Other civilizations in the Milky Way?

[Van Rijn]

I could easily build a longevity parameter into the model, if it would make you happy.

The issue is that it is an *assumption*. How do you, for instance, differentiate between long lived but not terribly expansive civilizations versus civilizations that just die out?

But it's not like you'd read that paper anyway, since it appears blog articles are all you require to be satisfied with your understanding of a topic under discussion.

You linked to the article. If it didn't properly represent your argument, some clarification would have been helpful. My concern is that, from the article, it sounded like the argument was very similar to ones I've already read (and no, not just blog entries) that make too many untestable assumptions.

But I'm not against reading your article. Is there a download location?

[Robert Tulip]

Literature says that civilizations could be millions of years older than us. Think of our technological progress in just the last hundred years. Voyager is leaving us at 61000 km/h. The speeds may be optimistic but I don't think they're unrealistic.

ETA: The model shows that the size of the holes depends mostly on the limiting value and not on travel time. The voids are emergent from resource consumption or other limiting factors, not including travel time.

I don't get this. You use a speed 45 times faster than Voyager, and then talk about 50 million years as a realistic age for an alien civilization. If you were conservative in your estimates, you would use the Voyager speed, but that would mean the time required to fill the galaxy would be two billion years, which is a very long time. Assuming a speed of C/400 makes it look like science fiction. Why does the size of the hole not depend mainly on travel time?

[Andrew D]

What literature? Based on what evidence?



But again, without knowing where technology will go, it's all speculation at this point.

The literature is cited in the paper. Of course its speculation, all science is to some extent, but its guided speculation.

[whimsyfree]

But the only civilizations we know about have life-spans of centuries, maybe millenia, if you assume optimistic definitions, and they're all strictly Earth based.

The last bit might be a clue that your sample is unrepresentative. I'm not sure what you mean by civilization but when people talk about alien civilizations I think they really mean alien species. The human species has been intelligentish for at least 1e5 years. If you mean civilizations in the historical sense, well the Chinese and Western civilizations both claim to have origins well over 2,000 years ago and they're both still going, more or less.

Why are these civilizations expanding to other stars in the first place? What's their motivation? How much does it cost? Unless star travel is pretty cheap I would wonder why, if they can build a starship, don't they just build another habitat in their home system?

That's a good question. The reasons could be metaphysical (e.g. desire to propagate life through the cosmos), but they are extremely hard to quantify. Attributing such motivations to intelligent aliens might seem condescending, but arguably much of the motivation for our space programs so far has been metaphysical. A more animal motivation is resource deprivation. Most animals will broaden their range when they find resources scarce. Eventually the materials needed to build new habitats will become scarce or the energy source used to power them fully exploited. The problem with this explanation is that interstellar travel is likely to be a very resource intense activity. If you're already short of resources investing in an interstellar spacecraft may be hard to justify, and be of no appreciable benefit to the population paying for it.

[Andrew D]

The issue is that it is an *assumption*. How do you, for instance, differentiate between long lived but not terribly expansive civilizations versus civilizations that just die out?

These are not blind assumptions; we can adjust parameters and evaluate the model at any value in their range. Proclivity to emigrate is a parameter, so we can adjust how not terribly expansive a model civ is. We do not model civilizations which just die out, every colony emigrates or does not each iteration based on a probabilistic parameter, so it is possible for a colony to fail to emigrate, which you can interpret as dying out if you wish.

You linked to the article. If it didn't properly represent your argument, some clarification would have been helpful. My concern is that, from the article, it sounded like the argument was very similar to ones I've already read (and no, not just blog entries) that make too many untestable assumptions.

But I'm not against reading your article. Is there a download location?

The article author oversimplified, as they always do, and made a few errors. If I would have known the majority of replies were going to be uninformed critiques by members who had no interest in reading the actual paper I would not have posted at all. I have to say that lesson is learned. PM me and I'll email it to you, it's not yet available for download. You have to understand, the paper is an evaluation of several hypothesis based on a realistic emigration algorithm, there are no three dimensional computational models in the literature. If you're referring to Landis, then we go into great detail about the shortcomings of that model, not including that he did not publish his algorithm or code or any three-dimensional images obtained from his "three dimensional" model. We intentionally avoid making some global assumptions in previous models. The only assumptions we make are that 1) a civilization will travel to the closest of a number of equally desirable systems 2) A civ with limited resources will limit their population density. The second assumption is soft, the maximum density is a parameter, so we can change it to a whole neighborhood and avoid it all together.

