957 research outputs found
Comments on Challenges for Quantum Gravity
We examine radiative corrections arising from Lorentz violating dimension
five operators presumably associated with Planck scale physics as recently
considered by Myers and Pospelov. We find that observational data result in
bounds on the dimensionless parameters of the order . These represent
the most stringent bounds on Lorentz violation to date
Searching for spacetime granularity: analyzing a concrete experimental setup
In this work we show that the spin pendulum techniques developed by the
E\:{o}t-Wash group could be used to put very stringent bounds on the free
parameters of a Lorentz invariant phenomenological model of quantum gravity.
The model is briefly described as well as the experimental setup that we have
in mind.Comment: 9 pages. For the proceedings of the VIII School of the Gravitation
and Mathematical Physics Division of the Mexican Physical Society 'Speakable
and unspeakable in gravitational physics: testing gravity from submillimeter
to cosmic scale'
Less Decoherence and More Coherence in Quantum Gravity, Inflationary Cosmology and Elsewhere
In Crull (2015) it is argued that, in order to confront outstanding problems
in cosmology and quantum gravity, interpretational aspects of quantum theory
can by bypassed because decoherence is able to resolve them. As a result, Crull
(2015) concludes that our focus on conceptual and interpretational issues,
while dealing with such matters in Okon and Sudarsky (2014), is avoidable and
even pernicious. Here we will defend our position by showing in detail why
decoherence does not help in the resolution of foundational questions in
quantum mechanics, such as the measurement problem or the emergence of
classicality.Comment: 37 page
Dark energy from quantum gravity discreteness
We argue that discreteness at the Planck scale (naturally expected to arise
from quantum gravity) might manifest in the form of minute violations of
energy-momentum conservation of the matter degrees of freedom when described in
terms of (idealized) smooth fields on a smooth spacetime. In the context of
applications to cosmology such `energy diffusion' from the low energy matter
degrees of freedom to the discrete structures underlying spacetime leads to the
emergence of an effective dark energy term in Einstein's equations. We estimate
this effect using a (relational) hypothesis about the materialization of
discreteness in quantum gravity which is motivated by the strict observational
constraints supporting the validity of Lorentz invariance at low energies. The
predictions coming from simple dimensional analysis yield a cosmological
constant of the order of magnitude of the observed value without fine tuning.Comment: Typos corrected, closer to published versio
- …