The Galactic Club or Galactic Cliques? Exploring the limits of interstellar hegemony and the Zoo Hypothesis

Abstract

The Zoo solution to Fermi's Paradox proposes that extraterrestrial intelligences (ETIs) have agreed to not contact the Earth. The strength of this solution depends on the ability for ETIs to come to agreement, and establish/police treaties as part of a so-called "Galactic Club". These activities are principally limited by the causal connectivity of a civilisation to its neighbours at its inception, i.e. whether it comes to prominence being aware of other ETIs and any treaties or agreements in place.If even one civilisation is not causally connected to the other members of a treaty, then they are free to operate beyond it and contact the Earth if wished, which makes the Zoo solution "soft". We should therefore consider how likely this scenario is, as this will give us a sense of the Zoo solution's softness, or general validity.We implement a simple toy model of ETIs arising in a Galactic Habitable Zone, and calculate the properties of the groups of culturally connected civilisations established therein. We show that for most choices of civilisation parameters, the number of culturally connected groups is greater than 1, meaning that the Galaxy is composed of multiple Galactic Cliques rather than a single Galactic Club. We find in our models for a single Galactic Club to establish interstellar hegemony, the number of civilisations must be relatively large, the mean civilisation lifetime must be several millions of years, and the inter-arrival time between civilisations must be a few million years or less.

Exoplanet transits as the foundation of an interstellar communications network

“…Using transits as a means of communication may permit intended or unintended off-axis transmissions – in effect, a form of highly directed signal leakage. This may present a more effective means by which humans can scout the local interstellar volume for civilizations transmitting to each other and avoiding the Earth (see also Forgan & Nichol 2010; Forgan 2016).…”

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

“…Optimistic estimates from the Drake equation contrast with the so-called Fermi paradox, which states the apparent contradiction between the expected abundance of life in the Galaxy and the lack of evidence for it (e.g. Hart 1975;Brin 1983;Barlow 2013;Anchordoqui et al 2017;Forgan 2017;Carroll-Nellenback et al 2019;Sotos 2019). There are many propositions aimed at solving this paradox, which make use of statistical (Horvat 2006;Maccone 2015;Solomonides et al 2016) or stochastic approaches (Forgan 2009;Forgan and Rice 2010;Glade et al 2012;Bloetscher 2019).…”

“…On this topic a number of works consider numerical simulations (Forgan 2009(Forgan , 2017Murante et al 2015;Forgan et al 2016;Vukotić et al 2016;Ramirez et al 2017). Although this approach does not rely on values that can be measured from observations (like the fraction of stars with planets), it depends on the definition of unknown or uncertain parameters required to carry out the simulations.…”

“…The absence of detections of extraterrestrial intelligent signals could be explained by astrophysical phenomena that makes life difficult to develop (Annis 1999). Besides the possible scarcity of life, alternative scenarios have also been discussed (Barlow 2013; Lampton 2013; Forgan 2017; Conway Morris 2018). The large distances in the Galaxy and the likely limited lifetime of civilizations may play an important role in determining how difficult it would be to obtain evidence for other inhabited worlds.…”

Spaceflight from Super-Earths is difficult

“…Can‘Super-Earthlings’ still use chemical rockets to leave their planet? This question is relevant for the search for extraterrestrial intelligence (SETI) and space colonization (Lingam, 2016; Forgan, 2016, 2017 and Dutil and Dumas, 2010).…”