David Blenkinsop wrote:
> Given those general points, what I'm asking about the smaller stars is,
> the advantage of longer stellar life balance off against the flare
> danger in such a way as to strongly discourage life on any but the largest
> terrestrial -type planets that may be orbiting those stars? This is a
> technical question, no doubt! If someone is able to crunch the numbers,
> maybe even complete with a good model of atmosphere thickness for
> different sized planets, *that* would be interesting, certainly beyond
> anything that I'm prepared to do. Admittedly, it's possible that this
> favour large planets" idea might be killed on some technicality in fairly
> short order, in the sense of disproving it as a statistical trend. For
> instance, possibly there just isn't all that much difference in radiation
> dangers for stellar life spans of interest? I have some sense that the
> uncertainties about such things as "frequency of stellar flaring" might
> enough to leave an idea like this on the back burner for a long time,
> enough is found out to either disprove it, or to solidly encourage it?
I'm not sure about the solar flare probability, but I can tell you that such events are probably no more dangerous to life than asteroid impacts. A big flare might kill a lot of land animals on the facing side of the planet, but sea life and land animals on the other hemisphere will be fine. A modest improvement in radiation resistance would prevent solar flares from even doing that much damage.
However, it would be very difficult to get liquid water on a planet orbiting a small, dim star. The star puts out so little energy that a planet must be extremely close in order to stay warm. We don't know all that much about how planets form, of course, but it is hard to build a model where that kind of thing will happen often enough to be significant.
> In terms of making a suggestion about why ET's might not have gotten
> off-planet, this seems not so much of a concern to me, since no one really
> knows what it would take to discourage your typical ET civilization from
> developing space settlements! If, as I've outlined, even the highest tech
> rocketry could arguably be too expensive or too dangerous for an ET
> civilization, who knows if they'd ever get around to building the really
> large-scale launchers that they'd need to surpass those limits?
But it isn't. Let's look at some options:
Note that I haven't even considered what could be done with fusion power, antimatter, laser ramjets, magnetic levitation, or other exotic technologies.
> Note that
> sending cheap little "seed" AI's into space might not be the answer,
> if small, cheap AI's tend to get fried by radiation, maybe our ET's always
> have to give up on that as well.
We can solve that problem now, with off-the-shelf technology. You just have to give your replicator a few ounces of shielding.
> What I really notice here is that the above comment from Billy Brown seems
> to suggest that an obstacle of something being "a few orders of magnitude
> more expensive" would necessarily be overcome eventually, maybe
> taking only a "few hundred years" at most before the cost barrier is
> to something manageable. The trouble with cost barriers is that, if the
> cost of breaking through the barrier is too high, maybe no one will do it!
> As the old saying says, "you have to walk before you can run"; what if
> would-be space travelers never learn to "walk"?
By that standard, scholars of the 10th century could confidently conclude that the idea of shipping an army across the Atlantic in giant steel boats is specious nonsense. Why, there isn't enough steel in the kingdom to build such a vessel! Where would you find the tens of thousands of blacksmiths? How could we ever grow enough hemp for the rope? Burn coal to power it, you say - but man, do you know how expensive it is to mine coal?
It isn't that technology magically makes everything cheap (although sometimes it does). Its that economies grow over time. We routinely do things now that would have been insanely expensive a hundred years ago, and there is no reason to expect this trend to change in the future.
Rocketry was developed for military purposes long before space travel became a serious possibility. There is a continuous progression of innovations leading from primitive fireworks to ballistic missiles, and from there to space flight. Making space flight more expensive would make development along this curve a bit slower, but that's all. To create a situation where virtually all civilizations remain planetbound for millions of years, you need a much larger obstacle than a 3G gravity well.
Billy Brown, MCSE+I