Counterfactual definiteness
Counterfactual definiteness or CFD
is a property of some
interpretations of quantum mechanics but not others.
It refers to the ability to speak meaningfully about
the results of measurements that were not performed.
For example, by the Heisenberg Uncertainty Principle,
one cannot simultaneously know the position and momentum
of a particle. Suppose one measures the position, this
destroys any information about the momentum. The question
then becomes, is it possible to talk about the measurement
one would have received if one did measure the momentum
instead of the position. In other words, if one conducted
a different experiment, is there a single alternate time
line that would have resulted from it?
CFD is a property of the Copenhagen interpretation of
quantum mechanics as well as the hidden variables interpretation. It is not a property of the many worlds interpretation, and this allows many worlds to resolve Bell's inequalities without violating the locality principle.
Referenced By
List of physics topics A-E
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