Is Indeterminacy Really Indeterminate?
Quantum indeterminacy gets a lot of visibility these days, and it's led to physics playing a much more significant role in philosophical, and especially metaphysical, arguments. Even though its been around for well over 50 years, and despite my distinct lack of knowledge concerning quantum physics, I still have a strong inkling that the world really isn't indeterminate at the quantum level. For those with even less understanding of quantum mechanics than I have, Wikipedia provides a nice introduction
Quantum indeterminacy is the apparent necessary incompleteness in the description of a physical system, that has become one of the characteristics of the standard description of quantum physics. Prior to quantum physics, it was thought that (a) a physical system had a determinate state which uniquely determined all the values of its measurable properties, and conversely (b) the values of its measurable properties uniquely determined the state. Albert Einstein may have been the first person to carefully point out the radical effect the new quantum physics would have on our notion of physical state. Quantum indeterminacy can be quantitatively characterized by a probability distribution on the set of outcomes of measurements of an observable. The distribution is uniquely determined by the system state, and moreover quantum mechanics provides a recipe for calculating this probability distribution.My issue with quantum indeterminacy stems from a failure to properly distinguish between metaphysical and epistemic indeterminacy. Metaphysical indeterminacy is the claim that the external world (at the quantum level) is indeterminate whereas epistemic indeterminacy is the merely claim that it is our understanding of the external world that is indeterminate, not necessarily the world itself. This is a significant distinction that the case of a coin flip and Schrodinger's Cat highlight. To say that when I flip a coin, the outcome is random and conforms to probabilistic behavour belies the reality that the outcome is causally determined. It is not the case that the coin 'randomly' or indeterminately lands on heads or tails - the outcome is determined by the angle and velocity of the flip, air resistance, arc and length of fall etc. My knowledge of the outcome may be indeterminate, but the outcome has a physical cause. Likewise, the paradox of Schrodinger's Cat is only paradoxical when metaphysical and epistemic indeterminacy are confused. We don't know whether the cat is alive or dead (or both alive and dead) until we open the box, but to claim that the cat is both alive and dead in reality seems, to me at least, clearly wrong. Just because we can't observe some causal state to explain quantum mechanics, doesn't support the claim that indeterminacy exists in a metaphysical sense. Absence of evidence is very different to evidence of absence.
