2 civs per galaxy?

Great Debates
1

Some time back, I ran across the idea that at any one time:

Across 100 galaxies
there are 200 civilizations
give or take 30.

Aside from being crushingly depressing, this figure also strikes me as being perfectly reasonable.

Essentially, we’re alone. In the entire universe, this leaves only a handful of galaxies where a couple of civilized stars are within hailing range… when both are occupied by a people who can listen to the heavens, at the same time. Odds that we’re in that crowd? My lottery ticket is as good as yours.

I’d really like to see this debunked. Failing that, I’d settle for some truth. Do we have any reason to think that out of those thousand points of light, there’s anybody pointing a radio telescope back at us?

2

Bottom line: we haven’t got a clue. We don’t have enough data to draw any reliable conclusions about how common life is in the universe. Apparently, it’s rare enough that only one planet in our solar system has life. We think. But our solar system might be the exception. Maybe most solar systems have several life-bearing planets. Or maybe the creation of life on Earth was such an incredibly unlikely event that no other planet anywhere in the universe has ever had living creatures on it.

And, of course, that’s just life. How common is it for life bearing planets to evolve higher-function sophonts that can create something recognizable by humans as a civilization? We can’t guess how common intelligence is until we can determine how common life is, and we can’t determine how common life is until we can examine planets outside our solar system.

3

Engywook, you are inserting your own WAG into a calculation of your own construction, which will naturally make plenty of sense to yourself.

But you’re not alone in your supposition. Mike Shermer, writing for Scientific American, said virtually the same thing in an article which is usually a cut-down version of the editorials he runs in his own magazine. If we take the sole example we have–our own–we humans have been advertising ourselves for a distressingly short period of time, and weakly at that. Now that we have the ability to completely reverse that level of progress back to the stone age or earlier in a few short hours, one must ask exactly what we expect to find out there, except a fortuitous glimpse of a few extra gamma rays on the day of that civilization’s demise.

4

My wild assed guess is incorporated into the Orion’s Arm website, where there are seven or eight high tech civilisations in a galaxy, and several hundred low tech civs that do not broadcast strongly in the EM spectrum (so would be undetectable by current SETI methods).
We are probably looking for the wrong sorts of emissions… instead of radio broadcasts we should be looking for visible light laser transmissions and infra-red heat from artificial megastructures…
high power radiowave **broad[**casts are surely too inefficient to be used by advanced civilisations.
but if none of these things are up there, it certainly helps to explain the Fermi Paradox.

5

The Drake Equation is a “useful” tool for approximating the number of communicative civilisations in our galaxy. I put ‘useful’ in quotation marks because it’s not actually useful at all - ok, that’s probably a bit harsh, but given that the values for several of its variables can only be utterly conjectural at our present level of cosmological knowledge, you can’t really expect the results to be all that reflective of what the actual situation might be.

Here’s a nifty little online Drake Equation calculator

Here’s my take on it:

Rate of formation of stars in our galaxy (aggregate): 200 billion is roughly the current best estimate, but I’ll be optimistic and say we’re somehow missing another 100 billion. So, 300 billion stars in the galaxy right now.

% of those stars with planets: A bit trickier to pin down. I think the default 20% figure is based on our current knowledge of exoplanets, which is biased towards the detection of very massive ones. So I’d say that planets in fact form around most stars (reasonable enough, given current models of solar formation) and say that a whopping 80% of stars have at least one planet. Again, I’m being optimistic, but perhaps not unreasonably so? This is probably a reasonable point of debate (unlike some of the points below).

Planets per solar system that could sustain life: Another tricky one. The standard answer seems to be 3, based on our solar system, which includes Venus and Mars in a ‘habitable zone’ around the sun. I think this is optimistic myself. Additionally, I think a fair number of solar systems will contain NO habitable planets - most of the other solar systems we’ve detected so far have one or two giant (multiple Jupiter masses) gas planets orbiting fairly close to their stars - possibly in that planet’s habitable zone, and, if so, probably to the exclusion of smaller, rocky planets. So, on average across all solar systems, I’ll be pessimistic and say only one in three solar systems has one planet that is habitable (ie .33 per solar system). I might actually go lower than that if the calculator let me.

From here on it gets pretty flexible/unreliable.

Percentage of those planets where life actually does develop: Who knows? If panspermia theory is correct, it’s probably a high percentage, if not, it might be high, might be low. It’s really hard to extrapolate from a sample size of one. I’ve always liked the sound of panspermia theory myself, so I’ll go with 70% (reasons for picking a particular % at this stage are essentially all as flimsy as the one I just gave). If life is discovered elsewhere in the solar system, I’d boost that up to 90% or even 100% - ie, if life can develop, it will develop.

