Re: Voting on LIGHT (was energy with Q)

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

On Fri, 16 Nov 2001, Richard L Bowman wrote:
        quoting me:
> > Here is one way that you can't measure the size:
> >         Shine a laser beam on an aperture with a shutter and put a photon
> > counter on the other side of the aperture.  Open the shutter for some
> > time interval, and keep shortening the interval.  If the photons had a
> > size L then there should be no clicks in the counter when the shutter is
> > open for times shorter that L/c.
> >         The experimental result, I am assured, is that there is no time
> > interval so short that the beam cuts off.  The click rate in the counter
> > just gets slower and slower as the time interval gets shorter and shorter.
> > The interpretation is that the shutter merely reduces the probability that
> > a photon gets through the aperture.
>
> The problem with this experiment is that the shutter must be some sort of
> mechanical device and thus it has a minimum speed at which it can close. So
> one can only talk about a lower limit for the length of a photon (unless I
> am not understanding the experiment). For example for a one-meter long
> photon, the shutter would have to operate (open and close) in about a
> nanosecond or less. Is this possible?
        There is no "in principle" limit on the length of time that the
aperture (of unspecified size) may be open.  The "gedanken" experiment I
have given you is essentially one that was discussed by Feynman and
recently (in the past couple of years) implemented with electrons instead
of photons.
        Incidently, and irrevelently, a shutter need not be mechanical -
there are opto-electronic shutters for very fast cameras.

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