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Wednesday, March 28, 2012

Go figure

The journal made me replace my crude but hopefully charming hand drawn figures with computer-generated ones. Which are better?

(Paper previously discussed here ;

Unfortunately I have no artistic talent, and even less when using a drawing program. My daughter must have gotten her abilities from mom :-)

FIG1: However, if the combined system S' = S + M evolves unitarily (in particular, linearly) as in (1), we obtain a superposition of measurement device states (see figure 1) ... At first, this seems counter to actual experience: properly executed measurements produce a single outcome, not a superposition state. But how do we know for sure? In fact, an observer described by the state M+ might be unaware of the second branch of the wave function in state M- for dynamical reasons related to a phenomenon called decoherence...

FIG2: We emphasize again that universal Schrodinger evolution only admits subjective, but not objective, randomness and probability. Just before the measurement depicted in figure 2, all of the observers are in identical states. ... The first line of the equation has been written to emphasize that in the m basis it appears as if there are 2^N identical observers, each of whom is destined to evolve into a particular one of the O_m. Of course, the observer does not know which of the O_m they will evolve into, because they do not (yet) know the spin state |m> on their branch. But this is a subjective uncertainty because, indeed, the outcome is already pre-determined. This perspective may appear more natural if one considers the time reversal of the final state ...

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