## And the number of intelligent civilisations in our galaxy is…

31573.52

No really. At least according to Duncan Forgan at the Institute for Astronomy at the University of Edinburgh.

The Drake equation famously calculates the number of advanced civilisations that should populate our galaxy right now. The result is hugely sensitive to the assumptions you make about factors such as the number of planets that orbit a host star that are potentially habitable, how many of these actually develop life and what fraction of that goes onto become intelligent etc.

Disagreement (ie general ignorance) over these numbers leads to estimates of the number intelligent civilisations in our galaxy that range from 10^-5 to 10^6.  In other words, your best bet is to pick a number, double it….

So Forgan has attempted to inject a little more precision into the calculation. His idea is to actually simulate many times over, the number of civilisations that may have appeared in a galaxy like ours using reasonable, modern estimates for the values in the Drake equation.

With these statistics you can calculate an average value and a standard deviation for the number of advanced civilisations in our galaxy.

Better still, it allows you to compare the results of different models of civilisation creation.

Horgan has clearly had some fun comparing three models:

i. panspermia: if life forms on one planet, it can spread to others in a system

ii. the rare-life hypothesis: Earth-like planets are rare but life progresses pretty well on them when they occur

iii.  the tortoise and hare hypothesis: Earth-like plants are common but the steps towards civilisation are hard

And the results are:

i. panspermia predicts  37964.97 advanced civilisations in our galaxy with a standard deviation of 20.

ii. the rare life hypothesis predicts 361.2 advanced civilisations with an SD of 2

iii. the tortoise and hare hypothesis predicts 31573.52 with an SD of 20.

Those are fantastically precise numbers. But before you start broadcasting to your newfound friends with a flashlight, it’s worth considering their accuracy.

The results of simulations like this are no better than than the assumptions you make in developing them. And these, of course, are based on our manifestly imperfect but rapidly improving knowledge of the heavens.

The real question is whether we’ll ever have good enough data to plug in to a model like this to give us a decent answer, without actually discovering another intelligent civilisation. And the answer to that is almost certainly not.

Ref: http://arxiv.org/abs/0810.2222: A Numerical Testbed for Hypotheses of Extraterrestrial Life and Intelligence

### 38 Responses to “And the number of intelligent civilisations in our galaxy is…”

1. Kent says:

How the hell can someone quote a mean at a precision of 37964.97 when the SD is 20?? That already tells me that this guy ain’t too good with his error analysis.

If one takes the weighted mean between the three hypothesese, one gets someone like 20,000 civilisations with an error of 15,000. (by inflating the weighted mean error by the terrible chi-squared).

But let’s be nice and take on the 30,000 number. If make the hypothesis that advanced civilisations tend to kill themselves off (or at least to a state such that they are no longer “advanced”). This period of time for us say started 50 years ago with first space flight and ends when destroy ourselves with nuclear weapons or global warming or one takes the average time for catastrophic collisions with meteors. It’s looking to be 1000-2000 years at most. This scales the number of intelligent civilisation to be in existence at any one time down to 0.4.

2. Robert says:

“Disagreement (ie general ignorance) over these numbers leads to estimates of the number intelligent civilisations in our galaxy that range from 10^-5 to 10^6.”

I would think, for most definitions of intelligence, that all scientists would accept a lower bound of 1 on the number of intelligent civilizations in our galaxy.

3. SAF says:

Why? Do you consider humans intelligent?

4. Michael says:

@Robert:

You’re assuming scientists consider our species as a whole intelligent. I know, completely different thing to the biological definition of intelligence; still funny to say though 😛

5. RPR says:

The calculations are for galaxies, not the universe. So the 10^-5 simply means that the chances of finding “intelligent” life forms in any particular galaxy is 1/100,000. So although in our galaxy we (if we are considered intelligent) are one, the odds are still 1/100,000 when considering galaxies of similar build.

RPR

6. […] El número de civilizaciones en nuestra galaxya es de 37,964 [eng]arxivblog.com/?p=674 por zokete hace pocos segundos […]

7. Learn to grammar.

8. […] And the number of intelligent civilisations in our galaxy is… […]

9. “The results of simulations like this are no better than than the assumptions you make in developing them. And these, of course, are based on our manifestly imperfect but rapidly improving knowledge of the heavens.”

Right. That’s the key point. The knowledge may be “improving”– and some of the parameters are now becoming known– but many of the numbers that go into the Drake equation have an uncertainty of “nobody know” or, “there are a lot of different speculations that can answer that question, but nobody has any good data to favor one hypothesis over another.”

