Originally Posted by Brian Rush

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

It was a rhetorical question, Mike, to which I provided the answer. You need not belabor the obvious and irrelevant.

It's not a rhetorical question and you provided the wrong answer.

Originally Posted by Brian Rush

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

It was a rhetorical question, Mike, to which I provided the answer. You need not belabor the obvious and irrelevant.

It's not a rhetorical question and you provided the wrong answer.

Originally Posted by HopefulCynic68

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

That's actually done more often than most people think. It isn't common, but it isn't unheard of.

I can think of several groups that would be more prone to do this:

• Those buying prefabricated homes;
• The elderly and empty-nesters, who are trading down;
• People buying a superfixer-upper in an inexpensive market;
• Investors;
• People who got a windfall (inheritances, people selling AOL stock in 1999);
• People moving from an expensive market to a less expensive market.

If you are a first-time buyer in an expensive market like Washington, DC (where my little "starter" 1500 square-foot townhouse condo would now sell for $325,000 to $325,00 and to get a single-family under $250,000, you have to be willing to commute 3 hours a day), trying to buy without taking out a mortgage would require literally a lifetime of saving.

I'd rather pay interest and get the tax deduction than pay rent. However, I am paying extra towards principal (I tried to refinance to a 15-year mortgage, but I didn't move quickly enough and interest rates rose).

Originally Posted by HopefulCynic68

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

That's actually done more often than most people think. It isn't common, but it isn't unheard of.

I can think of several groups that would be more prone to do this:

• Those buying prefabricated homes;
• The elderly and empty-nesters, who are trading down;
• People buying a superfixer-upper in an inexpensive market;
• Investors;
• People who got a windfall (inheritances, people selling AOL stock in 1999);
• People moving from an expensive market to a less expensive market.

If you are a first-time buyer in an expensive market like Washington, DC (where my little "starter" 1500 square-foot townhouse condo would now sell for $325,000 to $325,00 and to get a single-family under $250,000, you have to be willing to commute 3 hours a day), trying to buy without taking out a mortgage would require literally a lifetime of saving.

I'd rather pay interest and get the tax deduction than pay rent. However, I am paying extra towards principal (I tried to refinance to a 15-year mortgage, but I didn't move quickly enough and interest rates rose).

Originally Posted by HopefulCynic68

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

That's actually done more often than most people think. It isn't common, but it isn't unheard of.

Before WW II mortgages were much shorter, typically 7 years or so and purchase with cash fairly common.

Originally Posted by HopefulCynic68

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

That's actually done more often than most people think. It isn't common, but it isn't unheard of.

Before WW II mortgages were much shorter, typically 7 years or so and purchase with cash fairly common.

Originally Posted by Mike Alexander '59

Originally Posted by Brian Rush

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

It was a rhetorical question, Mike, to which I provided the answer. You need not belabor the obvious and irrelevant.

It's not a rhetorical question and you provided the wrong answer.

It was my question, so I think I should know if it was rhetorical or not, and what the right answer is. :P

Originally Posted by Mike Alexander '59

Originally Posted by Brian Rush

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

It was a rhetorical question, Mike, to which I provided the answer. You need not belabor the obvious and irrelevant.

It's not a rhetorical question and you provided the wrong answer.

It was my question, so I think I should know if it was rhetorical or not, and what the right answer is. :P

Originally Posted by Brian Rush

Originally Posted by Mike Alexander '59

Originally Posted by Brian Rush

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

It was a rhetorical question, Mike, to which I provided the answer. You need not belabor the obvious and irrelevant.

It's not a rhetorical question and you provided the wrong answer.

It was my question, so I think I should know if it was rhetorical or not, and what the right answer is. :P

This is a wonderfully delicious dialogue. I think it is time for one of Virgil's contests.

Originally Posted by Brian Rush

Originally Posted by Mike Alexander '59

Originally Posted by Brian Rush

Originally Posted by Mike Alexander '59

Why do I pay interest?

You don't have to. Just save the money necessary to buy the house.

It was a rhetorical question, Mike, to which I provided the answer. You need not belabor the obvious and irrelevant.

It's not a rhetorical question and you provided the wrong answer.

