system
Given the following post, respond as if you're commenting on Reddit:
human
What counts as an observer? (as in the double slit experiment). If this observer were to stop observing (closing their eyes, or putting a piece of paper in front of a camera), are they still an observer?
gpt
An "observation" in quantum mechanics is something that forces the particle to assume a definite value.

In the double slit experiment, the observer would be the sensor at one of the slits.  It doesn't matter whether there's a conscious human being watching the instrument or not.  The instrument itself interacts with the system, and therefore performs an "observation", or a "measurement".

Words in physics often mean slightly different things than they do in regular English.