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Diffraction: Does the electron determine the hole to travel through?

  1. Jan 23, 2006 #1
    This is my initial post here so I hope I am within the guidlines for posting on this forum.
    Years ago when reading Richard Feynman's textbook, 'lectures on phyics' I caught a phrase where RF was describing quantum mechanics and two hole electron diffraction. RF was arguing for the current QM model (circa '64) and he asked a rhetorical question: Can the electron determine which hole it is going to go through before it reaches the hole?
    This isn't an exact quote, but it conveys the meaning as I remember it. "Of course not", was my ininitial reaction, but over the years the germanation of RF'S thought seed took a fateful hold. In all my QM readings and discussions, this matter had not been explored scientifically, much less mentioned, as far as I could determine. So, I took a look at the problem and asked the same question:
    Does the electron determine which hole it is going to travel through before it arrives at the hole?.
    This tinme I canme up with a different answer,
    "The electron has to determine the hole it is going through before arriving at the plane of the holes".
    Here is how I cam up with my reply, which astounded me.
    The electron for all its many descirptions, has a rigorously linked associated mass and charge distribution. As the electron is heading toward the plane containing the two holes, the charge field precedes the electron's arrival. The reflected charge field is mixed with more of the oncoming charge field, which behaves like a self-induced repelling force force on the the electron motion.
    Assuming the plane of the hole surface is "flat", the repelling force is evenly distributed across the mass of the on coming electron. The exception to this, of course, is the existence of a potential force well immediately adjacent to, and in line with, the hole and the moving electron. A dimished charge density distribution due to the absence of a reflecting surface located at the hole(s) defines the geomentry of the potential force well. This potential well determines the fate of the electron as it is self-guided into one of the two (or more) available holes.
    Which of the holes selected is in part statistically determined. The properties of electron velocity, spatial relation of electron and hole location, etc would be deciding factors predicting, or determining, the actual hole selected. I am not suggesting this is a trivial experimental process, only that it is within the realm of practical possibility.
    As all known and unknown physical parameters offer some information leading to predictability regarding causal effects regarding hole selection, it is imprecise to assert that the hole selection process in electron diffraction is limited to a purely random "coin toss" mechanism.
    I would appreciate any comments.
    Ninki :cool:
  2. jcsd
  3. Jan 23, 2006 #2
    hmmm... but what you did is just like getting the holes closer to the emmition point... if youd look at the electron before its electrostatic effects take effect, it cant pre-determine which hole would affect it by your reasoning.
  4. Jan 23, 2006 #3
    One can easily calculate the diffraction pattern from a double slit system from first principles. If QM isn't correct about this how on earth can experiments and theory agree so well?
  5. Jan 23, 2006 #4


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    It astounded me too because you have totally ignored the wave-like description of electrons.

    Note also that if an electron only pass through a slit, it will NEVER form the interference pattern, nor the diffraction pattern. Try it. Shoot 20 gazillion electrons, but one at a time. If you have 2 slits, and each electron only passes through one slit OR the other, then you'll have two gaussian peaks at your detector, each centered behind each slit. This isn't the interference pattern. It is a pattern you will get IF you put a detector at each slit such that you CAN determine which which an electron passes through. Remove the detector so that this knowledge no longer exists, and you get the interference pattern.

    There are MANY other measurements that exhibit this wave-like behavior, such as LEED, crystal diffraction, SQUID, etc. You will be hard pressed to explain all of these with you description above.

  6. Jan 23, 2006 #5
    Dear ninki,

    I have two questions in order to understand the meaning of your post.

    You express the idea that: "As the electron is heading toward the plane containing the two holes, the charge field precedes the electron's arrival", but can you discriminate the two physical terms of "electron" and of "charge field", in the context that you are proposing ? What do you mean by this phrase?

