7,761 research outputs found
Measure, Topology and Probabilistic Reasoning in Cosmology
I explain the difficulty of making various concepts of and relating to
probability precise, rigorous and physically significant when attempting to
apply them in reasoning about objects (e.g., spacetimes) living in
infinite-dimensional spaces, working through many examples from cosmology. I
focus on the relation of topological to measure-theoretic notions of and
relating to probability, how they diverge in unpleasant ways in the
infinite-dimensional case, and are difficult to work with on their own as well
in that context. Even in cases where an appropriate family of spacetimes is
finite-dimensional, however, and so admits a measure of the relevant sort, it
is always the case that the family is not a compact topological space, and so
does not admit a physically significant, well behaved probability measure.
Problems of a different but still deeply troubling sort plague arguments about
likelihood in that context, which I also discuss. I conclude that most standard
forms of argument used in cosmology to estimate the likelihood of the
occurrence of various properties or behaviors of spacetimes have serious
mathematical, physical and conceptual problems.Comment: 26 page
On the Existence of Spacetime Structure
I examine the debate between substantivalists and relationalists about the
ontological character of spacetime and conclude it is not well posed. I argue
that the so-called Hole Argument does not bear on the debate, because it
provides no clear criterion to distinguish the positions. I propose two such
precise criteria and construct separate arguments based on each to yield
contrary conclusions, one supportive of something like relationalism and the
other of something like substantivalism. The lesson is that one must fix an
investigative context in order to make such criteria precise, but different
investigative contexts yield inconsistent results. I examine questions of
existence about spacetime structures other than the spacetime manifold itself
to argue that it is more fruitful to focus on pragmatic issues of physicality,
a notion that lends itself to several different explications, all of
philosophical interest, none privileged a priori over any of the others. I
conclude by suggesting an extension of the lessons of my arguments to the
broader debate between realists and instrumentalists.Comment: 42 pages, 2 figures, forthcoming (2015) in British Journal for
Philosophy of Scienc
The Birth of a Cinematic Storyline Normalizing Violence against Black Lives
The first Hollywood blockbuster, The Birth of a Nation, did more than establish cinematic conventions of camera techniques and movie distribution, for it also established a conventional storyline whereby white, patriarchal power is re-established through violence led by a white savior. This storyline can be traced throughout the history of major blockbusters such as Gone with the Wind of 1939, the cavalry trilogy by John Ford in the 1940s, The Omega Man from 1971, and The Outlaw Josie Wales from 1976. A quandary thus arises as to why The Birth of a Nation is held in such infamy and disdain when subsequent films that employ the same storyline are held in such high regard? I pose one explanation of this double standard in judgment as being caused by what I call “social distance by layering.” The larger issue is this storyline normalizes white male gun violence against blacks, liberals, and feminists
Classical Black Holes Are Hot
In the early 1970s it is was realized that there is a striking formal analogy
between the Laws of black-hole mechanics and the Laws of classical
thermodynamics. Before the discovery of Hawking radiation, however, it was
generally thought that the analogy was only formal, and did not reflect a deep
connection between gravitational and thermodynamical phenomena. It is still
commonly held that the surface gravity of a stationary black hole can be
construed as a true physical temperature and its area as a true entropy only
when quantum effects are taken into account; in the context of classical
general relativity alone, one cannot cogently construe them so. Does the use of
quantum field theory in curved spacetime offer the only hope for taking the
analogy seriously? I think the answer is `no'. To attempt to justify that
answer, I shall begin by arguing that the standard argument to the contrary is
not physically well founded, and in any event begs the question. Looking at the
various ways that the ideas of "temperature" and "entropy" enter classical
thermodynamics then will suggest arguments that, I claim, show the analogy
between classical black-hole mechanics and classical thermodynamics should be
taken more seriously, without the need to rely on or invoke quantum mechanics.
In particular, I construct an analogue of a Carnot cycle in which a black hole
"couples" with an ordinary thermodynamical system in such a way that its
surface gravity plays the role of temperature and its area that of entropy.
Thus, the connection between classical general relativity and classical
thermodynamics on their own is already deep and physically significant,
independent of quantum mechanics.Comment: 30 pages; revised so as to address possible counter-example due to
Bob Wald, that treating black holes purely classically may lead to violations
of the GS
If Metrical Structure Were Not Dynamical, Counterfactuals in General Relativity Would Be Easy
General relativity poses serious problems for counterfactual propositions
peculiar to it as a physical theory. Because these problems arise solely from
the dynamical nature of spacetime geometry, they are shared by all schools of
thought on how counterfactuals should be interpreted and understood. Given the
role of counterfactuals in the characterization of, inter alia, many accounts
of scientific laws, theory confirmation and causation, general relativity once
again presents us with idiosyncratic puzzles any attempt to analyze and
understand the nature of scientific knowledge must face.Comment: 10 page
On Tensorial Concomitants and the Non-Existence of a Gravitational Stress-Energy Tensor
The question of the existence of gravitational stress-energy in general
relativity has exercised investigators in the field since the inception of the
theory. Folklore has it that no adequate definition of a localized
gravitational stress-energetic quantity can be given. Most arguments to that
effect invoke one version or another of the Principle of Equivalence. I argue
that not only are such arguments of necessity vague and hand-waving but, worse,
are beside the point and do not address the heart of the issue. Based on a
novel analysis of what it may mean for one tensor to depend in the proper way
on another, I prove that, under certain natural conditions, there can be no
tensor whose interpretation could be that it represents gravitational
stress-energy in general relativity. It follows that gravitational energy, such
as it is in general relativity, is necessarily non-local. Along the way, I
prove a result of some interest in own right about the structure of the
associated jet bundles of the bundle of Lorentz metrics over spacetime.Comment: 20 pages (including 2 1/2 pages biblio
Non-decoupling effects of SUSY in the physics of Higgs bosons and their phenomenological implications
We consider a plausible scenario in the Minimal Supersymmetric Standard Model
(MSSM) where all the genuine supersymmetric (SUSY) particles are heavier than
the electroweak scale. In this situation, indirect searches via their radiative
corrections to low energy observables are complementary to direct searches, and
they can be crucial if the SUSY masses are at the TeV energy range. We
summarize the most relevant heavy SUSY radiative effects in Higgs boson physics
and emphasize those that manifest a non-decoupling behaviour. We focus, in
particular, on the SUSY-QCD non-decoupling effects in fermionic Higgs decays,
flavour changing Higgs decays and Yukawa couplings. Some of their
phenomenological implications at future colliders are also studied.Comment: Invited talk given by M. J. Herrero at the X Mexican School of
Particles and Fields, Playa del Carmen, Mexico, November 200
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