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Thread: Implications of Double Slit

  1. #1 Implications of Double Slit 
    Forum Freshman Quantumologist's Avatar
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    The double slit experiment demonstrated wave-particle duality through the interference pattern without leaving room for doubt. But did it raise further questions, also?

    In 2015 Andrew Truscott of the Australian National University conducted a variant of the double-slit using atoms deflected by laser pulses. To quote the IoP article in Physics World: "I can't prove that isn't what occurs," says Truscott, "But 99.999% of physicists would say that the measurement – i.e. whether the beamsplitter is in or out – brings the observable into reality, and at that point the particle decides whether to be a wave or a particle."

    Does this experiment raise the matter of decision-making processes at the particle level? And if so, what are the implications?


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    KJW
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    The wave-particle duality is a false dichotomy, and I think most of the conceptual difficulties people have with quantum mechanics arises from a failure to realise that. The wave-particle duality is based on the Heisenberg uncertainty principle between position and momentum, but position and momentum are not the only domains of a quantum state. Thus, a quantum state is not either a wave or a particle, but can be something else depending on the nature of the measurement. Particles arise when position is measured, but a measurement need not be of position. And if the observable being measured is not position, then the quantum state will not become a particle.


    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Brassica oleracea Strange's Avatar
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    Hard to comment without knowing what the experiment was. I assume it was this one: http://www.nature.com/nphys/journal/...nphys3343.html

    The behaviour is exactly as predicted and show that quantum properties are not definite until they are measured.

    There is a good description here https://briankoberlein.com/2015/06/04/real-and-unreal/
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    Duplicate post
    ei incumbit probatio qui dicit, non qui negat
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    Forum Freshman Quantumologist's Avatar
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    From the linked article above: Where things get fuzzy is in the interpretation. Onepopular way to interpret quantum theory is to presume quanta have apotential wavefunction, which then collapses into a definite state whenobserved. In this view the act of measurement gives reality to the quantum. Inthe delayed-choice experiment that would mean the quantum doesn’t become “real”until you measure it, which could be billions of years after its origin inthe case of quasar light. But this is an overly simplistic take on things. Quantumobjects are real, but simply have indefinite properties. These properties aredefined by the experiments we do. What the delayed choice experiments reallyshow is that quanta don’t exist as particles or waves, but are trulyunique objects which can exhibit particle and wave properties in certainexperiments.

    Quanta don't exist? I've not seen this clause before. A Get Out of Jail Free card? Perhaps the more rational view would be that particle existence comes about during the present moment, that is, immediately preceding the future and proceeding the past, where the advanced/retarded wave (form) collapses the packet through observation. Experimental observation in the lab cannot rationally be taken as the only legitimate form of observation, and while we are still groping in the dark about what constitutes consciousness, it is conceivable that all objects observe each other, including particles, and that therefore "reality" is relative to all versions of material in the universe which are, after all, relating to each other.

    The very fact that quantum particles cannot be described as 'definite until they are measured' throws the box wide open in terms of how they actually behave, for their 'indefinite' versions of existence cannot be determined any less real than the 'definite' ones.
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    Quote Originally Posted by Quantumologist View Post
    From the linked article above: Where things get fuzzy is in the interpretation. Onepopular way to interpret quantum theory is to presume quanta have apotential wavefunction, which then collapses into a definite state whenobserved. In this view the act of measurement gives reality to the quantum. Inthe delayed-choice experiment that would mean the quantum doesn’t become “real”until you measure it, which could be billions of years after its origin inthe case of quasar light. But this is an overly simplistic take on things. Quantumobjects are real, but simply have indefinite properties. These properties aredefined by the experiments we do. What the delayed choice experiments reallyshow is that quanta don’t exist as particles or waves, but are trulyunique objects which can exhibit particle and wave properties in certainexperiments.

    Quanta don't exist? I've not seen this clause before.
    Then, apparently, your "research" hasn't been as in-depth as you believed.

    Perhaps the more rational view would be that particle existence comes about during the present moment
    Why, exactly, is this a "more rational" view?

