Reduction of chemistry

Eric Scerri studied chemistry at the Universities of London, Cambridge and Southampton, and obtained a Ph.D. in the history and philosophy of science from King s College, London on the question of "The Reduction of Chemistry to Quantum Mechanics," He has been a research felloiu in the history and philosophy of science at the London School of Economics and at the California Institute of Technology. He is currently an assistant professor of chemistry at Bradley University, where he also teaches histoiy and philosophy of chemistry, which are also his main research interests. He is editor of the new journal Foundations of Chemistry. Address Department of Chemistry, Bradley University, Peoria, IL 61625. Internet scerri bradley.edu. 

It is indeed a great honor to be invited to contribute to this memorial volume. I should say from the outset that I never met Lowdin but nevertheless feel rather familiar with at least part of his wide-ranging writing. In 1986 I undertook what I believe may have been the first PhD thesis in the new field of philosophy of chemistry. My topic was the question of the reduction of chemistry to quantum mechanics. Not surprisingly this interest very soon brought me to the work of Lowdin and in particular his analysis of rigorous error bounds in ab initio calculations (Lowdin, 1965). 

In this article I hope to introduce chemical educators to some of the work carried out in the philosophy of chemistry. The relevance of such work and especially that carried out on the reduction of chemistry to physics is considerable, and especially so in the case of physical chemistry. As the very name of the discipline implies, physical chemistry juxtaposes aspects of chemistry with aspects of physics. The relationship between these two classical areas of science needs to be considered in order to ascertain the extent to which chemistry should be taught as applied physics or to inform the teaching of physical chemistry per se. 

How philosophers of science have approached the reduction of chemistry to physics... 

Responses to this further question appear to fall into two camps. One prominent metaphysician believes that the question needs to be approached independently of any theories of chemistry and of physics. Robin Le Poidevin has published an extensive article in which he argues in favor of the ontological reduction of chemistry to physics. He does this through what he has termed a combinatorial approach. 

Le Poidevin writes that because the thesis of ontological reduction is about properties, we do have to have a clear conception of what is to count as a chemical property. He then takes the identity of an element, as defined by its position in a periodic ordering, and its associated macroscopic properties to be paradigmatically chemical properties. About these properties we can be unapologetic realists. He also claims that a periodic ordering is a classification rather than a theory, so this conception of chemical properties is as theory-neutral as it can be.v He believes that the question of the ontological reduction of chemistry is the question of whether these paradigmatically chemical properties reduce to more fundamental properties. He then adds,... 

Finally there is a somewhat general objection to the use of combinatorialism in order to ground the ontological reduction of chemistry. Surely the assumption of that fundamental entities combine together to form macroscopic chemical entities ensures from the start that the hoped for asymmetry is present. But it seems to do so in a circular manner. If one assumes that macroscopic chemical entities like elements are comprised of sub-atomic particles then of course it follows that the reverse is not true. The hoped for asymmetry appears to have been written directly into the account, or so it would seem. 

The remedy is not to attempt the reduction of chemistry to the one-particle solutions of quantum physics, without taking the emergent properties of chemical systems into account. Chemical reactions occur in crowded environments where the presence of matter in molar quantities is not without effect on the behaviour of the quantum objects that mediate the interactions. It is only against this background that quantum theory can begin to make a useful contribution to the understanding of chemical systems. 

The characteristic differences between the laws and theories of chemistry and physics largely arise from differences in complexity between the systems studied in the two disciplines and can be related to specific problems in the reduction of chemistry to physics. 

This acceptance leads to an apparent reduction of chemistry to physics, in which the science of chemistry may continue to have some practical importance as a specialized subdiscipline but ceases to have any fundamental significance as an independent... 

So, looked at as a whole, the reduction of chemistry to physics fails, not because of any problems of principle (though these may remain Scerri McIntyre, 1997), but because of impracticality. The application of the equations of physics to the questions raised in chemistry is ultimately intractable. 

It is our contention, then, that in some sense the program of reduction of chemistry to physics fails one of the grounds for this failure lies in practical issues of intractability rather than in any conceptual incompleteness or incompatibility. 

I will draw liberally on the work of my thesis grandfather, the chemist, Fritz Paneth. I use the term somewhat unusually, because Paneth was not the person who advised my own advisor Heinz Post but was, in fact, his natural father, from whom Heinz presumably developed an interest in the philosophical aspects of science. I will touch on such areas as realism, including naive realism, the nature of the periodic system, metaphysical aspects of chemistry, and, as suggested by the editors, the reduction of chemistry. 

