444 research outputs found
Gravitomagnetism and gravitational waves
After extensively reviewing general relativistic gravitomagnetism, both
historically and phenomenologically, we review in detail the so-called magnetic
components of gravitational waves (GWs), which have to be taken into account in
the context of the total response functions of interferometers for GWs
propagating from arbitrary directions. Following the more recent approaches of
this important issue, the analysis of such magnetic components will be reviewed
in both of standard General Theory of Relativity (GTR) and Scalar Tensor
Gravity. Thus, we show in detail that such a magnetic component becomes
particularly important in the high-frequency portion of the range of ground
based interferometers for GWs which arises from the two different theories of
gravity. Our reviewed results show that if one neglects the magnetic
contribution to the gravitational field of a GW, approximately 15% of the
potential observable signal could, in principle, be lost.Comment: To appear in the Special Issue of The Open Astronomy Journal "The Big
Challenge of Gravitational Waves, a New Window into the Universe", Editors
Christian Corda, Herman J. Mosquera Cuesta, Oswaldo Miranda and Theodore
Simo
Feasibility analysis of gravitational experiments in space
Experiments on gravitation and general relativity suggested by different workers in the past ten or more years are reviewed, their feasibility examined, and the advantages of performing them in space were studied. The experiments include: (1) the gyro relativity experiment; (2) experiments to test the equivalence of gravitational and inertial mass; (3) an experiment to look for nongeodesic motion of spinning bodies in orbit around the earth; (4) experiments to look for changes of the gravitational constant G with time; (5) a variety of suggestions; laboratory tests of experimental gravity; and (6) gravitational wave experiments
Gravitational sensing with weak value based optical sensors
Using weak values amplification angular resolution limits, we theoretically
investigate the gravitational sensing of objects. By inserting a force-sensing
pendulum into a weak values interferometer, the optical response can sense
accelerations to a few 10's of
, with optical powers of
. We convert this precision into range and mass sensitivity,
focusing in detail on simple and torsion pendula. Various noise sources present
are discussed, as well as the necessary cooling that should be applied to reach
the desired levels of precision.Comment: 9 pages, 4 figures, Quantum Stud.: Math. Found. (2018
The next detectors for gravitational wave astronomy
This paper focuses on the next detectors for gravitational wave astronomy
which will be required after the current ground based detectors have completed
their initial observations, and probably achieved the first direct detection of
gravitational waves. The next detectors will need to have greater sensitivity,
while also enabling the world array of detectors to have improved angular
resolution to allow localisation of signal sources. Sect. 1 of this paper
begins by reviewing proposals for the next ground based detectors, and presents
an analysis of the sensitivity of an 8 km armlength detector, which is proposed
as a safe and cost-effective means to attain a 4-fold improvement in
sensitivity. The scientific benefits of creating a pair of such detectors in
China and Australia is emphasised. Sect. 2 of this paper discusses the high
performance suspension systems for test masses that will be an essential
component for future detectors, while sect. 3 discusses solutions to the
problem of Newtonian noise which arise from fluctuations in gravity gradient
forces acting on test masses. Such gravitational perturbations cannot be
shielded, and set limits to low frequency sensitivity unless measured and
suppressed. Sects. 4 and 5 address critical operational technologies that will
be ongoing issues in future detectors. Sect. 4 addresses the design of thermal
compensation systems needed in all high optical power interferometers operating
at room temperature. Parametric instability control is addressed in sect. 5.
Only recently proven to occur in Advanced LIGO, parametric instability
phenomenon brings both risks and opportunities for future detectors. The path
to future enhancements of detectors will come from quantum measurement
technologies. Sect. 6 focuses on the use of optomechanical devices for
obtaining enhanced sensitivity, while sect. 7 reviews a range of quantum
measurement options
Matters of Gravity, the newsletter of the APS Topical Group on Gravitation
News:
TGG session in the April meeting, by Cliff Will NRC report, by Beverly Berger
MG9 Travel Grant for US researchers, by Jim Isenberg Research Briefs:
How many coalescing binaries are there?, by Vicky Kalogera Recent
developments in black critical phenomena, by Pat Brady Optical black holes?, by
Matt Visser ``Branification:'' an alternative to compactification, by Steve
Giddings Searches for non-Newtonian Gravity at Sub-mm Distances, by Riley
Newman Quiescent cosmological singularities by Bernd Schmidt The debut of LIGO
II, by David Shoemaker Is the universe still accelerating?, by Sean Carroll
Conference reports:
Journ\' ees Relativistes Weimar 1999, by Volker Perlick The 9th Midwest
Relativity Meeting, by Thomas BaumgarteComment: 35 pages, LaTeX with psfig and html.sty, ISSN 1527-3431, Jorge Pullin
(editor), html, ps and pdf versions at http://gravity.phys.psu.edu/mog.htm
Reflections on a Measurement of the Gravitational Constant Using a Beam Balance and 13 Tons of Mercury
In 2006, a final result of a measurement of the gravitational constant
performed by researchers at the University of Z\"urich was published. A value
of G=6.674\,252(122)\times
10^{-11}\,\mbox{m}^3\,\mbox{kg}^{-1}\,\mbox{s}^{-2} was obtained after an
experimental effort that lasted over one decade. Here, we briefly summarize the
measurement and discuss the strengths and weaknesses of this approach.Comment: 13 pages, 5 figures accepted for publication in Phil. Trans. R. Soc.
Relevance of the weak equivalence principle and experiments to test it: lessons from the past and improvements expected in space
Tests of the Weak Equivalence Principle (WEP) probe the foundations of
physics. Ever since Galileo in the early 1600s, WEP tests have attracted some
of the best experimentalists of any time. Progress has come in bursts, each
stimulated by the introduction of a new technique: the torsion balance, signal
modulation by Earth rotation, the rotating torsion balance. Tests for various
materials in the field of the Earth and the Sun have found no violation to the
level of about 1 part in 1e13. A different technique, Lunar Laser Ranging
(LLR), has reached comparable precision. Today, both laboratory tests and LLR
have reached a point when improving by a factor of 10 is extremely hard. The
promise of another quantum leap in precision rests on experiments performed in
low Earth orbit. The Microscope satellite, launched in April 2016 and currently
taking data, aims to test WEP in the field of Earth to 1e-15, a 100-fold
improvement possible thanks to a driving signal in orbit almost 500 times
stronger than for torsion balances on ground. The `Galileo Galilei' (GG)
experiment, by combining the advantages of space with those of the rotating
torsion balance, aims at a WEP test 100 times more precise than Microscope, to
1e-17. A quantitative comparison of the key issues in the two experiments is
presented, along with recent experimental measurements relevant for GG. Early
results from Microscope, reported at a conference in March 2017, show
measurement performance close to the expectations and confirm the key role of
rotation with the advantage (unique to space) of rotating the whole spacecraft.
Any non-null result from Microscope would be a major discovery and call for
urgent confirmation; with 100 times better precision GG could settle the matter
and provide a deeper probe of the foundations of physics.Comment: To appear: Physics Letters A, special issue in memory of Professor
Vladimir Braginsky, 2017. Available online:
http://dx.doi.org/10.1016/j.physleta.2017.09.02
- …