Subject: orbitals

From: Eric Scerri <scerri_at_chem.ucla.edu>
Date: Fri, 30 May 2003 16:07:46 -0700

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

Although I may not have fully digested every subtle nuance and 
technicality concerning orbitals that has been voiced in recent days 
I believe I may still be able to contribute to one major aspect of 
the discussion.

This is on the question of usefulness and reality.

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.

Very briefly realists believe that we can attribute physical reality 
to scientific terms that are used in successful scientific theories 
regardless of whether or not these terms can be observed.  Indeed 
most realists believe that we should attribute physical reality to 
unobservable terms or entities like quarks.

Modern realism arose as a reaction against logical positivism whereby 
every scientific term would need to be grounded in observation.  The 
failure of the program of logical positivism (Carnap, Schlick, Nagel, 
Reichenbach etc.) came about for many reasons among them being the 
inability to draw a sharp distinction between theoretical and 
observational terms.

But logical positivism has not died away altogether and there is a 
sense in which it survives in the modern anti-realism view of 
scientific theories.  According to this view, of which Bas van 
Fraassen is the leading proponent, observability remains an important 
criterion.  If a scientific term or entity cannot or has not been 
observed then we have no warrant for assigning physical reality to 
it.  No matter how useful a scientific theory or scientific term 
might be this does not warrant us in the further belief that this 
theory or particular scientific term might have physical reality.  As 
I mentioned in an earlier posting there have been many terms that 
were temporarily useful in now defunct theories.  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.

Of course I am not suggesting that orbitals will necessarily turn out 
be be a mistake, except in the general sense that all scientific 
theories and approaches are eventually refuted.  This view, called 
the pessimistic meta-induction, provides a rather powerful argument 
against regarding any scientific theory realistically and similarly 
any scientific terms from current theories.

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.  So it is a 
little puzzling to discover that some quantum chemists are prepared 
to go beyond this general philosophical framework when it comes to 
one particular term within quantum chemistry and to attribute 
physical reality to orbitals.

regards,

eric scerri
-- 

Dr. Eric Scerri ,
UCLA,
Department of Chemistry & Biochemistry,
607 Charles E. Young Drive East,
Los Angeles,  CA 90095-1569
USA

E-mail :   scerri_at_chem.ucla.edu
tel:  310 206 7443
fax:  310 206 2061
Web Page:    http://www.chem.ucla.edu/dept/Faculty/scerri/index.html

Editor  of  Foundations of Chemistry
http://www.kluweronline.com/issn/1386-4238

Also see International Society for the Philosophy of Chemistry
http://www.georgetown.edu/earleyj/ISPC.html