It was my question, so I think I should know if it was rhetorical or not, and what the right answer is. :P

This is a wonderfully delicious dialogue. I think it is time for one of Virgil's contests.

Krasnikov Tube

Lost in Translation and/or a modified Slow Boat-FTL may be possible but that still doesn't necessrily mean extraterrestrials will find us anytime soon.

Scale of the Universe

Prime Directive

"The genocide was brutal, criminal and disgusting and continued for 100 days under the eyes of the international community." - Romeo Dallaire, Force Commander of UNAMIR (Rwanda, 1993-1994)

I don't think humanity will ever be ready for aliens/visitors.

The idea that the aliens would have to be more morally advanced than us because they're, well, they're more advanced, does not make sense to me. Indigenous people all over this planet could give you chapter and verse on why not. However, I see two reasons they would not be here.

First - if there is no way around the light speed barrier. No wormholes, jump points, hyperspace, or warp drive. Totally impossible. Then the only way to get here would be to send robots, downloads, or other forms of non-meat-based-life. And perhaps none of them have any reason to do so.

The second - pity we couldn't have multiple choices here - is that planets may be common, but life may be rare. Life may be common, but complex life may be rare. Complex life may be common, but intelligent life may be rare. Then, postulating intelligent life, there are several booby traps our own species has narrowly avoided --

We domesticated plants and animals and started the agricultural age. Most civilizations dead-ended there, with huge masses of subsistence-level peasants, a steep social pyramid, and very little innovation.

The one civilization that didn't was a successor to one that did, and hence had some cultural capital to work with. It started with a lot of land that was essentially open, broken up into various regions by the terrain, and by and large, could be farmed by anyone with tools and a handful of people. It was rainfall-farming country from the edge of the Med on up to northern Scandinavia. Lots of untapped resources to start with.

They started with a labor shortage and hence innovated; and started with a tribal ----> feudal social structure that was decentralized enough not to stifle innovation. The vast majority of machinery not requiring fossil fuels or electrical power did not come out of any of the great classical civilizations; they were Medieval.

Then in the early modern period a vast amount of land settled by people with neither iron working nor horses nor firearms was discovered; and as the period wore on, fossil fuels and their uses were discovered. So our technical civilization received three mighty boosts: the conditions of a wide-open Medieval Europe; the Americas to conquer; and the undiscovered capital assets hidden in the ground, which we have been using at a high rate of speed ever since.

So given intelligence, a high-tech civilization depends on a fair amount of luck and resources coming available at just the right time. Then there are two more traps, one of which we avoided in my lifetime, and one we may not avoid:

The civilization destroys itself in war before they can get out into space. Either total holocaust (not likely) or a setback serious enough to knock them out of the running for a long, long time --- and with the capital assets no longer readily available.

They use up the capital assets before getting out into space.

So there you have it. Fermi --- no paradox whatsoever.

There is another theory, BTW. It's "Somebody has to be the first. Why not us?"

Originally Posted by Matt1989

Scale of the Universe

This is SO cool!

Edit: I cannot overstate how fundamentally cool this is!

Originally Posted by The Grey Badger

The idea that the aliens would have to be more morally advanced than us because they're, well, they're more advanced, does not make sense to me. Indigenous people all over this planet could give you chapter and verse on why not. However, I see two reasons they would not be here.

First - if there is no way around the light speed barrier. No wormholes, jump points, hyperspace, or warp drive. Totally impossible. Then the only way to get here would be to send robots, downloads, or other forms of non-meat-based-life. And perhaps none of them have any reason to do so.

The second - pity we couldn't have multiple choices here - is that planets may be common, but life may be rare. Life may be common, but complex life may be rare. Complex life may be common, but intelligent life may be rare. Then, postulating intelligent life, there are several booby traps our own species has narrowly avoided --

We domesticated plants and animals and started the agricultural age. Most civilizations dead-ended there, with huge masses of subsistence-level peasants, a steep social pyramid, and very little innovation.

