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Does there need to exist a person reading the results of a double slit experiment?

  1. Jun 15, 2012 #1
    Hi.
    I would like to know if the results of the observations of electrons passing through double slits needs to be observed by a person for the electrons to act like theyve been observed?

    Or, is the equipments observation of the electron is enough for it to act like its been observed?

    Thanks
     
  2. jcsd
  3. Jun 15, 2012 #2
    Re: Does there need to exist a person reading the results of a double slit experiment

    Some interpretations require a conscious observer to read the equipment for the result to actualise.

    Strictly speaking, the electron becomes entangled with the apparatus, and thus according to QM does not go through any one of the slits yet.
     
  4. Jun 15, 2012 #3

    krd

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    Re: Does there need to exist a person reading the results of a double slit experiment

    Yes.....That's enough.

    The other interpretations come from the sixties. When people like Feymann started smoking marijuana, playing the bongos and attending hippie sex parties.

    If there were no concious observers there wouldn't be any science. The universe does not happen because we're here to see it happen.

    We can look at stars and galaxies that were here billions of years before we were. That they wouldn't exist if we weren't here to observe them is an absurd idea.

    Young man, stay away from marijuana.
     
  5. Jun 15, 2012 #4
    Re: Does there need to exist a person reading the results of a double slit experiment

    As a proponent of the conscious-interpretation, I don't appreciate those comments at all. An idea might be absurb, but doesn't imply its incorrect. I fail to get such logic when people dismiss propositions because they look unattractive.
     
  6. Jun 15, 2012 #5
    Re: Does there need to exist a person reading the results of a double slit experiment

    How could one possibly know that if one does not observe the electrons or the observation equipment?
    Please take no offense, but the whole question is totally meaningless.

    The whole point of science is to observe and make predictions about what one is going to observe next.
    Therefore what one cannot observe is by definition void of any meaning.
    To speculate about it, that's the absurd idea. And it is not science.
     
  7. Jun 15, 2012 #6
    Re: Does there need to exist a person reading the results of a double slit experiment

    "The modern Copenhagen way to talk about these questions is to assume that it only makes sense to talk about the property of a system if one actually cares to determine it or if at least the possibility for determining it exists. Or, in an even more modern way, the interference fringes arise if and only if there is no possibility, not even in principle, to determine which path the particle took. And, most importantly, it is not relevant whether or not we care to take note of that information. All that is necessary is whether or not the information is present somewhere in the universe. Only if such information is not present do interference patterns occur."

    -- Časlav Brukner & Anton Zeilinger, http://tinyurl.com/75w296h
     
  8. Jun 15, 2012 #7
    Re: Does there need to exist a person reading the results of a double slit experiment

    That last posting makes me refer to the quantum eraser experiment. Although no interference fringes are seen - the whole set-up is that everything is entangled. The electron has not gone through one slit or the other just because there is information in principle obtainable. The 'information' erased in quantum eraser experiments is not classical.
     
  9. Jun 15, 2012 #8
    Re: Does there need to exist a person reading the results of a double slit experiment

    I ask the poster to look at numerous books and articles that contain differentiating between proper and improper mixtures. Googling the topic is a good start, or you might like to try Barrett's "The Quantum Mechanics of Minds and Worlds", specifically pages 224-32.
     
  10. Jun 15, 2012 #9
    Re: Does there need to exist a person reading the results of a double slit experiment

    The most important issue in all this is the role of "the observer". And it's largely a red herring that was most (in)famously promulgated by Schrödinger in the Cat gedanken and inaccurately (perhaps disingenuously) ascribed at that time to Bohr and Heisenberg. Bohr certainly never took the bait. If the Geiger counter reads an emission (makes a measurement) the hammer strikes the vial of cyanide gas then the gas is released and QCat dies. There's no subsequent superposition of live-dead cat states. You don't need to wait for a sentient observer to open the box and say, "Golly, the cat's dead" for the cat to be dead. Bohr was clear about this. You could've made an infrared time-stamped videotape of what goes on inside the box, run the tape weeks later and proved this. And it's purely classical information.

    The fundamental point, as Brukner and Zeilinger try to clarify, is that the definitions of "observation" and "observer" need to be more subtly formulated so as to include the possibility of observation whether or not the observation is actually effected. This is true for all information, classical and quantum. Once the Cat dies (or the particle passes through the slit) the Information is out there. Double-slit information can be erased (measurement in the image plane versus measurement in the focal plane). Classical information is erased too, all the time (try to decipher the information in the knotted cords the Incas used, etc.). Observation is an informational act and the observer is an informational agent. The information comes first.
     
  11. Jun 16, 2012 #10
    Re: Does there need to exist a person reading the results of a double slit experiment

    I've pretty much come to think that if you muck around (in any way) with anything that exhibits particle-wave duality it will coalesce into it's particle form. Works for me.
    DC
     
  12. Jun 16, 2012 #11
    Re: Does there need to exist a person reading the results of a double slit experiment

    Hi. Thanks for all the replies. Everyone seems to be saying that the mechanism observing the electron will be enough for it act like a particle. But what about the schroedingers cat experiment? In that one the persons observation affects the result and not some equipment?
     