    Then you write: "The exception to this, of course, is the existence of a potential force well immediately adjacent to, and in line with, the hole and the moving electron". What is the meaning of the phrase "in line with" ? What do you mean by that? Do you mean a geometrical alignment or a "cause - effect" alignment ? Can you explain, please ?

  7. Jan 23, 2006 #6
    Is there a good theory that explains how a single particle or wave-like object can interfere with itself ? I find this extremely interesting and at the risk of sounding like a nut case, I would like to learn more about this.

    All of the information that I seem to be able to find on the web explains this and other interference phenomena as if the photons and electrons are waves that interfere with each other in a classical way, not as individual entities that somehow become two or more entities interfering with themselves and having the effect of a single particle interacting with whatever measuring device is set up to measure them. I had always thought that this interference phenomena would still occur, even if the two slits were replaced by individual emitters of photons or electrons that were in phase or close to it. Is this incorrect ? I would appreciate a push towards some link, book or other resource that could clear me up on this and explain it further. Thanks !

    Michael E.
  8. Jan 23, 2006 #7
    Yes Michael,

    There is an extremely popular, widely accepted theory (which has stood up to every test that experimenters can throw at it) that explains how objects interfere with themselves and other such phenomena - it's called quantum mechanics. Any of that rubbish (on the web or popular science books) that says electrons are waves sometimes and particles at other times should not be taken seriously. Electrons, photons etc. (and all matter in fact) are neither waves nor particles. They are quantum objects; they cannot be mathematically represented by the same mathematical structures that represent waves and particles.

    In quantum mechanics, we use state vectors (or wavefunctions) to represent them, and this formalism perfectly explains most of the intriguing quantum phenomena. Depending on your level of mathematics one could recommend different texts. If you have the mathematical ability, I suggest Shankar, "Principles of quantum mechanics."
  9. Jan 23, 2006 #8
    Thank you, I'll get that book and most likely several others. I do try to avoid popular science fiction related descriptions of these things.I do have one question about this,

