Subject: Dirac Citation - Summary

From: Wibke Sudholt <[email-masked]>
Date: Thu, 15 Mar 2001 14:08:23 +0100

Hello CCLers,

thank you very much for your quick response,
Tucker Carrington, Irena Efremenko, Stefan Grimme, Sara Martinez, Martin
Mueller, Ignacio Nebot-Gil, Lars Sandberg, Georg Schreckenbach, Jens
Spanget-Larsen, Joris Van Droogenbroeck and Christoph van Wüllen!

The original question was:
"Could anybody give me - for educational purposes - the sentence Dirac - I think
- said about that "in principle one can calculate the whole chemistry" - if
possible in German - and where and when he stated this?"

The most extended version of the citation sent to me was:
"§1. Introduction
The general theory of quantum mechanics is now almost complete, the 
imperfections that still remain being in connection with the exact 
fitting in of the theory with relativity ideas.   These give rise to 
difficulties only when high-speed particles are involved, and are 
therefore of no importance in the consideration of atomic and 
molecular structure and ordinary chemical reactions, in which it is, 
indeed, usually sufficiently accurate if one neglects relativity 
variation of mass with velocity and assumes only Coulomb forces 
between the various electrons and atomic nuclei.   The underlying 
physical laws necessary for the mathematical theory of a large part 
of physics and the whole of chemistry are thus completely known, and 
the difficulty is only that the exact application of these equations 
leads to equations much too complicated to be soluble.   It therefore becomes
desireable that approximate practical methods of applying quantum mechanics
should be  developed, which can lead to an explanation of the main features of
complex  atomic systems without too much computation."

The original reference is:
P. A. M. Dirac, "Quantum Mechanics of Many-Electron Systems", Proceedings of
the Royal Society of London, Series A, Vol. CXXIII (123), April 1929, pp 714.

Stefan Grimme and Ignacio Nebot-Gil point to a discussion article:
Werner Kutzelnigg, "Perspective on "Quantum mechanics of many-electron systems"
Dirac PAM (1929) Proc R Soc Lond Ser A 123: 714", Theor Chem Acc 103 (2000)
3/4, 182-186
http://link.springer.de/link/service/journals/00214/tocs/t0103003.htm

Martin Mueller gave the weblink:
http://www.linux-magazin.de/ausgabe/1999/01/Quantenchemie/quantenchemie.html

Georg Schreckenbach added:
"It is worthwhile, perhaps, to look up the context - the paragraphs before are
quite  interesting, too. 
 Often, only the first sentence is cited. I find that the rest is important as well: It 
describes pretty well what many of the CCL readers are doing, 'developing 
approximate practical methods of applying quantum mechanics.' The ideas of 
what 'too much computation' might mean has changed a bit since Dirac's time but 
the task as such is still the same!"

Jens Spanget-Larsen gave the comment:
"Hence, Dirac only stated that "the underlying physical laws ... for the whole 
of chemistry are complete known".  He did NOT claim that all aspects of 
chemistry could be derived from these fundamental laws.  Knowledge of the 
"underlying physical laws" does not, in general, allow us to anticipate all 
aspects of 'reduced' sciences.  More or less like the concept of 'chaos' is not 
easily anticipated solely from a knowledge of Newton's classical mechanics, or 
the phenomenon 'life' is not easily derived from a knowledge of chemistry, and 
so on."

Thank you very much once again!

Best regards,

Wibke Sudholt
Institute of Theoretical Chemistry
Heinrich-Heine-University
Duesseldorf, Germany
[email-masked]