You say/ask

"Of course it is easy to "explain'' diffraction with the use of a wave but what is the behavior of the of the particle when it is near the slit. Does it interact with the wall, and if yes by what mechanism. If there is a mechanism why do we need QM . . ." 

As Prof. El Naschie recommended, in the 3rd volume of Feynman's "Modern Physics" there are chapters on QM and they are excellent. They are written clearly and intuitively.

Now, some explanations from me: of course we need the QM, because it proved itself as predicting excellently all the results of measurements on quantum systems. About the behavior of a particle, the QM works with the Schrodinger equation, not with Newton's equations. The Schrodinger equation has as solution a wave, not a particle. Thus, the QM doesn't speak of particles, i.e. something as billiard balls. It treats a quantum system as if all the way from source to detector we have a wave, and only at the contact with a detector, appears a phenomenon that looks like as if produced by a particle. For instance, on a photographic plate, an electron-wave leaves isolated spots.

All the way from the source to the detector, the wavelike description given by the wave-function is satisfactory, while if we would have used the Newtonian mechanics of particles, it wouldn't have worked. The discrete points on the photographic plate are considered as an effect of what we call "collapse of the wave-function", a phenomenon NOT described by the QM formalism, and which is NOT fully understood until today. We say that the collapse is a phenomenon outside the QM.

Now, you should now that because of this not-understood collapse that we need to add to the QM, there came a series of physicists, Louis de Broglie, David Bohm, Basile Hiley, and others, who proposed to interpret the wave-function as some sort of a guide-wave, in which floats a particle, s.t. the movement of the particle is guided by the wave-function. This proposal is very appealing, but it is full of unsolved difficulties, s.t. most of the physicists preferred to stay with the inconvenience of the collapse.

Just one question. Which "Wall" do you mean: the Wall where the slit is, or the final screen?

Hi Sofia,

you are explaining what QM explains. I am not interested in this.

I simply ask what is the interaction of a particle with the walls when this particle is diffracted?  

Has someone made experiments in the sense I propose in the first post?

By the way there are not such book Modern Physics from Feynman. Do yoy refer to the Feymnan Lectures in Physics? There is nothing about my question!

Dear Aleksei

I know QM quite well. I think it is a mathematical theory which is so suited to give MOST precise answers  to some (right) questions in physics. It explains what would happen on a screen (with help of the wavefuction collapese postulate - but nevertheless).

But what about interaction with walls of the slit? Do you think it (QM) answers the question about interaction with walls? I know it doesnt.It ignores it as you ignore what I ask.

Ask yourself - Is there an interaction with walls or not according to QM? What is the viewpoint of QM on this question? Or is it a wrong question?

Balyan, I've  really never heard of this. You mean the quantum wave is scattered by all atoms or electrons in the edges with the same phase? You must give citation on this or it

Or it doesn't make sense and I consider it an illusion of you.

Sorry, the following lengthy comment is actually an answer to another question raised by an Egyptian colleague. But I think, it might also be of interest to you. Your question on what happens to a particle at a diffracting wall is to some extent adressed in the first article quoted at the end of this comment.

It is amazing that quantum mechanics about 90 years after its inception is still in a state of complete confusion. Objects that obey the time-dependent Schroedinger (or Pauli- or Dirac-) equation represent (usually) idealized point masses that carry zero or plus(minus) one elementary charge.(In certain cases, e.g. in diffraction experiments at planar gratings, these objects may also represent molecules whose center of mass plays the role of a point mass.) The modulus square of the associated time-dependent wave function describes the particle’s probability of being in an elemental volume around a particular position r at time t and nowhere else. I think it rather thoughtless – to say the least – that authors (or lecturers) who use the term “probability” in that context for the first time, insinuate that the students are completely familiar with its implications. It is usually not precisely explained that this probability is defined as a relative frequency n(r,t)/N where N is the (very large) number of identical members forming an ensemble which the particle under study belongs to. All members of the ensemble consist of the same setup (spatial configuration) with a single particle moving in it, and n(r,t) is the small subset of particles which – at time t – are in the respective same elemental volume around the position r. The N particles of the ensemble have been prepared at the same time under identical (macroscopically controllable) conditions, for example by emitting them from the same tip position at a cathode. It should be clear from this definition that a wave cannot possibly have this property, viz. at time t being at some position and nowhere else. For that reason one can only side with Nevill Mott who states in an article (published in the 60’s):

"Students should not be taught to doubt that electrons, protons and the like are particles....The waves cannot be observed in any way than by observing particles."

