Established Member
You are making a statement of certainty without any evidence whatsoever.Originally Posted by Trakar
We have no idea how energy usage will scale as technology increases. I have my doubts that it will be a simple extrapolation across the many orders of magnitude required to go from "planetary" to "galactic".
Order of Kilopi
We do know the laws of physics, or at least we think we do, as pertain to moving mass. Moving a lot of mass, really fast, requires lots of energy. The energy in the Saturn V was about equivalent to small nuclear bomb, and that is a pittance compared to move such masses across interstellar distances in a timely fashion, let alone something that would allow the occupants to survive that long. Even known theoretical 'hacks', like wormholes, would require vast amounts of energy. Maybe we're missing something and there is evidence of alien activity all around us, but as we understand things now, we don't.
Established Member
Very little in this universe is simply derived, particularly when speaking of interactions with unknown components and unwitnessed end-results. Care to expand upon and share your considerations, regarding the leap from planetary to galactic? Likewise, if you feel my assessment is off-base, please feel free to point out where it is in error and why you feel that different considerations are more appropriate.
Established Member
Following up on Raven's Cry post about energy requirements, it's clear that an astronomical amount of energy (heh) is required for interstellar travel -- given our current understanding of physics.
That alone suggests that there would need to be a very compelling reason for a technological civilization to expend that kind of energy on travel when it could be spent upon improving the habitability of their home system.
It seems, to me at least, a lot more practical for a civilization to hop from star to star only when their home system is on the verge of becoming unlivable. And once they've selected, traveled to, and settled in a new system, they hang out there for another billion or so years.
So there's an highly-technological alternative to the concept of a galactic civilization right there.
Established Member
First things first: there are NO galaxy empires. If every v must be < c, it CANNOT be. Sure, galaxy can be colonized, but colonists will inevitably fragment in separate enitites.
Order of Kilopi
This is merely ill defined speculation, with obvious potential counter-examples. Depending on the nature of the alien civilization, the definition of "colonist" might be ill defined, much less the definition of "fragment" or "separate entities".
One obvious potential counter-example would be the counter-example of a single mind civilization. In this counter-example, there is only one sentient being--the central "queen". The rest of the civilization is nothing more than mindless machines. The mindless machines are no more "separate entities" than your fingers are "separate entities".
Order of Kilopi
1) It's not at all clear that a galactic scale civilization would be using energy at a galactic scale. Our own civilization is a global scale, but we're not using energy at a global level (really quite pathetic compared to the amount of sunlight which hits the Earth).
One might wonder why humans consume so little energy, when there is the theoretical capability to consume so much more. For example, we still use slow ocean-going ships to move cargo and bulk goods, even though we could instead use supersonic jetliners or even suborbital rockets to do the shipping instead.
Of course, the truth is that we don't just go out of our way to waste energy when there are compelling more efficient alternatives. We don't go around in suborbital rockets because it just isn't worth the expense. Similarly, why would a galactic civilization go around slinging relativistic starships all over the place? Oh, it might be worth doing it ONCE, in order to colonize the galaxy before anyone else. But why bother doing so billions of years after the galaxy has already been colonized?
2) Even if there are indeed galactic levels of emissions, it's not at all clear that we would recognize them as artificial. Our galaxy does in fact emit galactic levels of emissions. There is a lot of hot stuff emitting a lot of waste heat out there. What specific emissions do you think there should be--which are lacking--if there were a galactic empire?
Established Member
If you only have a single civ. that only hops from system to system every few billion years (probably closer to every few thousand years as it ages and becomes more proficient in the extraction and utilization of stellar system resources - then it isn't a "galactic civilization." Besides if you are talking about the transference of an entire mature civilization from one star to another, you are talking vastly larger amounts of energy than the launch of an occassional colony towards the stars!! Such would emit vastly more energy and be eminently more obvious throughout most of the galaxy than even a widespread individual colonization spread throughout a large sector of the galaxy. At best, your senario holds if this is the only way tech civs ever spread and there are very, very few tech civs in our galaxy or throughout the cosmos.
If alternately, it spawns off a handful of colonies every time a neighboring star approaches within a couple of light years, then we are back to the low end of my original premise and it would only take a few millions - billions of years (depending upon rate of expansion) to colonize the entire galaxy, and much less than that to make themselves apparent and obvious throughout much of the rest of the galaxy through their energy use signature.
