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B Is there an experiment proving observer dependency exists?

  1. Sep 12, 2018 #1
    The idea of the outcome of an experiment depending on whether or not it is being observed is strange. I have never seen this happening in real live.
    Still in physics it is held that it does exist: the double slit experiment using very low-energy laser light (assuming that one photon passes the slits at the time), can show observer dependency.

    However, as the assumption here above already mentions, we have to, at a minimum, assume photons exist. Is this then a given? There appear to be many other assumptions underlying this kind of experiment.

    Also, for 'observing' usually a photon detector is used. What does that do to the assumed photon? Does the detector influence the experiment? Is there an interaction between the detector and the photon?

    Also, when exactly is the photon 'observed'? When it hits the screen? When it passes the detector? When the observation hits my retina? When I have processed the information in my brain?

    Also, who can be an observer? Another person, an animal, a computer, a stone, me?

    So, to me, there are too many assumptions and open questions...
    My question for this forum is: does anyone know of an obvious, simple, not-too-many assumptions based experiment that makes 'observer dependency' existence realistic?
     
  2. jcsd
  3. Sep 12, 2018 #2

    davenn

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    Hi there
    just be careful you don't stray into philosophy … some of your post is getting close



    The photon doesn't really exist till it's detected, that is, you cannot say that it exists here or there at some point between the source and the detector.
    Then its energy is absorbed into the detector and it is gone … be that an electronic detector or an eye



    see my previous comment

    well if it passes the detector, then it hasn't been detected yet and we still don't know it's actual position


    yes, when it is absorbed into your eye


    no …. see previous comment


    an "observer" assumes something living


    Dave
     
  4. Sep 12, 2018 #3

    Drakkith

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    Typically the detector absorbs the photon. Afterwards the photon no longer exists.

    These assumptions underlie all of modern physics with the exception of perhaps General Relativity. Note that these assumptions aren't normal 'everyday' assumptions (aka 'guesses'), they are extremely well supported by evidence. Experiments such as the photoelectric effect along with everyday devices like lasers demonstrate the existence of photons. Or, rather, they demonstrate that light interacts with matter in a quantized fashion. Photons as bosonic force carrier particles is probably better supported by experiments and devices which confirm the extremely precise accuracy of Quantum Electrodynamics (the theory governing how light and matter interact with each other). Here's a list of experiments: https://en.wikipedia.org/wiki/Precision_tests_of_QED

    Basically, it sure as all heck looks like photons exist. If they don't, then the fundamental laws of the universe work in such a way as to make it look, to within the limits of our observations, like photons exist.

    Note that you don't actually need a detector at one of the slits. You just need to have some way of getting the 'which-way' information. The double-slit experiment can be done using polarizing filters placed at each slit and at various other locations in the experimental setup. Properly rotating the filters lets you determine which slit the photon must have passed through, destroying the interference, despite the filters not being 'detectors' as we usually think of the term.

    I believe a better way to understand it is that all it requires is some sort of interaction(s) that lets you determine which way the photon went.

    Basically anything that can interact with a photon.

    The standard double-slit experiment already meets my standards for such an experiment. All of the underlying 'assumptions' are well supported, the experiment is simple, and the two possible results (interference vs no interference) are extremely easy to see. Keep in mind that we are beyond the realm of normal everyday experience. You might as well ask if atoms actually exist, as you've never seen, felt, heard, smelled, or tasted just a single atom. It takes specific experiments to come to the conclusion that atoms exist, just as it takes specific experiments to show the complementarity nature of photons (and other particles).
     
  5. Sep 12, 2018 #4

    Dale

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    Certainly. The goal of science isn’t to eliminate all assumptions, but rather to get a set of assumptions that allow for the accurate prediction of a wide variety of experimental results

    Detectors need not be alive. Any measuring device will do.
     
  6. Sep 12, 2018 #5

    Drakkith

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    That's not how I understood it. In fact I've always understood that the idea that we need a conscious person to be the observer is a misunderstanding.
     
  7. Sep 12, 2018 #6

    davenn

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    OK interesting thought :smile:
     
  8. Sep 12, 2018 #7

    Dale

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    Same here. Basically it is as unfortunate a choice of language as “particle”
     
  9. Sep 12, 2018 #8

    Nugatory

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    There is an interaction between the detector and the photon. That interaction is what causes the detector to change its state from "no photon detected" to "photon detected"; if there were no interaction there could be no detection.

    This interaction influences the experiment: it changes the wave function of the particle in such a way that it no longer produces an interference pattern.
     
  10. Sep 12, 2018 #9

    sophiecentaur

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    The problem is that the term "observer" is used as if it means that someone is actually there, doing a measurement. What is really meant is that a 'result' occurs. No one needs to see that but that result could contribute (by further interactions) to setting up a set of conditions and possibly a whole string of events which a Physicist, somewhere could observe. Cosmologists are studying the results of countless "Schroedinger" situations and testing their models against them. If there were no Cosmologists, we (surely) believe that the models that the Cosmologists are developing would still be followed. So you don't actually need an explicit 'Observer'.
    @Dale +10 on the comparison with the term 'particle'.
     
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