It should also be clear from this definition that a point-like detector in a plane behind a two-slit diaphragm, for example, can only monitor one particle out of the set of N. That one has moved from the cathode through one of the slits and finally hit the detector. It cannot be predicted where it hits the monitor plane. The other particles move in their associated setup all of which are, by definition, separate and therefore independent of the one just considered. For this reason it appears to me rather absurd to associate the detection of the one in question with a “collaps of the wave function” which describes the particle distribution of the entire set of N independently moving particles. As Ballentine states in his seminal article (Rev. Mod. Phys. 42, pp. 358-381 (1970)):

“..in general, quantum theory predicts nothing which is relevant to a single measurement (excluding strict conservation laws like those of charge, energy or momentum)”

and further:

“...quantum theory is not inconsistent with the supposition that a particle has at any instant both a definite position and a definite momentum, although there is a widespread folklore to the contrary.”   

So, obviously, all N particles which start at the cathode under identical conditions take different paths. Why? Where does this randomness come from? This is the fundamental question to be answered by a theory of quantum mechanics. It cannot possibly be observer-induced, caused by some effect of “the measurement” which somehow escapes control. The theory of quantum mechanics should not only be capable of describing particle behaviour in a double-slit setup but also, for example, the groundstate of a hydrogen electron. What causes the distribution of the electron’s  position to be an exponential function? This can definitely not been measured. If one would try this by light- or particle-scattering, for example, the theory yields a differential cross section which involves matrix elements between the ground state and excited hydrogen states. Hence, the groundstate must exist before the interaction takes place. I take the liberty of considering statements of Heisenberg’s like

“. . . the idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them . . . is impossible” W. Heisenberg in Physics and Philosophy (Harper and Row, New York, 1958), p. 129

pure bunk. What has fundamentally been missing so far in the established form of quantum mechanics is the insight that the old macroscopically suggested   concept of the vacuum as representing just some empty space is at variance with reality if one looks into it at a microscopic scale. Energy fluctuations, known from the temporary occurrence of messenger particles (“virtual particles”), appear permanently as vacuum fluctuations and are – among other phenomena – also responsible for the zero-point motion of atomic constituents in molecules and solids. The spreading of a wave packet is another example. But again: A wave packet is a solution to the time-dependent Schroedinger equation and represents, for example, a narrow Gaussian which widens as a function of time. As stated above: the modulus square of this solution describes the behavior of an ensemble of point masses whose starting points in their separate (but otherwise identical) real-spaces have been chosen within a narrow environment around a point r. The center of mass of this distribution moves at a constant velocity v in some direction. In a co-moving coordinate system each particle performs a random walk motion which obeys Einsteins law Drp2=(h/2p m0) Dt where Drp2 is the mean square displacement perpendicular to v, h denotes Planck’s constant, Dt the time that has evolved since the start of the motion, and m0 is the  rest mass of the particle under study. Hence, the individual velocities vi(t) of the particles in their associated spaces are very irregular. If one picks a particular elemental volume D3r around some point r’ (the same in each of the associated spaces) one can form the mean value of the velocities of the particles within that volume D3r and obtains v(r’). Within the co-moving coordinate system these average velocities define a velocity field whose flow lines prove to be smooth radial lines all of which emerge from the center of the Gaussian. In Bohm’s theory of quantum mechanics these flow lines are – for no obvious reason - interpreted as the true particle trajectories. Bohm doesn’t derive his equation of motion from a concept of vacuum fluctuations. He merely uses an idea of E. Madelung published in 1926 and transforms the time-dependent Schroedinger equation into a form that closely resembles Newton’s second law. Otherwise the time-dependent Schroedinger equation falls out of the blue as in conventional quantum mechanics. A true derivation of the time-dependent Schroedinger equation from the concept of vacuum fluctuations explained above has been carried out by L. Fritsche and M. Haugk, Ann. Phys. (Leipzig) 12, No.6, 371 (2003), s. also L. Fritsche and M. Haugk, arXiv:0912.3442v1.

Remi,

Thank you very much. You seem to got to the point of my investigation.

Minas and Lothar also many thanks. Lothar I would need some more time to study your post about QM.

In fact I know that QM prohibits the mere probability to ever observe any interaction of the particle with the slit (break of interference). So from point of view of QM it is unobservable. That by all physical rules means that it doesn’t exist, e.g. said in plain text THERE IS NO INTERACTION OF THE PARTICLE WITH THE SLIT. (Sorry but that is what follows). If there is any interaction (as Balyan points out) it is not involved in the diffraction (and moreover in building the diffraction or interference picture).

