I think that in this case we have to consider the size of the particle, the photon or electron while entering the slit gets confined in a small volume (this influences the wave function.) The square of the wave function gives the probability amplitude of the particle which has physical significance especially when we consider an ensemble. I think that for such a small particle the wave nature becomes quite significant leading to the diffraction. This is not action without cause since the probability of such an event occurring is not zero even when we don't consider external factors other than heisenberg uncertainity(which is intrinsic to the phenomena).

What interaction does the particles has with the walls? They are neutral so the force they exert is none. Talking about wavefunction is just a way to describe what happens but not why. The size of photons and electrons are almost zero so they have nothing to do with diffraction.

You have to use the wave description of the particle to explain the diffraction. Search in Wikipedia under diffraction of electrons

Of course diffraction is described by waves. But here one has a wave which is not a physical object but rather would show the possible directions of the particle after the slit and nothing about the physical interaction. In fact there is a lack of such. Newton thought that there is scattering at the edges but there is not. Here the first law of physics fails imo. No force but accelaration. Or the wavefunction should be regarded as a real wave.

Let me hope that I attract the attention of specialists in QM and CM.

In QM a "particle" is described by the square of a wave-function. You can go to popular explanations by Richard Feynman on the diffraction of a particle in a slit or rather when going to 2 slits at the same time

i will just tell you to go through the popular discussion of Bohr and Einstein to get the complete knowledge of the concept. I was having the same problem and has discussed a lot with many researchers but the best answer I got was from the discussion of the two scientists. the same was the thinking of Einstein and he imagined the thought experiments to prove Bohr wrong. and every time Bohr gives the answers its really interesting to read so go through it and be satisfied with the problem

it is not a only a matter of wave description, there is no particle passing through the slit but a wave. When this physical phenomena passing through the slit is identified as a particle there will be no diffraction at all

Do you mean particles dont exist at all?

I think that solves this puzzle immediately.

But then we are left inly with waves?

And the real object is the wave function?

Note however thats its complex. And its

impossible to solve its collapse when

interacting. When going tru a beam splitter

it can be registered in one arm only. What

happens to the wave in the other arm? Does

It disapear completely by miracle?

Ilian

There are other questions here in ResearchGate on the same issue, where it is discussed in every detail. This is basic Quantum Mechanics and you should read Richard Feynman google and you will find free publications enough

By the way it is not the wave-function but the product of the wave-function and its complex adjunct that gives the probability to find a particle at a given location. Again consult a book on QM. Also Mertzbacher is free on the web

Harry,

I prefer Mertzbacher, it gives more mathematical backround on QM

Harry

I ve read many books in QM. They never give

anwers about diffraction. This issue is circumvented.

They talk about two slit and interference.

And explain what happens after the slits.

But never talk whay happen on the slits.

What interaction can bring the interference

pattern. Diffraction of one slit is the simplest

Form of the problem. I understand that QM

can predict exactly what happens after the slit.

It can not say what is going on the slit in

Order to get diffraction pattern.

This is the very key to QM because of the dualistic nature including wave it is a non-question in QM. When the position is precisely known inside the slit the impulse is undefined. meaning no way to know where the particle went.

The diffraction pattern is constucted in QM and in wave optics explicitly from the amplitudes and phases which went tru the slit e.g. had no contact wiht the edges. So there is nothing about interaction of the particle associated with this wave. In fact particle looses great part of its wave. The Heisenberg principle says that than momentum has a broad spectrum. All this kind of description but says nothing about the mechanism of transfer of momentum.

What transfer of momentum? What about transfer of momentum in wave optics? Similarly there is the particle concept of the photon

If the position of the physical event is exactly known in the spacetime, there is no wave at all and the deep origine of the Heisenberg relation doesn't have any physical meaning at that stage

Hi Ilian!

Possible answer:

Newton's first law applies to macroscopic objects described by Newtonian mechanics while difffraction applies to a large number of microscopic objects that make up the light and which are described by quantum mechanics?

