# Does the uncertainty principle require information to actually not exist, or just be inaccessible?

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I understand that the uncertainty principle places limits on how precisely certain pairs of properties can be measured. But does this require that the information about these properties actually not exist in the first instance? That is, I understand that the uncertainty principle goes beyond a simple observer phenomenon, but It's not clear where the boundaries are, and specifically, whether it applies to information about properties, as opposed to the properties themselves. For example, does the principle assert the non-existence of information about a particle's position and momentum, or rather, does it imply that this information cannot be accessed by any observer?

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QM is an intrinsically* probabilistic theory. So if the system is in a generic (non-eigenstate) state, you do have information about any specific observable A, but it is a distribution of possible values.
Repeated experiments to measure that observable on identically prepared initial states will yield a spread of values.

The Heisenberg-Robertson uncertainty principle says that if you choose your initial state to minimise your uncertainty (standard deviation) in observable A, then you will end up increasing your uncertainty in an observable B that does not commute with A.

(*The probabilistic element of QM is not as in classical statistical mechanics where particles have definite positions and momenta described by deterministic Newtonian mechanics. In QM there is no underlying local hidden variable theory --- this possibility has been ruled out by Bell inequality experiments).

answered Mar 26, 2018 by (0 points)

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