I am fascinated by the double slit experiment, and can't claim to understand it completely but am curious to know what would be observed with the experiment I would like to describe. First off, I just watched a youtube video: http://www.youtube.com/watch?v=LW6Mq352f0E
.. and the professor describes how the experiment was executed with the detectors off, and they observed an interference pattern, and then the detectors were then turned on and recorded the data (i.e which slit each photon went through) and they observed a double slit on the target screen (since it was now appearing to act as a particle). However, he goes on to say that the experiment was performed again, and the detectors had been (accidently) turned on, but it was not recording the data.. and it showed an interference pattern.. presumably because despite the detectors being on it wasn't recording and so there was no data to be observed at a future date? I am a computer programmer and so imagine I was to write the program which received input from the detectors and recorded which slit each photon went through. Ok, and imagine I introduced a control to enable/disable whether or not the data was recorded.. would i observe an interference pattern switch to 2 slits every time i disabled/enabled this control?
Ok, to take it a step further, how about i made the software decide completely randomly on a per photon basis whether or not to record which slit it passed through? What would i be likely to observe? Or in another case, imagine if the program recorded which slit every photon passed through and then immediately deleted that data entry? What could i expect to observe?