Monday, November 21, 2005

The Duality at the Heart of Physics

I’m speaking of the measurement problem or paradox in quantum physics. One the one hand we have the continuous deterministic dynamical evolution of the wave function (in Schrödinger’s formulation of quantum mechanics), and on the other we have the discontinuous process of measurement which “collapses” the wave function into a definite state. What, if anything, does quantum physics mean for the nature of reality?

Interpretations of this problem historically have tended to devalue the ontological status of one or the other side of this duality. Some versions of the Copenhagen interpretation treated the wave function as a mere calculation framework which shouldn’t be accorded the status of something real. Over recent times, variants of the many-worlds hypothesis have become more popular: these emphasize the reality of the well-behaved wave function, and dismiss our perception of the everyday classical world as either a limited or illusory view of true reality. As I wrote in (the last part of) this post, more careful analysis of Neils Bohr’s own views tend to show he understood that the two quantum processes were irreducibly interdependent.

My own view is that quantum measurements are the events which make up the concrete fabric of our world. The wave function also exists, however, and can be considered the space of abstract possibilities which provide the raw material for the actualization of each event. While we can only observe "inter-measurement" phenomena associated with the wave function (e.g. entanglement) in carefully constructed laboratory situations, it comprehensively enters into our everyday world as well.

In fact, each larger system in nature is an extended event complex which continually self-implements measurements as interactions with the environment. Each set of measurements gives rise to a new possibility space which is raw material for further events.

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