Starward ho!
Posted by aogSaturday, 11 July 2009 at 11:40 TrackBack Ping URL

The Daily Duck mentioned this article on galactic colonization and the Fermi Paradox and I commented on how I had saved it for later abuse because it was so obviously bogus. Let’s get started!

Growth of these civilizations would be exponential, Fermi implied

No, he didn’t. This is the primary error of the article and puts it on the wrong track from the start. To start with, our universal is three dimensional so to occupy space you would only need cubic expansion, which is enormously less than exponential. Our galaxy is a disk, so quadratic would probably suffice. If the expansion proceeded along arms it might only require linear expansion.

What Fermi really observed was that even at very low speeds compared to lightspeed a civilization could cover the galaxy in what, in galactic terms, is a short period. There was no requirement for exponential growth.

For any expansion to be sustainable, the growth in resource consumption cannot exceed the growth in resource production. And since Earth’s resources are finite, and it has a finite mass and receives solar radiation at a constant rate, human civilization cannot sustain an indefinite, exponential growth.

I have never seen any discussion of the Fermi Paradox that contained the assumption, as this does, that a single planet would handle colonizing the entire galaxy. Quite to the contrary, the presumption was always that it would be driven by n[th] generation colonies. That is, further expansion is generated by colonies on the fringe so no single planet ever colonizes anything but nearby stars. In this model, the overall resource base grows faster than what is needed for expansion. This argument is akin to arguing against bonfires because a match does not have enough wood for a large blaze.

A more minor error is that even this shows that indefinite exponential growth is not possible, but it doesn’t show that the limits to growth are smaller than the requires for colonizing the galaxy. The galaxy is, after all, also finite. The argument doesn’t even work on its own terms.

What’s funny is that Skipper didn’t notice that much of this was layed out in the very first comment on the article.

Comments — Formatting by Textile
Harry Eagar Saturday, 11 July 2009 at 13:31

Yeah, but if we assume that the motivations of the creatures are remotely like ours (a wild assumption), and consider the one datum we have: it took us 4 billion years to get to the point where we are capable of thinking about it; then think about the first exploring society.

They spend X effort in looking and find nothing. So they give up. No. 2 spends X effort with a very slightly higher probability of success, so they give up. . . .

If the mean time between the rise of civilizations is long, and if — as I speculated at DD — ZPG has taken over, then there might not be a whole lotta searchin’ goin’ on.

Peter Burnet Saturday, 11 July 2009 at 16:45

It’s funny how everyone assumes space colonizers and explorers would have to have good, rational, cost-effective reasons for embarking on such a quest. Can’t they imagine a distant planet whose leader, when asked why they should travel so far at such expense to invade Earth and eat its inhabitants, might answer: “Because it’s there!”

Annoying Old Guy Saturday, 11 July 2009 at 18:16

What any expanding civilization finds is mass, energy, and living space. That’s easy to find, so I don’t see why the first exploring species would give up, since they would find what they’re looking for. It’s the second one that’s in trouble, because the first one will have taken all the good stuff.

My presumption of motiviations comes from evolutionary psychology, which is that life expands as much as it can. If one presumes a species that expands to cover its world, why would it stop there?

We also have no idea where our 4 gigayears lies on the distribution. 100 megayears earlier and the galaxy could be filled. Moreover, the galaxy is much older than 4 gigayears so it’s entirely possibly that some other species got to where we are today before the Earth even formed.

I don’t see any alien species coming here to consume us — the proteins are likely incompatible. Disassembling the Earth for building material, that’s what we should worry about.

Peter Burnet Sunday, 12 July 2009 at 07:24

I don’t see any alien species coming here to consume us — the proteins are likely incompatible.

Touché. But think what cool coffee table ornaments our heads would make.

pj Sunday, 12 July 2009 at 09:22

Peter - True, they can probably figure out how to animate our nerves and make the eyes follow everyone around the room, like the portraits in Harry Potter. I could see poachers getting 50 Grotznits per head.

Harry Eagar Sunday, 12 July 2009 at 14:12

‘It’s funny how everyone assumes space colonizers and explorers would have to have good, rational, cost-effective reasons for embarking on such a quest’

Just my point, Peter, though I may not have made it very well. We have exactly one datum point, beyond which we can speculate in any direction. Most speculations sneak in limiting assumptions. I was always amused by Carl Sagan, who liked to imagine improbable forms of life like floating silicon creatures but was incapable of imagining any intelligent life that wasn’t pretty much like Carl Sagan.

I don’t know who I learned it from, but he was almost certainly right when he said that the only thing we can be sure of about other life, if it exists, is that it will experience darwinian competition.