Single colonies on the other side of the galaxy would most likely be largely invisible to us; tens of millions of colonies leaving a single system and transitting to a new star over a fairly tight timeframe should be obvious. What is the density and scale where tech civs transition between invisible and obvious,...I'm really not sure, but it is interesting to consider.
Established Member
This depends upon your definition of empire, more than any other single factor.
http://en.wikipedia.org/wiki/Empire
Order of Kilopi
Not really. Such a mature civilization would be able to see the end coming billions of years in advance--plenty of warning time for them to transfer to another star system that was passing by. The amount of delta-v required could be on the order of tens of kilometers per second, and the transfer could take place over many thousands of years so high acceleration is not required.
Although, I think that a civilization which was content to just sit in a single star system for all this time might just stick it out anyway. So what if the star huffs and puffs through a couple red giant stages? Just stay out of its way for some millions of years until it settles down into a nice stable white dwarf.
Established Member
This seems more a quibble over terms and definitions, but yes, I used the term "galactic scale" in a similar manner to the way you seem to think of "planetary scale," as a significant but minor fraction of total energy available. For the most part, even a few trillionths percentage of the galactic total energy should create a visible signature across the galaxy.
Because it is more efficient given needs and resource costs to do so. No surprises there.One might wonder why humans consume so little energy, when there is the theoretical capability to consume so much more. For example, we still use slow ocean-going ships to move cargo and bulk goods, even though we could instead use supersonic jetliners or even suborbital rockets to do the shipping instead.
Who is suggesting such is so?Of course, the truth is that we don't just go out of our way to waste energy when there are compelling more efficient alternatives. We don't go around in suborbital rockets because it just isn't worth the expense. Similarly, why would a galactic civilization go around slinging relativistic starships all over the place?
The only use I see for relativistic travel are military ventures.Oh, it might be worth doing it ONCE, in order to colonize the galaxy before anyone else. But why bother doing so billions of years after the galaxy has already been colonized?
A much more pointed and relevent consideration. For the most part, our look out into the galaxy are restricted by our own technology to the relatively local neighborhood, but by being able to rule out civs only minorly more advanced nearby and large scale greatly superior tech civs at greater distances, we can refine the constraints and limitations (with a high degree of uncertainty) of many other potential galactic scale tech civs within our galaxy and beyond. There are analyses that can and have been done at various scales related to this line of thought, we can certainly discuss it in more depth, but first it is probably good to look at the relevent work of others. I'm throwing in several that should cover a significant range of considerations on the subject and then we can evaluate them and our own considerations, if you'd like:2) Even if there are indeed galactic levels of emissions, it's not at all clear that we would recognize them as artificial. Our galaxy does in fact emit galactic levels of emissions. There is a lot of hot stuff emitting a lot of waste heat out there. What specific emissions do you think there should be--which are lacking--if there were a galactic empire?
"Placing a limit on star-fed Kardashev type III civilisations" - unfortunately, without a JBIS subscription you are probably going to be limited to the abstract at - http://adsabs.harvard.edu/abs/1999JBIS...52...33A
"Starry Messages: Searching for Signatures of Interstellar Archaeology" - this one has a full paper available for public reading at http://arxiv.org/PS_cache/arxiv/pdf/...001.5455v1.pdfA civilisation that uses the bulk of a galaxy's starlight for its own power requirements is a remarkably obvious entity. This is because galaxies naturally obey scaling laws between the surface brightness, the radius of the stellar distribution and the thermal velocities of the stars. The latter two quantities reflect the mass and its resulting gravitational potential, while the former is the result of this same mass emitting light as stars. If civilisation takes that light for its own purposes, the scaling laws are broken and the galaxy becomes an outlier on plots showing the scaling laws. For a sample of 137 galaxies no such outliers are found.
"Macroengineering in the Galactic Context: A New Agenda for Astrobiology" - full paper available at - http://arxiv.org/ftp/astro-ph/papers/0606/0606102.pdfSummary:Searching for signatures of cosmic-scale archaeological artifacts such as Dyson spheres or Kardashev civilizations is an interesting alternative to conventional SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization. This type of search is called interstellar archaeology or sometimes cosmic archaeology. The detection of intelligence elsewhere in the Universe with interstellar archaeology or SETI would have broad implications for science. For example, the constraints of the anthropic principle would have to be loosened if a different type of intelligence was discovered elsewhere. A variety of interstellar archaeology signatures are discussed including non-natural planetary atmospheric constituents, stellar doping with isotopes of nuclear wastes, Dyson spheres, as well as signatures of stellar and galactic-scale engineering. The concept of a Fermi bubble due to interstellar migration is introduced in the discussion of galactic signatures. These potential interstellar archaeological signatures are classified using the Kardashev scale. A modified Drake equation is used to evaluate the relative challenges of finding various sources. With few exceptions interstellar archaeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are within reach.
