[BloodEagle]

we do know that Earth-type worlds don't grow on trees, at least from what we've seen of the galaxy).

You win the Strangest Use of a Common Saying award, hands down.

[DarkBasilisk]

we do know that Earth-type worlds don't grow on trees, at least from what we've seen of the galaxy).

You win the Strangest Use of a Common Saying award, hands down.

I do that a lot. I spend a lot of time trying to figure out whether I'm CHR 6 or 8. Lately i think i've been leaning closer to going with 6

[castor]

Re: Contact, good or bad?
I'd argue that any civilization advanced enough to be capable of travelling between star systems is more likely to not be hostile, because I can't fathom how a hostile race would manage to survive long enough to reach that kind of capability.

Well, for some reason the warrior Europeans conquered both Americas and mostly deleted whoever was in their path.

They managed to survive long enough to do that, even though they were advanced enough to be able to travel across oceans and have firearms, which puts them as far ahead of native Americans as anyone travelling across the galaxy and colonizes planets is ahead of us Terrans today.

I think it's a different issue you're talking about. What matters in watsisnames's point is their absolute level of technology, not the level of technology relative to the population they're visiting.

[cloneof]

On a related note, last week one of my astronomy professors discussed his views on whether or not it is likely for us (or aliens) to be capable of readily colonizing other star systems.  He argued that this is not very likely based on our current observations.  The supporting argument goes like this:

First, assume that there is one civilization in our galaxy with the ability to travel to and colonize nearby star systems, and let us assume that they are limited by the speed of light but are capable of traveling at a significant fraction of it – and finally, let us assume that it takes them 500 years to travel to and colonize a new star system.
If this is the case, then by virtue of exponential growth, we would expect that the entire habitable region of the galaxy would be colonized within a tiny fraction of the age of the galaxy.  (IIRC my professor gave a value of 30,000 years for this, but I’d like to actually see the math).  Anyways, because we do not see evidence of the entire galaxy being colonized, it’s probably a safe assumption that the capability to do so either does not exist, or that we really are the only advanced life in our galaxy.  I’m under the belief that the former case is the correct one.

Well that works only if the species that wants to colonize, breeds.

However, as we can see from hi-tech nations of today (the First World) do we even now see high grow of population?

I would be willing to argue that a space civilizations has the same (if not better) energy technology that would have allowed it to create almost same conditions in wich people don't really want to make that many babies.

[DarkBasilisk]

I think it might be a matter of there not being many habitable worlds in the galaxy. Like i said with earth's not growing on trees, most of the extra-solar planets we've identified are down-right inhospitable to life as we know it. Lots of dead rocks and gas giants. Maybe you could terraform them, but even if you have the technology that takes a lot of work, so you wouldn't colonize freely, more on a infrequent basis. You also have the problem of colonization being slowed by contact with other advanced life. And in that example, if you were limited to traveling at a speed less than light, it's going to take a number of years to get there/send later supplies. Which is dwarfed by the amount of time the galaxy has existed for, yes.

But time isn't the only variable. The harder it is to do something, the less willing people are to try unless there's a sweet payoff. And it's sounding like colonization is pretty hard.

Not to mention is that colonization vessels that travel at sub-light would have to be HUGE. Packed with people, supplies, fuel, etc. Exponential growth doesn't work on this since a colonization ship is something that would have to built at a large scale shipyard, something that probably is only at the homeworld and nearby worlds. They're not something that would be built at every colony since building up the industry to create and maintain a shipyard would be a large scale project, and it makes sense to keep things specialized too.  Not every city in the US has farmland and factories. We have farming areas of the country along with manufacturing areas.

So you'd really have colonization speed decreasing with each world, as the worlds you try to travel to become farther away from the homeworld, which makes it longer to travel,more costly (need more supplies), and higher risk. Additionally, all of these things make people less enthusiastic to go in the first place.

EDIT: Just to add on, your astronomy professor's argument assumes that each colony would become a copy of the homeworld, matching it in population and industry. Which just isn't going to happen unless breeding rates are out of control, and you're REALLY good at quickly building up all the infrastructure to support that expanding population.

[General Battuta]

I think it might be a matter of there not being many habitable worlds in the galaxy. Like i said with earth's not growing on trees, most of the extra-solar planets we've identified are down-right inhospitable to life as we know it. Lots of dead rocks and gas giants.

That's in no small part because these planets are easiest to identify. Once we have better search techniques, I'm betting garden worlds will turn out to be fairly common.

[Mongoose]

Doesn't Prof. Hawking know that the first aliens we meet will look just like us, only with pointy ears?

