[ExI] Old Chemically Mature Galaxies and Fermi Paradox

Jeff Davis jrd1415 at gmail.com
Sat Nov 5 21:51:24 UTC 2011


On Sat, Nov 5, 2011 at 3:07 AM, Anders Sandberg <anders at aleph.se> wrote:


                           <snip>


> One reset mechanism that was suggested by Milan Circovic (and then, with
> some minor input from me, developed by him into a paper with Robert
> Bradbury)

Is there a link to that paper?

> is that gamma ray bursts acts as the reset. The data suggests that
> gamma ray bursts were much more common in the past, and it is not hard to
> imagine that every time one hits a biosphere it slides back to a simple
> stage.

Regarding the intensity, and consequent destructiveness of a GRB:  I'd
like to get some idea of the damage as a function of  distance.  How
close for utter obliteration (ie planet flat out gone)?  how close to
reduce the entire planet to scorched rock?  How close for scorched
rock on one side?  How close for atmosphere stripping?  How close for
surface searing without loss of atmosphere? And finally, how close for
a severe, transient, non-lethal climate "excursion" with substantial
survival on the planet's far side?  (This last question assumes that
the duration of the GRB is shorter than half the  rotation period of
the affected planet.  So one last question:  What's the typical
duration of a GRB?)

Best, Jeff Davis

         "Everything's hard till you know how to do it."
                                     Ray Charles



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