🚀 go-pugleaf

In article <BxA2GC.6yE@wsrcc.com> alison@wsrcc.com (Alison Chaiken) writes:
>music@erich.triumf.ca (FRED W. BACH) writes:

>As far as the theory of the electron goes, QED has had
>no impact on solid-state physics whatsoever.
>Solid-state physics doesn't really even use the full Dirac equation,
>except that we are interested in the magnetic moment of the electron,
>which the equation explains qualitatively.

   Dirac equation has been used in band structure calculations
   of heavier elements. It is true, however, that most of
   Solid State physics can be done without it.

>Having said all that, the theories of broken symmetry and elementary
>excitations (Goldstone bosons) in solid-state physics have been heavily
>influenced by particle theories.  Here solid-state is using the
>_concepts_ of field theory, not the results!

   Solid State physics uses _techniques_ originally developed
   for QED all the time.
   Feynman diagrams are a standard tool used in everyday work.
   Path integrals, also developed by Feynman for QED, have been 
   used in a number of areas of solid state physics.
   And do not forget the renormalization group theory of phase
   transitions -- its origins are as much in field theory as they
   are outside of it.
   I really would not underestimate the impact of field theory on
   condensed matter.
   I will go as far as saying that solid state physics would have been
   much less today without those techniques  -- it is a perfect
   illustration of the need support many kinds of basic research,
   not just the ones that `look useful'.

>My understanding is that
>particle theories have been in turn influenced by solid-state theories
>(e.g., non-perturbative field theories are greatly influenced by the
>BCS theory of superconductivity).

   True enough.

-- 
David Frenkel                        | e-mail:   frenkel@stcst1.mrl.uiuc.edu 
Department of Physics,               | 
University of Illinois at            |
Urbana-Champaign, Urbana, IL, USA    |