I read that state preparation is simply measuring and confirming the system. Filtering type observation is when the observation doesn't destroy the system. But googling doesn't produce the extra words "Filtering type observation".. why is these words only in physicsforums.. what are the other synonyms of it.. can you give example of a filtering type observation? Also someone (bill) said after I know the meaning of state preparation and filtering type observation.. then can chat whether the universe is in pure state (is it.. can someone explain categorically)... How are the three ideas related at all? I'm confused as hell. Thanks.