9,449 research outputs found
The Anthropic Argument against Infinite Past and the Eddington-Lemaitre Universe
This study in the philosophy of cosmology is a part of an ongoing effort to
investigate and reassess the importance of the anthropic (Davies-Tipler)
argument against cosmologies containing the past temporal infinity. Obviously,
the prime targets of this argument are cosmological models stationary on
sufficiently large scale, the classical steady state model of Bondi, Gold and
Hoyle being the best example. Here we investigate the extension of application
of this argument to infinitely old non-stationary models and discuss additional
constraints necessary to be imposed on such models for the edge of the
anthropic argument to be preserved. An illustrative counterexample is the
classical Eddington-Lemaitre model, in the analysis of which major such
constraints are presented. Consequences of such an approach for our
understanding of the nature of time are briefly discussed.Comment: 7 pages, no figure
The Anthropic Principle and the Duration of the Cosmological Past
The place of an anthropic argument in the discrimination between various
cosmological models is to be reconsidered following the classic criticisms of
Paul C. W. Davies and Frank J. Tipler. Different versions of the anthropic
argument against cosmologies involving an infinite series of past events are
analyzed and applied to several instructive instances. This is not only of
historical significance but presents an important topic for the future of
cosmological research if some of the contemporary inflationary models,
particularly Linde's chaotic inflation, turn out to be correct. Cognitive
importance of the anthropic principle(s) to the issue of extraterrestrial
intelligent observers is reconsidered in this light and several related
problems facing cosmologies with past temporal infinities are also clearly
defined. This issue is not only a clear example of the epistemological
significance of the anthropic principle, but also has consequences for such
diverse topics as SETI studies, epistemological status of cosmological
concepts, theory of observation selection effects, and history of astronomy.Comment: 45 pages, 1 figur
On the First Anthropic Argument in Astrobiology
We consider the little-known anthropic argument of Fontenelle dealing with
the nature of cometary orbits, given a year before the publication of Newton's
Principia. This is particularly interesting in view of the rapid development of
the recently resurgent theories of cometary catastrophism and their role in the
modern astrobiological debates, for instance in the "rare Earth" hypothesis of
Ward and Brownlee.Comment: 16 pages, 2 figures, submitted to "Earth, Moon, and Planets
Is Quantum Suicide Painless? On an Apparent Violation of The Principal Principle
The experimental setup of the self-referential quantum measurement, jovially
known as the "quantum suicide" or the "quantum Russian roulette" is analyzed
from the point of view of the Principal Principle of David Lewis. It is shown
that the apparent violation of this principle--relating objective probabilities
and subjective chance--in this type of thought experiment is just an illusion
due to the usage of some terms and concepts ill-defined in the quantum context.
We conclude that even in the case that Everett's (or some other "no-collapse")
theory is a correct description of reality, we can coherently believe in
equating subjective credence with objective chance in quantum-mechanical
experiments. This is in agreement with results of the research on personal
identity in the quantum context by Parfit and Tappenden.Comment: 9 page
Stability of the Protogalactic Clouds: I. Field Length in the Adiabatic Models
All gasdynamical models for the evolution of gaseous content of galaxies
assume that cooling from the hot, virialized phase to the cold phase occured
through some sort of thermal instability. Subsequent formation of colder clouds
embedded in the hot, rarefied medium is a well-known process appearing in many
astrophysical circumstances and environments. The characteristics of the
condensed clouds depend on the relevant timescales for cloud formation and
disruption due to either collisions or one of the operating instabilities. In
this paper, the importance of the Kelvin-Helmholtz instability is investigated
for the clouds forming in huge gaseous haloes of galaxies. Recent
treatment of this problem by Kamaya (1997) is extended and a more realistic
cooling function employed. Results show that the Kelvin-Helmholtz instability
proceeds effectively on the same timescale whether we account for self-gravity
or not. This has multiple significance, since these objects may have been seen
as high-column density absorption line systems against the background QSOs, and
probably represent the progenitors of the present-day globular clusters.Comment: 7 pages, 2 figures, Latex (uses psfig.sty
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