20,027 research outputs found
Gravitational Effects in Quantum Mechanics
To date, both quantum theory, and Einstein's theory of general relativity
have passed every experimental test in their respective regimes. Nevertheless,
almost since their inception, there has been debate surrounding whether they
should be unified and by now there exists strong theoretical arguments pointing
to the necessity of quantising the gravitational field. In recent years, a
number of experiments have been proposed which, if successful, should give
insight into features at the Planck scale. Here we review some of the
motivations, from the perspective of semi-classical arguments, to expect new
physical effects at the overlap of quantum theory and general relativity. We
conclude with a short introduction to some of the proposals being made to
facilitate empirical verification.Comment: 24 pages, 3 figures, review article. Submitted to Contemporary
Physic
Operational definition of (brane induced) space-time and constraints on the fundamental parameters
First we contemplate the operational definition of space-time in four
dimensions in light of basic principles of quantum mechanics and general
relativity and consider some of its phenomenological consequences. The quantum
gravitational fluctuations of the background metric that comes through the
operational definition of space-time are controlled by the Planck scale and are
therefore strongly suppressed. Then we extend our analysis to the braneworld
setup with low fundamental scale of gravity. It is observed that in this case
the quantum gravitational fluctuations on the brane may become unacceptably
large. The magnification of fluctuations is not linked directly to the low
quantum gravity scale but rather to the higher-dimensional modification of
Newton's inverse square law at relatively large distances. For models with
compact extra dimensions the shape modulus of extra space can be used as a most
natural and safe stabilization mechanism against these fluctuations.Comment: 9 page
Selected topics in Planck-scale physics
We review a few topics in Planck-scale physics, with emphasis on possible
manifestations in relatively low energy. The selected topics include quantum
fluctuations of spacetime, their cumulative effects, uncertainties in
energy-momentum measurements, and low energy quantum-gravity phenomenology. The
focus is on quantum-gravity-induced uncertainties in some observable
quantities. We consider four possible ways to probe Planck-scale physics
experimentally: 1. looking for energy-dependent spreads in the arrival time of
photons of the same energy from GRBs; 2. examining spacetime
fluctuation-induced phase incoherence of light from extragalactic sources; 3.
detecting spacetime foam with laser-based interferometry techniques; 4.
understanding the threshold anomalies in high energy cosmic ray and gamma ray
events. Some other experiments are briefly discussed. We show how some physics
behind black holes, simple clocks, simple computers, and the holographic
principle is related to Planck-scale physics. We also discuss a formulation of
the Dirac equation as a difference equation on a discrete Planck-scale
spacetime lattice, and a possible interplay between Planck-scale and
Hubble-scale physics encoded in the cosmological constant (dark energy).Comment: 31 pages, 1 figure; minor changes; to appear in Mod. Phys. Lett. A as
a Brief Revie
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