Re: Two-slit experiment

On Sat, 1 Jul 2006, FrediFizzx wrote:

"Timo A. Nieminen" <timo@xxxxxxxxxxxxxxxxx> wrote:
On Fri, 30 Jun 2006, Oz wrote:

Clearly (to me at any rate) the 'size' of a massive particle is
determined (like the photon) by its environment (typically
quantised). So an electron, say, can have a different physical size
when undisturbed in an orbital This can in some circumstances be
very large indeed when orbitals become macroscopic, for example in
conductors.

Don't confuse localisation with size. If a photon is "large", it
should be able to interact with and be detected by two spatially
separated detectors at the same time.

I don't think we actually know the answer to that "question" since
"large" photons might be radio wave photons and so far individual
detection of such photons is not possible. Do you know of any
experimental limits that we might have for this? IOW, what is the
lowest frequency at which individual detection is experimentally
possible with current technology?

The claim regarding electrons having different sizes depending on whether "they are undisturbed in an orbital" reads to me as an identification of size with spread of wavefunction. This being independent of wavelength (but see below), low frequency isn't necessary. In fact, it's best to use the highest frequencies available, so that the energy required for detection is only a small fraction of the total energy. Put a gamma source in the middle of some, preferably many, detectors. Each gamma photon can go in any direction, the radiation field of each emission is spherically symmetric (well, perhaps a dipole field, but spherically symmetric averaged over many). Count, and look for coincidences. Has this been done? I don't know offhand. You should look; if it hasn't been done, it could be a cheap and useful entry into experimental physics for you.

But yes, there is a problem with trying to make sub-wavelength individual photon detectors. Except for single atoms/molecules, but then you still need an individual photon detector to detect the re-emission. IME, this is in the near IR.

I guess that you're wondering about size of photons as it might depend on wavelength. The above means that it's hard to answer experimentally. I think that illuminating a group of atoms, all within a wavelength, and only one of them absorbs and re-emits, is conclusive - the "size" of a photon is no larger than an atom. Compton can be interpreted as saying that the size of a photon is the size of an electron, ie zero AFAWCT.

But do consider the above gamma experiment. Data is good for you. All theoreticians should be forced into labs at some point!

--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html

.

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