7,260 research outputs found
Gravity and the Quantum: Are they Reconcilable?
General relativity and quantum mechanics are conflicting theories. The seeds
of discord are the fundamental principles on which these theories are grounded.
General relativity, on one hand, is based on the equivalence principle, whose
strong version establishes the local equivalence between gravitation and
inertia. Quantum mechanics, on the other hand, is fundamentally based on the
uncertainty principle, which is essentially nonlocal in the sense that a
particle does not follow one trajectory, but infinitely many trajectories, each
one with a different probability. This difference precludes the existence of a
quantum version of the strong equivalence principle, and consequently of a
quantum version of general relativity. Furthermore, there are compelling
experimental evidences that a quantum object in the presence of a gravitational
field violates the weak equivalence principle. Now it so happens that, in
addition to general relativity, gravitation has an alternative, though
equivalent description, given by teleparallel gravity, a gauge theory for the
translation group. In this theory torsion, instead of curvature, is assumed to
represent the gravitational field. These two descriptions lead to the same
classical results, but are conceptually different. In general relativity,
curvature geometrizes the interaction, while torsion in teleparallel gravity
acts as a force, similar to the Lorentz force of electrodynamics. Because of
this peculiar property, teleparallel gravity describes the gravitational
interaction without requiring any of the equivalence principles. The
replacement of general relativity by teleparallel gravity may, in consequence,
lead to a conceptual reconciliation of gravitation with quantum mechanics.Comment: 15 pages, 2 figures. Talk presented at the conference "Quantum
Theory: Reconsideration of Foundations-3", June 6-11, 2005, Vaxjo University,
Vaxjo, Swede
Gravitation without the equivalence principle
In the general relativistic description of gravitation, geometry replaces the
concept of force. This is possible because of the universal character of free
fall, and would break down in its absence. On the other hand, the teleparallel
version of general relativity is a gauge theory for the translation group and,
as such, describes the gravitational interaction by a force similar to the
Lorentz force of electromagnetism, a non-universal interaction. Relying on this
analogy it is shown that, although the geometric description of general
relativity necessarily requires the existence of the equivalence principle, the
teleparallel gauge approach remains a consistent theory for gravitation in its
absence.Comment: Latex, 11 pages, no figures. Minor presentation changes. Version to
appear in Gen. Rel. Grav. (2004
Doing without the Equivalence Principle
In Einstein's general relativity, geometry replaces the concept of force in
the description of the gravitation interaction. Such an approach rests on the
universality of free-fall--the weak equivalence principle--and would break down
without it. On the other hand, the teleparallel version of general relativity,
a gauge theory for the translation group, describes the gravitational
interaction by a force similar to the Lorentz force of electromagnetism, a
non-universal interaction. It is shown that, similarly to the Maxwell's
description of electromagnetism, the teleparallel gauge approach provides a
consistent theory for gravitation even in the absence of the weak equivalence
principle.Comment: 7 pages, no figures. Talk presented at the "Tenth Marcel Grossmann
Meeting", July 20 to 26, 2003, Rio de Janeiro, Brazil; to be published in the
Proceedings (World Scientific, Singapore, 2005
Bringing Together Gravity and the Quanta
Due to its underlying gauge structure, teleparallel gravity achieves a
separation between inertial and gravitational effects. It can, in consequence,
describe the isolated gravitational interaction without resorting to the
equivalence principle, and is able to provide a tensorial definition for the
energy-momentum density of the gravitational field. Considering the conceptual
conflict between the local equivalence principle and the nonlocal uncertainty
principle, the replacement of general relativity by its teleparallel equivalent
can be considered an important step towards a prospective reconciliation
between gravitation and quantum mechanics.Comment: 9 pages. Contribution to the proceedings of the Albert Einstein
Century International Conference, Paris, 18-22 July, 200
The observation of photon echoes from evanescently coupled rare-earth ions in a planar waveguide
We report the measurement of the inhomogeneous linewidth, homogeneous
linewidth and spin state lifetime of Pr3+ ions in a novel waveguide
architecture. The TeO2 slab waveguide deposited on a bulk Pr3+:Y2SiO5 crystal
allows the 3H4 - 1D2 transition of Pr3+ ions to be probed by the optical
evanescent field that extends into the substrate. The 2 GHz inhomogeneous
linewidth, the optical coherence time of 70 +- 5 us, and the spin state
lifetime of 9.8 +- 0.3 s indicate that the properties of ions interacting with
the waveguide mode are consistent with those of bulk ions. This result
establishes the foundation for large, integrated and high performance
rare-earth-ion quantum systems based on a waveguide platform.Comment: 5 pages, 5 figure
Thermo-poro-mechanical coupled processes during thermal pressurization around nuclear waste repository
This paper investigates the thermo-hydro-mechanical behavior of Callovo-
Oxfordian claystone, a potential host formation for prospective nuclear waste disposal in
France. Thermal pore pressure appears in low permeability soils and rocks due to the
difference between the thermal expansion coefficients of water and the argillaceous skeleton,
as well as the low permeability of the media and the its relative rigidity, which prevent
dissipation of the fluid pressure. Coupled thermo-hydro-mechanical numerical analyses have
been carried out to enhance the understanding of the Callovo-Oxfordian claystone behavior
subjected to heat emitted from radioactive waste that diffuses through the near-field rock to
the far-field. In this view, the “thermal pressurization coefficient”, defined as the increase of
pore pressure due to 1°C increase of temperature, was calculated. This coefficient depends on
the nature of the rock, i.e the thermo-poro-mechanical parameters such permeability, Biot’s
coefficient, rigidity, thermal conductivity as well as their anisotropies. Finally, the effect of
parameters’ variability on the thermal pressurization coefficient is discussed through a
sensibility analysis
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