Heidelberg 2007 – wissenschaftliches Programm

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SYEU: Symposium Knowledge of the Early Universe

SYEU 1: Knowledge of the Early Universe

SYEU 1.4: Plenarvortrag

Montag, 5. März 2007, 17:45–18:45, KIP Gr. HS

Time and the Cosmic Measurement Problem — •Henrik Zinkernagel — Department of Philosophy, Faculty of psychology, Campus de Cartuja, University of Granada, E-18071 Granada, Spain

The spectacular success of quantum theory is often taken as a pointer towards the `quantum fundamentalist' idea that the theory should be able to describe everything in the universe, and perhaps even the universe in its entirety. It is well known, however, that quantum fundamentalism ought to provide a satisfactory answer to what may be called the cosmic measurement problem: If the universe -- either its content or in its entirety -- was once (and perhaps still is) quantum, how come that there are classical structures now? In cosmology, the gradual emergence of classicality is framed in terms of a cosmic time parameter associated with the standard Fridmann-Lemaître-Robertson-Walker model. In this talk I examine the physical foundations for setting up the FLRW model -- and I examine what is required for interpreting the t parameter of the model as time. I discuss how the definition of cosmic time in the FLRW model is related to the behaviour of the material constituents of the universe (e.g. via the Weyl principle), and how this point threatens to undermine the physical basis for the comoving reference frame if the material constituents of the universe are to be described exclusively in terms of quantum theory at some early stage of the universe. As a possible response to this threat I reconsider Bohr's interpretation of quantum mechanics which -- contrary to the quantum fundamentalist point of view -- reserves a privileged role for classical physics.