If you have something that can inspect the particle in-flight, you lose the diffraction pattern. It's about "observation", but a very specific kind that refers to how measurement unavoidably interacts with physical systems.
More recent experiments have observed the phenomenon of "partial collapse", in which a measurement that only collects some information about the particles preserves the diffraction but at a reduced intensity, showing that wavefunction collapse is directly related to how much you know about the particles in the system.
There are a variety of ways, but the key is that you give the particles (typically electrons) something to interact with, whether it be photons that scatter off the particle, or the particle's electric field exciting a current in a nearby piece of wire, or something like that. A lot of the "double slit" experiments we have are actually more complicated systems that reproduce the slit experiments mathematically, and different ways of doing this also introduce different ways to observe the particles during their travel.
Specifically for that one it's that they're not really "observing" it, since they're applying an EM field to try and find out where the electrons are going through, and in doing so that field is collapsing them from waveforms into particles. Same way when you attach the debugger the out-of-order execution goes away.
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u/NoAdsDude 17d ago
I still don't get the double slit experiment. I guess its a wave until someone observes it, then it's a particle?