    Experimental observation in the lab cannot rationally be taken as the only legitimate form of observation
    So you'd also suggest adding... what?

    it is conceivable that all objects observe each other
    That's true (for a given value of "observe").

    and that therefore "reality" is relative to all versions of material in the universe which are, after all, relating to each other.
    Um, what?

    The very fact that quantum particles cannot be described as 'definite until they are measured' throws the box wide open in terms of how they actually behave, for their 'indefinite' versions of existence cannot be determined any less real than the 'definite' ones.
    Has anyone said that they're "less real"?
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    Quote Originally Posted by Quantumologist View Post
    Quanta don't exist?
    The article doesn't say that. (Although whether they exist or not is a philosophical question: are they real things or just a useful mathematical model. The same could be said of things like the electromagnetic field, or even numbers.)

    The very fact that quantum particles cannot be described as 'definite until they are measured' throws the box wide open in terms of how they actually behave, for their 'indefinite' versions of existence cannot be determined any less real than the 'definite' ones.
    Indeed. We cannot say anything about the path of a photon between the source and where it is detected. But it is convenient to consider that they travel in straight lines at the speed of light. (Even though QED throws some doubt on that.)
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    I have posted this question essentially to discuss the element of 'choice' inferred by the DS experiment, or at least being one of any number of possible explanations for particle behaviour, and to explore the implications of this on other levels. We know that particles - even quanta - are real, and that they have strange modus operandii. QED throws some doubt even on the most basic principles to which physics adheres and these aspects are worth exploring.
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    Genius Duck Dywyddyr's Avatar
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    Quote Originally Posted by Quantumologist View Post
    QED throws some doubt even on the most basic principles to which physics adheres
    Such as?

    and these aspects are worth exploring.
    So far you haven't even got close to "exploring". Your posts to date have been either vague or wrong. (Or perhaps both).
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    Quote Originally Posted by Quantumologist View Post
    I have posted this question essentially to discuss the element of 'choice' inferred by the DS experiment, or at least being one of any number of possible explanations for particle behaviour, and to explore the implications of this on other levels. We know that particles - even quanta - are real, and that they have strange modus operandii. QED throws some doubt even on the most basic principles to which physics adheres and these aspects are worth exploring.
    Maybe it will be helpful to ask what -you- think "choice" means in this context. What's doing the choosing, and is it an explicit conscious choice, or a commonly used metaphor for probabilistic behaviour? Something else entirely? Please be specific. I'd just like us to be on the same page.
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    Choice as we determine it to mean, essentially the option to do one thing or another. The mechanism of making the decision is what interests me here, and the probability - or otherwise - of consciousness adhering to that mechanism. Machinery determines what to do through its programming, so it can't be said that a cutter chooses where to fall on the material it's programmed to cut - or can it? Computer processing might raise the same kind of question. But in terms of free-moving particles which have had no previous influence from humans, yet appear to respond to observation, that opens a wholly separate line of enquiry.
    (To my mind, anyway, and you've seen what's been made of my mind already )
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    Brassica oleracea Strange's Avatar
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    There is no "choice" made by the particles. They are constrained (deterministically but probabilistically) to behave in certain ways. As shown by the double slit experiment. We can choose to change the experimental set-up and hence change the outcome.
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    Please elucidate on the term 'constraint'.

    In questioning the behaviour of the particle and the mechanism behind that behaviour, does it make sense to paralyse its potential prior to exploring the reason/s (potentially) for the effects it demonstrates?
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    Quote Originally Posted by Quantumologist View Post
    Please elucidate on the term 'constraint'.

    In questioning the behaviour of the particle and the mechanism behind that behaviour, does it make sense to paralyse its potential prior to exploring the reason/s (potentially) for the effects it demonstrates?
    What does "paralyse its potential" mean?