Percentage of planets with life that have intelligent life: Oh geez, who even knows? Define ‘intelligence’. Do the cetans (dolphins, whales) count as a separate incidence of intellegence on earth? What about other primates? There’s no way at all of even making a good guess at this one, as far as I can see. 1%? I’ll go with that.

Percentage of planets with intelligent life where technology develops: I was about to confidently say 90% or 100%, but it occured to me that if we accept the cetans as intelligent, then we have an example of intelligence arising but never producing technology. So I’d drop my estimate right down to 50%. Again, though, it’s darn near impossible to make any kind of guess. The whole Drake Equation thing is well and truly crumbling at this point.

And finally, the lifetime of these technological (and presumably communicative) civilisations: Again, who knows? There have been many technological human civilisations, none of which has lasted more than a couple thousand years, but society has changed so much that it’s impossible to use these as the basis for predictions of how long our current civilisation will last. And our current civilisation has only been galactically communicative for a few tens of years. I’ll be an optimist here (although not a really wild one), and say intelligent populations will remain communicative for an average of 10,000 years. Again, though, as with the last three variables, it’s basically a complete WAG.

So, all of that yields 277.2 communicative civilisations in our galaxy. Huzzah. Fiddling with those latter, very variable variables, we can alter that final figure to be incredibly small (essentially meaning Earthlife is the only life among ALL the galaxies), or, for 100% probabilities for intelligent, technological life arising and lasting essentially forever, we end up with more civilisations than there are stars in the galaxy.

My bold prediction is that the true answer lies somewhere within this range of possibilities.

Of course, the real purpose of the Drake Equation is simply to stimulate general debate and interest in the subjects of life, the universe and everything, rather than to make a scientifically sound prediction of the number of civilisations in the galaxy.

6

Sure there can be only 2 civs per galaxy–you just have to set that option in the pregame screen.

7

Well, according to E. E. Smith, Ph. D. planets in most galaxies are quite rare, and only arose in such abundance in our galaxy because of its collision with another galaxy aeons ago. Thus the great number of civilizations in our galaxy. Before that, there were only Arisia (home of Mentor, source of the Lens), and Eddore (with the unspeakable Gharlane!)

Of course, Doc Smith got his Ph. D. in doughnut science so one should take his opinion in context. But he wrote some dynamite space operas!

8

Can we count Qadgop as evidence of alien intelligence? I sure as hell ain’t never been to Mercota.

9

From an evolutionary viewpoint; Look how long, and how many different events and lifeforms it took just for us to appear.
Once you get habitable planets with the precursors to life on them, you still have to keep up the pressure, and produce periodic mass extinctions, across billions of years.
I’d heard somewhere, the figure 5-10 civs. per galaxy:Across several hundred million years!
Odds are not in our favor for ever stumbling over any of them.
And of course the other question; How do civilizations survive technological adolescence?

10

I’m not a fan of the Drake equation, because it’s basically just a complex formulation of a wild-assed guess. We don’t know nearly enough about our universe to make even reasonable guesses.

For example, a new theory says that a solar system needs a Jupiter-sized planet to act as a cosmic vaccuum cleaner, or else the inner planets would be bombarded by ‘dinosaur killer’ meteors often enough to prevent intelligent life from arising.

And we still don’t understand dark energy or dark matter. It may be that there are ‘habitable zones’ in entire galaxy, and the 3rd spiral arm that we’re in is in it.

There may be other longshot flukes involved in the creation of our solar system that we don’t understand yet. There could be lots and lots of things that should go into that equation that we can’t even formulate yet.

But the universe is very, very big. Here’s a really cool site that gives you a sense of how vast it is: The Universe. Click on the url, then start zooming out.

Another thing that needs an explanation. If you look at the evolution of mankind over what is a mere blink in the existence of the universe, and project that into the next thousand years, then ten thousand, then 100 thousand, then 1 million years, you would expect that a civilization that arises would very quickly expand throughout the universe, like a virus. It’s hard to imagine that if Mankind survives another 1 million years that we won’t have expanded throughout our own region of the galaxy. Hell, we can envision a time just hundreds or thousands of years from now when we might be dismantling planets, terraforming them, probing other stars, etc.

So it seems to me that once a civilization develops, it should expand throughout a siginificant junk of its galaxy in a very short period of time by cosmological time scales. So why hasn’t one?

Maybe because we’re the first. The universe is still in the early stages of its development - maybe there is life on millions or billions of planets, but we are at the head fo the race for cosmological dominance.

