Good eye for assumptions, those are them. I&#x27;ll defend one and weaken the other.<p>I. 5BY<p>I had a somehow longer version where I explained why I chose the 5 billion year figure. There are a lot of factors that could make life on Earth harder than it currently is, but really only a few that could make Earth less hospitable than Mars. Mars is basically just a gravity well. Maybe with usable water. An Earth worse than that is a long way off.<p>On the other hand, if Mars isn&#x27;t enough, and we need interstellar travel, then we need either near instant travel or generational ships.<p>Generational ships mean we&#x27;ve mastered living in space without a planet. If we&#x27;re sustainable in space without a planet, then orbiting destroyed Earth (for minerals) is as good as leaving it, unless the sun is expanding.<p>Near instant travel obviates the need for learning lessons about survival in space.<p>(I suppose we could get a tech that could take us to any planet in the galaxy in a FTL but five year long trip similar to sublight trips. That seems unlikely though.)<p>Impacts could destroy Earth. So sure, we should spend good money to look for asteroids (telescopes in space!) and learning how to divert them (with robots!). Note though, mammals somehow survived a mass extinction event from a massive asteroid before. So it&#x27;d have to be pretty big to prevent us from just making (maybe underground) shelters.<p>If the atmosphere or magnetic field weakened, there&#x27;d be a huge radiation hazard. Underground or undersea habitats would be more technologically feasible for us than space, though, and would provide better radiation shielding than anything we could build.<p>II. 1000:1 was silly.<p>Tech costs though, yeah. Good call. Maybe more like a factor of 10. Possibly as high as 50:
<a href="http:&#x2F;&#x2F;www.tellmehowmuch.net&#x2F;how-much-did-the-hubble-space-telescope-cost.html" rel="nofollow">http:&#x2F;&#x2F;www.tellmehowmuch.net&#x2F;how-much-did-the-hubble-space-t...</a><p><a href="http:&#x2F;&#x2F;www.businessinsider.com&#x2F;mars-rover-curiosity-cost-each-american-8-2012-9?op=1" rel="nofollow">http:&#x2F;&#x2F;www.businessinsider.com&#x2F;mars-rover-curiosity-cost-eac...</a><p><a href="http:&#x2F;&#x2F;www.nbcnews.com&#x2F;id&#x2F;14505278&#x2F;ns&#x2F;technology_and_science-space&#x2F;t&#x2F;whats-cost-space-station&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.nbcnews.com&#x2F;id&#x2F;14505278&#x2F;ns&#x2F;technology_and_science...</a><p><a href="http:&#x2F;&#x2F;www.space.com&#x2F;12166-space-shuttle-program-cost-promises-209-billion.html" rel="nofollow">http:&#x2F;&#x2F;www.space.com&#x2F;12166-space-shuttle-program-cost-promis...</a><p>None of these are easy to compare though. Is the Hubble platform equal to the ISS? How many shuttle launches equal one rover? I don&#x27;t know. Maybe that brings them even further in line.<p>But if you ask me, at what exchange rate would I change unmanned tech points for manned tech points, based on the relative contributions to science from each, I think it&#x27;d be like 5:4 in favor of unmanned. Even if unmanned was more expensive, I think it&#x27;s tackling some pretty interesting problems right now. I&#x27;m weird though, I know.<p>N.B. - Musk&#x27;s point was really interesting too, thanks, kind of like &quot;Foundation.&quot; I&#x27;m not sure where it takes me. It&#x27;s like, &quot;If humanity could develop only one more technology, what would it be?&quot; Interstellar travel would be pretty compelling. I can think of interesting alternatives, but sure, interstellar seems like it might win.