[Andrew D]

I don't get this. You use a speed 45 times faster than Voyager, and then talk about 50 million years as a realistic age for an alien civilization. If you were conservative in your estimates, you would use the Voyager speed, but that would mean the time required to fill the galaxy would be two billion years, which is a very long time.

Oh please, it took 75 years to get from kittyhawk to Voyager. As for the maximum age of a civilization, and I've already said this, we don't offer any sort of definition for what a civilization is, our interest is in the probability of a path between two distant systems.

With that said, it's quite sad how many objections I've gotten on this site to long-lived civilizations. I think you'll find that the scientific community is much more optimistic than BAUTforum. You might even say that your pessimism is ATM...

Why does the size of the hole not depend mainly on travel time?

Travel time was a parameter in the earlier versions, but it was a waste of processing; we've just built it into the interpretation of an iteration of the algorithm. Think about it, travel time didn't change how the civ grows (ie voids), only how fast it grows. If we held the other parameters constant and changed travel time, the same shapes would be apparent, they would just grow faster or slower. To get holes you need some sort of density limiting parameter, and even then the big holes mostly close up over time.

[Andrew D]

...but that would mean the time required to fill the galaxy would be two billion years, which is a very long time.

Yes, it is. However, the astrobiological literature says it has been possible for intelligent life to emerge within the galaxy anytime in the last five billion years, so that still gives a three billion year leeway even at Voyager speeds, which you know are far too slow.

[Robert Tulip]

Hello Roobydo, I confess I might be a bit of a dummy, but I just did not get in your paper why an expanding alien civilization needed such a complex lattice algorithm to model its growth. Why not just a simple expanding sphere? Surely, if they were, say, on Sirius, they could tell which nearby stars would be prospective, and would check them out without leaving big random Swiss Cheese holes in their empire? Especially if they had millions or billions of years to decide where to go, and could zoom around at millions of miles per hour.

[Andrew D]

Hello Roobydo, I confess I might be a bit of a dummy, but I just did not get in your paper why an expanding alien civilization needed such a complex lattice algorithm to model its growth. Why not just a simple expanding sphere? Surely, if they were, say, on Sirius, they could tell which nearby stars would be prospective, and would check them out without leaving big random Swiss Cheese holes in their empire? Especially if they had millions or billions of years to decide where to go, and could zoom around at millions of miles per hour.

We wanted to specifically evaluate Landis' hypothesis, which was that was that the clusters are grossly un-spherical and full of huge voids. Based on his models, we knew that it was possible for random graphs to take shapes indeed not spherical, so we intentionally introduced a parameter to cause the same phenomenon. We found that over time and the whole range of the parameter, the voids were much smaller than those reported by Landis (because of global assumptions he makes), so the shape is mostly spherical within a realistic range of parameters. The model shows that despite the shape, the radial growth is the same.

[NEOWatcher]

Oh please, it took 75 years to get from kittyhawk to Voyager.

But that is due to technological limits, not physical limits. Eventually the technology is going to be bumping into physical limits and stop growing.
It took 44 years to go from Kittyhawk (actually Kill Devil Hills - the gliders were in Kittyhawk) to the first supersonic flight.
And only about 15 years later we reached mach 6.
Now, about 40 years after that, we are stuck around mach 3 for production craft and only mach 9+ with experimental aircraft.

Eventually; the energy needed for such speeds in space is going to be prohibitive.

[Andrew D]

Eventually; the energy needed for such speeds in space is going to be prohibitive.

I agree, but I don't think c/100 is out of reach for a civilization capable of undertaking interstellar emigration on a large scale, which is what were talking about. The physical barriers of atmospheric flight are much different than for spaceflight, as you know, and I agree, the amount of energy needed to accelerate a large vessel to c/100 is staggering. However, we're really talking about civilizations who are capable of staggering energy use, civilizations which could be hundreds of thousands or millions of years old when they begin emigration.

The model can alternately be thought of as a search algorithm for self-replicating probes, so powered spaceflight concerns become less profound, but the results maintain validity.

[Ara Pacis]

Maybe it's in your paper, but it's not clear how many ships are sent and how often. I get that you're claiming 500 years from landing to launching a new ship, but does the new planet only launch one ship? It would seem to be to be a simple economic extrapolation, even for aliens, that economies of scale are more efficient. So, to quote a line from S.R. Haddon in "Contact", "Why build one when you can have two for twice the price?". I'd expect that the alien homeworld instead of launching 1 ship every 500 years might be just as likely to launch 500 ship in 1 year, every year, for hundreds to millions of years. If they can survive 500 years enroute, then how it would seem to suggest that recycling technology is robust enough to last even longer. This is why my standard reply to the start-stop-hop model of expanding galactic civilizations is to essentially plot a single route from the homeworld to the farthest edge of the galaxy and call this the nominal expansion timeframe, give or take a few years (there may be dropouts, but there's an unending stream coming up behind in short order).

