[ExI] Fermi Paradox and GRB bursts

[BillK]

On Thu, Oct 2, 2014 at 5:34 PM, Anders Sandberg wrote:
> The problem with the GRB explanation is that it is too noisy. GRBs produce
> mass extinction within a few kilo-parsec, but they are really directional -
> if you are outside the beam the exposure is way lower. If GRBs were
> spherical in effect, then they could cover volume well, but most jet models
> fall off as theta^-2 or worse - nearly all energy is along the jet, within a
> few degrees. And the jet is typically pointed out of the galactic plane. So
> when you try to model this, in order to ensure that every inner system get
> whacked with a mass extinction say ever 100 million years you need a very
> high rate of GRBs in order to make it work. That is tough to balance with
> observed rates, which are on the order of one every million years. Even if
> you have a lot of GRBs, there are going to be unaffected systems fairly
> nearby too: the chance of some stars being lucky over several galactic
> rotations is pretty high. So the overall probability distribution of GRB
> impact ends up with a huge variance - it won't work as an effective Fermi
> paradox answer.
>


No argument there! But I don't think there is *one* Fermi paradox
answer. It's a big dangerous universe out there. I see many many ways
that intelligent life can be stopped. It is like weaving a safe path
through a maze of possible failure modes. GRBs are just one more
hurdle to be lucky enough to avoid.

BillK