A Numerical Testbed for Hypotheses of Extraterrestrial Life and Intelligence

[0810.2222] A Numerical Testbed for Hypotheses of Extraterrestrial Life and Intelligence.

The study in question by Duncan Forgan. It uses pretty standard assumptions based on Panspermia, Habitable Zones (Stellar & Galactic), plus some stochastic guesstimation of the emergence and fate of ETIs. Even assuming they last as long as their stars once they spread to all the planets of their system, there aren’t too many in the Galaxy.

Of course the question then is: what happens if They proceed to colonize other systems?

At “The Habitable Zone” a Belgian amateur astronomer, Raoul Lannoy, frequently gives us space-optimists a space-pessimist take on things. Recently Raoul brought up a Space Review piece on mass colonization of space – i.e. billions leaving Earth to inhabit the rest of the Solar System and beyond. Mark Eby had this to say… Mark’s response …essentially that in human history small bands of intrepid wanderers have been the ones to spread far and wide, beyond the ancestral range.

Unless a star-system is being evacuated then mass colonization seems rather more difficult than it is worth. As independent New Beginnings for the human race, Star Colonies would have great practical and symbolic value, helping preserve humanity against system-scale collapses from whatever cause might destroy a system. Spread across the Galaxy our species would seem protected against the largest known energetic events in the Universe… except, so far spread, we wouldn’t remain the same species for very long in cosmic terms. We’d undergo divergent evolution, unless a deliberate policy of genetic mixing was pursued. Even more rapid divergence would occur if the pioneers were those posited small bands – the so-called Founder Effect
would result in rapid fixation of any new alleles and genes while the effective population was small. Each new band settling into a different system would be a species divergence point unless more colonists followed.

Keeping those small intrepid bands in mind, once settled and grown strong, we have to ask if they will then spawn a new band of intrepid pioneers eager to venture further into the Galaxy. Geoff Landis modelled such a process as a discrete percolation process, which spread into the Galaxy not as an inexorable wave, settling every star system, but as dendritic filaments that left large unoccupied voids between them. This suggests our Galaxy could be well settled and we could still be left alone, as per the Fermi Paradox.

Alternatively They’re here and They’re watching us, but keeping quiet in any frequency we can scan. An old saying is that perfectly coded signals should be indistinguishable from noise…