Subject: Orbitals and reality

From: "Phil Hultin" <hultin=at=cc.umanitoba.ca>
Date: Thu, 20 Jan 2005 17:05:30 -0600

I think Alan Shusterman's comments are very much to the point regarding this
discussion.  On the other hand, he is perhaps taking the argument that I and
others have made a little bit narrowly.

"since Y comes 

> from an experiment ("Y is real" !), it is inappropriate to object to 

> "Y

tells us about X" on merely theoretical grounds."

What I (at least) actually said was:

"if you are going to criticise their interpretation of the data you should
present an alternative explanation of the origin of their spectra that is
consistent with your view of electronic theory as well as with their
observations.

While the fact that orbitals are "only a model" means we must not assume
that they are "real", I suggest that it is inappropriate to take it as
axiomatic that the orbital model cannot embody at least some aspect of
physical "reality".  It is entirely possible that electronic structure
behaves under certain specific probes as if orbitals were real, that is,
that our artificial model fortuitously captures an observable aspect of
electrons."

That is, theory is indeed the lens through which data are interpreted, but
that to object to an interpretation you must do more than simply say "no, it
cannot be so".  It is at least possible as I remarked that one indeed cannot
observe orbitals or wavefunctions, but that nonetheless the spatial
distribution of electronic density in a simple molecule can be probed as the
authors assert in the Nature paper.  The way to criticize this is, in my
opinion, to say "you are not observing orbitals, neither are you observing
the interference pattern between two electronic wavefunctions.  The reasons
for this are X, Y, Z.  On the other hand, you are observing something, and
based on your description of your experiment, I believe that the origin of
the spectra you obtain and their angular dependence lies in phenomena A, B
and C."

I for one am glad that a serious discussion of this topic has evolved.  I
was beginning to think that CCL was going to be nothing but technical
questions about how to make programs work ;-).

Dr. Philip G. Hultin

Associate Professor of Chemistry,

University of Manitoba

Winnipeg, MB

R3T 2N2

hultin=at=cc.umanitoba.ca

http://umanitoba.ca/chemistry/people/hultin