"Observable Characteristics of Extraterrestrial Technological Civilizations" - full paper available at - http://www.rfreitas.com/Astro/ObservableETC1985.htmAbstract: We consider the problem of detectability of macro-engineering projects over interstellar distances, in the context of Search for ExtraTerrestrial Intelligence (SETI). Freeman J. Dyson and his imaginative precursors, like Konstantin Tsiolkovsky, Olaf Stapledon or John B. S. Haldane, suggested macro-engineering projects as focal points in the context of extrapolations about the future of humanity and, by analogy, other intelligent species in the Milky Way. We emphasize that the search for signposts of extraterrestrial macro-engineering projects is not an optional pursuit within the family of ongoing and planned SETI projects; inter alia, the failure of the orthodox SETI thus far clearly indicates this. Instead, this approach (for which we suggest a name of “Dysonian”) should be the front-line and mainstay of any cogent SETI strategy in future, being significantly more promising than searches for directed, intentional radio or microwave emissions. This is in accord with our improved astrophysical understanding of the structure and evolution of the Galactic Habitable Zone, as well as with the recent wake-up call of Steven J. Dick to investigate consequences of postbiological evolution for astrobiology in general and SETI programs in particular. The benefits this multidisciplinary approach may bear for macroengineers are also briefly highlighted.
Many more along these lines, but this should give us a broad overview of the types and range of signatures and emissions I was referring to, and provide a basis for additional consideration and discussion.abstract - Advanced extraterrestrial civilisations which make extensive use of the fusion fuel resources of their local star and planetary system have numerous potentially observable characteristics. A circurnstellar nuclear fuel molecular effusion cloud, the principal observable, rapidly dissociates and neutralises to the atomic ground state, permitting the detection of hydrogen and tritium hyperfine transition radio lines at 1420 MHz and 1516 MHz, respectively. The negligible natural abundance of neutral atomic ground-state tritium suggests that its hyperfine line, the "tritium waterspout" centred in the radio SETI "waterhole" band, is ideal for interstellar communication and future SETI searches. Other possible observables of advanced civilisations include redshifted neutrino point sources, an artificial radio spectrum, anomalous blackbody radiation, fission waste absorption lines, Doppler and stellar spectral anomalies, and extraordinary magnetic fields.
Order of Kilopi
I really don't think that we would have detected anything unusual if it's only a few trillionths. The emissions would be utterly swamped by the emissions of the nearby stars.
This survey would definitely not detect a difference on the order of a few trillionths. But it does have a leg up on the others below--it actually looks at observational data.I'm throwing in several that should cover a significant range of considerations on the subject and then we can evaluate them and our own considerations, if you'd like:
"Placing a limit on star-fed Kardashev type III civilisations" - unfortunately, without a JBIS subscription you are probably going to be limited to the abstract at - http://adsabs.harvard.edu/abs/1999JBIS...52...33A
This one actually notes that it would be impossible for us to currently detect most of the discussed signatures. The two possible ones are noted to be within technological reach, but we have not yet made the required observations."Starry Messages: Searching for Signatures of Interstellar Archaeology" - this one has a full paper available for public reading at http://arxiv.org/PS_cache/arxiv/pdf/...001.5455v1.pdf
Since we haven't made the required observations to rule them out, you can't use these as examples of emissions which are conspicuously lacking. We simply don't know if they're lacking or not!
This is a proposal for new observation attempts, but not a study about the results of those observations (which have not been made). In particular, the author claims this is a promising possible way to detect alien civilizations, as opposed to an interesting piece of observational data disproving the possibility of alien megastructures."Macroengineering in the Galactic Context: A New Agenda for Astrobiology" - full paper available at - http://arxiv.org/ftp/astro-ph/papers/0606/0606102.pdf
Okay, this one also looks at some actual observational data. The money line, though, is this:"Observable Characteristics of Extraterrestrial Technological Civilizations" - full paper available at - http://www.rfreitas.com/Astro/ObservableETC1985.htm
Thus existing SETI searches cannot yet exclude the existence of an artificial hydrogen cloud near even the closest stars.