[perihelion]

In my opinion, unless there is some amazingly cheap form of FTL to be discovered, most civilizations will find that interstellar colonization offers no tangible benefit to the home system.  Any resources you could hope to obtain from another star system would be much more easily obtained from the home system (i.e., asteroids, moons, gas giants, local sun(s), an Oort Cloud, etc).  And if you are hurting for additional living space... look at it this way.  If you have the technology and the resources to build a colony ship capable of surviving the decades (or more likely centuries) of travel to another star system, then why bother?  Why not just use those technologies and resources to build local habitats that can be put to immediate use?  Colonization is a gamble you will not hope to see any payoff from for centuries.

[Turambar]

Which is more likely:
a) The human race ended when one asteroid impacts one planet, killing all humans.
b) The human race ended when ten asteroids impacted ten planets within a short timeframe, killing all humans.

gotta get all of our eggs out of this one basket, even if it is a really nice basket.

[perihelion]

There are a lot more planets than just the Earth in this solar system.

And I'm not limiting us to living on planets.  You shouldn't either.  From the perspective of a space-faring civilization, planets are about the worst places to live.  Assuming some basic biological hurdles are cleared (space radiation, bone and muscle degradation due to living in free-fall, etc.), the biggest attraction of planets is going to be nostalgia.  You cannot move a planet out of harm's way.  And planets are subject to some nasty misbehavior of their own, a la the Haitian earthquake, the Sumatran tsunami, and the Icelandic volcano just for some more recent examples.

[IronBeer]

But a planet like Earth is also a self-correcting biological machine.

[TopAce]

Do you have massive orbital stations and space metropolises in mind? Like Nar Shaddaa from Star Wars?

[Scotty]

Nar Shadda was still a moon.  At one point, at least.  I think he had some thing more probably like the Citadel from Mass Effect.

[perihelion]

Small moons / asteroids are the most obvious places to start.  There are any number of NEAs that would be ideal.  Eros comes to mind.  There have been quite a few science fiction stories involving that particular asteroid.  The moons of Jupiter and Saturn are of particular interest to me just because that would provide so much variety in a relatively small area.  The biggest problem there is going to be radiation.  Jupiter's magnetic field is truly frightening.  I'm given to understand that Saturn's is more benign, but I am not sure how much more benign.

We have been able to enjoy trips into space thus far with relative impunity because we have (almost) always been traveling no further out than low-earth orbit, well inside the van Allen Belts.  In other words, all human beings except those on the Apollo moon missions have been safely protected by the earth's magnetic field from the freakish vagaries of charged particle radiation sleeting through space, both from the sun and from elsewhere.  As of yet, I have not heard any good plan to protect humans from this radiation during long periods of exposure.

But, assuming you can harden your ships against this radiation, small moons and asteroid can give you protection so long as you build your colonies underground.  Also has the benefit of giving you a source for raw materials for your bioplants.

If you are really interested in this sort of thing, I recommend Paul McAuley's "The Quiet War" and "Gardens of the Sun."  I was a bit disappointed by the stories themselves, but the biologist's perspective on intrasystem colonization was very interesting and very practical.  The books highlighted a lot of the problems we're going to have to overcome, and some of how to do it.

[Bob-san]

Which is more likely:
a) The human race ended when one asteroid impacts one planet, killing all humans.
b) The human race ended when ten asteroids impacted ten planets within a short timeframe, killing all humans.

gotta get all of our eggs out of this one basket, even if it is a really nice basket.

It's not just about the eggs, man. It's about the sperm too!



Until First Contact is made, we won't know anything about the technology of an alien race. So who the **** knows if they'll obliterate us or not.

[watsisname]

Well that works only if the species that wants to colonize, breeds.

However, as we can see from hi-tech nations of today (the First World) do we even now see high grow of population?

I would be willing to argue that a space civilizations has the same (if not better) energy technology that would have allowed it to create almost same conditions in wich people don't really want to make that many babies.

Notice though that all observations so far indicate that a population grows exponentially for as long as space and resources are available.  The reason humanity is reaching the point of diminishing growth is because we no longer have the space/resources to sustain such growth.  I’d think that if a civilization has better technology, then its growth rate would actually be increased as long as it has the space to do so.  In short, exponential growth appears to be inevitable as long as the means for continuing it exists.

To further clarify my above example considering a hypothetical space-faring civilization with the capability to colonize new star systems, we can assume it has nearly limitless space and resources (the entire galaxy), therefore it will have a tendency to grow exponentially, and continue to grow for as long as new habitable planets can be found.  The question is how long would it take for this growth to reach out over the entire galaxy, and the answer is that even if you allot 100,000 years for the population to double, then it’d take only 3,000,000 years to colonize a billion planets (2³⁰ iterations).  It’s doubtful that there are even a billion habitable planets within our galaxy, and the galaxy has been around for a *lot* longer than three million years, so therefore it is unlikely that such capability actually exists.  (Or there isn’t other advanced life in the galaxy, but I don’t believe that).

Battuta: “That's in no small part because these planets are easiest to identify. Once we have better search techniques, I'm betting garden worlds will turn out to be fairly common.”