[Andrew D]

"I am pleased to tell you that your revised manuscript entitled "Spatial dispersion of interstellar civilizations: a probabilistic site percolation model in three dimensions" has been accepted for publication in the International Journal of Astrobiology in its current form."

I know that BAUTers think they have a grip on things. I know that they spend a great deal of time reading popular science publications and science news, and have learned many things from that reading. But until you are able to abandon everything you already know, you will never really learn a thing.

[Swift]

I know that BAUTers think they have a grip on things. I know that they spend a great deal of time reading popular science publications and science news, and have learned many things from that reading. But until you are able to abandon everything you already know, you will never really learn a thing.

Congratulations on your paper, but that comment is borderline insulting. Do not make assumptions about what other members may or may not know or believe. Some members here probably do spend time reading popular science publications, other members spend time writing science textbooks and publications; don't dismiss their knowledge as just gleaned from the popular press.

[TooMany]

Let's suppose life is common, that evolution commonly leads to intelligent forms and that such intelligent forms develop a sophisticated technology such that interstellar travel is feasible. Then the galaxy could already be entirely "colonized" by self-reproducing "robotic" ships. (It is highly unlikely that our civilization would be the first to be capable of interstellar travel.)

Would alien life (or it's non-biological extension) actually try to "colonize" the galaxy?

It can be argued that mindless life forms always fill a system so long as resources are available. In fact, humanity currently acts as mindless life form. We are unable to control our population and our consumption and destruction of available resources. (I think it's very likely that the world is already overpopulated and that there is a real possibility of another collapse of world civilization.)

In our way of thinking, the only meaningful goal for humanity is to continually grow and to populate and dominate the galaxy. And yet, given the assumptions above, some other alien civilization should have already done this.

I suspect that the assumptions about life and interstellar travel are true. So it seems to me that a sufficiently advanced civilization either does not have the desire to colonize the galaxy or is prevented from doing so by a dominating civilization.

I can't rule out the possibility that an interest in other planetary systems exists, but if it does, then this interest is expressed without disturbing civilizations like our own (as in the Star Trek prime directive).

[Ara Pacis]

It can be argued that mindless life forms always fill a system so long as resources are available. In fact, humanity currently acts as mindless life form. We are unable to control our population and our consumption and destruction of available resources. (I think it's very likely that the world is already overpopulated and that there is a real possibility of another collapse of world civilization.)

I think you confuse lack of unitary control for lack of endeavor. Humanity has been controlling it's population through birth and death rates for millenia.

[Andrew D]

Congratulations on your paper, but that comment is borderline insulting. Do not make assumptions about what other members may or may not know or believe. Some members here probably do spend time reading popular science publications, other members spend time writing science textbooks and publications; don't dismiss their knowledge as just gleaned from the popular press.

I didn't mean to sound arrogant, just the opposite: I don't suppose I know more than them, but rather far less. My point is that their conviction to what they already know (what assumptions can and can't be made, how things are etc.) should be minimized for the sake of progress. My point is that in this thread people were quick to say "this can't be" and slow to say "can this be?" This is the opposite of science. I know that in reality, the model is certainly mostly wrong. And so was Bohr's.

[caveman1917]

I didn't mean to sound arrogant, just the opposite: I don't suppose I know more than them, but rather far less. My point is that their conviction to what they already know (what assumptions can and can't be made, how things are etc.) should be minimized for the sake of progress. My point is that in this thread people were quick to say "this can't be" and slow to say "can this be?" This is the opposite of science. I know that in reality, the model is certainly mostly wrong. And so was Bohr's.

Is this the paper based on that strategy game you worked on? If so, it's really cool you made it into a scientific paper that got accepted for publication.

[Swift]

I didn't mean to sound arrogant, just the opposite: I don't suppose I know more than them, but rather far less. My point is that their conviction to what they already know (what assumptions can and can't be made, how things are etc.) should be minimized for the sake of progress. My point is that in this thread people were quick to say "this can't be" and slow to say "can this be?" This is the opposite of science. I know that in reality, the model is certainly mostly wrong. And so was Bohr's.

I have the opposite opinion. Science is all about questioning assumptions that go into one's model.