Since the observational data is not conclusive for even the closest stars, it is hardly evidence that these emissions are conspicuously lacking!
The bottom line: I still maintain that you don't appreciate how incredibly difficult it would be for us to observe alien life across interstellar distances.Many more along these lines, but this should give us a broad overview of the types and range of signatures and emissions I was referring to, and provide a basis for additional consideration and discussion.
Established Member
A colony capable of sustaining life for thousands of years on stored resources is going to be large enough that even limiting its ultimate transit speed to a thousandth of c is going to require massive amounts of energy to accelerate, and hundreds of millions of such launches (at the least) to transfer an entire mature stellar civilization to another star. Even over 10,000 years (which is an extremely long period for a stellar close encounter) that is on the order of 100,000,000/10,000 = 10,000 colonies per year, or roughly 30 colony ships a day for 10,000 years on an average (not the most efficient means of transfer - where you might have a few go early when transit distances were extended, and a few late catching up to a receding system, but the bulk of the transfer would occur during the few centuries of closest approach).
largely agreed, and this is, again, a single stellar level civ., not a galactic level civ. There may well be may stellar level civs that we can't detect that are centuries ahead of us technologically, and simply more than a few 100/1000 light years distant and beyond our capacity to clearly detect, but if such are relatively common, why aren't there any more advanced that we could detect,...and so on. it eventually comes down to either a "just so" universe, or one where tech civs are extremely rare.Although, I think that a civilization which was content to just sit in a single star system for all this time might just stick it out anyway. So what if the star huffs and puffs through a couple red giant stages? Just stay out of its way for some millions of years until it settles down into a nice stable white dwarf.
Banned
" Alien life deemed impossible." What utter rubbish. I find this statement wrong on every level.
It might be rare. It might not be. By the simple but obvious fact that there is life on this planet. Whats left to argue ?
This little thought never seems to win favor but just seems to have some relevance to this...
That the development of technical ability might not be the best indication of intelligence.
It is my contention that advanced intelligence might not need for space travel, or technical ability.
The answer is easy. We have the want to go look. To search out. To go where no man has gone before... familiar.
Order of Kilopi
These colonies have been sustaining life for billions of years. A few thousand years isn't a big deal. The only possible sticking point might be the availability of solar power (assuming they use solar power). But they can deal with this using large mirrors and/or beamed power and/or atomic power if necessary.
At 30km/s, the target system would be within about 30,000AU for that time. Assuming Oort clouds with a radius of 50,000AU, their Oort clouds will be overlapping for perhaps 30,000 years.Even over 10,000 years (which is an extremely long period for a stellar close encounter)
There may well be galactic level civilizations, and are simply more than a couple light years distant and beyond our capacity to clearly detect.There may well be may stellar level civs that we can't detect that are centuries ahead of us technologically, and simply more than a few 100/1000 light years distant and beyond our capacity to clearly detect,
Order of Kilopi
One method of restricting growth in a galactic civilisation is by imposing population control, a method in use in China at the moment. During the expansion phase of a colony rapid population growth may be regarded as desirable; the new colony can happily expand until a certain level of population and infrastructure is reached, enough to ensure a good breeding population, diversity and cultural richness. But exceed the comfort level and population pressure starts to bite.
I can imagine some benevolent ways of controlling population; simply explaining the situation cogently to a race of suitably intelligent aliens might be sufficient. But intelligent aliens, if they exist, are likely to be a diverse bunch; some form of coercion might be necessary in some cases- culling, ritual warfare, baby-eating...
http://lesswrong.com/lw/y5/the_babyeating_aliens_18/
Established Member
Though I can't support the claim, I like to think that population control is not much of an issue as the age of your population vastly increases or actual immortality is increased. I don't think it's too unreasonable to assume that a galactic civilisation would have very long life spans if not immortality.
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Actually there is a pretty big difference between sustaining life in the close proximity of a star and it's resources and sustaining life while on the move between stars, regardless, the thrust of my discussion was over the level and rate of energy released in transferring these colonies from one star system to a close approaching neighboring star system. Estimates usually assess something like 10,000 neighboring stellar close approaches where stars came within a few hundred thousand AU over the last 5By with an average transiting velocity difference of about 40km/sec.
very few stars ever approach each other this closely, at least in our section of the galaxy and the numbers I'm used to for the Oort cloud gives it a short radius of about 80,000AU and a long radius of about 100,000AU, of course these boundaries are more gravitational than populated.At 30km/s, the target system would be within about 30,000AU for that time. Assuming Oort clouds with a radius of 50,000AU, their Oort clouds will be overlapping for perhaps 30,000 years.
