So I'm embarking through Brian Greene's magnificent book The Fabric of The Cosmos and in the quantum section he goes through the whole idea about how observation of a particle leads to collapse of the wavefunction into a definite location. He also uses the double slit experiment for photons and electrons and using the resultant interference pattern to explain the wave-like nature. My question is...why is the double slit experiment not considered a form of observation? It seems that other tools such as the photon splitter can potentially act as detectors but yet a double-slit and screen do not act as "observers"? Why is that? This has been a problem I've had when reading anything about quantum and I'm yet to find a substantial answer.