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Thread: Double slit experiment and CERN

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    Double slit experiment and CERN

    In the double slit experiment a light source or electron beam gun is shot at the plate with two slits. If one sets up the experiment to observe which slit the particles go through result in particle impact pattern, else a wave interference pattern.

    How about CERN. Getting impact patterns means observation of particles or photons when leaving the source so they become particles prior to impact. Who does the observing?

    Thanks...

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    I assume youíre asking about the LHC (CERN is an organization). The LHC is not used for running double-split experiments. Itís a particle accelerator.
    As above, so below

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    As noted, there are no double slit experiments are done at LHC or any other of the CERN facilities which are particle accelerators and 1 decelerator.
    There should be no "observation of particles or photons when leaving the source" in the CERN facilities, e.g. the LHC detectors are spaced around the accelerator ring and the source of the LHC protons are separate accelerators.

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    The OP isn't about the double slit experiment, but about the fact that quantum systems answer particle questions with particle answers, and wave questions with wave answers.
    So the LHC detectors ask particle questions, and they therefore give answers that involves particle collisions.

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    You misunderstood my question: I know CERN has a particle accelerator and they do not do double slit experiments. I am asking what causes the particles not to be waves in the accelerator and act as particles. In both experiments there is a generator of particles. At what point are the CERN particles, particles and not waves is what I am asking.
    Last edited by gzhpcu; 2018-Feb-08 at 07:23 AM.

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    Quote Originally Posted by gzhpcu View Post
    You misunderstood my question: I know CERN has a particle accelerator and they do not do double slit experiments. I am asking what causes the particles not to be waves in the accelerator and act as particles. In both experiments there is a generator of particles. At what point are the CERN particles, particles and not waves is what I am asking.
    as far as i know they are always both, but the energy levels are so high that the location is pretty narrowed down.
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    Quote Originally Posted by gzhpcu View Post
    You misunderstood my question: I know CERN has a particle accelerator and they do not do double slit experiments. I am asking what causes the particles not to be waves in the accelerator and act as particles. In both experiments there is a generator of particles. At what point are the CERN particles, particles and not waves is what I am asking.
    When an electron or photon is detected, it is detected as a "particle" - it is detected at a single location (e.g. it interact with a single atom in the detector) and it is completely detected (you can't detect half an electron, an atom can't absorb half the energy of a photon).

    But you can also describe the behaviour of the electron or photon as a wave. It isn't really one or the other.

    I don't know if it is correct to describe the different behaviours of the dual slit experiment in terms of either wave or particle behaviour depending on whether you know which slit the electrons went through, but it certainly seems misleading.

    But I like Grant's answer: whether you see particle-like or wave-like properties depends what you measure.

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    With the dual slit experiment, observing the holes, collapses the wave function, resulting in a particle, if I understand it correctly. I can not say I want to observe particle behavior. I need to look. If I do not look, it acts as a wave and displays a wave interence pattern. Where does this happen for the particle accelerator? As the magnetic field interacts with it?
    Last edited by gzhpcu; 2018-Feb-08 at 11:33 AM.

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    Quote Originally Posted by gzhpcu View Post
    With the dual slit experiment, observing the holes, collapses the wave function, resulting in a particle, if I understand it correctly. I ca not say I want to observe particle behavior. If I do not look, it acts as a wave and displays a wave interence pattern. Where does this happen for the particle accelerator? As the magnetic field interacts with it?
    In the detectors that observe each experiment. Up to that point, the accelerated and colliding particles are described by a complicated wavefunction - the detectors "collapse the wavefunction" into a particular experimental outcome.

    Grant Hutchison
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    But up to the point of collision are the particles waves? Is the LHC initially accelerating waves?

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    Quote Originally Posted by gzhpcu View Post
    But up to the point of collision are the particles waves? Is the LHC initially accelerating waves?
    The particles are wavefunctions (whatever that corresponds to in "reality") even after the collision. They're localized particles only when they interact with the detectors. So we can (in principle) use a complete description of the wavefunction to tell us the probabilities of certain detector outcomes from a given collision experiment design. For each experiment the detectors then "collapse the wavefunction" into a particular outcome.
    In practice, we're using the detector outcomes to tell us more about the wavefunction and its associated probabilities.

    Grant Hutchison
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    Are you saying we are detecting particles after the collision? So prior to collision the particles are waves?
    Last edited by gzhpcu; 2018-Feb-08 at 01:57 PM.

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    Quote Originally Posted by gzhpcu View Post
    Are you saying we are detecting particles after the collision? So prior to collision the particles are waves?
    They are always both. Or, more accurately, neither.

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    Quote Originally Posted by gzhpcu View Post
    Are you saying we are detecting particles after the collision? So prior to collision the particles are waves?
    He is saying we are detecting particles after the collision because the detectors being used are designed to detect particles. If the detectors were designed to detect characteristics of waves, then they would detect waves. The things are neither or both.
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    Quote Originally Posted by gzhpcu View Post
    But up to the point of collision are the particles waves? Is the LHC initially accelerating waves?
    According to physicist Sean Carroll physics has answered the "are they waves or particles" question and that the answer is that they are fields. Quantum field theory (QFT) describes everything as interactions among fields, and particles as excitations in fields. It seems that while thinking of photons, electrons, etc., as particles or waves can be useful in certain circumstances, if the intent is to try to better understand the underlying reality of these things then one needs to accept that they actually are not waves or particles and do not behave like macro scale waves and particles that humans are familiar with and may therefore have some intuitive understanding of.
    Last edited by Darrell; 2018-Feb-08 at 02:12 PM. Reason: Attempt at clarity.