    I recommend this series of non-technical lectures for a lay audience to get some insight into the behaviour of photons: The Vega Science Trust - Richard Feynman - Science Videos
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    Quote Originally Posted by Quantumologist View Post
    Choice as we determine it to mean, essentially the option to do one thing or another. The mechanism of making the decision is what interests me here, and the probability - or otherwise - of consciousness adhering to that mechanism. Machinery determines what to do through its programming, so it can't be said that a cutter chooses where to fall on the material it's programmed to cut - or can it? Computer processing might raise the same kind of question. But in terms of free-moving particles which have had no previous influence from humans, yet appear to respond to observation, that opens a wholly separate line of enquiry.
    (To my mind, anyway, and you've seen what's been made of my mind already )
    I don't think you're being explicit enough. I don't want to have the wrong idea about what you really mean. We'll all just be talking past each other then. So please...
    - Do you believe that quanta make a conscious decision to perform an action? Explicitly, "I'm a photon, these are my choices, I want to take this one." If no, then what do you mean?
    - Do you believe that it is the "influence from humans", very specifically "humans", that makes the outcome of the experiment occur? Explicitly again, "I'm a photon. There's a human nearby. I shall behave accordingly." If no, what do you mean?
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    Thank you for the questions, Karsus. In responding, I must stress that my views are my own and not to be taken as any attempt to educate anyone,

    Do I believe that quanta make a conscious decision to perform an action? I don't know what to believe on this one. Freedom of choice is, in itself, a line of enquiry - as we freely debate it in the human context, maybe the question would be "how far does it apply"? Do we stick to applying it to life forms, and if so, where do you draw the line at what constitutes a liife form?
    As far as I understand it, given that I accept the MWT, an upcoming decision-making process creates a junction whereby either/any decision is rendered possible, and is actualised elsewhere regardless of which one is selected in this 'reality'. Does the photon somehow morph itself into a 'virtual particle' in order to perform the decision-making process in line with the requirements of physics, 'choose' both options and both options remain visible to the observer for some reason, hence the interference pattern we interpret as a wave? That's opening another line of questioning, I know, but it's where my thoughts have taken me on pondering the answer to yours.

    Which kind of leads into your second question.... I don't believe that humans are necessary for physics to work, but the nature of our conscious activity- i.e. the mechanics of our own questioning process - might affect the results we observe. Is it that the particle is responding to the observation, or is the conscious nature of that observation causing the response? Is there some kind of symmetry at work here? To perform the experiment, the number of photons has to be reduced to a minimal number. Shine a torch at two slits and you see two bars of light on the other side. Only when the number of particles is very small, can the strangeness of the interference pattern be observed. Under natural circumstances, the isolation of such small numbers of such miniscule particles under such conditions would not occur, so is the nature of the experiment changing the behaviour of nature in some way?
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    Genius Duck Dywyddyr's Avatar
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    The above "answer" is somewhat flawed. The most obvious being:
    Quote Originally Posted by Quantumologist View Post
    As far as I understand it, given that I accept the MWT, an upcoming decision-making process creates a junction whereby either/any decision is rendered possible, and is actualised elsewhere regardless of which one is selected in this 'reality'.
    If the MWT is correct then there is no "decision".
    ALL possibilities occur and ALL are observed.
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  19. #18  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by Quantumologist View Post
    Is it that the particle is responding to the observation, or is the conscious nature of that observation causing the response?
    There is absolutely zero evidence that consciousness has anything to do with it.

    To perform the experiment, the number of photons has to be reduced to a minimal number. Shine a torch at two slits and you see two bars of light on the other side. Only when the number of particles is very small, can the strangeness of the interference pattern be observed.
    The experiment was originally performed by Thomas Young in 1801 using beams of light. The presence of the interference pattern confirmed the wave nature of light.
    https://en.wikipedia.org/wiki/Young%...nce_experiment
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    Quote Originally Posted by Quantumologist View Post
    Thank you for the questions, Karsus. In responding, I must stress that my views are my own and not to be taken as any attempt to educate anyone,
    Thanks, Quantumologist for the detailed response. I like your disclaimer. Would I be right in guessing that you strongly agree with the statement, "Everyone's opinion is equally valid and should be granted equal time and weighting?"

