3,200 research outputs found
Asymptotic states of the bounce geometry
We consider the question of asymptotic observables in cosmology. We assume
that string theory contains a landscape of vacua, and that metastable de Sitter
regions can decay to zero cosmological constant by bubble nucleation. The
asymptotic properties of the corresponding bounce solution should be
incorporated in a nonperturbative quantum theory of cosmology. A recent
proposal for such a framework defines an S-matrix between the past and future
boundaries of the bounce. We analyze in detail the properties of asymptotic
states in this proposal, finding that generic small perturbations of the
initial state cause a global crunch. We conclude that late-time amplitudes
should be computed directly. This would require a string theory analogue of the
no-boundary proposal.Comment: 20 pages, 7 figures. v2: reference adde
Science and ethics in the post-political era: strategies within the Camp for Climate Action
Despite a peak in activism against climate change in the UK, new environmental direct action networks have not yet received much academic attention. This article takes as a case study perhaps the most prominent of such networks â the Camp for Climate Action â which held several high-profile protest events between 2006 and 2011. Using a theoretical framework which understands society as being distinctly âpost-politicalâ in character, we ask questions about the knowledge claims that form the foundations of radical environmental politics. Drawing on published statements and press releases, as well as from our insights as active participants in the Camp, we analyse the strategy of environmental protest where climate change has become its focus. The Camp for Climate Action was a contested political arena. We argue that this contestation existed over the Campâs strategy in the context of a âscientisedâ, âpost- politicalâ politics which operated
within an ethical framework that prescribed individual responsibility as the primary basis for action
Probabilities in the landscape: The decay of nearly flat space
We discuss aspects of the problem of assigning probabilities in eternal
inflation. In particular, we investigate a recent suggestion that the lowest
energy de Sitter vacuum in the landscape is effectively stable. The associated
proposal for probabilities would relegate lower energy vacua to unlikely
excursions of a high entropy system. We note that it would also imply that the
string theory landscape is experimentally ruled out. However, we extensively
analyze the structure of the space of Coleman-De Luccia solutions, and we
present analytic arguments, as well as numerical evidence, that the decay rate
varies continuously as the false vacuum energy goes through zero. Hence,
low-energy de Sitter vacua do not become anomalously stable; negative and zero
cosmological constant regions cannot be neglected.Comment: 18 pages, 13 figures, Mathematica notebooks available from the
authors. v2,v3: typos and omissions fixe
A geometric solution to the coincidence problem, and the size of the landscape as the origin of hierarchy
Without assuming necessary conditions for observers such as galaxies or
entropy production, we show that the causal patch measure predicts the
coincidence of vacuum energy and present matter density. Their common scale,
and thus the enormous size of the visible universe, has its origin in the
number of metastable vacua in the landscape.Comment: 5 pages, 2 figures. v2: minor editin
Fomalhaut b: Independent Analysis of the Hubble Space Telescope Public Archive Data
The nature and even the existence of a putative planet-mass companion
("Fomalhaut b") to Fomalhaut has been debated since 2008. In the present paper
we reanalyze the multi-epoch ACS/STIS/WFC3 Hubble Space Telescope (HST)
optical/near infrared images on which the discovery and some other claims were
based. We confirm that the HST images do reveal an object in orbit around
Fomalhaut but the detailed results from our analysis differ in some ways from
previous discussions. In particular, we do not confirm flux variability over a
two-year interval at 0.6 microns wavelength and we detect Fomalhaut b for the
first time at the short wavelength of 0.43 microns. We find that the HST image
of Fomalhaut b at m may be extended beyond the PSF. We cannot
determine from our astrometry if Fomalhaut b will cross or not the dust ring.
The optical through mid-infrared spectral energy distribution (SED) of
Fomalhaut b cannot be explained as due to direct or scattered radiation from a
massive planet. We consider two models to explain the SED: (1) a large
circumplanetary disk around an unseen planet and (2) the aftermath of a
collision during the past 50-150 years of two Kuiper Belt-like objects of radii
50 km.Comment: 24 pages, 9 figures, 5 tables, accepted on April, 3rd, 201
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Geometric origin of coincidences and hierarchies in the landscape
We show that the geometry of cutoffs on eternal inflation strongly constrains
predictions for the timescales of vacuum domination, curvature domination, and
observation. We consider three measure proposals: the causal patch, the fat
geodesic, and the apparent horizon cutoff, which is introduced here for the
first time. We impose neither anthropic requirements nor restrictions on
landscape vacua. For vacua with positive cosmological constant, all three
measures predict the double coincidence that most observers live at the onset
of vacuum domination and just before the onset of curvature domination. The
hierarchy between the Planck scale and the cosmological constant is related to
the number of vacua in the landscape. These results require only mild
assumptions about the distribution of vacua (somewhat stronger assumptions are
required by the fat geodesic measure). At this level of generality, none of the
three measures are successful for vacua with negative cosmological constant.
Their applicability in this regime is ruled out unless much stronger anthropic
requirements are imposed.Comment: 34 pages, 5 figure
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