    Does this perfect explanation give an idea of what happens to the electron or photon as it approaches the slits, passes through the slits and then interacts with the measuring device or is QM strictly related to the final effect of the interaction with a measuring device ? The math shouldn't present an insurmountable problem to at least get a feel for this, but my feeling towards the math is that it will only be concerned with the final result and not so much with the process that causes that result, (for instance does the math have a state vector or wavefunction at every point along the path of the electron ? Does that wavefuntion separate into two distinct wavefunctions along the path after the slits, that can interact to give the probabilistic distributions of interactions with the measuring device ? If so does this mathematical representation coincide with an actual physical process, say the electron actually splitting into two parts ?). This is not meant as an argument, as I don't have a clue about the details in the math, just curious. I'll shut up now and get the book, thanks !
  10. Jan 23, 2006 #9
    The electron cannot reach the hole without the "electrostaic effects" occuring first. Think about it and draw a schematic.
  11. Jan 23, 2006 #10
    Thjereis nothing QM in the post. Also, the fact that QM does what it does is not a negation of the rather trivial physics described in the opening post of this thread.
  12. Jan 23, 2006 #11
    I am proposing that the charge field contains a volume larger than the mass of the electron. This simply says the electron is made up of matter, (mass) and charge (at least). I can see where I was remiss. Thank you for pointing this out. The electron is the sum of its parts that include, mass, charge (field) and spin state generator.
    Assume the electron is bearing down perpendicularly to the surface of the material where the holes are located. Assume further that the electron is not heading directly, deadcenter, toward any of the two holes, but it does feel the effects of the minimum force volume of the reflected charge field more or less centered on the holes where the reflection of the field is minimal.
    I see the effect of the holes as producing a minimum force region within the now mixed and reflected charge field that the electron will naturally fall into and which then guides the electron to one of the available holes. Obviously the charge field is not stripped from the electron which will drag the field into the hole as the electron motion continues.
    The physical spin function of the electron as proposed in Stern-Gerlach transition experiments takes the other hole if available, otherwise this physical function is dragged through the "single available" hole.
    Notice also, the combination effects of the reflected charge field creates a time varying electric field which produces an inhomogeneous magnetic field that poduces the environment to observe Stern-Gerlach like transitions. This means the physical spin state functions of the electron are affected in a like manner and in the presence of the inhomogeneous magnetic field the spin state function, otherwise nonlocal, is forced into a local observable mode.
  13. Jan 23, 2006 #12
    Most of the literature regarding two-hole diffraction are written with the condition in mind that th eelectrons pass throuigh the holes one at a time. When there is one hole the "interference" is destroyed. When there are two holes the electron can interfere with itself and produce the well known pattern on the scintillation screen. As far as I am abnle to determine the QM descriptions of "interference", in the single electron mode, is mathematical only and does not offer a descroiption of what is occuring physically. I will be targeted for some enegetic replies on this perhaps, but this is how i see it.
    Not as I understand the literature.
    The two photon emnitter scheme you proposed is different than the common two-hole diffraction setup.
    I can only give sources that meant simething to me. First, is Feymans 'Lectures on Physics' Volume III, chapter 5; and JS Bell's collection of papers, 'Speakable and Unspeakable in Quantium Mechanics", both a must. The latter is more mathematically sophisticated, but the Feynman reference is basic to understanding the construction of QM models [and should be taken with a grain of salt].Look closely at Feynman's description of the four main experiments (chapter 5, vol III) and see if you can detect some logic and physics errors.
  14. Jan 24, 2006 #13
    I disagree. The wave particle duality was introduced to explain the two-hole diffraction results and the wave explains away the problem of a single particle transitioning through two holes. We must recognize that the electron that is seen in the scintillation screen is of a tiny particle. The electron does not strike the screen with any observed, “wave properties”, ever.
    I disagree with some of your assumptions. An electron will never pass through one available hole and provide the same interference pattern as when two holes are available. Your post assumes all the restrictions (and then some) that QM theory has imposed. This thread is not a criticism or negation of QM, but it certainly offers another interpretation that QMT ignores.
    How do you determine, if there are two holes that an electron passes through only one hole at a time? before the electron enters the hole? This seems like a very tricky experimental problem that a detector placed at the exit of the holes does not address. It isn’t the “information” that drives the physics here.
    ZapperZ, your objections are directed is the description of what occurs after the electron selects the holes it passes through. That is another question entirely and in a sense premature as a question for the topic of this thread.
    I will not be hard pressed to explain anything associated with the general topic this thread encompasses. I would, however, prefer a specific question that I may address instead of responding to your objections as framed.
    I prefer to stay tuned to the elements of the thread as written. However, since you brought the matter up perhaps you can inform me where the description of the “guided mode” thesis in this thread is physically impossible. Citing some abstraction of, “wave-like behavior” is not pertinent to the thread, which is the “self-guided mode” of electron transitions through holes in materials.
    An electron is constructed of, at least,
    1. mass,
    2. a charge field surrounding the electron mass and
    3. an apparent “spin state generator”.
    The spin state generator is that physical function that produces the ‘up’ or ‘down’ spin state characteristics of the electron when subjected to the conditions of an inhomogeneous magnetic field as observed in Stern-Gerlach transition experiments.
    Finally, and I do emphasize the point, this thread is not an attack on quantum mechanical theory.
  15. Jan 24, 2006 #14
    Michael E,
    Another quality book is David Bohm's 'Quantum Theory' Dover Press, this explains the current state of QM and is written clearly if not slightly dated, but I have seen no technical criticism of Bohm's book.
  16. Jan 24, 2006 #15


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    And I could say the SAME thing about high energy photons. Are you making that same claim?

    You are forgetting that a "detection" in such cases means a POSITION observable. That is what a "screen" does! But solve the Schrodinger equation for an electron in a potential. Tell me what do you get? And when an electron condenses into a supercurrent in a superconductor, what do you think dictates its long-range order? It's "tiny particle" behavior?