And I suppose that a lifestyle that searched and searched without finding might throw up a minority sect that insisted on continuing to search — as we have with ghost hunters — but you cannot be sure.

Annoying Old Guy Sunday, 12 July 2009 at 15:33

What is it, exactly, for which you think that minority would continue searching?

Harry Eagar Monday, 13 July 2009 at 00:10

Dunno, but it could be inward rather than outward. I was thinking of Louis Agassiz who, when asked how he had spent his summer, said, ‘I spent it traveling. I got halfway across my backyard.’

Annoying Old Guy Monday, 13 July 2009 at 07:57

That’s a theory that comes up frequently, especially among the trans-humanists. It’s sometimes known as the “Holodeck Trap” — once you have really good virtualized environments, why go anywhere?

Hey Skipper Monday, 13 July 2009 at 10:52

No, [Fermi did not imply growth of these civilizations would be exponential]. This is the primary error of the article and puts it on the wrong track from the start. To start with, our universal is three dimensional so to occupy space you would only need cubic expansion, which is enormously less than exponential.

The article’s used the term exponential to refer to the required growth rate to colonize a large volume over a certain amount of time. The author’s use of “exponential” is completely consistent with the most common definitions for the term.

I have never seen any discussion of the Fermi Paradox that contained the assumption, as this does, that a single planet would handle colonizing the entire galaxy.

I don’t see where it states a single planet colonizes a galaxy, but rather that any life form capable of producing a civilization will not have exponential population growth, and that without that kind of growth, colonization will proceed extremely slowly.

Assume 10,000 people colonize a planet Earth like in all respects except for the absence of humans. What kind of population growth rate would be required for those 10,000 people to be resource driven to further expand?

A more minor error is that even this shows that indefinite exponential growth is not possible, but it doesn’t show that the limits to growth are smaller than the requires for colonizing the galaxy. The galaxy is, after all, also finite. The argument doesn’t even work on its own terms.

The terms I read into the article is that life forms capable of technological civilization will not have indefinite exponential growth, because the two are incompatible. Therefore, even granting all of the rest of the Fermi Paradox’s assumptions, the growth in total population will severely limit the rate of colonization: even presuming capability, there will be scarcely any need.

What’s funny is that Skipper didn’t notice that much of this was layed out in the very first comment on the article.</i.

Oh, I noticed it alright, I just didn’t buy it.

My presumption of motivations comes from evolutionary psychology, which is that life expands as much as it can. If one presumes a species that expands to cover its world, why would it stop there?

Does it? More to the point, does human life expand as much as it can? We have not colonized the oceans at all, and much of Earth’s landmass is effectively unpopulated. For the one data point we do have — which is, after all, what you are basing your evolutionary psychology claim upon — a life form capable of a technological civilization does not expand anywhere near as much as it can, either in terms of area or numbers.

Annoying Old Guy Monday, 13 July 2009 at 11:20

Skipper;

I don’t see any of those definitions being “required growth rate to colonize a large volumne over a certain amount of time”. Could you point me to one more specifically? Most of them define it as a fixed rate of increase, but I don’t see what that’s required.

I don’t see where it states a single planet colonizes a galaxy

Here’s the money quote, emphasis added —

And since Earth’s resources are finite, and it has a finite mass and receives solar radiation at a constant rate, human civilization cannot sustain an indefinite, exponential growth

That is, the counter-argument to continued exponential growth is the single planet Earth. On the flip side, find me any mention of using non-terrestial resources in the article.

Assume 10,000 people colonize a planet Earth like in all respects except for the absence of humans. What kind of population growth rate would be required for those 10,000 people to be resource driven to further expand?

Over what time period? At what level of per capita resource consumption? At a 1% annual grow rate, the planet has 10 billion people in less than 1400 years. Need I point out that’s an eyeblink on the galatic time scale?

The terms I read into the article is that life forms capable of technological civilization will not have indefinite exponential growth, because the two are incompatible.

Yes, I agree with that. My point is — what is the limit point of exponential growth? When does it cease? “Indefinite” is, well, indefinite. The article provides no basis on which to believe that the limit point is reached before the galaxy is colonized. In fact, to the contrary - even the article’s argument is based on the assumption that exponential growth is stopped by resource limitations, which implies (if you allow interstellar travel at all) that growth stops when galatic resources become limited. That is, after the galaxy is colonized. Unless, of course, you start with the assumption that only a single planet contributes to the colonization effort :-).

