[ExI] Fermi Paradox and GRB bursts

[Dan]

In a way, the "rare earth" crowd are arguing for a multi-factor approach, no? 

Regards,

Dan
 My latest Kindle book, "Born With Teeth," can be previewed at:
http://www.amazon.com/gp/product/B00N72FBA2

> On Oct 2, 2014, at 10:05 AM, BillK <pharos at gmail.com> wrote:
> 
>> 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
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