208 research outputs found
Penrose Diagram for a Transient Black Hole
A Penrose diagram is constructed for a spatially coherent black hole that
smoothly begins an accretion, then excretes symmetrically as measured by a
distant observer, with the initial and final states described by a metric of
Minkowski form. Coordinate curves on the diagram are computationally derived.
Causal relationships between space-time regions are briefly discussed. The life
cycle of the black hole demonstrably leaves asymptotic observers in an
unaltered Minkowski space-time of uniform conformal scale.Comment: 14 pages, 9 figures, spelling correction
Self-consistent solutions of canonical proper self-gravitating quantum systems
Generic self-gravitating quantum solutions that are not critically dependent
on the specifics of microscopic interactions are presented. The solutions
incorporate curvature effects, are consistent with the universality of gravity,
and have appropriate correspondence with Newtonian gravitation. The results are
consistent with known experimental results that indicate the maintenance of the
quantum coherence of gravitating systems, as expected through the equivalence
principle.Comment: 13 pages, 7 figure
Black Hole - Never Forms, or Never Evaporates
Many discussion about the black hole conundrums, such as singularity and
information loss, suggested that there must be some essential irreconcilable
conflict between quantum theory and classical gravity theory, which cannot be
solved with any semiclassical quantized model of gravity, the only feasible way
must be some complete unified quantum theory of gravity.
In \cite{Vachaspati2007a}, the arguments indicate the possibility of an
alternate outcome of gravitational collapse which avoids the information loss
problem. In this paper, also with semiclassical analysis, it shows that so long
as the mechanism of black hole evaporation satisfies a quite loose condition
that the evaporation lifespan is finite for external observers, regardless of
the detailed mechanism and process of evaporation, the conundrums above can be
naturally avoided. This condition can be satisfied with Hawking-Unruh
mechanism. Thus, the conflict between quantum theory and classical gravity
theory may be not as serious as it seemed to be, the effectiveness of
semiclassical methods might be underestimated.
An exact universal solution with spherical symmetry of Einstein field
equation has been derived in this paper. All possible solutions with spherical
symmetry of Einstein field equation are its special cases.
In addition, some problems of the Penrose diagram of an evaporating black
hole first introduced by Hawking in 1975 \cite{Hawking1975} are clarified.Comment: 17 pages, 7 figures. Compared to the published version in JCAP, some
minimal typeset error has been correcte
The Classical Electron Problem
In this paper, we construct a parallel image of the conventional Maxwell theory by replacing the observer-time by the proper-time of the source. This formulation is mathematically, but not physically, equivalent to the conventional form. The change induces a new symmetry group which is distinct from, but closely related to the Lorentz group, and fixes the clock of the source for all observers. The new wave equation contains an additional term (dissipative), which arises instantaneously with acceleration. This shows that the origin of radiation reaction is not the action of a “charge” on itself but arises from inertial resistance to changes in motion. This dissipative term is equivalent to an effective mass so that classical radiation has both a massless and a massive part. Hence, at the local level the theory is one of particles and fields but there is no self-energy divergence (nor any of the other problems). We also show that, for any closed system of particles, there is a global inertial frame and unique (invariant) global proper-time (for each observer) from which to observe the system. This global clock is intrinsically related to the proper clocks of the individual particles and provides a unique definition of simultaneity for all events associated with the system. We suggest that this clock is the historical clock of Horwitz, Piron, and Fanchi. At this level, the theory is of the action-at-a-distance type and the absorption hypothesis of Wheeler and Feynman follows from global conservation of energy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44465/1/10701_2004_Article_346165.pd
Virtual discussions to support climate risk decision making on farms
Climate variability represents a significant risk to farming enterprises. Effective extension of climate information may improve climate risk decision making and adaptive management responses to climate variability on farms. This paper briefly reviews current agricultural extension approaches and reports stakeholder responses to new web-based virtual world ‘discussion-support’ tools developed for the Australian sugar cane farming industry. These tools incorporate current climate science and sugar industry better management practices, while leveraging the social-learning aspects of farming, to provide a stimulus for discussion and climate risk decision making. Responses suggest that such virtual world tools may provide effective support for climate risk decision making on Australian sugar cane farms. Increasing capacity to deliver such tools online also suggests potential to engage large numbers of farmers globally
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