    I can detect the "non-particle" behavior via examining the non-commuting observable! I don't have to measure the position observable and collapse that eigenstate to make such determination. The bonding-antibonding state of H2 molecule is one very clear example.

    And there are no "wave-particle" duality in quantum mechanics, thank you.

    Not if you put a detector at one of the holes and is able to determine which hole it passes through! That's the point that I made earlier! Try it yourself! But having the knowlege of which hole an electron passes through, you removed the superpostion of PATHS that the electron had, and you'll end up with two gaussians, not an interference pattern.

    And I say it is. The act of measurement at ANY stage of the experiments affecta the outcome you will get. That's the WHOLE POINT of having non-commuting observables! Did you not come across such a thing in QM already?

  17. Jan 24, 2006 #16
    Dear ninki,

    The wave nature of particles is present in many experiments.

    Have a look at the following sites:

    http://www.st-andrews.ac.uk/~atomtrap/Research/atoms.htm [Broken]


    http://www.quantum.physik.uni-mainz.de/bec/gallery/ [Broken] (very nice graphics here!)

    http://www.aip.org/png/html/alaser2.htm [Broken]

    http://online.itp.ucsb.edu/online/plecture/ketterle (very nice lecture)

    In our days laser light is used to apply forces over atoms, because atoms too are material physical agents with wave nature. In the above experiments the "exit" and the "entrance" of the "holes" are one. We can not discriminate them, in the way you do.

    All material particles, electrons, even neutrons (with no charge), and atoms do behave with wave nature.

    Your hypothesis is examining only electrons.

    What about the wide wave rule that is applied to all material particles ?

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  18. Jan 24, 2006 #17
    I am not attacking QM or the wave-particle duality of nature. The problem is simple: The electron is guided to the hole by the reflected charge field force potential well or it isn't so guided. ​
    Do you have any specific physical arguements why the original post of this thread is in error, or is it just because there is a sense that the QM description of nature is being attacked?
    However, in regard to your universal "wave" nature of reality perhaps you can inform us how the wave nature of protons comes into play when discussing the ionization of water molecules?
    When H2 is ionized and H+ ions are created and accelerated and strike a crystal and dislodge atoms connected electronically, how does the wave description take some descriptive precedence over particle descriptions?​
    The so called "wave" nature of matter is described with QM models, that for the most part (or all part) do not contain the slightest referencxe to "nonlocal" force centers. Whatever can be said of JS Bell, I do strongly agree with his proved hypothesis that QM models void in "nonlocal force centers" are incomplete. Using QMT, tennis balls and passenger trains can be described as "wave like". So why isn't this the norm, even in the physics community?
    Leandros_P, I implore you, find a physical reason why the model I presented is not a physically realizable model.​
    Question: Does the electreon charge distribution precede the arrival of the electron "mass" at the surface of the mnaterial in which the holes are prsent?
    Does the reflected charge distribution operate to repell the motion of the electron?
    Do the holes operate to create a force potential well that is experienced by the on coming electron as it approaches the hole?
    What is more practical, useful, least complex and easiest to understand when reviewing the design of the EM guidance/aiming of electrons that strike the backside of the CRT you are looking at at this very second, "wave" or "particle" modes? Can you indicate where "wave" theory can be employed in this problem to the unambiguous advantage of electron aiming protocols?​
    One very crucial aspect of electron (and other simple particles) that is not coherently addressed is the summed description of mass, charge (or absence of charge) and spin characteristics that are always subject to manipulation. A spin-1 particle, an atom, can be polarized to one state in a Stern-Gerlach environment, and subsequently polarized into another state. I have only seen treatments of these phenomena in isolation and see no attermpt to bring the descriptions to a coherent and reognizable unity. I mean by all of this QM is rife with "ad hoc" band aids. This is not to mean that the band aids are erroneous or even that there may be improvements over the structure of QMT, only that the theory is largely, if not exclusively, ad hoc. ​
    Finally, this thread is intended to introduce a discussion of the self-guided mode in which electrons are directed to the holes in which they are diffracted. Can you focus on this problem alone?​
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  19. Jan 24, 2006 #18


