In quantum double slit experiment would the the wave function collapse if we place a particle detector at the slit but do not read it and just keep looking at the screen?

  • $\begingroup$ Questions like these don't really have answers, because wavefunction collapse doesn't exist. Wavefunction collapse is a cartoonish feature of one particular interpretation of QM, the Copenhagen interpretation (CI). There are other interpretations, such as the many-worlds interpretation (MWI). Experiments can't even tell us whether MWI or CI or some other interpretation is correct. $\endgroup$ – Ben Crowell Sep 1 '17 at 17:53
  • $\begingroup$ @Ben OK then in that case does interference pattern disappear from the screen while detectors are detecting particles at the slits BUT we keep gazing at the screen? $\endgroup$ – user650585 Sep 1 '17 at 17:57
  • $\begingroup$ @Ben Crowel: Any idea of "multiple worlds", quantum or classical, is much more cartoonish than the wave function collapse. Are there better alternatives? $\endgroup$ – safesphere Sep 1 '17 at 22:14

Yes: the mere existence of the entanglement between the detector and the flying photon is enough to remove the interference pattern on the screen.

  • $\begingroup$ Put another way, how does the detector know if it is being read or not. The detector sends out a signal - it is the 'observer's problem that they ignore it. $\endgroup$ – Jon Custer Sep 1 '17 at 17:36

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