Subject: CCL:orbital and reality

From: Per-Ola Norrby <pon|at|kemi.dtu.dk>
Date: Thu, 3 Feb 2005 08:50:31 +0100

I've been itching to enter this discussion, and now I feel I 
can't stay out of it anymore.  I want to drag it down to a much 
simpler, even childish level, by using the analogy between an orbital 
and an orbit.  They are, in many ways, very similar.  One descibes 
the possitions of electrons, the other of planets.  There is the 
difference that if we bounce a photon off an electron to observe it, 
it changes, whereas a planet is hardly affected :-)  We also have a 
difference in speed, the electron is moving so fast that we can only 
observe an average, but we can get the same effect with orbits by 
using time-lapse photography.  If you do it from outside the solar 
system, for several years, you'll get a picture of a number of 
near-circles, orbits (very much like the electron density cloud that 
we can see with good Xray).  What you really have is a large number 
of overlaid positions of planets, but the net effect will be a nice 
circle, so I'd say this is a way to visualize orbits.  Now, if we 
blow up a planet and repeat the procedure, we'll get a picture with 
one circle less.  Taking a difference between the two pictures will 
ideally result in a picture of only one circle, which I would say is 
a damned good way to visualize an orbit.  As far as I understand it, 
this is exactly what the paper under discussion has done, except that 
it's easier to remove an electron than a planet, so don't expect me 
to verify my analogy by experiment.

	The analogy can even be extrapolated a bit further.  Taking 
away one planet would affect the positions of all the others, so that 
the subtraction of the two pictures will include artifacts where you 
get shadows where the other planets are.  In electron terms, the 
wavefunction will relax, so that the difference does not correspond 
exactly to the original orbital, but it's a fair first approximation.

	Now please flame me for ignoring all the complications 
arising from things like the uncertainty priciple.  I still think the 
analogy helps thinking about the problem in macroscopic terms.

	Cheers,

	Per-Ola
-- 
Per-Ola Norrby, Assoc. Professor, http://organisk.kemi.dtu.dk/PON/
Technical University of Denmark, Department of Chemistry
Building 201, Kemitorvet, DK-2800 Kgs. Lyngby, Denmark
Email: pon|at|kemi.dtu.dk  tel +45-45252123,  fax +45-45933968