Are There Really Instantaneous Velocities?

Arntzenius, Frank

doi:10.5840/monist20008328

Cited by 51 publications

(40 citation statements)

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“…For example, 'I cannot know whether the absolute mass is twice the actual mass' is clearly false, as is 'I cannot know, in principle, whether the absolute mass is the same as the absolute mass of that other object'. This failure of expressibility should not surprise us 66 : this is the content of kinematic comparativism, this is what it means, by definition, to be a dimensionful magnitude-in fact, as Table 1 shows, typical examples of expressible ignorance and knowledge are all dimensionless notions, and typical examples of inexpressible ignorance and knowledge are all dimensionful notions. This is why the Leibniz Scaling is (necessarily) formulated 'comparatively', as a multiplication mapping from the absolute masses in one possible world to the absolute masses in another possible world.…”

Section: Italics In Original]mentioning

confidence: 98%

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The (un)detectability of absolute Newtonian masses

Martens

2019

Synthese

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Absolutism about mass claims that mass ratios obtain in virtue of absolute masses. Comparativism denies this. Dasgupta (2013) argues for comparativism about mass, in the context of Newtonian Gravity. Such an argument requires proving that comparativism is empirically adequate. Dasgupta equates this to showing that absolute masses are undetectable, and attempts to do so. This paper develops an argument by Baker to the contrary: absolute masses are in fact empirically meaningful, that is detectable (in some weak sense). Additionally, it is argued that the requirement of empirical adequacy should not be cashed out in terms of undetectability in the first place. The paper closes by sketching the possible strategies that remain for the comparativist. Along the way a framework is developed that is useful for thinking about these issues: Ozma games-how could one explain to an alien civilisation what an absolute mass is?

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Section: Italics In Original]mentioning

confidence: 98%

“…This idea originates with Aristotle and was developed in the Middle Ages[66][67][68]. In more modern times it is associated, amongst others, with Russell[25] 57.…”

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confidence: 99%

The (un)detectability of absolute Newtonian masses

Martens

2019

Synthese

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“…Responses by Earman (2002), Floyd (2003), and Smith (2003 Arntzenius (2000). But most of what they have to say applies equally well to Albert (2000).…”

Section: It Follows That the Induced Operator T Takes The History T →mentioning

confidence: 99%

On the time reversal invariance of classical electromagnetic theory

Malament

2004

Studies in History and Philosophy of Science Part B: Studies in

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David Albert claims that classical electromagnetic theory is not time reversal invariant.He acknowledges that all physics books say that it is, but claims they are "simply wrong" because they rely on an incorrect account of how the time reversal operator acts on magnetic fields. On that account, electric fields are left intact by the operator, but magnetic fields are inverted. Albert sees no reason for the asymmetric treatment, and insists that neither field should be inverted. I argue, to the contrary, that the inversion of magnetic fields makes good sense and is, in fact, forced by elementary geometric considerations. I also suggest a way of thinking about the time reversal invariance of classical electromagnetic theory -one that makes use of the invariant four-dimensional formulation of the theory -that makes no reference to magnetic fields at all. It is my hope that it will be of interest in its own right, Albert aside. It has the advantage that it allows for arbitrary curvature in the background spacetime structure, and is therefore suitable for the framework of general relativity. The only assumption one needs is temporal orientability.Keywords: time reversal invariance; electromagnetic theory; relativity theory. IntroductionIn the first chapter of Time and Chance, David Albert (2000) argues that classical electromagnetic theory (in contrast, for example, to Newtonian mechanics) is not time reversal invariant.He acknowledges that all physics books say that it is, but claims they are "simply wrong" because they rely on an incorrect account of how the time reversal operator, properly understood, * E-mail address: dmalamen@uci.edu. 1 acts on magnetic fields. Once that account is corrected, he believes, it is perfectly obvious that the theory is not time reversal invariant. No deep mathematics or physics is called for, only a clear understanding of the nature of the time reversal operation.Received opinion, no doubt, is often wrong. But I don't believe it is here. Physics books tell us that the time reversal operation leaves the electric field E intact, but inverts the magnetic field B. Albert sees no reason for the asymmetric treatment, and insists that neither field should be inverted. He even suggests (p. 18) that the inversion of B is nothing but an ad hoc maneuver to save the time reversal invariance of classical electromagnetic theory. I'll argue, to the contrary (section 6), that the inversion of B makes good sense and is, in fact, forced by elementary geometric considerations. The argument -really just a version of one that can be found in any book on the subject -traces the asymmetric treatment of E and B to the fact that the latter, unlike the former, is not a vector field in the usual sense. (In traditional language, E is a "polar" vector field, while B is an "axial" vector field.)Before giving this response to Albert's claims, I'll make a somewhat different point. It seems to me that the inversion of magnetic fields by the time reversal operator is really something of a distraction. One ca...

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“…For a classic defense of the reductionist at-at theory of velocity, seeRussell (1937). SeeTooley (1998),Arntzenius (2000; 2012, ch.2),Carroll (2002),Lange (2005), and Easwaran (2014) for further discussion on both sides of the debate.…”

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confidence: 99%

A puzzle about rates of change

Builes

Teitel

2019

Philos Stud

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Most of our best scientific descriptions of the world employ rates of change of some continuous quantity with respect to some other continuous quantity. For instance, in classical physics we arrive at a particle's velocity by taking the time-derivative of its position, and we arrive at a particle's acceleration by taking the time-derivative of its velocity. Because rates of change are defined in terms of other continuous quantities, most think that facts about some rate of change obtain in virtue of facts about those other continuous quantities. For example, on this view facts about a particle's velocity at a time obtain in virtue of facts about how that particle's position is changing at that time. In this paper we raise a puzzle for this orthodox reductionist account of rate of change quantities and evaluate some possible replies. We don't decisively come down in favour of one reply over the others, though we say some things to support taking our puzzle to cast doubt on the standard view that spacetime is continuous.

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Are There Really Instantaneous Velocities?

Cited by 51 publications

References 6 publications

The (un)detectability of absolute Newtonian masses

The (un)detectability of absolute Newtonian masses

On the time reversal invariance of classical electromagnetic theory

A puzzle about rates of change

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