All manner of potenials and possibilities exist beyond the limits of our measure.There may well be galactic level civilizations, and are simply more than a couple light years distant and beyond our capacity to clearly detect.
Order of Kilopi
That actually makes the population problem worse; in a population with very-long-lived individuals, the death rate is very low, that means that the birth rate must also be very low.
The birth rate must not exceed the death rate plus the emigration rate or the overall population will increase. Interstellar emigration (as Trakar noes above) is likely to remain expensive and slow, so the birth rate will not be much higher than the death rate. This implies some sort of population control, voluntary or otherwise.
Perhaps immortals could be designed to be sterile (or almost sterile)?
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I like to think that anyone who is immortal would not be very fussed about having children, but I think you could probably argue more successfully that they would end up having more children. On the issue of designing beings to be sterile, I can easily imagine that a government that lets its citizens get the immortality treatment may want to introduce sterility or at least strong population controls.
Established Member
I still think the lack of visible exo-civ activity out there is strong evidence that these things are extremely rare, and quite probably we are unique.
Don't let's forget when we talk of spaceships etc, that is a mindset, it is what we can reasonably foresee for the next few centuries or couple of millenia. But what we are considering here are races that should have evolved hundreds of millions of years ago. We have no idea what their technology, if that is the right word, might be like.
On another point, let's consider the structure of the MW. The habitable zone (HZ) in the stellar disc has been moving out from the centre over time. The stellar density of the disc falls off on a natural-log scale. That is, if you plot ln(stars per cu. parsec) against galactocentric distance, you get a straight line with local variations due to spiral arms etc.
The scale-length of the MW disc varies in the literature between about 2 and 4 kpc, but the shorter scale length is favoured by most recent publications. If we pick on a value like 3kpc, that means the stellar density is 2.7 times greater when we move 3kpc closer to the MW centre. Move 6kpc further in and there are 7.3 times more stars per cu parsec than there are around here.
All this means that the first MW civilisations should've had an easier time with interstellar travel than the distances we are faced with, at our galactocentric distance of 8.4kpc.
Order of Kilopi
Actually, very many stars approach this closely.
Using the close stellar encounters calculator at orbitsimulator.com, there would be about 970 such close stellar encounters every billion years, or about one every million years. I use a figure of 50,000AU as a conservative guess for Oort cloud radius. We don't really know the radius of our own Oort cloud, much less the hypothetical Oort clouds of other star systems. (Enter 100,000AU into the calculator, since I'm talking about overlapping Oort clouds.)
Since this alien civilization could see the death of their star coming billions of years away, there are plenty of chances for them to be picky about which passing star to transfer to.
Order of Kilopi
This sort of gets cause and effect backwards. In the real world, the hard truth that can't be escaped is "some sort of population control". There is always a limit on population growth, period. Carrying capacity might be limited by food, or water, or space, or some other resource, but in any case there is always a limit of some sort.
Given that hard limit, all life forms always have "some sort of population control" limiting them. No exceptions. But this does not mean some sort of totalitarian regime imposing draconian birth control measures. The time and resource investment involved in reproduction is such that most life forms regulate themselves--they reduce their own reproduction rate by themselves if the investment of reproduction is less likely to pay off.
There can be circumstances where culture and/or economic systems provide perverse incentives to maintain an excessive birth rate despite straining against population limits, in which case some sort of government action may be necessary. However, this is only a possibility, not an inevitability.
Order of Kilopi
What exo-civ activity out there should be visible to us already? As I've noted, it would be very hard for us to detect alien activity across interstellar distances.
So, you have no idea what their technology might be like, but you're certain that it should be really visible.
I take the opposite approach. I like to speculate on what alien technology might be like, including what sort of star systems they would like to exploit with their technology. This gives ideas on how to go about detecting them, if they exist. By taking this approach, it becomes clear that it would plausibly be quite a technological challenge to even try to detect them.
Established Member
first time I think I've heard one in a million attributed as common. Not sure what the discrepancy is, but when I plug in 30,000AU and 1 Billion years I get ~85, which strtches the timeline to more like a little less often than once every 10 Million years.
Which is the approach distance you specified.
