*Quantum
Bayesianism*

The US scientists Christopher Fuchs and Carl Caves and the German scientist Ruediger Schack ("Quantum probabilities as Bayesian probabilities", 2002) tried to explain away the uncertainty of Quantum Mechanics by interpreting the wave function as describing the state of the observer, not of the system. They argued that the wave function's probabilities could as well be interpreted as information about the observer, not about the system; in other words, as "Bayesian" probabilities, a measure of the observer's subjective belief, not of the system's state. In this alternative view, the wave function is interpreted as describing the observer, not the world. Just like Bohr, Fuchs does not consider the wave function to be real. The "collapse" of the wave function represents a change in the observer's beliefs due to having performed an experiment. This also means that the same system has as many wave functions as there are observers. The catch, of course, is that in this interpretation we know virtually nothing about the world: the equations of Physics only tell us something about the observers, i.e. about us.

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