199 research outputs found
On the interpretation of Michelson-Morley experiments
Recent proposals for improved optical tests of Special Relativity have
renewed interest in the interpretation of such tests. In this paper we discuss
the interpretation of modern realizations of the Michelson-Morley experiment in
the context of a new model of electrodynamics featuring a vector-valued photon
mass. This model is gauge invariant, unlike massive-photon theories based on
the Proca equation, and it predicts anisotropy of both the speed of light and
the electric field of a point charge. The latter leads to an orientation
dependence of the length of solid bodies which must be accounted for when
interpreting the results of a Michelson-Morley experiment. Using a simple model
of ionic solids we show that, in principle, the effect of orientation dependent
length can conspire to cancel the effect of an anisotropic speed of light in a
Michelson-Morley experiment, thus, complicating the interpretation of the
results.Comment: To appear in Phys.Lett.
Space--time fluctuations and the spreading of wavepackets
Using a density matrix description in space we study the evolution of
wavepackets in a fluctuating space-time background. We assume that space-time
fluctuations manifest as classical fluctuations of the metric. From the
non-relativistic limit of a non-minimally coupled Klein-Gordon equation we
derive a Schr\"odinger equation with an additive gaussian random potential.
This is transformed into an effective master equation for the density matrix.
The solutions of this master equation allow to study the dynamics of
wavepackets in a fluctuating space-time, depending on the fluctuation scenario.
We show how different scenarios alter the diffusion properties of wavepackets.Comment: 11 page
Atomic Interferometer with Amplitude Gratings of Light and its Applications to Atom Based Tests of the Equivalence Principle
We have developed a matter wave interferometer based on the diffraction of
atoms from effective absorption gratings of light. In a setup with cold
rubidium atoms in an atomic fountain the interferometer has been used to carry
out tests of the equivalence principle on an atomic basis. The gravitational
acceleration of the two isotopes 85Rb and 87Rb was compared, yielding a
difference Dg/g =(1.2 +-1.7)x10^{-7}. We also perform a differential free fall
measurement of atoms in two different hyperfine states, and obtained a result
of Dg/g =(0.4 +-1.2)x10^{-7}.Comment: 4 Pages, 4 figures, accepted for Physical Review Letter
Long range gravity tests and the Pioneer anomaly
Experimental tests of gravity performed in the solar system show a good
agreement with general relativity. The latter is however challenged by the
Pioneer anomaly which might be pointing at some modification of gravity law at
ranges of the order of the size of the solar system. As this question could be
related to the puzzles of ``dark matter'' or ``dark energy'', it is important
to test it with care. There exist metric extensions of general relativity which
preserve the well verified equivalence principle while possibly changing the
metric solution in the solar system. Such extensions have the capability to
preserve compatibility with existing gravity tests while opening free space for
the Pioneer anomaly. They constitute arguments for new mission designs and new
space technologies as well as for having a new look at data of already
performed experiments.Comment: 8 page
General Relativistic Chronometry with Clocks on Ground and in Space
One of geodesy's main tasks is to determine the gravity field of the Earth.
High precision clocks have the potential to provide a new tool in a global
determination of the Earth's gravitational potential based on the gravitational
redshift. Towards this clock-based gravimetry or chronometry in stationary
spacetimes, exact expressions for the relativistic redshift and the timing
between observers in various configurations are derived. These observers are
assumed to be equipped with standard clocks and move along arbitrary
worldlines. It is shown that redshift measurements, involving clocks on ground
and/or in space, can be used to determine the (mass) multipole moments of the
underlying spacetime. Results shown here are in agreement with the Newtonian
potential determination from, e.g., the so-called energy approach. The
framework of chronometric geodesy is exemplified in different exact vacuum
spacetimes for illustration and future gravity field recovery missions may use
clock comparisons as an additional data channel for advanced data fusion.Comment: 15 pages, 4 figure
On Loop Quantum Gravity Phenomenology and the Issue of Lorentz Invariance
A simple model is constructed which allows to compute modified dispersion
relations with effects from loop quantum gravity. Different quantization
choices can be realized and their effects on the order of corrections studied
explicitly. A comparison with more involved semiclassical techniques shows that
there is agreement even at a quantitative level.
Furthermore, by contrasting Hamiltonian and Lagrangian descriptions we show
that possible Lorentz symmetry violations may be blurred as an artifact of the
approximation scheme. Whether this is the case in a purely Hamiltonian analysis
can be resolved by an improvement in the effective semiclassical analysis.Comment: 16 pages, RevTeX
Quantum Tests of the Foundations of General Relativity
The role of the equivalence principle in the context of non-relativistic
quantum mechanics and matter wave interferometry, especially atom beam
interferometry, will be discussed. A generalised form of the weak equivalence
principle which is capable of covering quantum phenomena too, will be proposed.
It is shown that this generalised equivalence principle is valid for matter
wave interferometry and for the dynamics of expectation values. In addition,
the use of this equivalence principle makes it possible to determine the
structure of the interaction of quantum systems with gravitational and inertial
fields. It is also shown that the path of the mean value of the position
operator in the case of gravitational interaction does fulfill this generalised
equivalence principle.Comment: Classical and Quantum Gravity 15, 13 (1998
Basics of Superluminal Signals
The paper elucidates the physical basis of experimental results on
superluminal signal velocity. It will be made plausible that superluminal
signals do not violate the principle of causality but they can shorten the
luminal vacuum time span between cause and effect. This amazing behaviour is
based on the property that any physical signal has a finite duration.Comment: 11 pages, 8 figure
Gravitational dynamics for all tensorial spacetimes carrying predictive, interpretable and quantizable matter
Only a severely restricted class of tensor fields can provide classical
spacetime geometries, namely those that can carry matter field equations that
are predictive, interpretable and quantizable. These three conditions on matter
translate into three corresponding algebraic conditions on the underlying
tensorial geometry, namely to be hyperbolic, time-orientable and
energy-distinguishing. Lorentzian metrics, on which general relativity and the
standard model of particle physics are built, present just the simplest
tensorial spacetime geometry satisfying these conditions. The problem of
finding gravitational dynamics---for the general tensorial spacetime geometries
satisfying the above minimum requirements---is reformulated in this paper as a
system of linear partial differential equations, in the sense that their
solutions yield the actions governing the corresponding spacetime geometry.
Thus the search for modified gravitational dynamics is reduced to a clear
mathematical task.Comment: 47 pages, no figures, minor update
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