[IsaacKuo]

(I think it's very likely that the world is already overpopulated and that there is a real possibility of another collapse of world civilization.)

In your view, when was there a previous collapse of world civilization? I apologize if this question sounds too obvious to you, but it honestly is not obvious to me. I don't think there ever was any collapse of world civilization. There have been some regional empires which have collapsed, of course, but even those didn't involve a civilization collapse--not even within their borders.

[Ara Pacis]

In your view, when was there a previous collapse of world civilization? I apologize if this question sounds too obvious to you, but it honestly is not obvious to me. I don't think there ever was any collapse of world civilization. There have been some regional empires which have collapsed, of course, but even those didn't involve a civilization collapse--not even within their borders.

I haven't read the Rise and Fall of the Roman Empire, but it sounds like a collapse from what I recall from Western Civ. Sure, life went on and it even had rules and government, but I wouldn't call it the same civilization. And while it may seem like the collapse of world civilization to locals, I agree it wasn't planetary in scope. I'd also like to know what TooMany's response to you is.

[Van Rijn]

I have the opposite opinion. Science is all about questioning assumptions that go into one's model.

Which is what I was doing. From the article linked in the OP, there appeared to be a lot of assumptions being made for this argument. That makes it a highly speculative argument. I have no problem with speculation as long as it is clearly stated to be speculation.

[neilzero]

Attempting to model off Earth civilizations is very speculative. It seems to me that a spire instead of a sphere, will be procedure for the first 10,000 years. We pick Centari A as the destination, and aim our spire where we think it will be in 10,000 years. We build several large manned craft that cruise the inner solar system for several years, doing sling shot maneuvers which boost their speed from average 5 million miles per year to 100 million miles per year. That is almost too fast, I think, to do a Jupiter sling shot maneuver, but we do it successfully and pass Neptune's orbital distance a few years later at 101 million miles per year. This is quite hyperbolic so we will average 100 million miles per year with respect to Centari A for the next 1000 years, as our Sun's gravity is quite weak beyond Neptune's orbit. The speed with respect to Earth or things in our solar system is unimportant as we are leaving. More craft do much the same about once per year, some achieving a bit more than 100 million miles per year up the spire towards Centari A. The faster craft will pass the slower craft in a few years to many centuries. At this time the slower craft transfers energy to the faster craft (perhaps with laser beams) allowing the faster craft to increase its speed to perhaps 102 million miles per hour. That isn't much, but done thousands of times we will have one (or a few) craft traveling perhaps 0.01% of C which will reach Centari A in 43,000 years. Most of the craft will be in serious distress many times in this long a period, so they will sometimes be taken in tow by a craft that is just barely passing them. This likely is not difficult and almost doubles the resources improving the probability of some live travelers in another century or two. These are of course generation ships with small crews.
More craft start up the spire approximately anually for 10,000 years or more. The improved technology craft typically pass the lower tech craft of previous centuries, but can still get an energy transfer from the slower craft if it has working systems to produce energy after many centuries. If this strategy works and a few survive near Centari A to build a civilization there, continuing with a working spire makes far more sense than starting a new spire. We may not know back home that the Centari A civilization is a success for many centuries as the long distance comunication system will have died of old age, and the survivers will be too occupied with surviving to learn how to retrofit the long range communications system. Logically, when, and if, the Centari A civilizations are able to launch there own generation ships they will launch in close to the opposite direction that they came from (thus continuing the spire for craft that arrive later and may not have sufficient energy etc to decellerate for a landing = swish right though the Centari A system. Another reason for continuing the spire, long term, is most of the crews enroute will die out, horribly, without occasional assistance from the newer passing craft. QED: spires not sphere. Neil

[Noclevername]

Most of the craft will be in serious distress many times in this long a period, so they will sometimes be taken in tow by a craft that is just barely passing them. This likely is not difficult...[snip]

Unless you have unobtanium-strength towing ropes, yes, it would be very difficult. Even at velocity differences of a few MPS, we're talking about truly masssive objects if they can contain enough life support for 43,000 years. Maybe they could shoot capsules of resources to each other with mass drivers, but towing? No.

[neilzero]

I'm glad you mentioned 43,000 years as I can imagine how angry the children will be if they are told there is maybe one year of disgusting supplies left, and estimated 43 years untill landing at Centauri terminal. They definately need to think more supplies than they will likely need. I did infer that technology advances might cut the trip time to 10,000 years for a few of the craft.
If the craft can exchange energy, then correcting for a few meters per second speed difference should be fairly easy (Minor direction differences may be extremely difficult, especially at 0.01% of c) even if both one million ton craft have few operational systems, which is likely after a few centuries. For a few kilometers per second, I agree, no way, even if they have invented the tractor beam. I did say SOMETIMES they would take them in tow. Obviously the spire is total insanity until we have at least a few more technological advances. Neil

[JustAFriend]

Voyager is leaving us at 61000 km/h. The speeds may be optimistic but I don't think they're unrealistic.

