Galactic civilizations - Population dynamics and interstellar diffusion

  title={Galactic civilizations - Population dynamics and interstellar diffusion},
  author={W. I. Newman and C. Sagan},
Abstract The interstellar diffusion of galactic civilizations is reexamined by potential theory; both numerical and analytical solutions are derived for the nonlinear partial differential and difference equations which specify a range of relevant models, drawn from blast wave physics, soil science, and, especially, population biology. An essential feature of these models is that, for all civilizations, population growth must be limited by the carrying capacity of the planetary environments… Expand
Homogeneous cosmology with aggressively expanding civilizations
In the context of a homogeneous Universe, we note that the appearance of aggressively expanding advanced life is geometrically similar to the process of nucleation and bubble growth in a first-orderExpand
Interstellar Travel and Galactic Colonization: Insights from Percolation Theory and the Yule Process.
Percolation theory is employed to place tentative bounds on the probability p of interstellar travel and the emergence of a civilization (or panspermia) that colonizes the entire Galaxy and it is suggested that the correlation function of inhabited exoplanets can be used to observationally constrain p in the near future. Expand
Discrete calculations of interstellar migration and settlement
Abstract Monte Carlo calculations of the expansion of space-faring civilizations are presented for a wide range of values of the population growth coefficient (α) and emigration coefficient (γ). EvenExpand
The demography of extraterrestrial civilizations
Studies carried out within the last ten years on the nature and distribution of extraterrestrial intelligent life are reviewed. Arguments for the absence of intelligent life in the Galaxy based onExpand
Galactic Colonization and Competition in a Young Galactic Disk
Even if long-lived advanced technical civilizations arise very frequently and interstellar colonization is possible and common among them, it is argued that this colonization process is unlikely toExpand
Spatial dispersion of interstellar civilizations: a probabilistic site percolation model in three dimensions
Abstract A model of the spatial emergence of an interstellar civilization into a uniform distribution of habitable systems is presented. The process of emigration is modelled as a three-dimensionalExpand
Population growth, energy use, and the implications for the search for extraterrestrial intelligence
Abstract Von Hoerner (“Population Explosion and Interstellar Expansion,” Journal of the British Interplanetary Society, 28, 691–712, 1975; hereafter VH75) examined the effects of human populationExpand
On the visible size and geometry of aggressively expanding civilizations at cosmological distances
If a subset of advanced civilizations in the universe choose to rapidly expand into unoccupied space, these civilizations would have the opportunity to grow to a cosmological scale over the course ofExpand
Triggering A Climate Change Dominated"Anthropocene": Is It Common Among Exocivilizations?
We seek to model the coupled evolution of a planet and a civilization through the era when energy harvesting by the civilization drives the planet into new and adverse climate states. In this way weExpand
Nonlinear population dynamics in a bounded habitat.
This paper obtains, analytically, exact expressions of the critical habitat size Lc for population survival, as a function of the exponents and initial conditions, which generalizes the usual statement that Lc represents the minimum habitat size. Expand


Abstract An estimate of the number of advanced technical civilizations on planets of other stars depends on our knowledge of the rate of star formation; the frequency of favorably situated planets ;Expand
On the detectivity of advanced galactic civilizations
Abstract Even with slow rates of technological advance, extraterrestrial civilizations substantially in our future will have technologies and laws of nature currently inaccessible to us, and willExpand
Random dispersal in theoretical populations.
The random-walk problem is adopted as a starting point for the analytical study of dispersal in living organisms. The solution is used as a basis for the study of the expanson of a growingExpand
Random dispersal in theoretical populations.
The random-walk problem is adopted as a starting point for the analytical study of dispersal in living organisms and the law of diffusion is deduced and applied to the understanding of the spatial distribution of population density in both linear and two-dimensional habitats. Expand
Spatial Heterogeneity and Population Stability
THE ability of populations to absorb perturbations is often investigated theoretically by some variant on the prey-predator, Lotka–Volterra, equations. Usually the treatment is in terms of linearisedExpand
On the diffusion of biological populations
Abstract This paper develops a model for the spatial diffusion of biological populations. Arguments are given in support of a degenerate, non-linear partial differential equation for the populationExpand
Computer simulations of planetary accretion dynamics: sensitivity to initial conditions. [Implications and limitations of ACRETE]
The implications and limitations of program ACRETE were tested. The program is a scheme based on Newtonian physics and accretion with unit sticking efficiency, devised to simulate the origin of theExpand
Computer simulation of the formation of planetary systems
Abstract One of the many hypotheses about the formation of the solar system postulates that the planets were formed by the aggregation of particulate matter within a cloud of dust and gas surroundingExpand
Habitable zones about main sequence stars
Abstract Calculations show that a main sequence star which is less massive than the Sun has a continuously habitable zone about it which is not only closer in than the corresponding zone about theExpand
Cosmic conclusions from climatic models: Can they be justified?
Abstract Climatic models are increasingly being used to answer “cosmic questions” such as the possibility of an ice-covered Earth or a runaway greenhouse effect, or to examine the coevolution ofExpand