The one civilization that didn't was a successor to one that did, and hence had some cultural capital to work with. It started with a lot of land that was essentially open, broken up into various regions by the terrain, and by and large, could be farmed by anyone with tools and a handful of people. It was rainfall-farming country from the edge of the Med on up to northern Scandinavia. Lots of untapped resources to start with.

They started with a labor shortage and hence innovated; and started with a tribal ----> feudal social structure that was decentralized enough not to stifle innovation. The vast majority of machinery not requiring fossil fuels or electrical power did not come out of any of the great classical civilizations; they were Medieval.

Then in the early modern period a vast amount of land settled by people with neither iron working nor horses nor firearms was discovered; and as the period wore on, fossil fuels and their uses were discovered. So our technical civilization received three mighty boosts: the conditions of a wide-open Medieval Europe; the Americas to conquer; and the undiscovered capital assets hidden in the ground, which we have been using at a high rate of speed ever since.

So given intelligence, a high-tech civilization depends on a fair amount of luck and resources coming available at just the right time. Then there are two more traps, one of which we avoided in my lifetime, and one we may not avoid:

The civilization destroys itself in war before they can get out into space. Either total holocaust (not likely) or a setback serious enough to knock them out of the running for a long, long time --- and with the capital assets no longer readily available.

They use up the capital assets before getting out into space.

So there you have it. Fermi --- no paradox whatsoever.

There is another theory, BTW. It's "Somebody has to be the first. Why not us?"

I think another fortunate thing about the earth is that we have the gas giants (Jupiter,Saturn,Neptune) as a gravity shield against wandering comets and asteroids. They hit them instead of us. This may be very unusual as well.

James50

Originally Posted by HopefulCynic68

True. But let's be fair here, and note that there are a lot of factors that chop the possibilities down. If we assume 'life as we know it, or something close to it' (and we have to, otherwise we have no constraints on pure speculation), we can say with some confidence:

1. Over half of all stars are dinky spectral-class-M 'red dwarfs'. These are by far the most common stars. They are, compared to the Sun, dim, cool, and long-lived. (Dim and cool are relative, of course).

Actually I think it's more like 80%. Our Sun is often considered "average" among stars because its spectral class (G or "yellow") is near (but below) the median of stellar spectral classes. But its luminosity is actually in the top 10th percentile of all stars. The less luminous G (e.g. Tau Ceti), and K ("orange"; e.g. Epsilon Eridani) class main-sequence stars, go down to about the 20th. Below that are the M ("red") dwarfs. F ("yellow-white"; e.g. Procyon), A ("white"; Sirius), B ("blue-white"; Regulus), and O ("blue-violet"; Alnitak in Orion's belt) occupy the higher percentiles.

I would postulate the general range among stars for life as we know it* to possibly develop to be lower F, G, and higher K stars--a group comprising probably 10%, at best, of all stars. The lower K and M stars would require planets to orbit closer than Mercury to bear liquid water, which would increase the likelihood of tidal locking or extremely slowed rotation which would present problems, as you describe. The higher F and above would probably emit too much UV radiation for a terrestrial-strength magnetic field and atmosphere to shield from, and would be too short-lived at any rate for the gigayears required for sufficient evolution. So this 10% would be the base group, which would in turn be heavily whittled down by other factors (below).

(* meaning, carbon-based life that uses water as a solvent and evolves at similar speed. Other bases for life (silicon, for instance), or life using other solvents aren't inconceivable however, but carbon-based would likely be the most common due to its relative abundance in the universe, with water (the most common bonding of abundant hydrogen and oxygen) also probably being the most popular solvent.)

2. Astronomers call all elements heavier than helium 'metals' (much to the disgust of chemists), and old stars tend to have low 'metalicity'. What that means is that they are short-changed on heavy elements, since at the time of their stellar formation, those heavy elements weren't around, not yet having been 'cooked' by nucleosynthesis inside big stars. Younger stars tend to have more heavy elements, since they incorporate more 'ash' from previous star generations.

Now, odds are good that a low-metalicity star will have star systems made up of gas giants and/or small worlds, not large planets like Earth. The Sun is a 2nd or maybe even 3rd generation star, and IIRC it's got a higher level of heavy elements than most of its generation and type. So the first-generation stars that still survive (mostly red dwarfs) are probably not likely abodes for life.