And the Voyagers, the best and fastest we could build, only weigh 1500lbs with only 200lbs of scientific equipment.
No payload.
No working drive.
No way to slow down.
No guidance.
By the time they even get to the middle of the Oort Cloud they will be cold and very very dead.

(I'm not saying we won't ever leave the Solar System, but too many people throw around the 'it can't be that hard to build a starship' from watching too much sci-fi.)

[Andrew D]

Is this the paper based on that strategy game you worked on? If so, it's really cool you made it into a scientific paper that got accepted for publication.

If only. Just the opposite. I noticed that the algorithm made incredibly interesting 3d structures that work great as "star maps," especially after randomly assigning a few resources to each node. I have thought that automating play or analyzing play between human players might shed light on competition strategies in randomly connected networks, but I've been working on some complex analysis and recurrence relations and just haven't gone back to it.

[Andrew D]

I have the opposite opinion. Science is all about questioning assumptions that go into one's model.

You misunderstand. I agree with your sentiment, which is the source of my frustration. Yes, question; but only with due diligence to the established literature. I insisted that assumptions were based on established literature that most of the discussion-contributors had not read (only one or two asked for the paper with references). This did not deter many early contributors from assuming that the assumptions were silly. In turn, they did not deter me from assuming that the early contributors were silly. The assumptions that the early contributors found silly were judged adequate by sitting professors who dedicate countless hours to the study of Astrobiology. So, as I had insisted, the early contributors were making silly assumptions of what we were assuming from a blog article, as I assume they had not read the literature necessary to adequately judge our assumptions.

[Andrew D]

For what it's worth, I don't see any problem with this sort of scientific paper and modelling. So what if some of the hypotheticals are untrue? This is about making predictions based on hypotheticals, which in turn may help falsify or confirm those hypotheticals.

As for this particular paper and model, I'm not sure what is novel compared to previous growth models. Some factors that I wish were accounted for are stellar motion, vastly uneven star system value, vastly uneven stellar density, variations in desired star system resources, territorial factions, and warring factions.

Stellar motion is a big deal for models which purport to show dead ends or some ultimate limit to growth on gigayear scales.

Vastly uneven star system value relates to the fact that some star systems have many orders of magnitude more power or resources than others. Star systems with black holes or neutron stars offer cheap relativistic propulsion. Red dwarf systems are numerous and long lived. White dwarfs offer some interesting possibilities. Systems with warm jupiters or brown dwarfs offer inexpensive exploitation of oort cloud objects.

Vastly uneven stellar density relates to how star clusters offer large numbers of star systems within easy access, so they would be more promising places to expand to than elsewhere.

Variations in desired system resources relate to how self replicating probes may only be programmed to exploit particular resources, available only in some fraction of star systems or in interstellar space (interstellar space resources may be particular desirable for military probes, since they are stealthy). It may also relate to biological aliens only desiring planetary resources of a certain type.

Territorial factions relate to how a faction may not accept incursions of other factions into their general territory, even if the incursions are into unoccupied star systems. The above factors represent various reasons why a faction may leave gaps of unoccupied star systems. Add in territoriality, and these gaps may be purposefully enforced against incursions.

Warring factions are essentially similar to territorial factions, especially if there are three or more factions. With three or more factions, there's a strong incentive to maintain border neutral zones rather than actively fight rivals. Engaging in an active conflict tends to weaken both of the parties involved by draining them of fighting units and resources. This punishes the aggressor by making him vulnerable to the other parties. This gets into some complexities of game theory.

Those are the sorts of things I'd like to see in interstellar expansion models.

Do you do any programming? I have half of a strategy game that you might be interested in. It's written in Matlab :/

[Andrew D]

And the Voyagers, the best and fastest we could build, only weigh 1500lbs with only 200lbs of scientific equipment.
No payload.
No working drive.
No way to slow down.
No guidance.
By the time they even get to the middle of the Oort Cloud they will be cold and very very dead.

(I'm not saying we won't ever leave the Solar System, but too many people throw around the 'it can't be that hard to build a starship' from watching too much sci-fi.)

Give it 50 million years. I'm sure we'll figure it out.