In the Kreisgang between classical and quantum physics

Author(s): Č. Brukner

Journal: UniMolti modi della filosofia

Volume: 2008

Year: 2009

DOI Number: --

Link: Link to publication

Abstract:

All our statements about the physical world are expressed in terms of everyday notions and thus in terms of classical physics. This necessity is behind each of our attempt to extract meaning out of empirical data and to communicate this knowledge to others. As such, it must apply also to the account of measurement arrangements and to the outcome in quantum experiments. On the other hand, however, if quantum mechanics is universally valid it should be possible to give a purely quantum mechanical description of objects of increasingly large sizes, eventually of the measurement devices themselves. It is suggested to resolve this dilemma by using the method of von Weizsaecker's circular and consistent movement in a reconstruction (Kreisgang) in which it is legitimate to recover the elements with which one started the reconstruction. The parameters entering the complex amplitudes of a quantum state have an operational meaning as parameters that specify the configuration of macroscopic instruments by which the state is prepared and measured. This classical aspect in each quantum description is at the "beginning" of the Kreisgang. The Kreisgang is "closed" by showing that under the every-day conditions of coarse-grained measurements a description of macroscopic instruments emerges in terminology of classical physics and the three-dimensional ordinary space from within quantum theory.

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