Not really sure why you are talking about the Oort cloud in the first place as it is largely irrelevent to the issue at hand, but there is no real need for guessing, it is quite easy to determine the orbital radius of this region based upon the mass of parent star.I use a figure of 50,000AU as a conservative guess for Oort cloud radius. We don't really know the radius of our own Oort cloud, much less the hypothetical Oort clouds of other star systems.
But you stated a close approach actually much closer than 30,000AU, in fact, you stated that the approaching star would be within 30,000AU for 10,000 years, which means that it would be much closer than 30,000AU at perisol.(Enter 100,000AU into the calculator, since I'm talking about overlapping Oort clouds.)
("...At 30km/s, the target system would be within about 30,000AU for that time. Assuming Oort clouds with a radius of 50,000AU, their Oort clouds will be overlapping for perhaps 30,000 years...")
I was simply trying to give you some benefit of the doubt, my bad.
I'm sure if every thing happens exactly as you imagine it to, reality would approximate your imagination.Since this alien civilization could see the death of their star coming billions of years away, there are plenty of chances for them to be picky about which passing star to transfer to.
BTW this sidetrack is irrelevent to the point of issue revolving around the energy expended and apparent from accelerating 30 colony ships a year for 10,000 years sufficiently for them to make the transfer from one star to another.
Order of Kilopi
Exactly true. But the fact that we are not swamped by ancient galactic civilisations chasing scarce resources implies that (if there are any civilisations out there) they are regulating their populations at an undetectably low level.In the real world, the hard truth that can't be escaped is "some sort of population control". There is always a limit on population growth, period. Carrying capacity might be limited by food, or water, or space, or some other resource, but in any case there is always a limit of some sort.
That seems to be a deliberate choice; there is still plenty of unused matter and energy out there which could be used in a more intensive fashion. The hard limits do not seem to have been reached.
Established Member
This presumes that stellar dense regions are capable and conducive to producing technological civ life, or life at all. The galactic habitable zone did not start out at the center and move outward. And "Habitable Zone" with reference to the galaxy, should probably be understood very, very loosely.
Order of Kilopi
Nonsense. It's not one in a million. We're talking about thousands of potential star systems to travel to, just by waiting for them. The lifespan of this civilization is in the billions of years, not a single year.
No, I didn't. I specified an approach distance of 100,000AU. That's the distance from star-to-star. The systems overlap, assuming each system has a radius of 50,000AU.
The Oort cloud defines the size of the star system. It defines the region where you can just "hitch a ride" by hopping from body to body, rather than going out of your way to make a "real" interstellar journey.Not really sure why you are talking about the Oort cloud in the first place as it is largely irrelevent to the issue at hand,
The size of the Oort cloud is not defined by the mass of the parent star, but rather by the location of the objects in the Oort cloud--if any exist. We simply don't know enough to even determine the radius of our own Oort cloud. We know even less about Oort clouds in other star systems (if they even exist).but there is no real need for guessing, it is quite easy to determine the orbital radius of this region based upon the mass of parent star.
Sorry about the confusion.But you stated a close approach actually much closer than 30,000AU, in fact, you stated that the approaching star would be within 30,000AU for 10,000 years,
Look. The fact is that we humans can already roughly predict when the death of our sun will occur. Maybe we're off by some hundreds of millions of years, but we can see it coming and we have plenty of time to try and do something about that future situation.I'm sure if every thing happens exactly as you imagine it to, reality would approximate your imagination.
I'm simply assuming that these hypothetical aliens would have similar scientific capabilities. It's not like the sun is suddenly going to die and they only have one year to hope for a passing star system to offer them sanctuary. (That's your "one in a million" chance.)
Nonsense, they will see it coming billions of years in advance. If they want to move to another passing star system, they will have thousands of chances to do so.
Order of Kilopi
Perhaps, so long as we remember that "undetectably low level" could easily mean "astronomically high levels". There could be thriving alien civilizations in the Alpha Centauri system and it would still be an "undetectably low level" simply because of the severe limitations of our interstellar observations so far.
In other words, these aliens might not actively regulate their populations at all, and it could still be "undetectably low levels".
It may be no more of a deliberate choice than the choice we make to not live absolutely everywhere here on Earth. Why don't we live inside volcanos? Why don't we inhabit every square meter of the arctic?That seems to be a deliberate choice; there is still plenty of unused matter and energy out there which could be used in a more intensive fashion. The hard limits do not seem to have been reached.
Order of Kilopi
Given a long life-span and a birth-rate exceeding the death-rate, we soon would.Why don't we inhabit every square meter of the arctic?
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