Observing the double slit experiment

  1. In this experiment wave particle duality is shown. Without observation the wave function is used. With observation the particle function is used.

    My question is what is the definition of observation? Specifically in the case of an electron gun is the observer a conductive piece of material in and around the electron path?
     
  2. jcsd
  3. "Observation" is not a very good concept. "Detection" is better (presence of human "observers" is irrelevant for the detection to take place). You have a detection when you have a detector (or several of them) coupled to your quantum system.
     
    Last edited: Aug 30, 2010
  4. Ok, anyone got some examples of detectors that influence the system?
     
  5. Photographic plate, Geiger counter, cloud chamber, fluorescent screen. Eye of a fly.
     
  6. I should add that in "Bohmian mechanics" the philosophy is different. But I do not think you want to know about Bohmian mechanics - it is a separate subject.
     

  7. How about ear?
     
  8. Ear is not that sensitive to individual quanta. Not a good detector for quantum events.
     


  9. Detection clicks are audiable. But my focus was on the "fly's ear" not just ear, or just 'eye'.
     
  10. Without observation, what is the wave function used for?? What is the "particle function"??
    A quantum experiment must include a measurement result that is obtained when the particle is detected. I think this is what you mean by observation; observation is the measurement result. This result is a necessary part of the experiment. (Bohr) Without a result (observation) there is no experiment to discuss. The wavefunction is used to calculate the probability of obtaining that result. Without observation, there is no wave function.
    Neither the theory nor the experiment describe what the particle is doing before it is detected. Quantum mechanics predicts only the possible results of a measurement and the statistical distribution of those results. We have no idea what the particle is doing before detection. (Wheeler)
    The particle is always detected as a particle. It is the statistical distribution of the results that we identify as an interference pattern, which is characteristic of classical waves. Thus, we see "a particle" when the individual particle hits a detection screen. We see an "interference pattern" (caused ?? by "a wave") when a large number of particles have hit the screen one at a time.
    An observation is a measurement result that gives a value for a specified observable, such as energy, momentum, spin, etc. The particle detector is part of the measuring apparatus, which is the observer. As noted by others, the experiment does not require a human observer.
    What are you trying to measure with " a conductive piece of material in and around the electron path?"
     
  11. Ear is not necessary. Irreversible recording of whatever kind is.
     
  12. That depends on which "theory". If your theory does not bother - then it does not describe. If it bothers - then it describes. Some people do not have an idea and do not care, some other people have an idea (right or wrong) and describe. Some theories bother only with the statistics, some with description of individual detection processes.
     

  13. If there is no "human observer", how does one acquire knowledge of the experimental results?
     
  14. Acquisition of knowledge is a separate branch of science. It is not needed if you want to discuss the behavior of detectors, interference, double slit experiments etc. For this you need physics, dynamics, evolution equation, a little bit of probability theory.
     
  15. But in order for such a discussion to take place, doesn't there at some point have to be "human observation"?
     
  16. Are you interested in human beings or are you interested in physics. Human beings, their psychology, neurobiology, etc. is a different branch. Of course quantum processes, in particular detection processes take also place in neural activities. But that does not influence the laws physics.
     
  17. But you agree that "human observation" is required for completion of the exercise?
     
  18. It depends on the exercise. Rats also exercise, frogs do, and birds exercise as well. Perahps the whole Nature exercises, one way or another. Physics is about making the patterns. Recognition of patterns is another thing.
     
  19. Quoting from J. A. Wheeler ("Geons, Black Holes & Quantum Foam", p. 343):

    "I wanted to emphasize in this talk that the essential feature of act of 'measurement' is amplification from the quantum thing observed to the classical thing doing the observing, which need have nothing to do with human intervention or human consciousness"

    Notice that "measurement" is in quotation marks. Means: be careful even with this concept.
     
  20. My question wasn't to imply observation was necessarily an act of measurement, merely that "human observation" was a conclusive requirement of experimentation.
     
  21. Human observation may be right or wrong. Some people see things that do not exist. Some see wrong colors. You would have to define the terms you are using. But this will take you out of the domain of physics. These forums are called "physicsforums", and this part of the forums is called "Quantum physics". You need to distinguish physics from philosophy, psychology etc.

    You do need to know anything about philosophy and psychology to study and analyze physics phenomena. Just learn physics and mathematics and how to apply them in real world.
     
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