barry@ames.UUCP (Kenn Barry) (04/15/85)
While the majority of scientists are willing to agree that
life elsewhere in the universe is quite likely, most estimates of
the number of advanced technological civilizations that might
presently exist in our galaxy are quite low. Even the most
optimistic estimates seem to predict only the tiniest percent of the
stars in our galaxy warm the homes of civilized beings.
Since we have *no* direct evidence on the subject at all, either way,
why should this be? I know of one main argument: The Sagan/Shklovsky
(sp?) Equation reasons that only some stars will have planets, only
some planets will be suitable, only some of those will actually spawn
life, etc., thru about 10 iterations. Any reasonable figures plugged
in to all the variables will yield only a few technological
civilizations, obviously.
I wish to suggest a more optimistic estimate. The reasoning
which follows is my own, but I'm sure I'm not the first to think of
it, and would appreciate any pointers to books or articles dealing
with this idea.
Let us suppose that, as per Sagan and Shklovsky, only a few
stars spawn high-tech civilizations that survive to at least a few
centuries past our present level of technology. My question is, what
is to prevent at least one of these civilizations from sending colonies out
to neighboring star systems? We are no more likely to be the only expansionist
culture than we are to be the only technological one. And what is to keep
those colonies from spawning further colonies, etc., etc., out to the edges
of the galaxy? What if this is, in fact, the present state of our galaxy?
Galactic overpopulation?
This is not unreasonable. There is no reason to believe that we
humans won't start doing it in a century or two, and someone may have
beaten us to it. We might kill ourselves off before that, of course, but the
statistical argument still applies: some hi-tech civilization somewhere
will manage colonization, or may have done so, already.
Faster-than light propulsion is not required; many means (suspended
animation, generation ships, near-light speeds) have been proposed whereby
we could colonize nearby stars without FTL. Given O'Neil-type colonies,
even stars without suitable planets could become the home stars of future
colonies.
How long would it take us to fill up the galaxy? Not as long as
you think. Let's say that each human colony only spawns a new colony
every 500 years. The number of human-settled star systems would then
double every 500 years. At this rate, we populate the galaxy in *less*
than the ~90,000 years it takes to *cross* the galaxy at the speed of
light!
Note also that, once the process is fairly under way, there
seems to be no stopping it. If disaster strikes some settlements,
others will still survive, sending out yet more colonies. Only a
disaster reaching across light years could stop it.
So, if it's possible for us, it would be possible for any
civilization who had the technology and the inclination. Even if we
conservatively assume it would take a couple of million years to
populate an entire galaxy, that's a mere eyeblink in cosmic time;
so, where are they?
I should probably point out that I am *not* a believer in "flying
saucers", because we haven't a shred of decent evidence that our planet
has ever been visited by Others. But I think this only makes my question
more intriguing. Must we believe that we are, indeed, the first hi-tech
civilization in our galaxy? This seems statistically unlikely, though
I suppose one could invoke the anthropic principle to explain away the
unlikelihood. Or is it, perhaps, possible, that technology is inevitably
fatal to the society that spawns it, at a point before colonization can
begin? Or perhaps they have simply overlooked us? Or they are hiding? To
me, all these possibilities seem unlikely, but I can't think of any other
explanations for the lack of visitors.
I hope all will understand that the above is meant as no more than
speculation. Comments are welcome.
PS - This is posted to sf-lovers because it seemed too speculative
for net.space or net.astro; frankly, I wasn't quite sure *where* to post
it.
- From the Crow's Nest - Kenn Barry
NASA-Ames Research Center
Moffett Field, CA
-------------------------------------------------------------------------------
USENET: {ihnp4,vortex,dual,hao,menlo70,hplabs}!ames!barrywalker@unc.UUCP (Douglas Walker) (04/16/85)
In article <ames.937> barry@ames.UUCP (Kenn Barry) writes: > >...most estimates of >the number of advanced technological civilizations that might >presently exist in our galaxy are quite low. Even the most >optimistic estimates seem to predict only the tiniest percent of the >stars in our galaxy warm the homes of civilized beings. ... > Let us suppose that, as per Sagan and Shklovsky, only a few >stars spawn high-tech civilizations that survive to at least a few >centuries past our present level of technology. My question is, what >is to prevent at least one of these civilizations from sending colonies out >to neighboring star systems? This may be nit-picking, but... When the Europeans expanded into the New World, did they spawn a new civilization? I think a colony of a planet is more accurately considered part of the same civilization as the parent. Sagan and Shklovsky's reasoning applies to the number of planets *producing* advanced civilizations, not *hosting* advanced civilizations. >... And what is to keep >those colonies from spawning further colonies, etc., etc., out to the edges >of the galaxy? What if this is, in fact, the present state of our galaxy? >Galactic overpopulation? Possible. The number of planets capable of supporting life is, at least according to S/S, small, so... > This is not unreasonable. There is no reason to believe that we >humans won't start doing it in a century or two... Whoa! I don't see us doing anything of the sort! I can see us expanding into space, perhaps L5-type colonies, exploitation of space for factories, etc. BUT I don't see the US or any other government funding a colony to another star without FTL. There would be little or no possible return from such a colony that could not be gotten from a smaller scientific team. The European powers expected gold, spices, etc from the new world; this implies two-way travel. Sure, it took several months to get there, but that's nothing compared to, say, 500 years to get to Alpha Centauri at 1240 kilometers/second average velocity. And Alpha Centauri is only 4.something light years away. > Faster-than light propulsion is not required; many means (suspended >animation, generation ships, near-light speeds) have been proposed whereby >we could colonize nearby stars without FTL. Given O'Neil-type colonies, >even stars without suitable planets could become the home stars of future >colonies. I've never heard of O'Neill-type colonies, but if they are colonies with no home planet, why do we need to put them around other stars? The only reason would be lack of room or resources here, and I don't see us using up all the surface space of a 93,000,000 mile radius sphere soon. Read up on Dyson Spheres and Niven-type Ringworlds. We might use up all easily accessible resources in the solar system at some point, but certainly not in the next few millenia. > How long would it take us to fill up the galaxy? Not as long as >you think. Let's say that each human colony only spawns a new colony >every 500 years. The number of human-settled star systems would then >double every 500 years. At this rate, we populate the galaxy in *less* >than the ~90,000 years it takes to *cross* the galaxy at the speed of >light! This assumes that when a colony is spawned, the sister colony instantly arrives at its location. This is not true even for the first colony, as argued above, but it is even less true of the original colonies. The picture you give has a constantly expanding sphere of colonied stars. The planets at the center of this sphere would be quite a ways from the edge of the sphere! Their colonies would need to travel thousands of light years instead of four or five light years. Another problem: if we are actually looking for habitable planets rather than sowing planetless colonies, we must work around the center of the galaxy. The center of the galaxy consists of population I stars, which are much older than our sun ( a population II star). These population I stars were formed when there were far fewer heavy elements in the universe - indeed, the heavy elements the earth was formed from probably were produced in the hearts of a pop I star. pop I stars will have no habitable planets. Thus, the sphere is even more skewed. I also question the ability of a brand-new colony to reproduce in only 500 years (as well as its motivation to) but that's another story. All in all, I don't see non-FTL (STL?) colonization of other solar systems. But then again, if some sort of CHEAP propulsion is developed that would allow private organizations to try... and some sort of near-perfect suspended animation or balanced ship-sized ecosystem is developed.... I sure hope I'm wrong!