I think it's very possible that our Sun could be among the first stars in the galaxy to yield (or host) intelligent life--maybe even the first, but the first nonetheless not being much older than the Sun, maybe a fraction of a billion years older at most. But as the eons roll on, such life will become more and more common as supernovae continue to release more of those heavier elements manufactured in the cores of large stars, and new solar systems are formed in the nebulae of these explosions, with higher and higher "metallocities".

A good candidate star for finding life as complex (and maybe as intelligent) as ours would be a lower F, G, or higher K star at least 4 billion years old with a metallicity similar to our Sun's or greater. Younger stars with higher metallicities may be in the process of producing such life but we'll have to wait another 1-3 billion years or so to see. And if we're not the first, more advanced, spacefaring races are probably still very, very few--few enough that they're still content in their particular small region of this large galaxy and not even close to getting here yet. But they will become more common.

3. There's a fair chance that if a star is too close to the inner regions of the galaxy, local conditions will not be very tolerant toward life. If, as is now suspected, inner regions of galaxies are sometimes flooded with radiation from the nucleus, that alone is a problem. Another is that the high stellar density in inner regions makes regular supernovae exposure more likely.

True. Another valid limiting factor.

4. This is iffier, but the star systems we've discovered so far haven't been terribly stable-looking places. Often, we find Jovian-sized worlds in the inner reaches of the system, which is very odd on the face of it. If Jupiter or Saturn had come wandering inward in the past, it's a fairly safe bet that Earth would have paid a high price. If this sort of situation is actually common, it cuts down the possibilities again.

The very nature of how we discover most extrasolar planets--measuring perturbations in the motions of stars--suggests that the first ones we'll find will be massive planets close to their stars, which would create the maximum perturbation. Hence all those "torch-Jupiters" we were finding when the first extrasolar planet discoveries were being made. I've noticed though that as our capabilities of detecting measurable perturbations have increased, we're finding less and less of these relative to smaller "giants" at more normal (but still within 4 or 5 AU) orbits--AND we have now been able to rule out torch-Jupiters within (IIRC) about 100 light years where we haven't already found them--which is the vast majority of stars within that range. So, they're the most easily detected, for sure--but it appears they really are a rarity overall. (I do note that you wrote this six years ago--we've come a good ways since even then.)

If we were native to a solar system within 20 or so light-years of ours, with our present abilities we'd have probably just discovered Jupiter around Sol--but none of the other gas giants (further away from Sol) yet, and certainly not the inner rocky worlds.

I also question whether the really torchy Jupiters, the ones ridiculously close to their stars that orbit them in 3 or 4 days or whatever, necessarily migrated there from the middle of the protoplanetary cloud they'd have formed in. I wonder instead if they formed similarly to the way close binary pairs form, only with one component of the binary being too small to ignite hydrogen fusion (i.e. be a "star"). I've noticed that many of these are actually more massive than Jupiter, closer to brown-dwarf territory (if not there--we've discovered a few of these in close orbits too IIRC)--so they could be analogous to binary systems (many or most close binaries are more symmetrically massed, but there are also close binaries where the stellar masses vary greatly--these may form from the same or different process, I don't know), not "planets" as we think of them, formed (a bit later) in protoplanetary clouds. As such, a planetary system could have still formed around them both and never been affected by the "torch-Jupiter". There'd probably be one mother of a magnetic "tail" behind the torch-Jupiter though, maybe increased flare activity on the star from their close interaction as well--which could be very disruptive to any potential ecosystem on a rocky planet beyond.

It does seem, though, that a sizeable percentage of the planets we are discovering have orbits a bit on the eccentric side--moreso than in our pretty well-ordered solar system. This would be a limiting factor if temperature variation throughout a planet's "year" is high enough as a result.

There are a lot of other potential limiting factors. But it's true that given the total stellar population, that still leaves lots of possible sites. But they may be spread out very, very thinly.

