scholarly journals Long-term implications of observing an expanding cosmological civilization

2017 ◽  
Vol 17 (1) ◽  
pp. 87-95 ◽  
Author(s):  
S. Jay Olson
Keyword(s):  
Angular Separation ◽  
Separation Distance ◽  
Speed Limit ◽  
Single Observation ◽  
Cosmic Expansion ◽  
Cosmological Distance ◽  
First Mover Advantage ◽  
Expansion Speed ◽  
The Universe

AbstractSuppose that advanced civilizations, separated by a cosmological distance and time, wish to maximize their access to cosmic resources by rapidly expanding into the universe. How does the presence of one limit the expansionistic ambitions of another, and what sort of boundary forms between their expanding domains? We describe a general scenario for any expansion speed, separation distance and time. We then specialize to a question of particular interest: What are the future prospects for a young and ambitious civilization if they can observe the presence of another at a cosmological distance? We treat cases involving the observation of one or two expanding domains. In the single-observation case, we find that almost any plausible detection will limit one's future cosmic expansion to some extent. Also, practical technological limits to expansion speed (well below the speed of light) play an interesting role. If a domain is visible at the time one embarks on cosmic expansion, higher practical limits to expansion speed are beneficial only up to a certain point. Beyond this point, a higher speed limit means that gains in the ability to expand are more than offset by the first-mover advantage of the observed domain. In the case of two visible domains, it is possible to be ‘trapped’ by them if the practical speed limit is high enough and their angular separation in the sky is large enough, i.e. one's expansion in any direction will terminate at a boundary with the two visible civilizations. Detection at an extreme cosmological distance has surprisingly little mitigating effect on our conclusions.

The long-term future of the universe

1979 ◽  
Vol 23 ◽  
pp. 265-277 ◽  
Author(s):  
Jamal N. Islam
Keyword(s):  
The Universe

Methods to Reduce Traffic Speed in High-Pedestrian Rural Areas

2003 ◽  
Vol 1828 (1) ◽  
pp. 31-37 ◽  
Author(s):  
Ali Kamyab ◽  
Steve Andrle ◽  
Dennis Kroeger ◽  
David S. Heyer
Keyword(s):  
Rural Areas ◽  
Speed Limit ◽  
Single Word ◽  
Short Term ◽  
Speed Reduction ◽  
Traffic Calming ◽  
Reduction Strategies ◽  
Long Term Impact ◽  
The Impact

Many Minnesota counties are faced with the problem of high vehicle speeds through towns or resort areas that have significant pedestrian traffic. The impact of speed reduction strategies in high-pedestrian areas in rural counties of Minnesota was investigated. Speed data were collected at two selected study sites under their existing conditions ("no-treatment" or "before" condition) and after the proposed speed reduction strategies were installed. Second "after" data conditions were collected to study the short-term and long-term impact of the implemented strategies. The traffic-calming techniques employed at the Twin Lakes site consisted of removable pedestrian islands and pedestrian crossing signs. A dynamic variable message sign that sent a single-word message ("Slow") to motorists traveling over the speed limit was installed at the Bemidji site. The research study shows that the traffic-calming strategy deployed in Twin Lakes was effective in significantly reducing the mean speed and improving speed limit compliance in both the short term and long term. Despite proven effectiveness, the deployed speed reduction treatment in Bemidji Lake failed to lower the speed at the study site. The single-word message on the sign and the location of the sign, as well as a lack of initial enforcement, were the primary reasons for such failure.

scholarly journals Can accelerated expansion of the universe be due to spacetime vorticity?

2018 ◽  
Vol 33 (40) ◽  
pp. 1850240
Author(s):  
Babur M. Mirza
Keyword(s):  
Magnetic Field ◽  
Accelerated Expansion ◽  
Newtonian Gravity ◽  
Hubble’S Parameter ◽  
Cosmic Expansion ◽  
Zero Curvature ◽  
Expansion Of The Universe ◽  
General Relativistic ◽  
The Universe ◽  
The Magnetic Field

We present here a general relativistic mechanism for accelerated cosmic expansion and the Hubble’s parameter. It is shown that spacetime vorticity coupled to the magnetic field density in galaxies causes the galaxies to recede from one another at a rate equal to the Hubble’s constant. We therefore predict an oscillatory universe, with zero curvature, without assuming violation of Newtonian gravity at large distances or invoking dark energy/dark matter hypotheses. The value of the Hubble’s constant, along with the scale of expansion, as well as the high isotropy of CMB radiation are deduced from the model.

