2,078 research outputs found
Measurement Theory and General Relativity
The theory of measurement is employed to elucidate the physical basis of
general relativity. For measurements involving phenomena with intrinsic length
or time scales, such scales must in general be negligible compared to the
(translational and rotational) scales characteristic of the motion of the
observer. Thus general relativity is a consistent theory of coincidences so
long as these involve classical point particles and electromagnetic rays
(geometric optics). Wave optics is discussed and the limitations of the
standard theory in this regime are pointed out. A nonlocal theory of
accelerated observers is briefly described that is consistent with observation
and excludes the possibility of existence of a fundamental scalar field in
nature.Comment: LaTeX springer style lamu.cls, 2 figures, 16 pages, published in:
Black Holes: Theory and Observation: Proceedings of the 179th W.E. Heraeus
Seminar, held August 1997 in Bad Honnef, Germany. F.W. Hehl et al.(eds).
(Springer, Berlin Heidelberg 1998
Wetland mapping from digitized aerial photography
Computer assisted interpretation of small scale aerial imagery was found to be a cost effective and accurate method of mapping complex vegetation patterns if high resolution information is desired. This type of technique is suited for problems such as monitoring changes in species composition due to environmental factors and is a feasible method of monitoring and mapping large areas of wetlands. The technique has the added advantage of being in a computer compatible form which can be transformed into any georeference system of interest
Effect of aggregation on chromophore structure in allophycocyanin studied by resonance CARS-spectroscopy
Evaluation of the application of ERTS-1 data to the regional land use planning process
The author has identified the following significant results. Employing simple and economical extraction methods, ERTS can provide valuable data to the planners at the state or regional level with a frequency never before possible. Interactive computer methods of working directly with ERTS digital information show much promise for providing land use information at a more specific level, since the data format production rate of ERTS justifies improved methods of analysis
Quantum state of the multiverse
A third quantization formalism is applied to a simplified multiverse
scenario. A well defined quantum state of the multiverse is obtained which
agrees with standard boundary condition proposals. These states are found to be
squeezed, and related to accelerating universes: they share similar properties
to those obtained previously by Grishchuk and Siderov. We also comment on
related works that have criticized the third quantization approach.Comment: 15 pages, 2 figure
Topology, Decoherence, and Semiclassical Gravity
We address the issue of recovering the time-dependent Schr\"{o}dinger
equation from quantum gravity in a natural way. To reach this aim it is
necessary to understand the nonoccurrence of certain superpositions in quantum
gravity.
We explore various possible explanations and their relation. These are the
delocalisation of interference terms through interaction with irrelevant
degrees of freedom (decoherence), gravitational anomalies, and the possibility
of states. The discussion is carried out in both the geometrodynamical
and connection representation of canonical quantum gravity.Comment: 18 pages, ZU-TH 3/93, to appear in Phys. Rev.
Semiclassical Black Hole States and Entropy
We discuss semiclassical states in quantum gravity corresponding to
Schwarzschild as well as Reissner Nordstr\"om black holes. We show that reduced
quantisation of these models is equivalent to Wheeler-DeWitt quantisation with
a particular factor ordering. We then demonstrate how the entropy of black
holes can be consistently calculated from these states. While this leads to the
Bekenstein-Hawking entropy in the Schwarzschild and non-extreme
Reissner-Nordstr\"om cases, the entropy for the extreme Reissner-Nordstr\"om
case turns out to be zero.Comment: Revtex, 15 pages, some clarifying comments and additional references
included, to appear in Phys. Rev.
On the Decoherence of Primordial Fluctuations During Inflation
We study the process whereby quantum cosmological perturbations become
classical within inflationary cosmology. By setting up a master-equation
formulation we show how quantum coherence for super-Hubble modes can be
destroyed by their coupling to the environment provided by sub-Hubble modes. We
identify what features the sub-Hubble environment must have in order to
decohere the longer wavelengths, and identify how the onset of decoherence (and
how long it takes) depends on the properties of the sub-Hubble physics which
forms the environment. Our results show that the decoherence process is largely
insensitive to the details of the coupling between the sub- and super-Hubble
scales. They also show how locality implies, quite generally, that the
decohered density matrix at late times is diagonal in the field representation
(as is implicitly assumed by extant calculations of inflationary density
perturbations). Our calculations also imply that decoherence can arise even for
couplings which are as weak as gravitational in strength.Comment: 31 pages, 1 figur
Issues In Space Radiation Protection: Galactic Cosmic Rays
When shielding from cosmic heavy ions, one is faced with limited knowledge about the physical properties and biological responses of these radiations. Herein, the current health is discussed in terms of conventional protection practice and a test biological response model. The impact of biological response on optimum materials selection for cosmic ray shielding is presented in terms of the transmission characteristics of the shield material. Although liquid hydrogen is an optimum shield material, evaluation of the effectiveness of polymeric structural materials must await improvement in our knowledge of both the biological response and the nuclear processes
Bianchi type I cyclic cosmology from Lie-algebraically deformed phase space
We study the effects of noncommutativity, in the form of a Lie-algebraically
deformed Poisson commutation relations, on the evolution of a Bianchi type I
cosmological model with a positive cosmological constant. The phase space
variables turn out to correspond to the scale factors of this model in ,
and directions. According to the conditions that the structure constants
(deformation parameters) should satisfy, we argue that there are two types of
noncommutative phase space with Lie-algebraic structure. The exact classical
solutions in commutative and type I noncommutative cases are presented. In the
framework of this type of deformed phase space, we investigate the possibility
of building a Bianchi I model with cyclic scale factors in which the size of
the universe in each direction experiences an endless sequence of contractions
and re-expansions. We also obtain some approximate solutions for the type II
noncommutative structure by numerical methods and show that the cyclic behavior
is repeated as well. These results are compared with the standard commutative
case, and similarities and differences of these solutions are discussed.Comment: 13 pages, to appear in PRD, typos corrected, Refs. adde
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