Re: Two-slit experiment
- From: "Timo A. Nieminen" <timo@xxxxxxxxxxxxxxxxx>
- Date: Tue, 25 Jul 2006 20:59:13 +0000 (UTC)
On Fri, 21 Jul 2006, Oz wrote:
Timo A. Nieminen <timo@xxxxxxxxxxxxxxxxx> writes
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.
Its a very excellent description of size.
We are talking size in meters here, not energy.
You are saying that the "spread of a wavefunction" = "size of particle"?
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.
Er, yes, but such an object has a very short wavelength so is inherently
more localised (or 'smaller').
No! Not at all! What does wavelength have to do with localisation? It is
relevant to _minimum possible_ localisation, but a monochromatic plane
wave mode is _completely_ unlocalised, in both space and time,
independently of the wavelength.
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).
I'm not actually completely in agreement with this statement.
On average this is so, and on average (that is, over many counts) you
get the right answer.
But the uncertainty of momentum may not be spherical because you could
measure the recoil of the source (if the gamma is energetic enough),
which would destroy the spherical symmetry.
So don't measure the recoil. No problem!
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.
Absolutely not, as diffraction will confirm.
No, diffraction just tells you that quantum "particles" are not classical
billiard balls. The wavefunction can have finite (ie non-zero) extent
(and, technically, extends to infinity in all directions, although the
amplitude of the wavefunction may be close enough to zero so you can
pretend it's bounded in space), but that doesn't mean that the "particle"
it prescribes the probability distribution of is as large as the
wavefunction.
Diffraction tells you about wavefunctions. Diffraction of EM waves tells
you about EM waves, not about whether energy is exchanged between EM waves
and matter in quanta.
If all the energy goes to one atom, and isn't divided among many, the
quantum is one atom in size, at most, regardless of how many atoms wide
the wave is.
Remember that an aerial does NOT have to be a wavelength long to
receive. In fact its normal for low frequencies to put appropriate L & C
on a short aerial so as to tune it to the required low frequency/long
wavelength. Similarly you can see an absorbing (or emitting) atom as
tuned to its transition frequency, with the masses of the
electron/nucleus and associated electromagnetic field interaction tuning
it to the very low (in wavelength terms) transition frequency.
Just as a properly tuned small aerial can transmit a very long
wavelength signal, so a very small atom is perfectly capable of being
tuned to a very long wavelength em wave.
Clearly most transitions take very many cycles of emission before the
transition is completed.
No. The energy difference between the upper and lower levels is hf. To go
through many cycles would mean pumping out and sucking back that energy
over and over. Yet the energy is launched out at c, and you can suck it
back. Yes, for a short dipole, you put energy into the near field, and get
it back. Yes, the wavefunction of the electron oscillates (and see my
recent post in sci.physics on a content-related thread for more on this,
and some nifty references supplied by others). However, classically, you
never have "the transition is completed". Never. This is a quantum
concept. Classically, you have a damped oscillator, which never decays to
zero, but a photon is emitted, and maybe detected, and the atom is
demonstrably in the lower state.
--
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
.
- Prev by Date: Re: Two-slit experiment
- Next by Date: Group view on connection
- Previous by thread: Re: Two-slit experiment
- Next by thread: Re: Two-slit experiment
- Index(es):
Relevant Pages
|