You make a different argument, which is similar to Mr. Eagar, about whether a civilization would want to expand that far. That is not, however, the argument made in the cited article. Just remember that your argument must apply to every technological civilization. If it’s not true for just one, we have the Fermi Paradox. Given that we may well not be able to understand the motivations of aliens, that seems a bit presumptious.

P.S. As for colonizing the oceans, they’re working on it. You are looking at this on a human time scale, when you need to look at it on a geological or galactic time scale, where a million years isn’t a long time.

Hey Skipper Monday, 13 July 2009 at 13:43

You are reading too much into the money quote. Earth’s resources are finite, therefore [Earth based] human civilization cannot sustain an indefinite, exponential growth. If, in fact, Earth based civilization experiences indefinite, exponential growth, that would drive us to one of two things: either stop the growth, or expand beyond Earth. To my eye, the words I put in brackets are so strongly implied as to be redundant.

Alternatively, if technological civilization and exponential growth are incompatible, or at least do not occur together, then Earth, or any other technological civilization will never be driven to colonizing space due to resource constraints.

Over what time period? At what level of per capita resource consumption? At a 1% annual grow rate, the planet has 10 billion people in less than 1400 years. Need I point out that’s an eyeblink on the galatic time scale?

Well, 1% growth rate is exponential. Think instead of average total lifetime fertility. In an technological civilization, what TLF is required to expand from 10,000 to 4 Billion in, say, 1,000,000 years? How long will it take if the TLF is 2.1? In the only civilization we know of, TLF decreases as technology advances. Unless something completely unforeseen happens, human population will stop growing and start decreasing during your lifetime. On what basis do you presume even sustained 1% population growth?

Your reading is very counter intuitive. Let’s take it your way. If resources alone are the growth limit, and there are other civilizations, then we would have seen them by now. Alternatively, we are alone, or first. That simply restates Fermi.

However, the article isn’t restating Fermi, but rather trying to show that there could be many civilizations in the galaxy, but no, or extremely slow, colonization, even if we ignore distance barriers.

In other words, the absence of evidence is not evidence of absence.

My argument has less to do with the desire to expand than the capability to do so. The impediments to interstellar travel alone are an extremely high hurdle.

Now, add just one more constraint: no colonization will occur without a destination, and that destination must already be tolerably close to habitable for the colonizing civilization.

The stellar density in the galactic core is too high for life; in the periphery, too low for suitable planets. So, confine ourselves to the stellar density in the Goldilocks region. Let’s presume we can eventually detect an M-class planet around any star, regardless of the ecliptic orientation, within 100 light years. What is the required frequency of M-class planets within that region for there to be an unbroken path of planets within that range as a civilization expands?

We don’t know the habitable planet rate, but we do know stellar density, and can make a good stab at detection distance. I don’t have time for the math, but I’ll bet the habitable planet rate has to be much higher than seems plausible for civilizations to occupy other than isolated “islands” within the galaxy.

As for colonizing the oceans, they’re working on it.

That’s not colonizing oceans, that is expanding land area in the very few places where ocean front property is extremely valuable. NB: there are no barriers to colonizing the oceans at this moment. Yet despite that, no one seems to have any desire to do so.

I am looking at this on a human scale, which is one of the few data points we have. There is no reason to believe that human population will do anything other than gradually decline starting in mid-century. Where that decline will end, who knows. But there is simply no reason to believe that, no matter the time scale, humanity will grow even to the limits of Earth’s resources.

Annoying Old Guy Monday, 13 July 2009 at 15:34

Skipper;

Having read the cited article and the original article, I stand by my interpretation of that money quote. If your reading is correct, then it’s incoherent, as a cessation of exponential growth on Earth is irrelevant to galactic colonization unless it is Earth, and Earth alone, supporting it.

What the authors do is argue by analogy that since human civilization on Earth cannot expand forever, neither will an interstellar. This fails because even a sustainable civilization on Earth expands everywhere. In fact, the real point of the article (and I encourage you to read the original) is to argue for switching our economic model to “sustainable development”, the Fermi connection being to me primary a rhetorical disguise.

if technological civilization and exponential growth are incompatible

You’ve gone wrong at this point, since that’s not an argument made in any of the articles. It was indefinite exponential growth. Your house is not compatible with the indefinite growth of your children, but that doesn’t mean your house is not compatible with any growth of your children.

what TLF is required to expand from 10,000 to 4 Billion in, say, 1,000,000 years?

