With the double slit experiment and it’s many modifications (Quantum Eraser type experiments), there have been attempts to try and sidestep the whole ‘observation’ of the particle phenomenon.

This is in an attempt to prevent the collapse, which only occurs when a particle is  ‘observed’

Understandably, many questions arise, such as ‘Who is observing’, Is it enough for a cat to be an observer? What about a fish? What if the observer has their back turned to the experiment but suddenly turns around just before the particle reaches the screen?

All these questions, though interesting, are meaningless.

As long as the particle’s PATH, is IN PRINCIPLE, detectable, it will NOT show an interference pattern (amplitudes will not interfere).

Only if it is not possible, in principle (using the existing experimental setup). to detect the path traversed, do we see an interference pattern.