I always found the notion that "If you measure it, it behaves differently" to be really confusing. When considering the double slit experiment - In both cases (whether we are observing the particle going through a single slit or otherwise observing the interference pattern left afterwards), we are in fact simply measuring 'observable effects' in both cases - It's just that we are measuring them in different ways.
If you didn't measure both cases, you wouldn't be able to compare their outcomes.
It seems that it is not about whether or not the event was measured/observed but about HOW and WHEN it was measured.
In neither case do we actually 'witness it happen' - In both cases, we are just observing effects of those events.
The light which allowed us to 'directly observe it' is as much a byproduct of the actual event as the interference pattern left behind on the surface.
If you didn't measure both cases, you wouldn't be able to compare their outcomes. It seems that it is not about whether or not the event was measured/observed but about HOW and WHEN it was measured.
In neither case do we actually 'witness it happen' - In both cases, we are just observing effects of those events.
The light which allowed us to 'directly observe it' is as much a byproduct of the actual event as the interference pattern left behind on the surface.