    Regardless, that is the feeling I get from reading your posts, and the kind of subjective thinking that represents isn't compatible with science (I'd argue it isn't compatible with 99% of things in life, but that's a topic for another time). Looking at other threads around the forum, there's been no shortage of people trying to tell you this. I wouldn't consider you rude enough to just be ignoring them, but I get the impression you simply don't believe them. So, approaching from a different direction, what merit do you think there is in such a subjective approach to science? Do you think it can be successful, and what would be the benchmarks for success?

    As far as your answers go, I see a bit of a theme. You like to bounce from topic to topic and back again, touching on so many unrelated things, that in the end you haven't really said anything at all. They seem very much like politician's answers. Maybe if I point it out, you'll see what I mean?

    Quote Originally Posted by Quantumologist View Post
    Do I believe that quanta make a conscious decision to perform an action? I don't know what to believe on this one. Freedom of choice is, in itself, a line of enquiry - as we freely debate it in the human context, maybe the question would be "how far does it apply"? Do we stick to applying it to life forms, and if so, where do you draw the line at what constitutes a liife form?
    Strong start. Don't know what to believe? That's great, it would be a good place to stop and have a discussion. Freedom of choice? A fair place to go, but then you wander further into speculative territory with "how far does it apply?" But you just said it hasn't been established yet, you can't advanced something that hasn't been established. And then, it's on to talking about what life is. Completely unrelated, the train of thought has been derailed.

    Quote Originally Posted by Quantumologist View Post
    As far as I understand it, given that I accept the MWT, an upcoming decision-making process creates a junction whereby either/any decision is rendered possible, and is actualised elsewhere regardless of which one is selected in this 'reality'. Does the photon somehow morph itself into a 'virtual particle' in order to perform the decision-making process in line with the requirements of physics, 'choose' both options and both options remain visible to the observer for some reason, hence the interference pattern we interpret as a wave? That's opening another line of questioning, I know, but it's where my thoughts have taken me on pondering the answer to yours.
    New topic again, many worlds, and unfortunately it's a very incorrect take on it, as Dywyddyr has pointed out. And then you discard it to talk about morphing photons into virtual particles (that's not what those words mean) with the assumption of a decision-making process. But you only said a few sentences ago that you didn't know if quanta made decisions at all, remember? At least know you are jumping around a bit, I just don't think you realise how much and how detrimental to a coherent discussion it is, though.

    Quote Originally Posted by Quantumologist View Post
    Which kind of leads into your second question.... I don't believe that humans are necessary for physics to work, but the nature of our conscious activity- i.e. the mechanics of our own questioning process - might affect the results we observe. Is it that the particle is responding to the observation, or is the conscious nature of that observation causing the response? Is there some kind of symmetry at work here? To perform the experiment, the number of photons has to be reduced to a minimal number. Shine a torch at two slits and you see two bars of light on the other side. Only when the number of particles is very small, can the strangeness of the interference pattern be observed. Under natural circumstances, the isolation of such small numbers of such miniscule particles under such conditions would not occur, so is the nature of the experiment changing the behaviour of nature in some way?
    This is well into speculative territory, and exactly where I figured your beliefs on the topic would lie. I don't think there's much I can say that would change your mind on the topic, except: 1. Nice buzzword, symmetry, isn't it? Sounds deep without actually saying anything. 2. Having performed a number of double slit experiments in high school and undergraduate physics classes myself, using laser, atomic, thermal and single photon sources of varying brightness, I can say that is definitely not how they work. See Strange's wiki link.

    So, can you see why it might be frustrating? Do you have a similar approach when you're talking on other topics? Cooking? i.e., being spectacularly facetious "First, crack two eggs into a bowl. I don't know if we can really call it a bowl. Might the eggyness also extend to mugs? I don't claim to be an expert, but have you heard the theory on egg-to-milk ratios? You whisk with the thick end. Is there some kind of symmetry at work here?" I don't imagine you do, so why do you think a similar approach is fine for science?
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