A measurement is a quantified observation of anything that can be observed.
"They STILL don't have a good answer for the Schrodinger's Cat question. When does the probability wave collapse? What particular event (on the particle scale) precipitates the collapse? Why doesn't the entire universe exist in a state of quantum superposition of ever-increasing complexity?
There are no points and there are no waves. They are mathematical representations of reality, not reality itself. The representations and mathematics describe and predict observations, that's all. They are not reality itself. The only useful understanding from the mathematical statement-superposition of states- is, that the entity is not interacting with anything at the moment. In otherwords, it can't be observed by anything any other entity that could observe it. When considering the word observer in physics, consider that a window and a ball are observers.
Look up what an "operational" definition is. Your definition is not "operational" until you define "observer" which is really the crux of the matter.
Suppose, for example, that we are doing an experiment along the lines of the classic two-slit single electron diffraction experiment. When the electron emerges through the slits it has no definite position, only a "wave" function that gives the probability of "measuring" it at various locations. While this "wave" is indeed a mathematical abstraction, we find that this mathematical abstraction appears to interfere with itself in a well-recognized interference pattern in the real world. However, when a "measurement" of the position of the electron is made, there is no longer a "wave" probability function. At the instant of "measurement" the electron is in a single position with probability one.
The question then is, what constitutes a "measurement"? Or in your wording (begging the question), what constitutes an "observer"?
Could a single particle be an "observer"? In a practical sense this question would seem to be unknowable for us, since we must then observe the "observer" particle to read its "observation." I believe, however, that experiments have succeeded in demonstrating that a system consisting of more than one particle into superposed states. If I am correct on that, the experimental evidence would suggest that if a single particle attempted to "observe" an electron in a superposed position, then rather than the "observation" forcing the electron to be found in a single position, the "observation" would force the "observer" particle into a superposed state. And this is what current quantum theory would predict.
The problem is that quantum theory currently predicts this outcome for any number of particles--even the enormous number of particles in a human body. How is it that our "observations" force the electron to manifest a single position, instead of the superposition of the electron forcing our "observations" into a superposed state?
The only useful understanding from the mathematical statement-superposition of states- is, that the entity is not interacting with anything at the moment.
But the "entity" WILL be continually interacting with other particles--virtual particles a la Richard Feynman. Also, as stated above, if the "entity" interacts with one other particle, then quantum theory predicts that they will both end in superposed states.
They are not reality itself.
Judging from this statement, it seems that you do at least believe in an objective reality. So, when we set up a single electron diffraction experiment, what is "really" happening?
In otherwords, it can't be observed by anything any other entity that could observe it.
Here your grammar is such that I can't make out your intent. Did you mean "In other words, it can't be observed by any other entity that could observe it?" That would be a grammatically-correct self-contradicting sentence.
When considering the word observer in physics, consider that a window and a ball are observers.
Here your grammar is fine, but I still can't make out your intent. Sarcasm? Irony? Absurdity? Seriousness? A reference to a ball breaking a window?