I'm inclined to think that we may be among only a handful, maybe a couple dozen at most, of "intelligent" races that have so far emerged in this particular galaxy. Intergalactic travel will probably never happen, or won't for billions more years--if you are swimming in a rich field of perhaps 99.999% uninhabited star systems, why bother with that ever?--so what goes on in other galaxies likely stays in other galaxies, and Fermi won't apply. So within our own, it becomes a question of when they reached spacefaring tech, how few did (and it seems it would be very few, for now), and just how much they really felt/feel they need to expand.

One such race may have stumbled upon Sol and Earth some time ago, but given the very narrow window when we humans have existed (in terms of cosmic time) they could have easily found dinosaurs, a planet covered in glaciers, our small mammalian ancestors, or whatever there was in any particular mega-year period before we emerged. And they could have said "meh" and moved on, maybe took some specimens with them for study--depending on how unique complex non-intelligent (or, non-civilized) life has been in the places they've already seen. If they were interested in colonizing liveable planets, chances are they'd also have reasonable terraforming skills and would have found hundreds or even thousands of planets less occupied or totally empty of life beyond at least the microbe, which they would make theirs. Why bother with one that would present them more problems? Study, yes--but that needn't imply a permanent presence. The same sensibility will probably apply to us when--if--we start ranging beyond our own solar system. There will probably still be plenty of empty worlds for us too.

So, in answer to the Fermi question, probably a little bit of "prime directive" (more like "let 'em be, there's plenty of other worlds we can have to ourselves"), and a whole lot of "the galaxy is a big place" (whether or not the speed of light is exceedable--as it may very well not be--even rabbits on Viagra can't expand fast enough to fill potentially billions of terraformable or virgin worlds). And if c is in fact inexceedable, interstellar colonization probably will be very rare, as each colonized world would for all practical purposes be "cut off" from the others (certainly in terms of there ever being an interstellar "empire") and for the most part have to fend for themselves. Religious utopists or various groups of malcontents might go for such an exodus, but few others probably would. Hence a VERY slow expansion, if we have one. Other intelligent races in the galaxy may feel similar inhibitions to such undertakings.

Originally Posted by Brian Rush

Any species that reaches a successful conclusion to Step 8 above is going to be both pacifist and environmentalist. If they're not pacifist they'll blow themselves up,

Originally Posted by HopefulCynic68

This is an assumption, it can not be stated as fact. It may be a general truth, it may not.

And of course, it could be (like, well, our generational history, only larger-scale) cyclical. As in, world war in megacrisis where they reached the brink; relief that they restrained themselves from going completely over that brink, with a long period of peace and rationality prevailing for a long era afterward; beginnings of spacefaring and interstellar travel sometime in that long era; some mega-awakening in that period, leading to factionalism in a mega-unraveling as planetary colonies assert their various identity issues or whatever; crisis as these factions clash in interstellar war--adopting a warlike nature once again. And if they encounter an alien race, the nature of their interaction could depend much on whether they're still in a pacifist phase or not.

Although I'm inclined to think that, if FTL isn't possible, interstellar war will likely be prohibitively impractical (magnitudes more impractical than war itself is, anyway).

Indeed, continuous contact/interaction/trade between colonies in different star systems would likely be impractical or extremely difficult, such that the various colonies rely pretty much exclusively on local resources past what they brought with them (which would include equipment to terraform, seeds and fauna, etc.), and leave each other alone for the most part (although they were likely formed by factional differences--religious utopists or other separatists that wanted to make clean breaks from homeworld society). Without FTL, there will be no "interstellar empires" or even much in "interstellar trade". Just islands, which within millenia might as well be distinct races, alien from each other.

Originally Posted by Mikebert

Actually, throwing sand or grit at relativistic speeds is a pretty devastating weapon. 60,000 tons of fine sand or grit (about one large freighter's cargo) at close to the speed of light contains sufficient energy if deposited fairly evenly to heat the atmosphere to over 900 degrees, pretty much wiping out civilization. A smaller amount dumped in a more concentrated fashion could wipe out civilization on localized portions of the earth surface.

This is why formal weapons in spacecraft capable ot interstellar travel is unnecessary. The ship itself or anything it carries is the ultimate weapon by virtue of its great speed.

Except, of course, against other ships travelling at similar speeds or with evasive capabilities against projectiles at such speeds. Ships that could be there to defend nearby planets.

