Invasion percolation solves Fermi Paradox but challenges SETI projects

Galera, E.; Galanti, Giorgio; Kinouchi, Osame

doi:10.1017/s1473550418000101

Cited by 10 publications

(8 citation statements)

References 24 publications

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“…Additional work has been performed by Landis (1998), who included maximum probe range in his percolation model and had some settlements permanently cease sending out probes. Kinouchi (2001) used an analogy to the large number of uninhabited portions of the Earth to derive a simple model for the "persistence" of uninhabited regions of the Galaxy, a model with Galera et al (2018) refined and expanded. Bjørk (2007) and Hair & Hedman (2013) performed numerical calculations in a 3D grid of stars representative of the Galaxy.…”

Section: Introductionmentioning

confidence: 99%

The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion, and Steady States

Carroll-Nellenback

Frank

Wright

et al. 2019

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We model the settlement of the galaxy by space-faring civilizations in order to address issues related to the Fermi Paradox. We are motivated to explore the problem in a way that avoids assumptions about the 'agency' (i.e. questions of intent and motivation) of any exo-civilization seeking to settle other planetary systems. We begin by considering the speed of an advancing settlement front to determine if the galaxy can become inhabited with space-faring civilizations on timescales shorter than its age. Our models for the front speed include the directed settlement of nearby settleable systems through the launching of probes with a finite velocity and range. We also include the effect of stellar motions on the long term behavior of the settlement front which adds a diffusive component to its advance. As part of our model we also consider that only a fraction f of planets will have conditions amenable to settlement by the space-faring civilization. The results of these models demonstrate that the Milky Way can be readily 'filled-in' with settled stellar systems under conservative assumptions about interstellar spacecraft velocities and launch rates. We then move on to consider the question of the galactic steady-state achieved in terms of the fraction X of settled planets. We do this by considering the effect of finite settlement civilization lifetimes on the steady states. We find a range of parameters for which 0 < X < 1 i.e. the galaxy supports a population of interstellar space-faring civilizations even though some settleable systems are uninhabited. In addition we find that statistical fluctuations can produce local over-abundances of settleable worlds. These generate long-lived clusters of settled systems immersed in large regions which remain unsettled. Both results point to ways in which Earth might remain unvisited in the midst of an inhabited galaxy. Finally we consider how our results can be combined with the finite horizon for evidence of previous settlements in Earth's geologic record. Using our steady-state model we constrain the probabilities for an Earth visit by a settling civilization before a given time horizon. These results break the link between Hart's famous "Fact A" (no interstellar visitors on Earth now) and the conclusion that humans must, therefore, be the only technological civilization in the galaxy. Explicitly, our solutions admit situations where our current circumstances are consistent with an otherwise settled, steady-state galaxy.

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Section: Introductionmentioning

confidence: 99%

The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion, and Steady States

Carroll-Nellenback

Frank

Wright

et al. 2019

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“…This analysis supports the idea that, in order to increase the possibilities of a contact, more active strategies of the emitter would be required. Some proposals in this direction include interstellar exploration, colonization and settlement (Brin 1983; Došović et al 2019; Galera et al 2019), although it would require large temporal scales. Došović et al (2019) use probabilistic cellular automaton simulations to explore the parameter space of a model with colonization and catastrophic events.…”

Section: Discussionmentioning

confidence: 99%

Monte Carlo estimation of the probability of causal contacts between communicating civilizations

Lares

Funes

Gramajo

2020

International Journal of Astrobiology

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In this work we address the problem of estimating the probabilities of causal contacts between civilizations in the Galaxy. We make no assumptions regarding the origin and evolution of intelligent life. We simply assume a network of causally connected nodes. These nodes refer somehow to intelligent agents with the capacity of receiving and emitting electromagnetic signals. Here we present a three-parametric statistical Monte Carlo model of the network in a simplified sketch of the Galaxy. Our goal, using Monte Carlo simulations, is to explore the parameter space and analyse the probabilities of causal contacts. We find that the odds to make a contact over decades of monitoring are low for most models, except for those of a galaxy densely populated with long-standing civilizations. We also find that the probability of causal contacts increases with the lifetime of civilizations more significantly than with the number of active civilizations. We show that the maximum probability of making a contact occurs when a civilization discovers the required communication technology.

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“…In astrobiology, the use of probabilistic cellular automata (PCA) models was pioneered by Vukotić and Ćirković (2012), and followed by Hair and Hedman (2014). Galera et al (2019), recently, built a model based on an earlier study by Kinouchi (2001). Djošović et al (2019) have also explored the relationship between spreading life and catastrophic processes in a similar discrete model.…”

Section: Introductionmentioning

confidence: 99%

On possible life-dispersal patterns beyond the Earth

Kovacevic

2022

Preprint

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The assumption that exoplanets are ' in equilibrium' with their surroundings has not given way to life's transmissivity on large spatial scales. The spread of human diseases and the life recovery rate after mass extinctions on our planet, on the other hand, may exhibit spatial and temporal scaling as well as distribution correlations that influence the mappable range of their characteristics. We model hypothetical bio-dispersal within a single Galactic region using the stochastic infection dynamics process, which is inspired by these local properties of life dispersal on Earth. We split the population of stellar systems into different categories regarding habitability and evolved them through time using probabilistic cellular automata rules analogous to the model. As a dynamic effect, we include the existence of natural dispersal vectors (e.g., dust, asteroids) in a way that avoids assumptions about their agency (i.e., questions of existence). Moreover, by assuming that dispersal vectors have a finite velocity and range, the model includes the parameter of 'optical depth of life spreading'. The effect of the oscillatory infection rate (b(t, d)) on the long-term behavior of the dispersal flux, which adds a diffusive component to its progression, is also taken into account. The life recovery rate (g(t, d)) was only included in the model as a link to macrofaunal diversity data, which shows that all mass extinctions have a 10-Myr 'speed rate' in diversity recovery. This parameter accounts for the repopulation of empty viable niches as well as the formation of new ones, without ruling out the possibility of genuine life reemergence on other habitable worlds in the Galaxy that colossal extinctions have sterilized. All life-transmission events within the Galactic patch have thus been mapped into phase space characterized by parameters b and g. We found that phase space is separated into subregions of long-lasting transmission, rapidly terminated transmission, and a transition region between the two. We observed that depending on the amplitude of the oscillatory life spreading rate, life-transmission in the Galactic patch might take on different geometrical shapes (i.e., 'waves'). Even if some host systems are uninhabited, life transmission has a certain threshold, allowing a patch to be saturated with viable material over a long period. Although stochastic fluctuations in the local density of habitable systems allow for clusters that can continuously infect one another, the spatial pattern disappears when life transmission is below the observed threshold, so that transmission process is not permanent in time. Both findings suggest that a habitable planet in a densely populated region may remain uninfected.

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Invasion percolation solves Fermi Paradox but challenges SETI projects

Cited by 10 publications

References 24 publications

The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion, and Steady States

The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion, and Steady States

Monte Carlo estimation of the probability of causal contacts between communicating civilizations

On possible life-dispersal patterns beyond the Earth

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