Jerzy

Diffraction also occurs with electrons

Harry

Electrons are also microscopic objects to which you have to apply quantum mechanics. In addition, diffraction does not apply to single photon or electron. As regards the mechanism of the interaction, it seems to me that its exact form is not important. It is important only that, I think, that the momentum of the photon or electron is significantly disturbed by it.

Jerzy, Newton mechanics is compatible with QM. The diffraction problem is amatter of concepts.Within NM a photon or any elementary particle refers to an other concept than I'm in QM. The real problem is not the violation of Newton's first law but if the created spacetime in the slit are the right boundary conditions to allow the classical particle concept

Jerzy

Diffraction is ye and no a single particle issue. The electrons for instance do land at a given place (of course) yet the ensemble of electrons show a diffraction pattern and therefore the possibility for ONE electron to land at a given point at the screen behind the slit(s) is given by a wave-function

Regarding "diffraction does not apply to single photon or electron..."

Please see http://en.wikipedia.org/wiki/Double-slit_experiment#Interference_of_individual_particles.

These results indicate to me that individual particles propagate simultaneously through both slits as a physical wave. Also note that, if the distance separating the slits exceeds the amplitude of the propagated wave (preventing a single wave from simultaneously propagating through both slits), there is no diffraction pattern produced.

Hi James

That's what we write in this discussion depends on understanding (interpretation) of the wave function (WF). I accept like Harry the kopenhagen interpretation , namely, the WF refers to the statistical ensembe, and not a single particle. In this interpretation, I think, the experiment with two slits says only that at large perturbations of the particle momentum it does not make sense to speak of a classical particle trajectory.

Hi Jerzy,

Certainly I may be misunderstanding, but in the experiments referenced only a single discrete particle is detected in each emission. That the aggregation of individually emitted discrete particle detections displays an interference pattern seems to require that, for each particle, spatially disperse waves traversed both slits, then physically interfering with each other. This suggests to me that particles propagate through space and time only in some physically disperse form - despite being detected only as a localized, discrete quantum particle.

Dear James!

The function e (IXP) can be interpreted as the physical plane wave associated with a particle of momentum p, or as information that the probability of finding a particle at the point x does not depend on x. In other words, the function e (ipx) expresses the Laplace's principle of equal ignorance! I prefer the latter, unorthodox interpretation, which seems to me to be more consistent with Max Born (kopenhagen) interpretation:-)

Dear Jerzy,

I certainly do not agree with the principle that all ignorance is equal! As a retired information systems analyst - and in more general contexts, IXP and IPX are not recognized as mathematical functions but as network protocol architectural features - please see http://en.wikipedia.org/wiki/IXP and http://en.wikipedia.org/wiki/IPX.

Dear james!

The Laplace principle of equal ignorance concerns symmetrical events like in the case of toss of the dice.

I'm sorry for the misunderstanding with the symbol e (ipx), which for me is an exponential function of a real variable, but I'm glad to see its relations with Internet traffic:-)

Dear Jerzy,

Thanks - I finally found a helpful discussion at http://arxiv.org/abs/math-ph/0002049.

Thank you, James, for this link. The author is an eminent English physicist. I did not know this work

Back to the posted question, the apparent conflict results from the presumptions that "[the propagating particle] doesn't interact with anything" and "the wavefunction is not a real physical object."

If, instead, it's considered that a propagating particle is manifested as a waveform, physically dispersed in spacetime, rather than a localized, discrete particle, the apparent conflict vanishes. In that case, the propagation space of a physically waving particle is constrained, allowing only part of the waveform to propagate - the directional momentum of the waveform segment that does pass through the slit causes the diffraction of the wave (and the subsequently detected particle) upon exiting the slit. Again, this seems to explain why the portion of a single particle (physical waveform) that propagates through each of several slits carries different momentum and produces differing diffractions.

Please excuse if my terminology is in some way improper or inconsistent with theory...

This very very flowed. Just one thing. The particle can not split. The wave splits and part of it stays behind the slit other portion propagates true the slit. One doesn't

register two particles ' one behind and one in front'. Also the transmitted portion of the wave spreads and would cover a huge region. This is not registered too for single particles.