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Perhaps I am completely wrong, but as I understand it our observation of a system can affect the outcome. The example I remember is the double slit experiment where electrons behave as a wave at first, but when observing it behaves as a particle. The conclusion, as I remember hearing, is that observing the system is what caused the different outcomes.

Why is this that case? Couldn't it have been the camera (or whatever is used to detect/observe/etc.) that causes the difference? It just seems like there are a few potential explanations that get skipped over here.

Excuse me while I most likely butcher this experiment with an example. Say I turn on the sink and water goes from the faucet to the drain. Now when I hold a cup under the water, it no longer hits the drain, instead it is captured in the cup. My explanation, having my hand there causes the behavior.

This has bugged me since I first heard it, and I have yet to find an explanation that I can accept. Given, that may be due to my inability to comprehend some of the more complex explanations, but I would still like to figure it out.

David Starkey
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  • Are you asking if an intelligent observer is required to collapse the wavefunction or whether a purely mechanical observer (like a camera) is sufficient? – The Photon Mar 18 '14 at 20:48
  • I'm asking why the conclusion is the act of observing, and not the device. For example, perhaps the device creates a magnetic field or some sort of interference that causes the different result. It would be like me saying 1+1 written in pencil makes 2 while 1+1+1 in written pen makes 3 because it is written in pen. – David Starkey Mar 18 '14 at 20:59
  • I assume you're talking about Young's double-slit experiment or any other optical diffraction experiment. If we use a film camera, or a CCD, or move a photodiode around, or just look at the light shone on a piece of paper in a dark room, we see the same pattern. Is there experimental evidence that a different mechanism for measuring the diffraction pattern gives a different result? – The Photon Mar 18 '14 at 21:04
  • @ThePhoton If I look at light going through 2 slits in a dark room, I should see it behaving as a wave, correct? So if I introduce equipment and that changes the behavior, it should be the equipment, not the act of observing, right? – David Starkey Mar 18 '14 at 21:09
  • If you shine coherent light through two appropriately-sized slits onto a screen, you will see a diffraction pattern. If you take a film or digital photo of the pattern, it won't change the pattern. If you replace the screen with a big piece of film, it will record the same pattern. – The Photon Mar 18 '14 at 21:12
  • But if you place your camera so that it blocks one of the slits, it will change the pattern. – The Photon Mar 18 '14 at 21:14
  • @ThePhoton As I understand it, when shooting electrons (particles) through the 2-slit setup, the resulting image is like how waves would act. However, if we introduce a device that observes which slit it goes through, the resulting image looks like that of a particle. Why do we conclude that the act of observing the slit causes the new outcome, and not the device itself. If we use this video, it is like saying the eye watching causes the outcome, not whatever makes the eye work. – David Starkey Mar 18 '14 at 21:33
  • possible duplicate of Isn't the uncertainty principle just non-fundamental limitations in our current technology that could be removed in a more advanced civilization? – DumpsterDoofus Mar 18 '14 at 21:44
  • @DumpsterDoofus I'm not sure how this is a duplicate of that. This question is asking how observation came to be the explanation for the wave-particle duality phenomenon while that question is discussing technical limitations and the Heisenberg principle. – David Starkey Mar 18 '14 at 21:46
  • @DavidStarkey: Try reading the first chapter of Feynmann's "Quantum Mechanics and Path Integrals: Emended Edition". He describes in detail the double slit results in a very pictoral fashion without math, and the essence of the idea is that it isn't so much the fact that observing changes the outcome, so much as the process used to observe the situation changes the result. So you are actually correct in your suggestion that it is the device itself (namely, the photons used to measure the electron paths) which causes the change, and not the observer. – DumpsterDoofus Mar 18 '14 at 21:58
  • @DavidStarkey: The notion that the act of consciousness making the observation is the culprit behind the change in experiment result is a popular misconception, in part due to psychic healers and pseudoscience sellers like Deepak Chopra, who like to reinterpret quantum mechanics to suit their business plans. – DumpsterDoofus Mar 18 '14 at 22:03
  • I have always taken the "observer" in this discussion not to mean an intelligent interpreter but "anything that collapses the wavefunction", by which I mean anything that eliminates uncertainty about the particle position. But I am not sure that is a complete or up-to-date explanation because I am not a physicist. – The Photon Mar 18 '14 at 22:03
  • @DumpsterDoofus So the act of observing is not the cause, but the process by which we observe is? So in the infamous Schrödinger's cat, is it not observing the cat, but the opening of the box or the light entering or something? – David Starkey Mar 18 '14 at 22:27

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A very simple answer to you question is that it's impossible to observe a system without interacting with it in some way. By weighing an apple, we are scraping atoms off its base which reduce its weight. Even by observing a star, our eyes are absorbing photons which may have otherwise been reflected right back into the same star. It is impossible to be completely detached from a system that you are observing.

At the subatomic level, observation becomes very tricky because the 'objects' are impossible to see and very difficult to detect. We "perceive" them by gathering evidence of their existence and compiling this evidence into models (which can be repeatedly verified.) This evidence is often incomplete and our models are often lacking important details. With some particle systems, we can see evidence of velocities and we can also see evidence of positions. However, it impossible for us to link a velocity with a position and say that we know both for a particle. We know where it is, but we can't predict where it is going to be.

There are many possible answers, the trick is compiling enough verifiable evidence to support you possible answers. That's what the scientific method is all about.

Hoytman
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  • I think you may have missed my question a bit. I understand it is impossible to remove ourselves from the experiment, in fact that is part of the reason for the question. The reason I am confused is at the end conclusion. Why is it the act of observing and not the tools used in observation? – David Starkey Mar 19 '14 at 00:04