Re: grinding versus understanding

["Bernard G. Cleyet & Nancy Ann Seese" <georgeann@REDSHIFT.COM>]

Interleaved below:

John Denker wrote:

> At 02:46 PM 6/25/00 -0400, Stefan Jeglinski wrote:
> > Wasn't it one of the famous
> > physicists from early in the century who said something to the effect
> > of "you should know the answer before writing down the solution"?
>
> I don't know if it was original with him, but Feynman said on innumerable
> occasions that you don't really understand an equation unless you can look
> at the equation and know the qualitative behavior of the solution, without
> grinding out the exact solution.
>
> -------------------------- cut

>  He didn't _need_ to make qualitative arguments -- he could grind out exact answers
> faster than most people could state the question.  A good example of what
> I'm talking about appears in volume I of the _Lectures_, where he says the
> electrodynamics of an atom is analogous to treating the electron as a
> classical charged mass connected to the nucleus by a classical spring --
> the atom is just a charged harmonic oscillator.

I thought this was the Drude-Lorentz model of a century ago


> Now there is no elementary
> reason to think that an atom is well described as a charged harmonic
> oscillator.

This is not obvious to me -- depends on how well is well described. The semi-classical result is rather similar, again subjective.

> So why did he choose that qualitative model?  Because he knew
> the exact answer, and he had carefully checked that such a model would
> parallel the actual behavior.

Probably done by the late 20's

bc