The Unmeasurability of Absolute Velocities from the Point of View of Epistemological Internalism

Abstract

Absolute velocities in Newtonian mechanics are commonly regarded as unmeasurable. Roberts (Br J Philos Sci 59(2):143–168, 2008) provides a justification for this thesis which appeals to the observational indistinguishability of boost-related models of Newtonian mechanics. Middleton and Murgueitio Ramírez (Australas J Philos, 2020) criticise his argumentation by pointing out that his analysis of the notion of measurement is too restrictive, and that, under a weaker analysis (based on counterfactuals), absolute velocities are measurable. Jacobs (Australas J Philos, 2020) opposes their view, arguing that, on a properly formulated counterfactual-based account of measurement, absolute velocities are unmeasurable. However, in his argument, observational indistinguishability plays no role, even though, intuitively, it is very relevant for the issue of (un)measurability. This paper’s aim is to bring observational indistinguishability back to this discussion. I build upon the observation that there is an analogy between possible views on knowledge and justification on the one hand, and on measurement on the other. In particular, I explore the distinction between externalist and internalist approaches. Counterfactual-based accounts are all externalist, whereas the observational indistinguishability of boost-related models becomes relevant if we are interested in an internalist concept of measurement.

Symmetries and Measurements

“…However, this is precisely what is needed for the […] process to take off. (Luc, 2023b) Notice, however, that contrary to what Luc says here, there seems to be a pair of values of absolute velocities such that it would make an observational difference if one, and not the other one, is instantiated. In the Basic World, if the train has some non-zero absolute velocity, the speedometer indicates "MOTION."…”

“…In a spirit similar to that of Roberts (2008), Luc (2023b) recently suggested an analysis of measurement that takes into account the epistemic side of things. According to Luc, agents can't measure a property Q with a device D if they do not have good reasons to believe that D responds in the right way to values of Q.…”

“…Regarding (i), it is convenient to follow Luc (2023b) and distinguish between an “externalist” analysis of measurement and an “internalist” one (the terminology is inspired by the internalist‐externalist debate in epistemology). The former approaches measurement purely from the perspective of the physical interaction between the measurement device and the physical system that is being measured; if the interaction satisfies certain physical or metaphysical conditions (e.g., if there is counterfactual dependence of some sort between the device and the target system), then we can say that the device measures the system (or, more precisely, that it measures a property of the system).…”

“…Before we move on, two remarks regarding (i) need to be made. First, the externalist‐internalist distinction introduced by Luc (2023b) closely tracks the difference between indication (such as the position of a pointer) and measurement outcome (what property can an agent attribute to the system based on the pointer's position) found in the recent philosophical literature on measurement (see Tal [2013, p. 1165]). Second, philosophers have approached the question of what measurements are from very different perspectives, ranging from questions about what kinds of mathematical objects can be used in order to represent the properties of a system, to questions about how theoretical concepts like mass or charge can be coordinated with empirical procedures (for a good overview, see Tal (2013)).…”