11

O

12

???
One estimate I read placed the nearest star-faring civilisation 500 million light years away, long enogh for no artifacts to have reached Earth in the history of life on this planet… we could look forward to meeting them perhaps a billion years from now.

13

I am a huge fan of the Drake equation, not because it provides useful answers, but because it gives us a scientific, quantitative way to think about a hugely hand-wavey, woo-woo subject like extraterrestrial intelligence.

We do not know the values of most of the variables in the Drake equation. However, that will change as our scientific knowledge increases. For example, as our techniques for detecting extrasolar planets are improve, we will be able to nail down the average number of planets per star. As we continue to explore our own Solar System, we will have much better idea of the fraction of habitable planets in a solar system. Perhaps as we learn more about abiogenisis (or panspermia!) we can narrow down the plausible ranges for the likelyhood of life evolving on planet.

Nonetheless, at the current time, the Drake equation doesn’t provide any useful results. However, it is useful for providing a framework for a discussion, so if someone makes a claim, like “the Universe is teeming with life” or “we are likely the only civilization in the Milky Way,” you can say, “What assumptions are you basing that on?” and you can get down to brass tacks about what variables we know and which ones we’re guessing at, and you can debate back and forth about what values we think the variables can have.

BTW, Erroneus, for the purposes of the Drake equation, the term “intelligent” means “able to build radio telescopes,” so, clever as they may be, until the dolphins or chimpanzees construct their own version of Arecibo, they don’t make the cut.

14

Another way to think about it. Let’s say, since the Universe is fairly young, that the earliest a civilization could have started anywhere was 100 million years ago. That would mean the farthest away we could possibly know about them would be in the Virgo Supercluster, which contains about 500 major galaxies, which would still be 100 TRILLION stars.

Our own galaxy has about 300 billion stars, and it’s only 100,000 light-years across.

Given the huge number of stars even in our local neighborhood, the total lack of signs of intelligence we’ve discovered so far is pretty baffling.

15

But remember, the Eddorians were not native to either the Milky Way or the other galaxy (let’s call it Milky Way Prime), or even to this plane of existence. So before the Big Smush of the Milky Way and Milky Way Prime, the Arisians were the only intelligent life that had arisen in either galaxy. So that gives a factor of 0.5 advanced life forms per galaxy, not 2.

Now, after the Big Smush life arose everywhere in both the galaxies, which might suggest a higher frequency than 0.5. per galaxy, but Smith indicated that was a consequence of panspermia. All the other life forms were descended in some way from the Arisians. (No life forms descended from the Eddorians, because they were utterly foreign to this plane of existence.)

So even by Smith’s own analysis, and even with the extremely unusual event of two galaxies colliding, the ratio remains at 0.5. There is no evidence either way whether that ratio holds true for all galaxies, or whether the evolution of life on Arisia was a unique event, not just for the Milky Way and Milky Way Prime, but for this entire universe. If the latter, the ratio may even go as low as one intelligent life form per universe.

(Although I wouldn’t say it’s decisive, one indication that this may in fact be true comes from the fact that the Eddorians surfed through several planes of existence before they settled on Milky Way Prime. They were looking for worlds to conquer and didn’t find any in sufficient numbers to satisfy their lust for dominance until this plane.)

16

Thanks for all the great posts.

Using the Drake Equation calculator, I get 3.7 civs out there who would have the technology to notice us.

100,000,000 stars - based on the admittedly shaky assumption that there are indeed regions of the galaxy that can be disqualified from the word go. If you’re not buying it, multiply the 3.7 figure proportionately.

80% of stars have planets. Again, we don’t know for sure, but that seems to be one of the less controversial numbers.

.33 life sustaining planets per solar system. There’s a lot of factors going into this one. I don’t really think there are two many solar systems out there with rocky planets, of the right albedo, in the rather narrow habitable orbit around the star. Then there are other factors that we have just considered (like the Jupiter consideration) and most definitely others we haven’t even thought of yet, so I’d actually be tempted to make this .33 much lower.

70% develop life. I can go with the assumption that if it can, it probably will.

1% chance that these life forms develop intelligence, capable of eventually developing technology. However it’s defined, intelligence is by no means an inevitable result of evolution. The long period of atypical climate stability on earth, the relatively sudden extinction of the dinosaurs, the disappearence of trees in Africa… not that these are the only conditions that allow intelligent life, but there’s no reason at all to think that a different form of intelligent life would have appeared instead under slightly different conditions. Witness, for example, the extreme success of dinosaurs, sharks, cockroaches, etc.

