Quantum ontological excess baggage
Section snippets
Ontic states, epistemic states and instrumental states
What is the essential meaning behind saying something is ontic? It is, simply, that a system actually has an underlying state. That is to say there is a real state of affairs and this real state of affairs is such and such. Consider a particular system. Let us assume that there is a real state of affairs and let us denote that real state of affairs by s. We will call this the ontic state. The ontic state could be different in which case we might denote it by s′≠s. In general, it is possible
Ontic embeddings and the quantum ontological excess baggage theorem
As stated already, any empirically useful theory must enable us to predict the instrumental state, . Call such a theory T. If we want to believe that the underlying state of affairs is ontic then there must exist an ontic theory T̃ which makes the same predictions. This will employ the epistemic state P which lists the probabilities for the different ontic states si. For consistency it must be the case that the probabilities pk in the instrumental state can be determined by the probabilities Pi
Discussion
A possible misunderstanding of the ideas in this paper might lead one to conclude that γ=∞ even in classical theories. Thus one could argue that only two parameters are required to specify the state of a particle moving in one dimension—the position and momentum—and therefore that Kinstrumental=2. Nevertheless, there are an infinite number of distinct ontic states (all the different points in the phase space) and therefore γ=∞. However this is the wrong notion of state for our purposes because
Acknowledgements
It is a great honour to dedicate this paper to the memory of Rob Clifton. He had a strong positive impact on me and my work especially in the early days when he was doing his PhD in Cambridge and I was doing mine in Durham. I have very happy memories of the hours we spent at that time (in the early 1990s) debating whether realistic interpretations of quantum theory could be consistent with Lorentz invariance. I am grateful to Chris Fuchs, Ian Gatensby, Rob Spekkens, and Antony Valentini for
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