Re: Stern-Gerlach Experiment2

Igor Khavkine wrote:


> Since the atom is (microscopically) heavy it has (microscopically)
> large momentum. Using the de Broglie relation between the momentum and
> the characteristic wavelength, lambda = h/p, we see that the atoms
> characteristic wavelength is very small.

Of course it depends on the circumstances whether you can treat a heavy
particle's motion classically or not. If you have well-isolated enough
particles (i.e. by suppression of any decoherence effects) and small
enough "gratings" of what kind ever, also very heavy objects can behave
quantum mechanically and show "wave character". This was demonstrated
clearly by a now famous experiment by A. Zeilinger and collaborators:
Even bucky balls (C_60 molecules) can show interference effects, which
vanish if they become too hot and sending out black-body radiation.
>
> Think about wave and ray optics. Ray geometric optics approximates
> well the propagation of short wavelength E&M radiation (say light).
> But the ray approximation fails for large wavelengths (say radio
> waves). Similar reasoning applies to the wave description of the atom.
> Here the ray approximation corresponds to the approximation that
> classical trajectories are well defined and correspond closely to the
> trajectory of the atom's wavepacket.

That's of course right, as long as all the stuff around the atom has
measures far larger than the de Broglie wave length, you can apply
singular perturbation theory and go to the classical limit (also known
as WKBS method).

--
Hendrik van Hees Texas A&M University
Phone: +1 979/845-1411 Cyclotron Institute, MS-3366
Fax: +1 979/845-1899 College Station, TX 77843-3366
http://theory.gsi.de/~vanhees/ mailto:hees@xxxxxxxxxxxxx

.

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