Models of galactic colonization based on diffusion (such as the Newman–Sagan proposal), percolation (the Landis proposal) or cellular automata (Bezsudnov and Snarski) make statements about the migratory behavior of species that are assumed to hold true over timescales measured in hundreds of thousands or even millions of years. Colin McInnes developed a model of migration that only needs to hold true over a period of a few millennia in order to account for the lack of extraterrestrial visitors here on Earth.
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