  13. Jun 16, 2012 #12
    Re: Does there need to exist a person reading the results of a double slit experiment

    No. In the case of the Cat you've got a radioactive isotope that either decays or doesn't decay within a given time. If it decays, then a Geiger counter (measuring equipment/measuring instrument) detects (measures) an emission. The Geiger counter is connected by an electrical circuit to a trip-hammer. When there's an emission and the counter clicks, an electrical impulse is generated which causes the trip-hammer to be released mechanically. The hammer breaks a vial of cyanide gas. The Cat inhales the gas and dies. And it dies at that time, not when the experimenter decides to open the box and collapse the Cat's (never existent) wavefunction.

    You could prove this by placing an infrared video camera with a time-stamp inside the box and running the tape later. But that's not necessary in order for the Cat to be dead.

    The Cat is always classical. It is never in quantum superposition. Schrödinger himself later said he wished he'd never come up with the gedanken, which was essentially designed to make fun of people he didn't much like, in support of EPR and his own revulsion at the idea that entanglement (Einstein's "spooky action") might be a valid concept. It's basically intellectual slapstick, as Niels Bohr understood.
     
  14. Jun 16, 2012 #13
    Re: Does there need to exist a person reading the results of a double slit experiment

    I'm no rocket scientist. (Not that being a rocket scientist would help in this instance) But it seems to me, that as Einstein might say, it's all relative. Let's set up the double slit experiment, so that there is a device to measure which slit (A or B) the electron went through. But let's isolate it, so that an outside observer, (You) has no information regarding the state of the device, (You don't know what it saw) then as far as the device is concerned the electron has been observed, and the wave function has collapsed, but as far as you are concerned, it has not been observed, and the wave function has not collapsed.

    What has happened is that the state of the electron, and the state of the device, have become entangled. From the device's point of view, the electron's wave function has collapsed, and the electron has gone through one slit or the other. Simple, end of story. But from your POV, you still have no information about which slit the electron went through, the wave function hasn't collapsed at all, the electron still exists in a state of superposition, having gone through both slits. But what has happened, is that now, the device also exists in a state of superposition, because you have no way of knowing what the device observed. You have no way of knowing what state it's in. To you the device has observed the electron going through both slit "A" and slit "B". Reality for you is dependent upon the information you have, and not the information that someone or something else has. For you, the electron and the device are both in a state of superposition.

    But it's not just that both the electron and the device are in a state of superposition, but they are in fact entangled, because if you know the state of one, you'll automatically know the state of the other. But as long as you don't know either one, the entire system of electron and device, is in a state of superposition, relative to you.

    So the correct answer, as I see it, is that it's all relative. The device "might" act as an observer, but only relative to itself. Everyone acts as an observer for themselves, and only for themselves. In reality we have no way of knowing if the device collapsed the wave function or not, to find out we would have to look, and that would effect the experiment. But what we can know, is that the device, or any other observer, cannot collapse the electron's wave function for us. The wave function as it pertains to us, is completely dependent upon the information that is available to us.

    But like I say, I'm no rocket scientist, and there is a very good chance that I'm completely and utterly wrong. In which case I'm sure that someone will set me straight. Or at least attempt to.
     
    Last edited: Jun 16, 2012
  15. Jun 16, 2012 #14

    256bits

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    Re: Does there need to exist a person reading the results of a double slit experiment

    :rolleyes:I thought it was LCD.
    And contemplating if a tree fell in the forest ....
    The conscious observer led to absurdity. I agree.
    Is the observation made when the first tester observed or does he become entangled. What about his assistant observing the observer and all the way down the line to others outside the lab. When does the entanglement end? Or even worse - the assistant observes before the tester - does he record a similar but somewhat different occurance of frequency than the tester would have. A lot of brain cells were totally destroyed in that era.
     
  16. Jun 17, 2012 #15

    krd

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    Re: Does there need to exist a person reading the results of a double slit experiment

    a


    I have a friend who has a theory about cable entanglement (cable entanglement is when cables of TV, computer, other electronics get tangled up in each other). In his theory, the cables can only entangle when there is no concious observer. The concious observer can lay the cables perfectly untangled....but only when they are not looking can the cables entangle themselves with each other. I think it's a pretty sound theory - I can not think of another plausible explanation for cable entanglement - or spooky automatic cable entanglement when the observer is at a distance and not looking, as it's also called.
     
  17. Jun 17, 2012 #16

    bhobba

    Staff: Mentor

    Re: Does there need to exist a person reading the results of a double slit experiment

    My highly sophisticated computer with sensors directly connected to the screen told me - it's so sophisticated it passed the Turing test. Its the same way I knew a tree made a sound when it fell in the forest when no one was listening.

    I think the whole idea consciousness is required for this stuff has taken a beating with modern computers - not that I ever gave it much credence really - it always seemed like pointless philosophical waffle to me.

    Thanks
    Bill
     
  18. Jun 17, 2012 #17
    Re: Does there need to exist a person reading the results of a double slit experiment

    Uh huh... right.
     
