Re: The Electron

[Jack Uretsky <jlu@HEP.ANL.GOV>]

        I would say it somewhat differently.  <Measurement> of the "fixed"
frequency would take infinite time.  Actually the photon is emitted by an
atomic transition with a certain lifetime, measured by the width of the
atomic line.  The photon frequency lies, with high probability, within
that width.
        "Photonic glue", used to bring atoms to rest, is based on such
considerations.  A photon from a moving atom is doppler shifted outside of
the width of a stationary atom, but the recoil momentum changes the
momentum of the emitter.  Similarly, that photon may be absorbed by a
moving atom which will experience an opposite change of momentum.  The
momentum of the photon is sharp, but its measurement has an associated
uncertainty that depends on the nature of the measurement.



On Wed, 12 Nov 2003, Brian Whatcott wrote:

> At 10:38 PM 11/12/2003, Jack,  you wrote:
> > ///.  Light of a fixed frequency "interacts" (is emitted and
> > absorbed) in discrete photons - parcels having definite energy-momentum.
> > The mistake often made is to try to assign a "length" to a photon.
> > Fourier tells us that this is impossible, since the photon has, by
> > definition, a definite frequency.  As is usual in QM, care must be taken
> > not to mix incompatible attributes (such as position and momentum).
>
> Taking Fourier at his word, we could advance the idea that something with a
> fixed frequency would have an infinite length or  duration - an unphysical
> idea to be sure.... so that for a  known detector position, the Heisenburg
> idea to which Jack alludes,  alerts us that the momentum, or what amounts
>   to the same, the frequency is indeed uncertain?
>
> Brian Whatcott    Altus OK    Eureka!

--
"Don't push the river, it flows by itself"
                                Frederick Perls