Observation means a detection method of the testing apparatus. Not an actual observer looking at it with eyes. So for example in the double slit experiment, if you pass molecules, atoms, electrons, or photons through the two slits you get an interference pattern on the other end which points to these things acting like waves. If you put a detector to determine which slit each molecule, atom, electron or photon goes through, the pattern just projects 2 rows which points to particles. The action of ‘observing’ which slit the stuff goes through changes the result.
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