First of all, I'm an undergrad. student of engineering physics, so I must explicit my lack of formal knowledge on the subject and total confusion with its implications. I also understand it may be impossible to explain in words, so feel free to do the math.
I've read and had some classes introducing the subject of wavefunction collapse, eigenstates and similar subjects, and understand that an "observation" is a casual term for "measurement", which can be said to be a synonym of "interaction". I also understand collapse is an allegory of the mathematical implications we can derive from formulas involved and does not represent reality necessarily.
The problem arises here and I can't find a satisfactory answer on the internet. What EXACTLY constitutes an "interaction"? Don't all particles in the universe interact with fields and particles all the time (unninterrupted)? If so, wouldn't all particles have its eigenstates determined all the time by endless interactions (if not true, what are examples of non-collapsing interactions?)? And, if the previous question is true, does that mean every particle "experience" different collapses of wavefunctions of other particles compared to us (therefore, meaning we could have a "relativistic" collapse)?