Subject: Re: CCL:orbitals

From: "Dr. N. SUKUMAR" <nagams|at|rpi.edu>
Date: Sun, 01 Jun 2003 16:09:02 EDT

On Fri, 30 May 2003 16:07:46 -0700 Eric Scerri wrote:

> 
> 
> As somebody working in philosophy of science and more specifically 
> philosophy of chemistry I have found the recent discussion very 
> interesting.
> 

While for my part, I have always been a "working computational chemist",
I've studied with great interest the debates between Bohr, Einstein, Bohm
and others.

> 
> There is a long-standing debate in philosophy of science going back 
> for hundreds of years which in modern terminology is referred to as 
> the realism versus anti-realism debate...
> 
> Finally, it should also be recalled that the most widely held 
> interpretation of quantum mechanics, the Copenhagen interpretation, 
> is essentially an anti-realistic interpretation regardless of what 
> people like Einstein and David Bohm may have wanted...

While I agree that this is indeed a long-standing debate, the problem was
exacerbated by the insistence of some, like Bohr and Heisenberg, that
science is concerned not with the physical universe ("physical reality")
per se, but with human knowledge/awareness of the physical universe. While
we might agree that the latter does fall within the purview of science,
most scientists today would opine that it falls within the discipline of
cognitive science rather than physics. Few are the physicists who are able
to get grants to study human cognition using acceleraters rather than EEGs
and MRIs!

> 
> For example 
> phlogiston was initially quite useful and successful in explaining 
> many chemical facts.	Some people may even have believed that this 
> meant that phlogiston was a real physical entity and yet as everybody 
> knows it turned out to be a mistake.

Perhaps a better example might be the aether and spacetime. While most
people today might say that the aether theory was a big mistake, I regard
spacetime as simply a modified version of the aether concept, in the same
way that modern DFT helped reformulate the concepts of hardness and
electronegativity. So does spacetime "exist"? Or do orbitals have "physical
reality" (to distinguish it from the real/imaginary/complex
classification)? To me, questions like this are inherently unanswerable, or
at least unanswerable at the level of science. Such questions belong in the
realm of philosophy and religion.

Science can ask: is the phlogiston concept still useful? The answer there
is no! Is the orbital concept still useful? Here the answer is that, within
bounds, yes! But is it absolute? Can it explain all observations? Certainly
not! Now a more difficult question (and one that calls for subjective
judgements): is it a reasonable working model? Here opinions seem to
differ.

It is possible to formulate and rationalize most of our observations
entirely without reference to orbitals. Several successful theories, such
as the variational formulation of density functional theory and some
Green's function theories, do just this. Does this make the orbital concept
any less valid? No, but it does argue against religious beliefs of orbital
reality. Does this make orbitals any less useful? Again, no. The most
widely used theoretical formulations (Hartree-Fock, CI, Kohn-Sham DFT) are
still constructed in terms of orbital expansions. But I would argue that it
makes little sense to try to "explain" all our observations in terms of
orbitals, a practice which is still widely prevalent.

> 
>  except in the general sense that all scientific 
> theories and approaches are eventually refuted.  This view, called 
> the pessimistic meta-induction, ...
> 
> 

There seems to be an inconsistency here: that of extrapolating beyond the
known range of validity of the model. I would modify this to say that all
scientific theories should be, in principle, falsifiable or refutable. A
theory that isn't so is not science, but religion. The only exceptions are
axioms and they are to be regarded as merely working hypotheses. Axioms are
not falsifiable, but they can cease to be useful. In science there are no
self-evident truths. Problems arise when axioms are confused for facts.
Replacement of one set of fundamental axioms (as for example, the
centrality of the earth) for another often leads to a major paradigm shift
in science.

Dr. N. Sukumar
http://www.drugmining.com/
Visiting Scientist
Rensselaer Department of Chemistry and
Wadsworth Center, New York State Dept.of Health