of both research methods and experimental observations must be unassailable, but the underlying molecular-level details responsible for the observations are open to interpretation.  

The reason for this is simple: research is performed in the present, and the methods used and observations made are both repeatable and visible. A chemist is in control of the methods she uses in the laboratory, and she sees—either with her eyes or with chemical instruments—the outcomes of her experiments.  Hence, she is certain of her research methods in the same way she is certain of her method of washing the dishes in her kitchen sink; and she is certain of her experimental observations in the same way she is certain that her dishes have become clean.  In fact, repeatability of both methods and results is the principle reason for the “Experimental Methods” and “Results” sections of research articles; they provide other scientists the opportunity to duplicate reported methods and to verify or contradict reported findings.

Hence, both experimental methods and experimental observations satisfy Ham’s definition of “observational science.”  To illustrate more fully, I take an example from my own research.

When my colleagues and I report that

Upon exposure to intense green laser pulses, orange solutions of beta–carotene rapidly become colorless,

we are detailing the results of “observational science” performed in our laboratory. Our results are obtained in the present, visible to the naked eye, and repeatable. Equipped with a narrow definition of Ham’s “observational science,” this is all we would be able to report even though we would like to answer the more interesting and important question:  

What happens to beta–carotene at the molecular level which causes it to lose its orange color?

Because molecules are so small that they are invisible under even the most powerful of microscopes, this process is not amenable to direct observation at the molecular level.  Our interpretations of our experimental results are thus somewhat ambiguous. When we attempt to explain what occurs during a chemical reaction at the molecular level, we are engaging in educated speculation.  

Continuing with the illustration above, when my colleagues and I report that

Our data are consistent with a two–step mechanism in which (1) the laser causes an electron to leave a beta–carotene molecule and adhere to a solvent molecule, resulting in highly reactive free radicals which (2) subsequently destroy the parent beta–carotene, thus giving rise to the observed loss of color,

we do not mean that we know this proposed mechanism to be true with absolute certainty.  We mean rather that we have performed a variety of experiments which preclude all possible mechanisms except for the one proposed.  

Ultimately, a chemist characterizes chemical mechanisms via a process of elimination. Most mechanisms prove inconsistent with the data; usually only a very small number (hopefully one) is completely consistent with all of the experimental observations.  The chemist is then free to conclude with reasonable certainty that this one mechanism is correct.  In this respect, the laboratory operates much like a courtroom: just as a prosecuting attorney attempts to establish the guilt of the accused beyond reasonable doubt, so a chemist attempts to prove the correctness of a chemical mechanism beyond reasonable doubt.  In the absence of a confession from the accused, establishing guilt beyond all conceivable doubt exceeds the capabilities of the prosecutor; similarly, establishing the correctness of a chemical mechanism beyond all conceivable doubt exceeds the capabilities of the chemist.  

This is not an attempt to create skepticism about the possibility of any certainty in physical science;  I am merely exposing the limitations of scientific epistemology.  In practice, I act as though a chemical mechanism about which I am only reasonably certain is absolutely true.  This is because I know the mechanism to be accurate beyond a reasonable doubt, so I use it with a qualified operational certainty when designing new experiments.  And just as a courtroom verdict can be overturned with the admission of new evidence, so a chemical mechanism previously believed to be true can be exposed as false when these new experiments are performed.

Hence, the conclusions regarding the invisible details underlying the results of “observational science” and the unrepeatable details of “historical science” are analogous.  In neither case are the underlying phenomena understood with absolute certainty.  In this regard I suspect Ham and I are in agreement.  But he and I would part ways with regard to the historical—to which he confers no certainty whatsoever, and to which I confer the same limited certainty I grant to the invisible mechanisms underlying the results of “observational science.”