Looks like a growth rate of .001%. I am not sure what that translates to in TLF values, but I suspect it is not detectably different from replacement level. Because these values are so nearly indistinguishable, I don’t see any civilization managing to hit that level over the long term.

the article isn’t restating Fermi, but rather trying to show that there could be many civilizations in the galaxy, but no, or extremely slow, colonization

No, it is trying to show that there are no civilizations that are not static or very slow growing. I am entirely in agreement that the galaxy could contain many static or very slowly colonizing civilizations. But even one, just one, that is not, creates the Fermi Paradox.

Jack Diederich Thursday, 16 July 2009 at 02:29

This bit from the article: since Earth’s resources are finite, and it has a finite mass and receives solar radiation at a constant rate, human civilization cannot sustain an indefinite, exponential growth

I know they aren’t specifically writing about current Earth politics but I couldn’t help flinching at the use of “sustainable” “finite” and “resources” in one sentence. The original article also talks about “expansion in population, environmental impact, and the consumption of resources.”

All my alarm bells are ringing that these folks might only be kinda talking about science sideways (if you squint funny).

Annoying Old Guy Thursday, 16 July 2009 at 08:51

Yes, I definitely got the impression that the sustainability meme came first, everything else later.

Hey Skipper Thursday, 16 July 2009 at 12:43

AOG:

I just read the original article, and stand by my interpretation of what it says: the expansion of the originating civilization and its colonies cannot be exponential over the time period in question. It says nothing about the originating planet supporting that expansion, other than seeding it. It does fail to note what should be an obvious observation. The originating civilization itself cannot expand exponentially, because even a small sustained compound increase will lead to arbitrarily large population density within the the time frame the Fermi paradox considers.

It also fails prey to the airy-fairy assumption that not only is interstellar travel possible, but that it is also possible to move substantial population from one star to another.

And it also completely neglects the consequences of the possibility that the mean distance between habitable planets exceeds detection range.

Annoying Old Guy Thursday, 16 July 2009 at 14:46

We’ll just have to disagree. Look at Jackie’s quote above, which again equates “Earth” and “human civilization”. This is done repeatedly in the article. Moreover, I don’t recall any discussion of “the timer period in question”. Again, if you presume the feasibility of interstellar travel, what stops the exponential expansion before the galaxy is colonized? Certainly that is not addressed in the paper. Instead it presumes that expansion stops at the planetary scale which then shapes the civilization in to a “sustainable” mode which then doesn’t expand even when interstellar travel becomes available. As I noted, that’s certainly a plausible scenario for any given technic civilization, but all of them? Much less plausible.

that it is also possible to move substantial population from one star to another

I didn’t see where that came up. After all, as we noted earlier in this string, it doesn’t take much of a starting population to yield a fully populated planet in short time periods.

P.S. We’ll also have to disagree on whether “Class M” planets are a requirement that cannot be constructed. All of the expansionists I know presume not (example).

Hey Skipper Thursday, 16 July 2009 at 17:01

Yes, they do refer to the Earth and human civilization; after all, it is the only data point we have.

… “the time period in question”.

The article says the galaxy could be thoroughly colonized in 650,000 years (presuming no time between stops).

Again, if you presume the feasibility of interstellar travel, what stops the exponential expansion before the galaxy is colonized?

Because the entire population is increasing exponentially throughout the period. That means the source planet and all successor planets would have to export an exponentially increasing number of people (or whatever). If the core civilization is expanding exponentially, as does every child colonies, etc, where does further exponential increase of the core civilization go?

Presuming the feasibility of interstellar travel, or terraforming, amount to religious beliefs required to make Fermi’s utterance a paradox. Sure, why not promiscuous planet formation like whipping up a Cup-o-Noodles? Why not accelerate however much mass we want as much as we want and then be able to stop at the other end?

It is worth noting that technical advances here on Earth over the last twenty years have gut-shot the entire presumption underlying SETI.

Annoying Old Guy Thursday, 16 July 2009 at 17:20

Usually when one speculates, one envisions things that are not yet data points.

As for the entire population growing exponentially, that is precisely the point I was making in the original post about exponential growth not being needed. It only has to last long enough per star system to kick off the next generation of colonies. After that, it’s irrelevant. It’s why the entire thrust of the article’s argument is so wrong.

Presuming the feasibility of interstellar travel, or terraforming, amount to religious beliefs required to make Fermi’s utterance a paradox

No, it is simply a stipulation for the purposes of this discussion, which is about a particular article that makes that assumption. As I noted previously, one can make an argument against the Fermi Paradox, as you do, by claiming that interstellar travel is too difficult to permit large scale expansion. That’s a valid argument BUT it’s not the argument being made in the article under discussion. I was merely pointing out where you were making an assumption about which other people, such as me, have different views.

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