Billy Brown wrote:
>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.
>From information that I've read about extrasolar planet searches it would
appear that stellar flaring *is* a major concern, at least in some astronomers' minds, as something that could greatly reduce the survival chances of life in general. I'll refer you here to http://www.kepler.arc.nasa.gov/nature.html, and the comment at the end of that page related to stellar flaring and the need for life-promoting stars to be more massive than M-class on that account. Now it may be that this concern over flares is relatively minor compared to the concern over tidal locking, mentioned in the same sentence, you may be right that sea life wouldn't be as affected by flares and radiation from space generally. We're mainly concerned here about land dwelling creatures, who'd be out in the open air to a great extent, or dependent on a surface ecology, and *not* safe in an ocean, since it seems there's a consensus of sorts that technology builders need to have access to open air to make fire, start refining metals, etc. As for saying that modest differences in atmosphere thickness would tend to totally remove this concern, that's the sort of detail where I don't have any special expertise to weigh those numbers at the moment. One interesting possibility is that a larger planet with a much thicker atmosphere would do better on the tidal locking problem as well, since the thicker atmosphere could easily lend itself to a nice greenhouse effect, thus keeping the planet warm at a greater distance from the star, where there's much less tidal influence to lock the planet into having a permanent "day" and "night" side. Such a "locked" situation is quite undesirable, apparently, but it would seem that a thicker atmosphere would tend to make the most hospitable planets less prone to this problem, besides providing more radiation protection.
>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.
See my above comment, and also again, see the graph at http://www.kepler.arc.nasa.gov/nature.html, where it would appear that for "K" stars, at least, there ought to be planets forming in the "life bearing" zone. One thing I'd note is that I've read elsewhere that some theories have tended to widen the outer edge of the Habitable Zone out considerably, so maybe even the smaller "M" stars could support life, especially if the planet has a relatively very thick atmosphere? As judge of a closely related claim on the Foresight Exchange "idea futures" market, I try to keep up (the claim being called "Earth2", "Habitable Earth-class planet").
>[David Blenkinsop wrote:]
>> 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:
>1) With chemical rockets, you might be stuck with having <1% of your
>vehicle as payload. Today that would be impractical, but with nanotech that
>1% can still do something useful. With low construction costs, the low
>efficiency also isn't nearly the problem it would be now.
>2) Nuclear rockets have been studied many times by various groups, and the
>general conclusion has been that they are no more dangerous than chemical
>versions. Besides, if you're really worried about it you can launch the
>thing from an island (or even a floating platform, like Sea Launch
>[. . . more about laser launchers, AI's, other technologies]
>> . . . 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 . . .
>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 . . .
>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.
These are the very points that interest me about a planetary situation that would be much tougher to launch out of than our own. Right at the outset, it would appear that regular bulk scale chemical rocket technology simply could not do the trick of launching satellites to twice the orbital speed that we require. Because of this, the ET's in that situation would miss out on the "dawn of the Space Age" as we've experienced it. At the same time, if they take awhile developing nanotech and any related technologies that might be helpful, it's difficult to say for certain what other problems might come about as a result of missing that early opportunity. For instance, suppose that some of the ET's make use of technology to boost their own reproductive capacity, maybe they just naturally produce more offspring than we do, or maybe it's an evolutionarily persistent pattern, to use nano/biotech in that direction *before* the advanced space stuff is available. In that sort of situation, who knows if a heavily populated planet will ever be rich enough to build the advanced launching devices? Maybe it'll be populated with floating islands all across any oceans, and no one willing to allow a nanotech space launcher next door!
Admittedly, this "ET's trapped on large planets" idea is mostly speculation, at this point. Although I don't claim any "burden of proof" on this, it just seems possible, that's all, a possible answer to how there might be some hundreds or thousands of technological civilizations in our galaxy, with maybe a few tens or hundreds of them just possibly being detectable message senders for someone with a *very* good receiver? Though I'm just guessing at numbers, if smaller stars are both longer-lived *and* more numerous than stars like our sun, and if it takes a special kind of planet to bear life in that longer-lived situation, the heavy planet scenario may be the result -- with ourselves being the lucky oddballs, evolving faster than anyone else, in a situation where bulk tech can actually get into orbit early in our history.
The thing to remember here is that it's the fundamentally progressive ideas behind the whole question of the Fermi Paradox that tend to inspire some sort of effort to explain why advanced ET's haven't expanded into our vicinity by now. From what I can see, people who advocate SETI programs mostly don't take Fermi's Paradox too seriously -- it's just assumed that advanced species wish to talk, but that they've never quite expanded steadily outward for some reason. In contrast to this "practical" lack of theorizing, it may be someday be important for ET searches to have one or two well developed theories on this -- theories might guide where we'd want a really big detector array to look, for instance. In the meantime, let's not just assume the negative answer of "no communicative ET's" just because it's hard to imagine that they've somehow missed the space development options that we're pretty sure they've must've missed in any case, if they *do* exist! Either they aren't here because they've failed to evolve in our past universe thus far, or because they've evolved but failed to go space settling, for whatever reason, or because they've gone settling, but somehow failed to occupy some really major niches, as in the "Burning the Commons" idea. No matter how you slice it, it seems that we here on Earth are in a very unusual, hopeful, situation in being the first to have a chance at starting a fairly efficient settlement wave, either that, or we face whatever doom or hidden limit which may have stopped potential "others" from expanding directly out to us.
David Blenkinsop <email@example.com>