4 ms·

I wanna know: how/why does the observer change the behavior of quantum systems?

• dougk16 13y ago
  In order to observe something you have to bounce photons off of it, which changes its behavior...little over-simplified, but I believe that's the gist.
• hcarvalhoalves 13y ago
  From what I understand, there are two phenomena at play, often mixed together. The observer might interfere when it tries to measure (the observer effect, which is true to any system), but there's also an inherent uncertainty on the way waves are measured (the uncertainty principle). The observer effect is well-understood, there's nothing magical about it. For example, a multimeter acts a (very small) resistor, affecting the circuit it's measuring. Sometimes the error you introduce can be ignored, but get unmanageable when you try to measure really small systems, where things are more easily disturbed. The uncertainty principle, on the other hand, is something else. There's a video that I think explains the uncertainty principle well, with a practical example (it's explaining why there's a limit to how many pulses you can send down a fiber optic and still be able to measure on the other side): http://youtu.be/0OOmSyaoAt0?t=7m28s http://youtu.be/0OOmSyaoAt0?t=7m28s
  • judk 13y ago
    Uncertainty principle is about shape, not measurement. Unless you mean "how you define the measured aspect of the system" . Position and momentum are Fourier transforms of each other, and therefore their waveforms cannot both be confined to small range at the same time. It is loosely analogous to the concept that a rectangle of area 1 can never have both side lengths less than 1.
• moultano 13y ago
  The observer becomes entangled with the quantum system.
  • greeneggs 13y ago
    Yes, this really is just a special case of one of the questions: "What is consciousness?" When we become entangled with a quantum system, why does our consciousness follow one path (apparently) and not another? If we can understand consciousness, then this is probably easy.
    • acqq 13y ago
      Quantum states simply aren't the medium of the interaction for our consciousness. Our brains work on electrical and chemical signals, ginormous orders of magnitude bigger levels than quantum ones.
    • lmm 13y ago
      It's not about consciousness. We can make a mechanical detector and it behaves exactly the same way as a human observer.
• gsteinb88 13y ago
  This is still an open question, and a really good one. The predictive power of quantum theory is amazing; it gives excellent numerical predictions as to the outcome of experiments. But as to how we interpret that, especially the question of what a measurement is, is not at all addressed by the theory, and remains a point of intense discussion and study.