Lucy Mason

How we define the present moment, what status we give it, and how it relates to physics, are central questions in the philosophy of time. One approach links the privileged status of the present to a perspective embedded within time; conversely, from a perspective outside of time all moments are equal. I will use this perspectival view, and the definition of an embedded present perspective as both localised and level-dependent, to make two central claims about the probabilities in statistical mechanics. First, the perspectival view can help us respond to the concern that these probabilities are merely epistemic, subjective, or anthropocentric. Second, we should treat the future as metaphysically open, due to both probabilities in statistical mechanics and the localised nature of the embedded present perspective.

There are two main styles of interpreting the quantum state: either focusing on the fundamentality of the quantum state (a state or wavefunction realist view), or on how projection operators represent observable properties (an observable-first approach). Rather than being incompatible, I argue that these correspond to taking a 3rd person and 1st person perspective respectively. I further contend that the 1st person perspective - and the observable-first approach that goes with it - is better suited to explain measurement, based on the way that the metrology literature characterises measurement through the quantifiable properties of a system. Finally, I show how the 1st person, observable-first approach can emerge in the world through the process of decoherence, hence showing the compatibility of the two approaches and resolving the need to choose absolutely between them.

One way to interpret the difference between presentism and eternalism is perspectively. This view argues that from a perspective outside of time, we should adopt eternalism, and from a perspective embedded within time, we should be presentist. I will use the perspectival view to make two central claims about the probabilities in statistical mechanics. First, the perspectival view can help us respond to the challenge that these probabilities are merely epistemic, subjective, or anthropocentric. Second, we should treat the future as metaphysically open, due to both probabilities in statistical mechanics and the localised nature of the present.

I will look at Bohr's contentious doctrine of classical concepts - the claim that measurement requires classical concepts to be understood - and argue that measurement theory supports a similar conclusion. I will argue that representing a property in terms of a metric scale, which marks a shift from the empirical process of measurement to the informational output, introduces the inherently classical assumption of definite states and precise values, thus fulfilling Bohr's doctrine. I examine how realism about metric scales implies that Bohr's doctrine is ontological, while more moderate coherentist or model-based approaches to realism render it epistemological. Regardless of one's stance towards measurement realism, however, measurement cannot be entirely quantum and quantum mechanics can model only the empirical side of measurement, not its informational output. Finally, I discuss how this might influence our understanding of the measurement problem.