20% chance of developing technology. I wonder if I might be overgenerous here. Even the wheel is not an inevitable innovation, much less electricity, the atomic bomb, space travel, and the radio telescope. Referring to Guns, Germs, and Steel, it strikes me as amazing that there was even one place on earth (the fertile crescent) where there was a broad range of domesticable crops and animals, and the spread of agriculture across a broad distance was possible, and so on. I’d bet that most planets will have a lot of “pretty good” places like Central America, which had a lot going for it but didn’t have everything. But what it takes, I’d WAG, is at least one almost-paradise like the fertile crescent.

Lifetime of communicating civilizations: 1000 years. Tim Ferris wrote an article for the New Yorker a few years ago about a physicist who had a very simple way of calculating the amount of time humanity will exist. It’s based on the assumption that between 5% and 95% of its history is over. I think about it a little differently… in terms of the length of time that technology will continue to exist. Using the 5 - 95% range, we can say anywhere between about 5 more years and, with very good luck, another 2000 years. In any case, allowing another 100 years seems more reasonable than another 10,000 years.

A lot of stuff went into that… mostly gathered from lay publications… so take it with at least 2 grains of salt. But even if there were 37 other technologically advanced civilizations out there… or 3700… that would still put the nearest communicating civ very far away from us. So I think it’s no surprise that the answering machine is still at zero messages.

Last thought: 500,000 light years to the nearest civilization that can do interstellar travel, as eburacum45 mentioned? I can believe it… would be interested to know what it would take for a civ to pull that off (and my WAG is that we’re not gonna be one of them). I’d think it’s a very rare situation indeed. So best not to get tossed out of any Vogon constructor fleet spacecraft…

17

Here’s yet another parameter to consider:

from http://www.solstation.com/habitable.htm

Galactic Habitable Zone:

One of Sol’s unusual features is its orbit around the center of the galaxy, which is significantly less elliptical (“eccentric”) than those of other stars similar in age (and therefore metallicity) and type and is barely inclined relative to the Galactic plane. This circularity in Sol’s orbit prevents it from plunging into the inner Galaxy where life-threatening supernovae are more common. Moreover, the small inclination to the galactic plane avoids abrupt crossings of the plane that would stir up Sol’s Oort Cloud and bombard the Earth with life-threatening comets.

In fact, the Sun is orbiting very close to the “co-rotation radius” of the galaxy, where the angular speed of the galaxy’s spiral arms matches that of the stars within. As a result, Sol avoids crossing the spiral arms very often, which would expose Earth to supernovae that are more common there. These exceptional circumstances may have made it more likely for life and human intelligence to emerge on Earth. According to Guillermo Gonzalez (an astronomer at Iowa State University), fewer than five percent of all stars in the galaxy enjoy such a life-enhancing galactic orbit. Other astronomers point out, however, that many nearby stars move with Sol in a similar galactic orbit.

18

I prefer 16 civs (well, actually 18 counting myself and the Antarans) in a small cluster galaxy. This is with Grey’s Mod, so you have both the tech slowdown and the greater AI aggression, makes for a very intense game, yet easy to micromanage as you will probably have only 15 or so planets until you start conquering neighbors (I got hemmed in and for a long time I only had 8 planets until turn 300, when I attacked my neighbors and annexed them).

19

The big conceptual problem Iam having with the Drake equasion is finding a reason for a successful civilisation to end.
Even if only one intelligent race in a thousand manages to start interstellar colonisation, the level of technology required implies a good method of preserving information, and once a civilisation can implement some of Freeman Dyson’s ideas for energy collection there is no reason such a civilisation should ever collapse.
The ultra high tech civilisation that may develop in the future of humanity could gather energy from red dwarfs, and eventually black holes for hundreds of billions of years, all the while constructing diverse virtual habitats for the individual virtual entities to interact in…
similar things should be possible for any other intelligent race, and if so the galaxy should by now be practically all civilised,
with Dyson energy collectors round every star.
What, apart from the rare earth hypothesis, could act to prevent this scenario, where the stars become saturated with intelligence and its constructions?
To be honest, I am not sure that the Infra-red astronomers have been looking for the tell tale signs of planet sized processors, or of Bradbury’s Matrioshka Brains… but if anyone can point me in the direction of such a study, I would be very interested.
Could it just be that the cultures of two divergent intelligent species would be so inimical that they wipe each other out on first contact?
Would that happen every time?

http://www.orionsarm.com/

20

Could ‘dark matter’ in fact be stars that are now enclosed in Dyson spheres? Could we detect the black-body radiation of a star enclosed by a Dyson sphere?