Lo so, non è molto “divulgativo” come post. Ma mi ha sempre fatto pensare e voglio condividerlo.

J. S. Bell contro il postulato di riduzione e la catena di von Neumann.

“When I say that the word ‘measurement’ is even worse than the others, I do not have in mind the use of the word in phrases like ‘measure the mass and width of the Z boson’. I do have in mind its use in the fundamental interpretive rules of quantum mechanics.
For example, here they are as given by Dirac (Quantum Mechanics Oxford University Press 1930):

‘. . . any result of a measurement of a real dynamical variable is one of its eigenvalues . . . ‘

‘. . . if the measurement of the observable [. . .] is made a large number of times the average of all the results obtained will be . . .’

‘. . . a measurement always causes the system to jump into an eigenstate of the dynamical variable that is being measured . . . ‘

It would seem that the theory is exclusively concerned about ‘results of measurement’, and has nothing to say about anything else. What exactly qualifies some physical systems to play the role of ‘measurer’? Was the wave function of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system. . . with a PhD? If the theory is to apply to anything but highly idealised laboratory operations, are we not obliged to admit that more or less ‘measurement-like’ processes are going on more or less all the time, more or less everywhere? Do we not have jumping then all the time?”

(da “Against measurement“,  J. S. Bell – qui il testo integrale)

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