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I was looking through Rovelli's Relational QM paper

http://arxiv.org/abs/quant-ph/9609002" [Broken]

and Unfortunatly I didn't find the initial set-up of the story compelling. In this set up, there is a system, S, and an observer O. S can be in one of two states [itex]|\psi\rangle =\alpha |1\rangle + \beta |2\rangle [/itex]. Assume that for a specific measurement at time [itex]t=t_2 [/itex] O observers S in state [itex]|1\rangle [/itex]. Now let a new observer, P, describe the S-O system quantum mechanically. Then without interacting with the S-O system, it is described by P as [itex]\alpha |1\rangle\otimes |O1\rangle + \beta |2\rangle \otimes |O2\rangle [/itex] where O2 and O1 indicate that O has interacted with S and observed result 1 or 2 respectively. Then from this Rovelli states,

and then that At time [itex]t_2[/itex], in the O description, the system S is in the state |1⟩ and the quantity q has value 1. According to the P description, S is not in the state |1⟩ and the hand of the measuring apparatus does not indicate ‘1’.

But to me this conclusion and argument aren't particularly compelling. To me this says that O has a value for S, say 1, but P doesn't have a particular value for the S-O system. That's okay with me, since P never made a measurement in the first place, I'd certainly not expect P to have a value at hand. This seems just like if Sally and Oscar have a box in front of them with two balls, red and green, and Oscar picks a ball at random and looks to see what it is, but Sally can't check either the box or Oscar. Then Oscar has a value for the ball color, but Sally doesn't know the ball color, or what Oscar knows as the ball color. In quantum mechanics different observers may give different accounts of the same sequence of events.

I don't see a problem with this... This seems completely normal and non-exclusive. Can someone help me see the profoundness in this example.

Thanks,

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# Relational QM as Compelling

Can you offer guidance or do you also need help?

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