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    Quote Originally Posted by Darrell View Post
    According to physicist Sean Carroll physics has answered the "are they waves or particles" question and that the answer is that they are fields. Quantum field theory (QFT) describes everything as interactions among fields, and particles as excitations in fields. It seems that while thinking of photons, electrons, etc., as particles or waves can be useful in certain circumstances, if the intent is to try to better understand the underlying reality of these things then one needs to accept that they actually are not waves or particles and do not behave like macro scale waves and particles that humans are familiar with and may therefore have some intuitive understanding of.
    Yes, I think that what we have is a mathematical theory that makes probabilistic predictions, and imagining that there's a moment a particular entity makes a transition from a thing that is a wave to thing that is a particle (or vice versa) is unhelpful. I'm not sure saying "it's a field" solves that problem in any useful way, though.

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    Quote Originally Posted by Swift View Post
    He is saying we are detecting particles after the collision because the detectors being used are designed to detect particles. If the detectors were designed to detect characteristics of waves, then they would detect waves. The things are neither or both.
    Yes, but aren’t there components which implicitly detect the entities proir to the collision?

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    ((
    Quote Originally Posted by Darrell View Post
    According to physicist Sean Carroll physics has answered the "are they waves or particles" question and that the answer is that they are fields. Quantum field theory (QFT) describes everything as interactions among fields, and particles as excitations in fields. It seems that while thinking of photons, electrons, etc., as particles or waves can be useful in certain circumstances, if the intent is to try to better understand the underlying reality of these things then one needs to accept that they actually are not waves or particles and do not behave like macro scale waves and particles that humans are familiar with and may therefore have some intuitive understanding of.
    How does QFT explain the dual split experiment?

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    Quote Originally Posted by grant hutchison View Post
    Yes, I think that what we have is a mathematical theory that makes probabilistic predictions, and imagining that there's a moment a particular entity makes a transition from a thing that is a wave to thing that is a particle (or vice versa) is unhelpful. I'm not sure saying "it's a field" solves that problem in any useful way, though.

    Grant Hutchison
    weird though are the results of the dual split experiment. The behaviour is wave-like until observed
    Last edited by gzhpcu; 2018-Feb-08 at 05:45 PM.

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    Quote Originally Posted by gzhpcu View Post
    ((How does QFT explain the dual split experiment?
    I am about as far from an expert on these issues as you can get, but my understanding is that QFT does not yield a different explanation for the double slit experiment than QM does. QM already resolves the apparent wave-particle duality issue. The particle states are not really either waves or particles. QFT merely offers a different model of the particle states, which happen to result in the same properties as in QM.

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    What I mean is how does QFT explain a wave interference pattern vs a particle impact pattern on the screen?

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    I have no problem with describing the things you are talking about
    as both particles and waves -- not neither. More specifically, I say
    that they are particles which display wave behavior. They certainly
    do not change from one to the other. Just forget that idea.

    Photons travel through the slits, but when they form an interference
    pattern on the screen, you cannot determine which slit each photon
    goes through, because they behave like waves. When you determine
    which slit a photon goes through, you mess up the wave, and thus
    mess up the pattern.

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    From the original post:

    Quote Originally Posted by gzhpcu View Post
    In the double slit experiment a light source or electron beam gun is
    shot at the plate with two slits. If one sets up the experiment to
    observe which slit the particles go through result in particle impact
    pattern, else a wave interference pattern.
    That is not how I would describe it. However, the grammar of your
    statements is slightly messed up. That might account for at least
    some of the problem. Can you fix the grammar so the statements
    say exactly what you meant?

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

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    Sure Jeff. Could you please point out which statements are not well expressed and I will try to restate them. (Being Swiss, my primary languages are Italian and German.)
    Last edited by gzhpcu; 2018-Feb-08 at 08:54 PM.

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    I assume Jeff is referring to:

    If one sets up the experiment to observe which slit the particles go through [it] result[s] in [a] particle impact pattern, else a wave interference pattern.
    But it seems pretty unambiguous even without being perfect. (I hadn't even noticed.)

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    Quote Originally Posted by gzhpcu View Post
    What I mean is how does QFT explain a wave interference pattern vs a particle impact pattern on the screen?
    By doing complicated mathematics in Fock space. The mathematics is the explanation. At some point, the mathematics is always the explanation.

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    Quote Originally Posted by gzhpcu View Post
    I am asking what causes the particles not to be waves in the accelerator and act as particles. In both experiments there is a generator of particles.
    In the experiments there are particles that also can act as waves. Or waves that can also act as particles. This is wave-particle duality. So the protons in the LHC ring have the properties of both particles and waves.
    In the Copenhagen interpretation, a measurement collapses the wave function to give a definite value. The LHC detectors measure the paths of the protons which means that we measure that they act like particles. In theory, we could put a diffraction grating in the LHC ring, measure a wavelength and conclude that the protons act like waves.
    Last edited by Reality Check; 2018-Feb-08 at 11:56 PM.

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    Thanks Reality Check, that is what I was wondering.

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    Baffling in Quantum Mechanics is the role played by consciousness...

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    Quote Originally Posted by gzhpcu View Post
    Baffling in Quantum Mechanics is the role played by consciousness...
    You have to bear in mind that the Copenhagen interpretation (which is what you are using) is only one way for people to put a description around what the mathematics are telling us we'll observe. In QM, there is no intrinsic role of conciousness in the underlying mathematical theory.

    See https://en.wikipedia.org/wiki/Interp...nterpretations

    Only a few have integral roles for observers and probably only a couple go as far as giving conciousness an integral role.

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