Cosmology: evidence for a ‘big bang’

1994 ◽  
Vol 2 (2) ◽  
pp. 155-164
Author(s):  
Martin J. Rees
Keyword(s):  
Present State ◽  
Background Radiation ◽  
Cosmic Background Radiation ◽  
Big Bang ◽  
Fundamental Physics ◽  
Cosmic Expansion ◽  
Cosmic Background ◽  
The Universe

During the last 25 years, evidence has accumulated that our universe has evolved, over a period of 10–15 billion years, from a hot dense fireball to its present state. Telescopes can detect objects so far away that the universe had only a tenth its present age when the light we now receive set out towards us. The cosmic background radiation, and the abundances of elements such as helium and lithium, permit quantitative inferences about what the universe was like when it had been expanding for only a few seconds. The laws of physics established in the laboratory apparently suffice for interpreting all astronomical phenomena back to that time. In the initial instants of cosmic expansion, however, the particle energies and densities were so extreme that terrestrial experiments offer no firm guidance. We will not understand why the universe contains the observed ‘mix’ of matter and radiation, nor why it is expanding in the observed fashion, without further progress in fundamental physics.

scholarly journals Comment on “Hubble flow variations as a test for inhomogeneous cosmology”

2019 ◽  
Vol 624 ◽  
pp. A12
Author(s):  
David L. Wiltshire
Keyword(s):  
Alternative Model ◽  
Inhomogeneous Cosmology ◽  
Cosmic Expansion ◽  
Standard Cosmology ◽  
Geometrical Features ◽  
Expansion Of The Universe ◽  
Expansion Model ◽  
Differential Expansion ◽  
The Universe ◽  
Hubble Flow

Saulder et al. (2019, A&A, 622, A83) have performed a novel observational test of the local expansion of the Universe for the standard cosmology as compared to an alternative model with differential cosmic expansion. Their analysis employs mock galaxy samples from the Millennium Simulation, a Newtonian N–body simulation on a ΛCDM background. For the differential expansion case the simulation has been deformed in an attempt to incorporate features of a particular inhomogeneous cosmology: the timescape model. It is shown that key geometrical features of the timescape cosmology have been omitted in this rescaling. Consequently, the differential expansion model tested by Saulder et al. (2019) cannot be considered to approximate the timescape cosmology.

Measurement Requirements for Climate Monitoring of Upper-Air Temperature Derived from Reanalysis Data

2006 ◽  
Vol 19 (5) ◽  
pp. 854-871 ◽  
Author(s):  
Dian J. Seidel ◽  
Melissa Free
Keyword(s):  
Air Temperature ◽  
Statistical Tests ◽  
Reanalysis Data ◽  
Climatic Data ◽  
Single Observation ◽  
Half Century ◽  
Climate Monitoring ◽  
System Requirements ◽  
Incomplete Sampling