Indeed.  We can’t even detect earth-size worlds yet, though we are getting extremely close.

Castor: “I think it's a different issue you're talking about. What matters in watsisnames's point is their absolute level of technology, not the level of technology relative to the population they're visiting.”

Well I think he’s comparing interstellar travel to overseas travel, and pointing out how that culture was able to accomplish such travel and yet was very much violent and aggressive against the technologically inferior Americans.  Therefore we can’t expect the same to not be true of space-faring races. To be fair, it’s possible that the morality point I brought up isn’t all that valid… perhaps it is inevitable that in the search for growth and riches, better morality is often tossed aside, like what the movie Avatar hints at.

[Bob-san]

Well that works only if the species that wants to colonize, breeds.

However, as we can see from hi-tech nations of today (the First World) do we even now see high grow of population?

I would be willing to argue that a space civilizations has the same (if not better) energy technology that would have allowed it to create almost same conditions in wich people don't really want to make that many babies.

Notice though that all observations so far indicate that a population grows exponentially for as long as space and resources are available.  The reason humanity is reaching the point of diminishing growth is because we no longer have the space/resources to sustain such growth.  I’d think that if a civilization has better technology, then its growth rate would actually be increased as long as it has the space to do so.  In short, exponential growth appears to be inevitable as long as the means for continuing it exists.

To further clarify my above example considering a hypothetical space-faring civilization with the capability to colonize new star systems, we can assume it has nearly limitless space and resources (the entire galaxy), therefore it will have a tendency to grow exponentially, and continue to grow for as long as new habitable planets can be found.  The question is how long would it take for this growth to reach out over the entire galaxy, and the answer is that even if you allot 100,000 years for the population to double, then it’d take only 3,000,000 years to colonize a billion planets (2³⁰ iterations).  It’s doubtful that there are even a billion habitable planets within our galaxy, and the galaxy has been around for a *lot* longer than three million years, so therefore it is unlikely that such capability actually exists.  (Or there isn’t other advanced life in the galaxy, but I don’t believe that).

Battuta: “That's in no small part because these planets are easiest to identify. Once we have better search techniques, I'm betting garden worlds will turn out to be fairly common.”

Indeed.  We can’t even detect earth-size worlds yet, though we are getting extremely close.

Castor: “I think it's a different issue you're talking about. What matters in watsisnames's point is their absolute level of technology, not the level of technology relative to the population they're visiting.”

Well I think he’s comparing interstellar travel to overseas travel, and pointing out how that culture was able to accomplish such travel and yet was very much violent and aggressive against the technologically inferior Americans.  Therefore we can’t expect the same to not be true of space-faring races. To be fair, it’s possible that the morality point I brought up isn’t all that valid… perhaps it is inevitable that in the search for growth and riches, better morality is often tossed aside, like what the movie Avatar hints at.

When we are reliably able to identify far-off planets, we'll find out if there actually are aliens. There's something like 100 billion stars in the galaxy. Say that 1/10th have a planet, 1/10th of those have multiple planets, and 1/10th of those have an earth-sized planet. That's .1% that have an earth-sized planet. Even saying that 1/10th have water and 1/10th of those have liquid water and 1/10th of those have a nitrogen/oxygen atmosphere. That's about 100,000 earth-like planets spread around the galaxy. The diameter of the galaxy is about 100,000 ly and it's about 1,000 ly thick. Assuming it's a cylinder, that's 100,000 earth-like planets in ~6 billion ly³ of space (taking away about 1/4 of the volume of a cylinder; probably should be closer to half). Even in the best case scenario, that's 400,000 earthy planets in ~4 billion ly³ space, or nothing habitable for at least 13 ly in each direction. Even worse odds if there's two or more earth-like bodies in the same system.

Now say 10% of those planets develop life, 10% of those lively planets develop intelligent life, and 10% of those intelligent planets survive to explore the cosmos? That's less than 400 civilizations that could be like us, not counting those destroyed after making it to space... spread over an area in excess of 4 billion cubic lightyears. And at our current rate, we'll sooner settle Mars than even explore Alpha Centauri, by hundreds of years margin.

[Solatar]

While I like the base logic there, how do you figure that 1/10 have a planet, etc.?  If the ratio is much smaller, we may never find another one.

[Scotty]

It's an arbitrary number to be sure, but it illustrates the already huge odds against finding a space-faring species in anything resembling adjacent space.

[watsisname]

Not 1/10 having a planet.  1/10th having a habitable planet.

edit:  whoops, I totally misread what you were quoting -- nevermind :X
edit2:  Actually, based on our current data, it appears that the rate of planet formation is higher than 10%.  It's possible that more than half of [population II] stars actually form planets, and the rates are higher for stars with higher metallicity (which makes sense because that means more metals/dust were incorporated into the accretion disk as well).  So using a 10% figure is actually pretty good in that it's probably lower than the true value.