4,485 research outputs found
The Mass of the Gravitational Field
By mass-energy equivalence, the gravitational field has a relativistic mass
density proportional to its energy density. I seek to better understand this
mass of the gravitational field by asking whether it plays three traditional
roles of mass: the role in conservation of mass, the inertial role, and the
role as source for gravitation. The difficult case of general relativity is
compared to the more straightforward cases of Newtonian gravity and
electromagnetism by way of gravitoelectromagnetism, an intermediate theory of
gravity that resembles electromagnetism.Comment: 39 pages, 1 figur
Fast Gravitational Approach for Rigid Point Set Registration with Ordinary Differential Equations
This article introduces a new physics-based method for rigid point set
alignment called Fast Gravitational Approach (FGA). In FGA, the source and
target point sets are interpreted as rigid particle swarms with masses
interacting in a globally multiply-linked manner while moving in a simulated
gravitational force field. The optimal alignment is obtained by explicit
modeling of forces acting on the particles as well as their velocities and
displacements with second-order ordinary differential equations of motion.
Additional alignment cues (point-based or geometric features, and other
boundary conditions) can be integrated into FGA through particle masses. We
propose a smooth-particle mass function for point mass initialization, which
improves robustness to noise and structural discontinuities. To avoid
prohibitive quadratic complexity of all-to-all point interactions, we adapt a
Barnes-Hut tree for accelerated force computation and achieve quasilinear
computational complexity. We show that the new method class has characteristics
not found in previous alignment methods such as efficient handling of partial
overlaps, inhomogeneous point sampling densities, and coping with large point
clouds with reduced runtime compared to the state of the art. Experiments show
that our method performs on par with or outperforms all compared competing
non-deep-learning-based and general-purpose techniques (which do not assume the
availability of training data and a scene prior) in resolving transformations
for LiDAR data and gains state-of-the-art accuracy and speed when coping with
different types of data disturbances.Comment: 18 pages, 18 figures and two table
Report by the ESA-ESO Working Group on Fundamental Cosmology
ESO and ESA agreed to establish a number of Working Groups to explore
possible synergies between these two major European astronomical institutions.
This Working Group's mandate was to concentrate on fundamental questions in
cosmology, and the scope for tackling these in Europe over the next ~15 years.
One major resulting recommendation concerns the provision of new generations of
imaging survey, where the image quality and near-IR sensitivity that can be
attained only in space are naturally matched by ground-based imaging and
spectroscopy to yield massive datasets with well-understood photometric
redshifts (photo-z's). Such information is essential for a range of new
cosmological tests using gravitational lensing, large-scale structure, clusters
of galaxies, and supernovae. Great scope in future cosmology also exists for
ELT studies of the intergalactic medium and space-based studies of the CMB and
gravitational waves; here the synergy is less direct, but these areas will
remain of the highest mutual interest to the agencies. All these recommended
facilities will produce vast datasets of general applicability, which will have
a tremendous impact on broad areas of astronomy.Comment: ESA-ESO Working Groups Report No. 3, 125 pages, 28 figures. A PDF
version including the cover is available from
http://www.stecf.org/coordination/esa_eso/cosmology/report_cover.pdf and a
printed version (A5 booklet) is available in limited numbers from the Space
Telescope-European Coordinating Facility (ST-ECF): [email protected]
Space-based research in fundamental physics and quantum technologies
Space-based experiments today can uniquely address important questions
related to the fundamental laws of Nature. In particular, high-accuracy physics
experiments in space can test relativistic gravity and probe the physics beyond
the Standard Model; they can perform direct detection of gravitational waves
and are naturally suited for precision investigations in cosmology and
astroparticle physics. In addition, atomic physics has recently shown
substantial progress in the development of optical clocks and atom
interferometers. If placed in space, these instruments could turn into powerful
high-resolution quantum sensors greatly benefiting fundamental physics.
We discuss the current status of space-based research in fundamental physics,
its discovery potential, and its importance for modern science. We offer a set
of recommendations to be considered by the upcoming National Academy of
Sciences' Decadal Survey in Astronomy and Astrophysics. In our opinion, the
Decadal Survey should include space-based research in fundamental physics as
one of its focus areas. We recommend establishing an Astronomy and Astrophysics
Advisory Committee's interagency ``Fundamental Physics Task Force'' to assess
the status of both ground- and space-based efforts in the field, to identify
the most important objectives, and to suggest the best ways to organize the
work of several federal agencies involved. We also recommend establishing a new
NASA-led interagency program in fundamental physics that will consolidate new
technologies, prepare key instruments for future space missions, and build a
strong scientific and engineering community. Our goal is to expand NASA's
science objectives in space by including ``laboratory research in fundamental
physics'' as an element in agency's ongoing space research efforts.Comment: a white paper, revtex, 27 pages, updated bibliograph
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