  19. Jun 17, 2012 #18
    Re: Does there need to exist a person reading the results of a double slit experiment


    I am wondering if you could name just one thing that you consider fundamental for the structure and existence of reality(i.e. that is not emergent). 'Observations', 'measurements', 'interactions', 'fields' and similar are grossly ambiguous terms and are the basis for the confusion that surrounds the issue.

    Thanks
     
  20. Jun 17, 2012 #19

    bhobba

    Staff: Mentor

    Re: Does there need to exist a person reading the results of a double slit experiment

    Sure - as soon as you can tell me what existence and reality mean. I have my own view on it - but if we are to avoid confusion that surrounds the issue then all the terms need to be well defined.

    Or maybe - just maybe - very fundamental terms like existence and reality gain meaning through discussion and dialectic rather than trying to pin it down in some definite way.

    Thanks
    Bill
     
  21. Jun 18, 2012 #20
    Re: Does there need to exist a person reading the results of a double slit experiment



    A minimalist definition would be - that which is observed. So my question was - what is the fundamental 'stuff' of that which is observed? If reality is real, there must exist at least one fundamental, non-emergent, mind-independent, observation-independent, interaction-independent, etc. constituent.

    In other words - is there a non-contextual constituent of reality anywhere at all? If not, maybe you can be wrong and the focus may need to be moved to the context(which might be a task for biology)
     
  22. Jun 18, 2012 #21

    bhobba

    Staff: Mentor

    Re: Does there need to exist a person reading the results of a double slit experiment

    Why?

    Physics consists of models like Euclidean Geometry. We observe things like points and lines and have axioms consistent with experience that describe them pretty well. All physics is is constant refinement of that paradigm. It doesn't set out answer questions like you pose.

    That said considerable progress with that paradigm has been made and I believe (and opinions are like bums - everyone has one - it doesn't make it correct) a broad outline has emerged that to some extent answers what you ask. It did not set out to do that but it has slowly emerged. And that is physics at rock bottom is quantum symmetries and there is some deep, extremely beautiful, awe inspiring foundational symmetry on which 'reality' is built waiting for us to discover. And in QM what exists is particles - exactly as Feynman says - that's it - particles - but particles obeying the rules of QM and the foundational symmetry awaiting for us to discover.

    Its not the answer you will probably like because it is highly abstract and mathematical and its likely to be labeled with this its just math rubbish ignoring it is specifically mapped to stuff out there like the points and lines of geometry. But there you have it. By starting without any preconceived notion of where it would lead and simply following the well established method of Euclidean Geometry its where I think it has lead.

    Thanks
    Bill
     
  23. Jun 18, 2012 #22
    Re: Does there need to exist a person reading the results of a double slit experiment



    I agree with that, that physics at this point cannot say what exists and what is real, that's a given. My point was made in reply to your statement that 'I think the whole idea consciousness is required for this stuff has taken a beating with modern computers' and was directed at the disconnect between the apparent non-contextuality of the classical world and the contextuality at the micro scale. If one is constructed by the other, then it makes sense that maybe the macro-scale is also contexual. This would be a problem for the kind of realism needed for statements like the quoted.





    Sure there is elegance in the symmetries found in nature, what i think is still problematic is the notion of 'particles' which should be more aptly called detections, as you only get a particle behavior at detection. And this isn't a particularly elegant description of a non-contextual world.




    That's likely the roadmap to a final theory, but unless the measurement problem is resolved, i am afraid there'd be no agreement on the question in the op.
     
  24. Jun 18, 2012 #23

    bhobba

    Staff: Mentor

    Re: Does there need to exist a person reading the results of a double slit experiment

    Whenever has anything but a particle been detected? Its properties such as momentum and position are non contextual - not that its a particle.

    I think it has been resolved - but this is not the subject of this thread.

    Thanks
    Bill
     
  25. Jun 18, 2012 #24

    Ken G

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    Gold Member

    Re: Does there need to exist a person reading the results of a double slit experiment

    I'm getting into this a bit late, but my answer to the OP question is "demonstrably yes." There does need to be a consciousness involved in any experiment, because the consciousness is where we find the meaning of an experiment. That is a very important form of involvement, it just might not be the meaning of "reading" or "act" that the OPer intended-- certainly we can usefully conceptualize (using our consciousness) a double slit experiment that has no consciousness involved anywhere in it-- except us. For example, there needn't be anyone looking at the results inside the closed room-- there only needs to be someone giving meaning to results that we can hypothetically imagine as going on in the closed room.

    This kind of argument often generates accusations of solipsism, but actually, I would say that the role of conciousness in physics is a very important element in understanding what physics is in the first place. A more careful accomodation of that relationship may stand squarely in the way of any physics "theory of everything", and I believe that is the source of the problems we have generating a consistent quantum ontology without such accomodation.

    The connection with the measurement problem is that the theory of quantum mechanics can easily explain how the results can be described as a set of possibilities with various probabilities. But if we then assert the actual outcome is fundamentally random, we have invoked a miracle that is completely outside of the mathematical (unitary) structure of quantum mechanics. This fundamental schizophrenia in the theory doesn't make it wrong, but it does make it ontologically awkward!
     
    Last edited: Jun 18, 2012
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