2,198 research outputs found
Typicality in spin network states of quantum geometry
In this work, we extend the so-called typicality approach, originally
formulated in statistical mechanics contexts, to -invariant spin-network
states. Our results do not depend on the physical interpretation of the spin
network; however, they are mainly motivated by the fact that spin-network
states can describe states of quantum geometry, providing a gauge-invariant
basis for the kinematical Hilbert space of several background-independent
approaches to quantum gravity. The first result is, by itself, the existence of
a regime in which we show the emergence of a typical state. We interpret this
as the proof that in that regime there are certain (local) properties of
quantum geometry which are "universal". Such a set of properties is heralded by
the typical state, of which we give the explicit form. This is our second
result. In the end, we study some interesting properties of the typical state,
proving that the area law for the entropy of a surface must be satisfied at the
local level, up to logarithmic corrections which we are able to bound.Comment: Typos and mistakes fixe
Statistical mechanics of covariant systems with multi-fingered time
Recently, in [Class. Quantum Grav. 33 (2016) 045005], the authors proposed a
new approach extending the framework of statistical mechanics to
reparametrization-invariant systems with no additional gauges. In this work,
the approach is generalized to systems defined by more than one Hamiltonian
constraints (multi-fingered time). We show how well known features as the
Ehrenfest- Tolman effect and the J\"uttner distribution for the relativistic
gas can be consistently recovered from a covariant approach in the
multi-fingered framework. Eventually, the crucial role played by the
interaction in the definition of a global notion of equilibrium is discussed.Comment: 5 pages, 2 figure
On the fate of the Hoop Conjecture in quantum gravity
We consider a closed region of 3d quantum space modeled by
spin-networks. Using the concentration of measure phenomenon we prove that,
whenever the ratio between the boundary and the bulk edges of the
graph overcomes a finite threshold, the state of the boundary is always
thermal, with an entropy proportional to its area. The emergence of a thermal
state of the boundary can be traced back to a large amount of entanglement
between boundary and bulk degrees of freedom. Using the dual geometric
interpretation provided by loop quantum gravity, we interprete such phenomenon
as a pre-geometric analogue of Thorne's "Hoop conjecture", at the core of the
formation of a horizon in General Relativity.Comment: 7 pages, 2 figures, minor improvement
Adapting to extreme environments: can coral reefs adapt to climate change?
Reef-building corals throughout the world have an annual value of tens of billions of dollars, yet they are being degraded at an increasing rate by many anthropogenic and environmental factors. Despite this, some reefs show resilience to such extreme environmental changes. This review shows how techniques in computational modelling, genetics, and transcriptomics are being used to unravel the complexity of coral reef ecosystems, to try and understand if they can adapt to new and extreme environments. Considering the ambitious climate targets of the Paris Agreement to limit global warming to 2°C, with aspirations of even 1.5°C, questions arise on how to achieve this. Geoengineering may be necessary if other avenues fail, although global governance issues need to play a key role. Development of large and effective coral refugia and marine protected areas is necessary if we are not to lose this vital resource for us all
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