We've learned that the wave function of a particle collapses when we measure a particle's location. If it is found, it becomes more probable to find it a again in the same area, and if not the probability to finding it in the place that was checked decreases dramatically.
My question is about the definition of measurement. What makes a measurement different from any other interaction between two particles (gravity and EM fields for example)?
In reality, almost every particle interacts with any other particle, so shouldn't there be constant collapse of the wave function all the time? If this happens we're right back in classical mechanics, aren't we?
Best Answer
What you describe in your question is the "Copenhagen interpretation" of quantum mechanics. There are more nuanced views of this nowadays that don't treat "measurements" quite so asymmetrically, see e.g. sources that talk about decoherence.
I recommend watching the classic lecture "Quantum Mechanics in your face" by Sidney Coleman for a nice take on this sort of thing.