Plus, this assumes that the goal is to wipe out population and/or make the world uninhabitable. If the goal were to instead enslave a race, or wipe them out without scorching the planet (so that you could settle it--assuming you were compatible with the biosphere/lower life forms in general), more precision/"surgical strike" ability may be called for.

Originally Posted by John J. Xenakis

This is an interesting topic and as I'm sure you know, Ray Kurzweil
has argued that there's only one reasonable answer to the Fermi
Paradox: That we're the most advanced civilization in the universe.
(See http://www.kurzweilai.net/articles/art0134.html and search for
"Why SETI Will Fail (and why we are alone in the Universe)" about
halfway down the page.)

His argument is, in essence: If there were some other civilization
more advanced then ours, then there must be many. If there are many,
then we would have noticed one of them through its transmissions. In
fact the SETI (Search for ExtraTerrestrial Intelligence - see
http://www.seti-inst.edu/ for example) project has scanned a
significant portion of the skies and has failed to find any such
transmissions.

Therefore, he concludes, since if there were one there would have to
many, and if there were many we would find at least one, and since we
haven't found even one, then no others must exist.

I don't see where "one" would necessitate "many". Certainly "two" or "three" or some other number that is not "many" per se could exist, no? And a good range of low numbers even in our own galaxy would be possible without their detection (or even any detecting any other)--assuming of course they even communicate using the electromagnetic spectrum instead of some other means we can't even begin to undertstand, or broadcast so strongly as to be "heard" a long way past the broadcast range necessary to them. (Which is why I agree that SETI will most likely fail, but not that there isn't anyone else out there necessarily.)

Originally Posted by Alioth68

Indeed, continuous contact/interaction/trade between colonies in different star systems would likely be impractical or extremely difficult, such that the various colonies rely pretty much exclusively on local resources past what they brought with them (which would include equipment to terraform, seeds and fauna, etc.), and leave each other alone for the most part (although they were likely formed by factional differences--religious utopists or other separatists that wanted to make clean breaks from homeworld society). Without FTL, there will be no "interstellar empires" or even much in "interstellar trade". Just islands, which within millenia might as well be distinct races, alien from each other.

I agree with you as far as you go, but would go further (which also provides what I think of as the obvious solution to the Fermi paradox).

Consider that a spaceship the size of an aircraft carrier traveling at 0.1 c would have kinetic energy of about 5000 quads. For comparison, global energy output today is around 500 quads. If we value this energy at a rate of $0.10 per kwh then the value of the kinetic energy in this single spaceship is $150 trillion.

Now a $150 trillion is a LOT of value. Our futuristic civilization, being so much more advanced than we will also be fabulously wealthy, so an expenditure of this magnitude would be peanuts. Nevertheless $150 trillion still represents a lot of capital that if used on a planet could do lot of work.

It could, for example, reverse any environmental damage on the home planet. It could build elaborate space habitats. The resources for just an handful of such expeditions could terraform planets in the home system. Long before such flights become practical, the advanced civilization would have removed all practical reasons for traveling outside their home system.

So the reasons to go would have to be non-practical, perhaps simple curiosity. And it couldn't be mere observation, since that can be done remotely. A very large array of space telescopes could let an advanced race see our world in some detail from the comfort of home. Closer up observation would be done with tiny robot probes that would be much more cost effective to send out. The only reason to go would be to experience the other in person.

But then the question arises that they might get bored. Perhaps once you've seen a 100 worlds you've seen them all, and so they would never get here unless their home worlds was very close, and the odds of that are small.

Originally Posted by Alioth68

And of course, it could be (like, well, our generational history, only larger-scale) cyclical. As in, world war in megacrisis where they reached the brink; relief that they restrained themselves from going completely over that brink, with a long period of peace and rationality prevailing for a long era afterward; beginnings of spacefaring and interstellar travel sometime in that long era; some mega-awakening in that period, leading to factionalism in a mega-unraveling as planetary colonies assert their various identity issues or whatever; crisis as these factions clash in interstellar war--adopting a warlike nature once again. And if they encounter an alien race, the nature of their interaction could depend much on whether they're still in a pacifist phase or not.