Abstract Using a reanalysis of the climate of the past half century as a model of temperature variations over the next half century, tests of various data collection protocols are made to develop recommendations for observing system requirements for monitoring upper-air temperature. The analysis focuses on accurately estimating monthly climatic data (specifically, monthly average temperature and its standard deviation) and multidecadal trends in monthly temperatures at specified locations, from the surface to 30 hPa. It does not address upper-air network size or station location issues. The effects of reducing the precision of temperature data, incomplete sampling of the diurnal cycle, incomplete sampling of the days of the month, imperfect long-term stability of the observations, and changes in observation schedule are assessed. To ensure accurate monthly climate statistics, observations with at least 0.5-K precision, made at least twice daily, at least once every two or three days are sufficient. Using these same criteria, and maintaining long-term measurement stability to within 0.25 (0.1) K, for periods of 20 to 50 yr, errors in trend estimates can be avoided in at least 90% (95%) of cases. In practical terms, this requires no more than one intervention (e.g., instrument change) over the period of record, and its effect must be to change the measurement bias by no more than 0.25 (0.1) K. The effect of the first intervention dominates the effects of subsequent, uncorrelated interventions. Changes in observation schedule also affect trend estimates. Reducing the number of observations per day, or changing the timing of a single observation per day, has a greater potential to produce errors in trends than reducing the number of days per month on which observations are made. These findings depend on the validity of using reanalysis data to approximate the statistical nature of future climate variations, and on the statistical tests employed. However, the results are based on conservative assumptions, so that adopting observing system requirements based on this analysis should result in a data archive that will meet climate monitoring needs over the next 50 yr.

scholarly journals COSMIC ACCELERATION AND CONCORDANCE FROM CAUSAL BACKREACTION WITH RECURSIVE NONLINEARITIES

2013 ◽  
Vol 22 (13) ◽  
pp. 1330026 ◽  
Author(s):  
BRETT BOCHNER
Keyword(s):  
Dark Energy ◽  
Large Scale ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Clustering Model ◽  
Hierarchical Nature ◽  
The Universe ◽  
Far Future ◽  
Apparent Acceleration

We review the causal backreaction paradigm, in which the need for Dark Energy is eliminated via the generation of an apparent cosmic acceleration from the causal flow of inhomogeneity information coming in from distant structure-forming regions. The formalism detailed here incorporates the effects of "recursive nonlinearities": the process by which already-established metric perturbations will subsequently act to slow-down all future flows of inhomogeneity information. Despite such effects, we find viable cosmological models in which causal backreaction successfully serves as a replacement for Dark Energy, via the adoption of relatively large values for the dimensionless "strength" of the clustering evolution functions being modeled. These large values are justified by the hierarchical nature of clustering and virialization in the universe, which occurs on multiple cosmic length scales simultaneously; moreover, the clustering model amplitudes needed to match the apparent acceleration can be moderated via the incorporation of a model parameter representing the late-time slow-down of clustering due to astrophysical feedback processes. In summary, an alternative cosmic concordance can be achieved for a matter-only universe in which the apparent acceleration observed is generated entirely by causal backreaction effects. Lastly, considering the long-term fate of the universe, while the possibility of an "eternal" acceleration due to causal backreaction seems unlikely, this conclusion does not take into account the large-scale breakdown of cosmological isotropy in the far future, or the eventual ubiquity of gravitationally-nonlinear perturbations.

Pulsar timing and relativistic gravity

1992 ◽  
Vol 341 (1660) ◽  
pp. 117-134 ◽  
Keyword(s):  
Gravitational Waves ◽  
Binary Systems ◽  
Strong Field ◽  
Low Frequency ◽  
Rate Of Change ◽  
Pulsar Timing ◽  
Basic Physics ◽  
Time Standards ◽  
The Universe

In addition to being fascinating objects to study in their own right, pulsars are exquisite tools for probing a variety of issues in basic physics. Recycled pulsars, thought to have been spun up in previous episodes of mass accretion from orbiting companion stars, are especially well suited for such applications. They are extraordinarily stable clocks, approaching and perhaps exceeding the long-term stabilities of the best terrestrial time standards. Most of them are found in binary systems, with orbital velocities as large as 10 -3 c. They provide unique opportunities for measuring neutron star masses, thereby yielding fundamental astrophysical data difficult to acquire by any other means. And they open the way for high precision tests of the nature of gravity under conditions much more ‘relativistic ’ than found anywhere within the Solar System. Among other results, pulsar timing observations have convincingly established the existence of quadrupolar gravitational waves propagating at the speed of light. They have also placed interesting limits on possible departures of the strong-field nature of gravity from general relativity, on the rate of change of Newton’s constant, G , and on the energy density of low-frequency gravitational waves in the universe.

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