RE: starship-design: WHERE ARE THEY?

[Steve VanDevender <stevev@efn.org>]

L. Parker writes:
 > As I understood your original response, you were saying that GRBs might be
 > anisotropic - which means to me we only see GRBs aimed directly at us. The
 > sterilization theory was based upon the OBSERVED incidence of GRBs and is
 > not materially affected by this change. Regardless of whether a particular
 > GRB is aimed at us or away from us (anisotropic) the summation of all GRBs
 > must be isotropic. Which means there are a great many GRBs that we never
 > see, in fact the majority of them are never seen. Either way, the statistics
 > are the same and the conclusion reached is the same. The only thing that has
 > changed is the number of GRBs that occur in order to perform the same act -
 > sterilization of large segments of the galaxy.

The statistics aren't necessarily the same, Lee.

Note that for as many GRBs as are visible us, our planet isn't
sterilized yet; that's because none of them are occurring within
our galactic neighborhood.  If GRBs are anisotropic then
relatively few star systems will be in the path of the GRB beams
and close enough to be affected; other nearby star systems will
see the supernova but not be inundated with gamma radiation.  A
lot more star systems will be far enough away to be in line with
the beams and see them without being sterilized by the radiation.

Unfortunately I don't know the exact "beam spread" predicted in
the theoretical models such that it would be possible to estimate
the number of GRBs that are occurring that we can't see directly
(although many supernovae we see may be producing them) or the
likelihood of being zapped by a GRB.  I'm quite sure, however,
than in the anisotropic case the probability of being zapped by a 
GRB is much lower than in the isotropic case.