To quote:

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.

Full item here:

http://www.centauri-dreams.org/?p=826