Although I'm inclined to think that, if FTL isn't possible, interstellar war will likely be prohibitively impractical (magnitudes more impractical than war itself is, anyway).

Indeed, continuous contact/interaction/trade between colonies in different star systems would likely be impractical or extremely difficult, such that the various colonies rely pretty much exclusively on local resources past what they brought with them (which would include equipment to terraform, seeds and fauna, etc.), and leave each other alone for the most part (although they were likely formed by factional differences--religious utopists or other separatists that wanted to make clean breaks from homeworld society). Without FTL, there will be no "interstellar empires" or even much in "interstellar trade". Just islands, which within millenia might as well be distinct races, alien from each other.

Cyclical civilizations in space? Hmmm, sounds familiar...*snaps fingers*

The Mote in God's Eye

About the Moties...

Each war typically ends in the complete destruction of the current civilization on Mote Prime. However, due to their high birth rates, enough Moties always survive to eventually repopulate the planet. A faster rise to civilization leads to a longer period between Collapses, since productivity increases more quickly than the population. The museums exist to accelerate this process after a collapse. They are located in unpopulated areas to avoid their destruction during the inevitable wars. Once the surviving population is advanced enough to solve the puzzle at the door, they have access to a literal catalogue of civilizations, and the weapons to put them into effect. Population is controlled by disease and injury between collapses and reconstructions, but the cycles have thus far never been stopped completely.

The Cycles of civilization, war, and collapse have apparently been repeating for hundreds of thousands of years. In some cases, Mote Prime was completely sterilized and then repopulated by those living in hollowed-out asteroids within the system. The current asymmetrical form is probably a mutation resulting from nuclear weaponry prior to a collapse.

A very good book IMO. Some others perhaps of interest...

"Rare Earth: Why Complex Life Is Uncommon in the Universe" is obvious in it's leanings. It's not bad but the authors reach to make their point.

"Life Everywhere" was written largely as a refutation to "Rare Earth". IMO opinion it was much more conclusive.

The two books between them largely recapitulate all the "sweet spots" necessary for life mentioned here and then some. The best information I found in them backs Alioth's analysis regarding scarce intelligence to a "t". Well stated!

Something maybe appropriate that has not been mentioned here. What is the likely hood of moving any significant percentage of the Earth's population off world? Will colonization solve any of the problems we have on Earth? specifically will colonization have any effect on the population boom?


Tone70

It amazes me that humans have never been beyond the orbit of Luna, yet many have the confidence to say that extraterrestrials don't exist because they can't find evidence looking through telescopes. If there IS a civilization advanced enough to travel through space (our civilization does not quite count yet as we have no sustainable presence in space and currently can't get humans out of LEO), then we should assume that either they have the scientific and technological sophistication necessary to avoid detection by us inferior humans (imagine current "invisibility cloak" technology advanced by at least several decades), or we simply don't have technology that's advanced enough to detect them. And it is wrong to assume that they will operate by OUR laws of physics, as if 20th century science is the final answer. I find it likely that our current physics laws will be replaced with better ones in the future.

I went with Rare Earth, though I feel that's only part of the answer.

It's a combination of Rare Earth, Slow Boat and Stay-At-Home; though Naked Ape might be a plausible contributor.

Slow Boat: my gut feeling is that any future revision of relativity is not going to possess a FTL shortcut that's easily exploitable through engineering with normal matter. Highly exotic states of matter may do, but they'll probably be required in astronomical quantities, making it beyond the means of even a Kardashev Type II civilization.

Stay-At-Home: Charles Stross posed this in his novel Accelerando. Basically, once a civilization achieves strong nanotechnology, he sees it as inevitable that they will quickly start building a Matrioshka brain around their star, eventually developing into a Kardashev Type II civilization using all of the collected energy for computation. The virtual denizens of the Matrioshka brain, the descendents of uploaded mind states of the original sapient species and various types of self-aware programs, will be accustomed to extreme amounts of low-latency bandwidth and giving it up in order to travel to other star systems is something he posits these entities will find very uncomfortable (I think of this as the end result of "Crackberry Syndrome" and web/game addictions).