1,040 research outputs found
Semantic externalism without thought experiments
Externalism is the thesis that the contents of intentional states and speech acts are not determined by the way the subjects of those states or acts are internally. It is a widely accepted but not entirely uncontroversial thesis. Among such theses in philosophy, externalism is notable for owing the assent it commands almost entirely to thought experiments, especially to variants of Hilary Putnam's famous Twin Earth scenario. This paper presents a thought experiment-free argument for externalism. It shows that externalism is a deductive consequence of a pair of widely accepted principles whose relevance to the issue has hitherto gone unnoticed
Epistemicism and modality
What kind of semantics should someone who accepts the epistemicist theory of vagueness defended in Timothy Williamsonâs Vagueness (1994) give a definiteness operator? To impose some interesting constraints on acceptable answers to this question, I will assume that the object language also contains a metaphysical necessity operator and a metaphysical actuality operator. I will suggest that the answer is to be found by working within a three-dimensional model theory. I will provide sketches of two ways of extracting an epistemicist semantics from that model theory, one of which I will find to be more plausible than the other
Notes on Branes in Matrix Theory
We study the effective actions of various brane configurations in Matrix
theory. Starting from the 0+1 dimensional quantum mechanics, we replace
coordinate matrices by covariant derivatives in the large N limit, thereby
obtaining effective field theories on the brane world volumes. Even for
noncompact branes, these effective theories are of Yang-Mills type, with
constant background magnetic fields. In the case of a D2-brane, we show
explicitly how the effective action equals the large magnetic field limit of
the Born-Infeld action, and thus derive from Matrix theory the action used by
Polchinski and Pouliot to compute M-momentum transfer between membranes. We
also consider the effect of compactifying transverse directions. Finally, we
analyze a scattering process involving a recently proposed background
representing a classically stable D6+D0 brane configuration. We compute the
potential between this configuration and a D0-brane, and show that the result
agrees with supergravity.Comment: 24 pages, LaTeX file. Minor typo correction
Williamson on Modality
This special issue of the Canadian Journal of Philosophy is dedicated to Timothy Williamson's work on modality. It consists of a new paper by Williamson followed by papers on Williamson's work on modality, with each followed by a reply by Williamson.
Contributors: Andrew Bacon, Kit Fine, Peter Fritz, Jeremy Goodman, John Hawthorne, Ăystein Linnebo, Ted Sider, Robert Stalnaker, Meghan Sullivan, Gabriel Uzquiano, Barbara Vetter, Timothy Williamson, Juhani Yli-Vakkur
M-momentum Transfer between Gravitons, Membranes, and Fivebranes as Perturbative Gauge Theory Processes
Polchinski and Pouliot have shown that M-momentum transfer between membranes
in supergravity can be understood as a non-perturbative instanton effect in
gauge theory. Here we consider a dual process: electric flux transmission
between D-branes. We show that this process can be described in perturbation
theory as virtual string pair creation, and is closely related to Schwinger's
treatment of the pair creation of charged particles in a uniform electric
field. Through the application of dualities, our perturbative calculation gives
results for various non-perturbative amplitudes, including M-momentum transfer
between gravitons, membranes, and longitudinal fivebranes. Thus perturbation
theory plus dualities are sufficient to demonstrate agreement between
supergravity and gauge theory for a number of M-momentum transferring
processes. A variety of other processes where branes are transmitted between
branes, e.g. (p,q)-string transmission in IIB-theory, can also be studied. We
discuss the implications of our results for proving the 11 dimensional Lorentz
invariance of Matrix theory.Comment: 16 pages, LaTeX, 1 Postscript figure, uses epsf.tex and fps.sty
macro
Moderate Modal Skepticism
This paper examines "moderate modal skepticism", a form of skepticism about
metaphysical modality defended by Peter van Inwagen in order to blunt the force of certain modal
arguments in the philosophy of religion. Van Inwagenâs argument for moderate modal skepticism
assumes Yablo's (1993) influential world-based epistemology of possibility. We raise two problems
for this epistemology of possibility, which undermine van Inwagen's argument. We then consider how one might motivate moderate modal skepticism by relying on a different epistemology of possibility, which does not face these problems: Williamsonâs (2007: ch. 5) counterfactual-based epistemology. Two ways of motivating moderate modal skepticism within that framework are found unpromising. Nevertheless, we also find a way of vindicating an epistemological thesis that, while weaker than moderate modal skepticism, is strong enough to support the methodological moral van Inwagen wishes to draw
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