Whereas Mendeleev was clearly ahead of his competitors when it came to the prediction of elements, he does not seem to have fared so well with regard to his views on the reduction of chemistry. More specifically, his denial of the reduction of chemistry has generally been held to have been mistaken, especially in view of the subsequent discoveries of radioactivity and the structure of the atom. That such a conclusion has been reached by historians of chemistry is not at all surprising, especially given some of Mendeleev s own pronouncements on the subject ... 

If reduction of chemistry as a whole is considered from a naturalistic viewpoint as I have advocated previously (Scerri, 1998a), the question of whether or not chemistry has been reduced to quantum mechanics is more subtle and depends on the present state of computational quantum chemistry and in particular ab initio calculations of chemical properties. In this sense, one might want to concede that chemistry has been approximately reduced to... 

Scerri, Eric R. 1998a. "Popper s Naturalized Approach to the Reduction of Chemistry." International Studies in Philosophy of Science 12 33—44. 

Eric Scerri studied chemistry at the Universities of London, Cambridge, and Southampton. He holds a Ph.D. in history and philosophy of science from King s College, London, where he wrote a thesis on the question of the reduction of chemistry to quantum mechanics. He has held several appointments in the United States, including a postdoctoral fellowship at Caltech, and is currently visiting professor in the chemistry department at Purdue University in Indiana. Scerri is the founder of the journal Foundations of Chemistry (http //www.wkap.nl/journals/foch), and has published extensively on the philosophy of chemistry in Synthese, the PSA proceedings. International Studies in Philosophy of Science, British Journal for the Philosophy of Science, and Erken-ntnis, as well as in American Scientist, Scientific American, the Journal of Chemical Education, and other chemistry journals. His research interests include philosophical and historical aspects of quantum chemistry and the periodic system, as well as general issues in philosophy of chemistry. 

It is relatively easy to talk and gesture about how chemistry either does or does not reduce to physics. It is much harder to spell out exactly what is required to make good on the claim that chemistry does (or does not) reduce to physics. Philosophers have a concept of supervenience. In the case we are focused on here chemistry putatively reducing to physics—supervenience requires that every chemical change be accompanied by a physical change. This is nearly universally held, for example, if two molecules are identical in all physical respects, they will not differ chemically. However, supervenience is not sufficient for the reduction of chemistry to physics. There could be downward causation, where it is the chemical facts and laws that drive the physical facts and laws, not the other way around. Robin Hendry (Chapter 9) argues that those committed to the reducibility of chemistry to physics have not ruled out the possibility of downward causation, and moreover, he presents substantial evidence from the manner in which quantum mechanical descriptions for molecules are constructed and deployed by chemists in favor of downward causation. Quantum mechanical descriptions of molecules that have explanatory and descriptive power are constructed from chemical—not physical—considerations and evidence. Here in precise terms, we see chemistry supervenient on physics, but still autonomous, not reducible to physics. 

Many explanations have been advanced for the fact that philosophers have so stubbornly neglected chemistry as if it were virtually non-existent. Is it the lack of big questions in chemistry, its close relationship to technology, or the historically rooted pragmatism of chemists and their lack of interest in metaphysical issues Or, is the alleged reduction of chemistry to physics (quantum mechanics) the main obstacle, so that, if chemistry were only an applied branch of physics, there would be no genuine philosophical issue of chemistry ... 

Since the advent of quantum mechanics, in addition to Kant s chemistry is not an eigentliche Wissenschaft, an obligatory reference to Dirac s authority has been used to justify the reduction of chemistry to physics, i.e., to the proper mathematics of quantum mechanics.17 Dirac (1929) said ... 

There is another area in philosophy of chemistry where I have been urging a naturalistic approach ever since the beginning of my work. This concerns the question of the reduction of chemistry to physics or more specifically quantum mechanics or relativistic quantum mechanics if one insists on being very precise. 

Let me also mention that Paul Needham has produced a detailed critique of my view on the reduction of chemistry in a debate between us which has been published in several issues of the International Journal for the Philosophy of Science (Scerri 1998b Needham 1999 Scerri 1999 Needham 2000 Scerri 2000a). 

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