Galactic gradients, postbiological evolution and the apparent failure of SETI

Abstract

Motivated by recent developments impacting our view of Fermi's paradox (absence of extraterrestrials and their manifestations from our past light cone), we suggest a reassessment of the problem itself, as well as of strategies employed by SETI projects so far. The need for such reevaluation is fueled not only by the failure of searches thus far, but also by great advances recently made in astrophysics, astrobiology, computer science and future studies, which have remained largely ignored in SETI practice. As an example of the new approach, we consider the effects of the observed metallicity and temperature gradients in the Milky Way on the spatial distribution of hypothetical advanced extraterrestrial intelligent communities. While, obviously, properties of such communities and their sociological and technological preferences are entirely unknown, we assume that (1) they operate in agreement with the known laws of physics, and (2) that at some point they typically become motivated by a meta-principle embodying the central role of information-processing; a prototype of the latter is the recently suggested Intelligence Principle of Steven J. Dick. There are specific conclusions of practical interest to astrobiological and SETI endeavors to be drawn from coupling of these reasonable assumptions with the astrophysical and astrochemical structure of the spiral disk of our Galaxy. In particular, we suggest that the outer regions of the Galactic disk are most likely locations for advanced SETI targets, and that sophisticated intelligent communities will tend to migrate outward through the Galaxy as their capacities of information-processing increase, for both thermodynamical and astrochemical reasons. However, the outward movement is limited by the decrease in matter density in the outer Milky Way. This can also be regarded as a possible generalization of the Galactic Habitable Zone, concept currently much investigated in astrobiology.

Astrobiological Complexity with Probabilistic Cellular Automata

“…Further improvement of boundary conditions can be implemented with including colonization by TCs of sites beyond the boundaries of GHZ (in particular the large volume beyond R out can be interesting for those advanced TCs motivated primarily by optimization criteria, Cirković and Bradbury 2006). An important extension of the present model would be incorporation of interstellar panspermia: the possibility of transfer of simple lifeforms (commonly envisaged in form of extremophiles of Bacteria or Archaea domains of life) from one planetary system to another.…”

“…11), demonstrates how this still seems acceptable within the "Copernican" framework, thus essentially confirming the conclusions of Landis (1998) and Kinouchi (2001), but with addition of catastrophic reset events. The downside of this is that one does not take into account the fact that at least some of the manifestations of advanced technological civilizations would be observable over large interstellar distances (e.g., Freitas 1985;Cirković and Bradbury 2006). More research will be necessary in order to quantify the conditions for such "Dysonian" approach to SETI (Dyson 1960;Sagan and Walker 1966;Carrigan 2009).…”

Application of the mid-IR radio correlation to the Ĝ sample and the search for advanced extraterrestrial civilisations

“…While Wright et al (2014a) venture that Type III civilisations should emerge rapidly from Type IIs, it might be that some specific galactic localities are preferred (see e.g. Cirkovic & Bradbury 2006) or are to be best avoided, e.g. the galactic centre.…”

Astrobiological Phase Transition: Towards Resolution of Fermi’s Paradox

“…It is enough for our purposes to consider that this timescale is well-defined, albeit not precisely known due to our ignorance on the possibilities and modes of interstellar travel. As discussed in more detail elsewhere (Ćirković and Bradbury 2006), there are reasons for finding Fermi's Paradox even more disturbing following recent results in astronomy, astrobiology, information theory and computer science. Particularly relevant is the result of Lineweaver (2001; see also Lineweaver et al 2004) that the difference between the median age of Earth-like planets in the Milky Way and the age of Earth is:…”