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    No, it is a sense that you are ignoring ALL of the observations associated with the QM predictions:

    1. The bragg diffraction of electrons

    2. The LEED patterns

    3. The SQUID interference.

    In NONE of these are there any "holes". Your idea of a "charge field" being affected by a "hole" does not work here. QM does not need to switch gears in describing the 2-slit interference and all of these phenomena. You do.

    I work in an electron accelerators, and one of the technique we use to measure the emittance of an electron beam is by using what is known as "pepper pots". These can be an arrangement of tiny holes with diameter ranging from a few microns, to up to 1 mm. If we apply your "theory", I should be seeing interference pattern when I have 2 of these pepper pot holes close together, or even a diffraction pattern when I have just one. I see no such thing.

    Is this consistent with QM? SURE! Here, the electron beam consist of free electrons that are no interacting with each other quantum mechanically - their wavefunctions do not overlap. Thus, they are now classical particles. Classical particles under classical conditions do not show QM properties. Furthermore, their deBroglie wavelength is way too small when compared to the size of the holes. Thus quantum mechanically, one does not expect to see any appreciable QM effects, and one doesn't!

    But look at your proposal. You make no quantitative predictions of such limits, and thus, the absence of any "reflection" of your charge field is STILL valid here and should have produced the same pattern. Yet, we don't see the same effects. All we see are classical effects.

  20. Jan 24, 2006 #19
    Are denying that the charge distribution of the electron is not reflected from the surface of the matter containing the holes?​
    Are you denying that the electron approaching the surface of material containing the holes is not preceded by the charge distribution of the electron [and does not precede the arrival of the electron]?​
    So, the holes then are of the size and separation one sees in the interference patterns during two-hole diffraction, such as in diffraction from crystal lattices? I suspect not.
    Not necessarily, you must still have the size and separation of the holes that will provide a diffraction (Airy?) pattern. The reflection from the surfaces of the charge distribution is a "classical effect".
    Likewise, you have made no quantitative reply disproving the hypothesis of charge distribution reflection directly. You have only alluded to other phenomena that are not pertinment here.​
    Try this experiment in your accelerator, it should be a simple matter to test.
    Determine the velocity diostribution as narrow as possible for the source beam prior to entering the "pepper pots" as mnear to the surface of the holes as possible. Then, test the velocity distribution after the electrons pass through the "pepper pot" holes. If there is a reflection from the walls of the material in which you drilled the non-QM sized holes, then the reflections would explain a decrease in particle velocity.
    However, you must conduct the experiment in such a way that the holes themselves do not contribute to any velocity losses. I would suggest the larger sized hoiles would be more appropriate here
    Is the experiment feasible? Have you discussed this matter with your colleagues? Is your accelerator located in the Fermi Labs?​
  21. Jan 24, 2006 #20


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    Say what?

    What exactly is a "charge distribution of an electron"?

    And where is this "surface" in a SQUID experiment? Where is this surface in a josephson loop?

    Please show me ANY experimental evidence of this "field" being "reflected" of surfaces. All you have done is make handwaving arguments with nothing to support your idea.

    And why does it have to be so based on what YOU have described? Look in your original post. Did you ever make any quantitative analysis (you know what that is, don't you?) of the nature of the incoming electrons and also the geometry of the slit? NOPE! So what are you complaining about with the scenario that I gave?

    Right.... Would you also like some fries with that?

    At this point, I would request that you cite specific sources that substantiate your idea. If you cannot do that in your very next post, then this thread has violated our guidelines and will be locked. You are then welcome to submit to the IR forum for further consideration.

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