What is the Philosophy Behind Relational Quantum Mechanics? I watched this video on Relational Quantum Mechanics yesterday and my brain has been trying to comprehend it since.
The interpretation I currently have is this:
If an observer O measures the state S of a system, in doing so they themselves become entangled with that system.
To another observer O', the state of both S and O are still completely probabilistic until he measures them himself. However the state of S to O is now deterministic as they have become perfectly correlated with one another (through the measurement/entaglement). This is why to observer O it seems the wavefunction of S has collapsed as there is no longer any randomness in S relative to O (but this is not to say there is no randomness in the system (S+O) to an outside observer). 
Further if I were not measuring a system (my friend let's say) they could be in one of a very large number of states with each having a certain probability. If I were to now look at them and 'measure' them, in effect one of these states is being sampled and I have become entangled/perfectly correlated with it.
My question is, have I completely missed the point or is this the general idea behind "Relational Quantum Mechanics"?
 A: You used the letter $S$ ambiguously to refer to both a system and the result of a measurement made on that system.  It's important to distinguish them.
So the situation is that two observers $O_1$ and $O_2$ independently make a measurement $M$ of a system $S$ and agree that the result of that measurement is $X$.  
It is tempting to conclude that the reason they agree is that $S$ is in fact in a state that corresponds to $X$, and that $X$ is a reflection of that underlying reality.
But that is not the case.  The math tells us that $O_1+O_2+S$ is a macroscopic system of mutually entangled particles.  
If you trace over $S$ (i.e. remove the degrees of freedom associated with $S$ from the description of the system) what you are left with is a description of a macroscopic system of mutually entangled particles in classical correlation.  That is the reason $O_1$ and $O_2$ agree.
It has nothing to do with the state that $S$ is "actually" in.  (I put "actually" in scare quotes because S is not actually in any particular state.)