Remi,  what you imply is that there is only Thompson scattering. Nevertheless I think that there must be some indication of this interaction in the outgoing photon (if there is an interaction with the walls of the slit!!!). First there must be some change in the wavelength (very small indeed but not principally unobservable) because Thompson scattering is a limit case of Compton scattering. Another possibility is the polarization because by Thompson scattering there is polarization (which can be also tracked). Also don’t believe that there is interaction which does not slow down the photon (so there must be some phase lag). If there is such interaction it must happen superluminally.

Lothar, I read carefully your answer. As far as I understand you imply that the diffraction picture is result from vacuum fluctuations. Not from interaction with the walls of the slit.

I am right?

Dear Ilian Peruhov,

Sorry for the delay of my answer to your response. I am convinced, fundamental phenomena like diffraction at slits will never be understood unless one clarifies the origin of randomness in quantum mechanics. I am appending a summary of remarks and explanations which concern these phenomena. It is my firm conviction that once one has derived the Schroedinger equation from a fundamental principle, which I have done,  everything in quantum mechanics follows. There is no extra theory of measurement.  I hope that my considerations will convince you.

Best regards,

Lothar Fritsche

Hello to all

Perhaps the question of Peruhov is equivalent to this one:

What is the Schrödinger Hamiltonian operator of the photon interacting with the electrons bound to the protons --these being the "protonic" edges of the slit-- its eigenfunctions, and its eigenvalues?

If the questions are equivalent, this is good news. But I do not know the answer. The problem seems approachable in abstract, with an appropriate electrostatic potential U for the aggregate of protons that conform the slit; and some superposition of wave functions for the bound electrons. It may take some effort to obtain the solutions in detail. Here I am extrapolating freely from my paper

https://www.researchgate.net/publication/308419467_Quantum_Wave_Collapse_is_Unsolvable

were a deterministic atomic model of hydrogen that includes proton, electron and photon is explained.

Due scarcity of time, I am in no position to elaborate in depth these remarks --somehow removed from my main line of research-- and at the moment they should be considered as light suggestions that may help to clarify the original question.

With the best of regards,

Daniel Crespin

Article Quantum Wave Collapse is Unsolvable

Dear Ilian Peruhov, I like you questions and a short description of the problems associated with it. You are absolutely rite that a particle approaching the slit starts to interact with the slit's wall. This is the reason of the diffraction phenomenon (and also the diffraction less in the case of single photons, and also in the case of the double slit experiment). The theory of the mechanism of diffraction was described in detail in my book entitled Structure of Space and Submicroscopic Deterministic Concept of Physics (2017). The phenomenon can be understood only in the framework of the submicroscopic approach, which starts from the Planck's scale. Note the approach allows one to derive also the formalism of quantum mechanics.

Dear Volodymyr Krasnoholovets ,

The origin of the diffraction of matter waves at two-slit diaphragms has been discussed already some time ago within this ResearchGate-community. I add again the respective article and recommend a more detailed elaboration for further reading: arXiv:0912.3442

Best regards

Lothar Fritsche

Dear Dr. Fritsche,

Thanks a lot for your references. I have read them. It is a pity we did not communicate in the past when I worked actively on the phenomena of spin and diffraction. Here is the link to my recent paper on spin: Article Issue 2 · 1000009 SF J Spin Quan Elect SciFed Journal of Spi...

Regarding the diffraction - it is described in detail only in my book mentions above (once again, the title is The Structure of Space and the Submicroscopic Deterministic Concept of Physics). Your approach to the solution is based on the formalism of conventional quantum mechanism, which simply unifies a particle and a wave in one object - the so-called "wave-particle". In my approach I start from the Planck scale and initially derive quantum mechanics as such. The allows one to separate a particle and a wave. Namely, there appear two subsystems in which present the particle and a cloud of excitations, which the particle generates passing through space. In turn, space has its own structure, this is a mathematical lattice of primary topological balls whose size is treated as the Planck one.

So, when a particle surrounded with the clouds of these spatial excitations (named "inertons") approaches the slit, the particle's cloud becomes to interacted with similar inerton clouds of atoms of the material of which the foil with slits is made. The wall of the material between two slits is characterised with its own acoustic resonance frequency. This is also the frequency of the appropriate inertons of the wall, which oscillate in space around the foil. These wall's inertons induce the tangential component to the velocity of the particle that passes the slit.

Of course, in the book I start from the determination of the basic notions used: space and its structure, particle, charge, mass, photon, inerton, the de Broglie wavelength, the Compton wavelength, etc. Besides, I show that in the submicroscopic world the Heisenberg uncertainties do not appear at all - the submicroscopic physics is 100% deterministic.