Galactic catastrophism — the idea that certain kinds of cosmic events can destroy life on a periodic basis and prevent the emergence of technological civilizations — comes in a number of variants. And some catastrophe theorists believe such events don’t necessarily rule out species survival because their effects change over time. As we saw yesterday, Israeli theorist Itzhak Shechtman believes super-civilizations do arise despite the hazards of periodic extinctions, and argues that we may well find traces of their activities.
I return to Shechtman today because his paper crystallizes this interesting debate, especially when we turn to gamma-ray bursts (GRBs) as the agent of catastrophe. Shechtman examines the work of James Annis, who speculated in 1999 that although gamma-ray bursts could be deadly, their rate of occurrence declines over time. If this is the case, the universe may move into a ‘phase transition’ when the time between GRBs comes to equal the time needed for the emergence of intelligence. Suddenly the cosmos allows intelligent life the time to develop — we may ourselves live in that epoch.
But Shechtman questions Annis on numerous grounds and plugs different values into the variables he considers, with the result that he arrives at an interval between bursts that is 30 times longer than the time needed for the emergence of intelligent life. In which case, the idea of GRBs as a limiting factor loses force, and the Fermi question arises again: Where are these surviving civilizations? Another issue is that even when frequent, gamma-ray bursts need not reset the history of complex life to zero. Here’s Shechtman on this point:
Life on Earth has endured 5 major mass extinctions, 23 less devastating extinctions and many other upheavals in the last 570 million years. The most severe, the End Permian extinction, even liquidated 96% of all marine species and more than 75% of all vertebrate families, but did not succeed in eradicating life completely from this planet. Life held out tenaciously, modified, persisted and developed into its present state when it enjoys the luxury of searching for life on other planets! Thus, though the history of life on Earth is a single-case statistics, it nevertheless shows that life cannot be so easily reset to zero by ‘run-of-the-mill’ catastrophes.
What would make for a true life extinguisher? A massive star exploding into a supernova could do the trick for nearby civilizations. Shechtman uses the example of Eta Carinae, 100-150 times more massive than Sol; its explosion would probably doom life on planets within several hundred light years of the star. But such events in nearby space are presumably not common, and Eta Carinae is a solid 7500+ light years away. All this is part of the argument that life will survive and must be widespread, and that intelligent life’s engineering may be observable.
Centauri Dreams‘ take: An exploding Eta Carinae recalls a similar scenario in Richard Cowper’s wonderful Twilight of Briareus (John Day, 1974), in which a supernova plays havoc with the world’s weather. Cowper was actually the son of writer John Middleton Murry; his deft and evocative prose made stellar catastrophism a wrenchingly real concept. Whether supernovae, GRBs or any variety of more local events can reset life to zero remains a matter of conjecture, but the debate is important. Either catastrophism gives us a solution to the Fermi Paradox or, if we must discount the effect of these periodic extinctions, then the Fermi question is more pointed than ever.