<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>In a way, the "rare earth" crowd are arguing for a multi-factor approach, no? <br><br><div><div style="font-size: 17px; line-height: normal; -webkit-tap-highlight-color: rgba(26, 26, 26, 0.301961); -webkit-composition-fill-color: rgba(175, 192, 227, 0.235294);"><font size="3"><span style="line-height: 20px; -webkit-tap-highlight-color: rgba(26, 26, 26, 0.294118); -webkit-composition-fill-color: rgba(175, 192, 227, 0.231373);">Regards,</span></font></div><div style="font-size: 17px; line-height: normal; -webkit-tap-highlight-color: rgba(26, 26, 26, 0.301961); -webkit-composition-fill-color: rgba(175, 192, 227, 0.235294);"><font size="3"><span style="line-height: 20px; -webkit-tap-highlight-color: rgba(26, 26, 26, 0.294118); -webkit-composition-fill-color: rgba(175, 192, 227, 0.231373);"><br></span></font></div><div style="font-size: 17px; line-height: normal; -webkit-tap-highlight-color: rgba(26, 26, 26, 0.301961); -webkit-composition-fill-color: rgba(175, 192, 227, 0.235294);"><font size="3"><span style="line-height: 20px; -webkit-tap-highlight-color: rgba(26, 26, 26, 0.294118); -webkit-composition-fill-color: rgba(175, 192, 227, 0.231373);">Dan</span></font></div></div><div style="font-size: 17px; line-height: normal; -webkit-tap-highlight-color: rgba(26, 26, 26, 0.301961); -webkit-composition-fill-color: rgba(175, 192, 227, 0.235294);"><span style="font-family: UICTFontTextStyleBody; -webkit-text-size-adjust: auto;"> My latest Kindle book, "Born With Teeth," can be previewed at:</span></div><div><span style="background-color: rgba(255, 255, 255, 0);"><a href="http://www.amazon.com/gp/product/B00N72FBA2" x-apple-data-detectors="true" x-apple-data-detectors-type="link" x-apple-data-detectors-result="2">http://www.amazon.com/gp/product/B00N72FBA2</a><br></span></div><dl style="margin: 0px 0px 0px 1em; padding: 0px; border: 0px; font-family: 'Helvetica Neue', Helvetica, 'Nimbus Sans L', Arial, 'Liberation Sans', sans-serif; font-size: 14px; line-height: 1.65; vertical-align: baseline; color: rgb(37, 37, 37); background-color: rgb(255, 255, 255);"></dl></div><div><br>On Oct 2, 2014, at 10:05 AM, BillK <<a href="mailto:pharos@gmail.com">pharos@gmail.com</a>> wrote:<br><br></div><blockquote type="cite"><div><span>On Thu, Oct 2, 2014 at 5:34 PM, Anders Sandberg wrote:</span><br><blockquote type="cite"><span>The problem with the GRB explanation is that it is too noisy. GRBs produce</span><br></blockquote><blockquote type="cite"><span>mass extinction within a few kilo-parsec, but they are really directional -</span><br></blockquote><blockquote type="cite"><span>if you are outside the beam the exposure is way lower. If GRBs were</span><br></blockquote><blockquote type="cite"><span>spherical in effect, then they could cover volume well, but most jet models</span><br></blockquote><blockquote type="cite"><span>fall off as theta^-2 or worse - nearly all energy is along the jet, within a</span><br></blockquote><blockquote type="cite"><span>few degrees. And the jet is typically pointed out of the galactic plane. So</span><br></blockquote><blockquote type="cite"><span>when you try to model this, in order to ensure that every inner system get</span><br></blockquote><blockquote type="cite"><span>whacked with a mass extinction say ever 100 million years you need a very</span><br></blockquote><blockquote type="cite"><span>high rate of GRBs in order to make it work. That is tough to balance with</span><br></blockquote><blockquote type="cite"><span>observed rates, which are on the order of one every million years. Even if</span><br></blockquote><blockquote type="cite"><span>you have a lot of GRBs, there are going to be unaffected systems fairly</span><br></blockquote><blockquote type="cite"><span>nearby too: the chance of some stars being lucky over several galactic</span><br></blockquote><blockquote type="cite"><span>rotations is pretty high. So the overall probability distribution of GRB</span><br></blockquote><blockquote type="cite"><span>impact ends up with a huge variance - it won't work as an effective Fermi</span><br></blockquote><blockquote type="cite"><span>paradox answer.</span><br></blockquote><blockquote type="cite"><span></span><br></blockquote><span></span><br><span></span><br><span>No argument there! But I don't think there is *one* Fermi paradox</span><br><span>answer. It's a big dangerous universe out there. I see many many ways</span><br><span>that intelligent life can be stopped. It is like weaving a safe path</span><br><span>through a maze of possible failure modes. GRBs are just one more</span><br><span>hurdle to be lucky enough to avoid.</span><br><span></span><br><span>BillK</span><br><span>_______________________________________________</span><br><span>extropy-chat mailing list</span><br><span><a href="mailto:extropy-chat@lists.extropy.org">extropy-chat@lists.extropy.org</a></span><br><span><a href="http://lists.extropy.org/mailman/listinfo.cgi/extropy-chat">http://lists.extropy.org/mailman/listinfo.cgi/extropy-chat</a></span><br></div></blockquote></body></html>