38 research outputs found
Superpositions of the cosmological constant allow for singularity resolution and unitary evolution in quantum cosmology
A novel approach to quantization is shown to allow for superpositions of the
cosmological constant in isotropic and homogeneous mini-superspace models.
Generic solutions featuring such superpositions display unitary evolution and
resolution of the classical singularity. Physically well-motivated cosmological
solutions are constructed. These particular solutions exhibit characteristic
features of a cosmic bounce including universal phenomenology that can be
rendered insensitive to Planck-scale physics in a natural manner.Comment: Version accepted to Physics Letters B. Minor revisions,
clarifications added. 7 pages, 3 figure
On the Empirical Consequences of the AdS/CFT Duality
We provide an analysis of the empirical consequences of the AdS/CFT duality
with reference to the application of the duality in a fundamental theory,
effective theory and instrumental context. Analysis of the first two contexts
is intended to serve as a guide to the potential empirical and ontological
status of gauge/gravity dualities as descriptions of actual physics at the
Planck scale. The third context is directly connected to the use of AdS/CFT to
describe real quark-gluon plasmas. In the latter context, we find that neither
of the two duals are confirmed by the empirical data.Comment: 15 pages + abstract, references. Submitted to "Beyond Spacetime"
volum
Hawking Radiation and Analogue Experiments: A Bayesian Analysis
We present a Bayesian analysis of the epistemology of analogue experiments
with particular reference to Hawking radiation. First, we prove that such
experiments can be confirmatory in Bayesian terms based upon appeal to
'universality arguments'. Second, we provide a formal model for the scaling
behaviour of the confirmation measure for multiple distinct realisations of the
analogue system and isolate a generic saturation feature. Finally, we
demonstrate that different potential analogue realisations could provide
different levels of confirmation. Our results provide a basis both to formalise
the epistemic value of analogue experiments that have been conducted and to
advise scientists as to the respective epistemic value of future analogue
experiments.Comment: 25 pages, 5 figure
On the Universality of Hawking Radiation
A physically consistent semi-classical treatment of black holes requires universality arguments to deal with the `trans-Planckian' problem where quantum spacetime effects appear to be amplified such that they undermine the entire semi-classical modelling framework. We evaluate three families of such arguments in comparison with Wilsonian renormalization group universality arguments found in the context of condensed matter physics. Our analysis is framed by the crucial distinction between robustness and universality. Particular emphasis is placed on the quality whereby the various arguments are underpinned by `integrated' notions of robustness and universality. Whereas the principal strength of Wilsonian universality arguments can be understood in terms of the presence of such integration, the principal weakness of all three universality arguments for Hawking radiation is its absence
On the Universality of Hawking Radiation
A physically consistent semi-classical treatment of black holes requires
universality arguments to deal with the `trans-Planckian' problem where quantum
spacetime effects appear to be amplified such that they undermine the entire
semi-classical modelling framework. We evaluate three families of such
arguments in comparison with Wilsonian renormalization group universality
arguments found in the context of condensed matter physics. Our analysis is
framed by the crucial distinction between robustness and universality.
Particular emphasis is placed on the quality whereby the various arguments are
underpinned by `integrated' notions of robustness and universality. Whereas the
principal strength of Wilsonian universality arguments can be understood in
terms of the presence of such integration, the principal weakness of all three
universality arguments for Hawking radiation is its absence.Comment: Version forthcoming to the The British Journal for the Philosophy of
Science. 23 journal pages + references, 1 figur
Dispositions and the principle of least action revisited
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Spacetime Conventionalism Revisited
We characterise and critically evaluate five formulations of the thesis that
the structure of spacetime is conventional, rather than empirically determined.
The proliferation of formulations comes from considering generalisation first,
via a more liberal Carnapian understanding of the conventionalism argument in
terms of universal effects, rather than Reichenbachian universal forces, and
second, via a more liberal understanding of the modal context of the empirical
underdetermination, that is as underdetermination between observers rather than
models. Whilst three of the five formulations of conventionalism will be found
to fail, two are found to open up new interesting problems for researchers in
the foundations of general relativity. In all five cases, our analysis will
explore interplay between geometric identities, symmetry, conformal structure,
and the dynamical content of physical theories. The conventionalism dialectic
is thus deployed towards as a tool of explication, clarification, and
exploration
Modelling Inequality
Econophysics is a new and exciting cross-disciplinary research field that applies
models and modelling techniques from statistical physics to economic
systems. It is not, however, without its critics: prominent figures in more
mainstream economic theory have criticised some elements of the methodology
of econophysics. One of the main lines of criticism concerns the nature
of the modelling assumptions and idealisations involved, and a particular
target are 'kinetic exchange' approaches used to model the emergence of
inequality within the distribution of individual monetary income. This paper
will consider such models in detail, and assess the warrant of the criticisms
drawing upon the philosophical literature on modelling and idealisation. Our
aim is to provide the first steps towards informed mediation of this important
and interesting interdisciplinary debate, and our hope is to offer
guidance with regard to both the practice of modelling inequality, and the
inequality of modelling practice