10. […] information about the modified Drake equations

It’s silly to pretend evolution is random yet claim life does not exist on Mars and or any planet older than the Earth. Quite a contradiction in logic. A lot of weak minds in the fields of Science. The true calculation for civilizations with the assumption random evolution is what created ours is minimum civilizations = magnitude( set{planets older than the earth}). so, we have discovered at least 150 planets or so which most probably have life (or else life did not begin from primordial soup).

12. Beauford says:

I don’t understand how the three scenarios are mutually exclusive.

Panspermia could coincide with Tortoise and Hare conditions, no?

I hope we find life on Mars before I die.
Interestingly, I’ve read that methane gas in the Martian atmosphere is out of equilibrium with known geological and atmospheric processes. Assuming scientists have a handle these processes, this is good evidence to support the existence life on Mars.

13. Joshua Gay says:

Mars has two rovers on it that appear to be acting with intelligence.

14. Morgauo says:

“I would think, for most definitions of intelligence, that all scientists would accept a lower bound of 1 on the number of intelligent civilizations in our galaxy.”

Hmm… here in the US I am thinking that I’ll delay forming an opinion on this one till after the elections….

15. Jonathan Sluggish says:

In the above number, I assume Earth is calculated as having 0.52 of the advanced civilizations.

16. […] mal mit einem Ameisenhaufen Die Anzahl intelligenter Zivilisationen [via] in unserer Galaxie könnte – je nach präferierter Hypothese, wie intelligentes Leben entsteht – […]

17. Chris says:

@Kent, what bearing does the SD have on the number of sig figs used to represent a calculated number?

18. jerry says:

The lifetime (L) of a technological civilization is part of the equation. Also, as destructive as global warming is, even if it causes billions of lives lost, we would still maintain our technology. Furthermore, the prinicpal technology we look at is RADIO, high power as well. So a civ could run out the top as well as out the bottom. And although we have been spacefaring for ~50 yrs, we have been radio using for ~80 yrs. BTW, global nuclear war is also unlikely to cause a permanent loss of our technology.

19. Koshchei says:

Evolution is not random.

Evolution is about adaptation, wherein the most adaptive members of a species survive to pass on their genes.

In regards to this statistical exercise, it’s a case of garbage-in/garbage-out, which will get more precise as the data becomes more accurate.

20. […] Er is een welbekend gezegde dat luidt: er zijn kleine leugens, grote leugens en statistieken. Met statistieken kun je alles in feite wel bewijzen. En daarmee denk ik dat het statistische onderzoek van Forgan goed omschreven is. Bron: ArXiv.blog. […]

21. […] paper considers three different models for the odds of alien life: i. panspermia: if life forms on one planet, it can spread to others in […]

22. elliot says:

There are no other civilizations out there. This is a myth that science maintains in order to divert attention from the obvious likelihood that scientists on other planets destroy themselves about as quickly as scientists here have done so. Intelligent civilizations, to the extent that they don’t stay gatherer/hunters, destroy themselves at a rapid pace. Look at our own example. The scientists have hardly had hold of our civilization for a hundred years and we are already on the verge of total self-destruction. Science’s infatuation with other civilizations “out there” is the equivalent of Christianity’s afterlife myth: both are tools meant to keep you chugging through your every day life (or research) without considering the larger implications.

23. Rob P says:

“The scientists have hardly had hold of our civilization for a hundred years and we are already on the verge of total self-destruction.”

Paranoid delusional much, elliot? Seriously, you think scientists are responsible for all the problems we’ve had in the last 100 years? You think a cabal of scientists is somehow “in charge” and made this all happen?

Nice bit of blame-shifting there, bucko. Scientists don’t invent internal combustion engines or automobiles, and they certainly don’t build factories to churn out thousands of them. That’s for engineers and industrialists, the captains of industry. Scientists may have invented nuclear weapons — at the behest of the military and government — but it is the government and the military that keeps producing them.

Stop blaming scientists for mass destruction and all the ills that have ever befallen our modern civilization, and stop blaming them for the collapse you think is coming. It’s unfair to blame someone (or worse, a group of people) for something that hasn’t even happened yet, and might not happen at all. Instead, start blaming greedy capitalists and war mongers for creating the ills of the world. It’s not the fault of scientists that their work is perverted so easily by others.

“Intelligent civilizations, to the extent that they don’t stay gatherer/hunters, destroy themselves at a rapid pace.”

That is an absolutely unsubstantiated statement; it is opinion being passed off as fact. If you want to count individual human civilizations as supporting empirical evidence, then I would argue that most of the so-called destroyed civilizations, including Rome and the Aztec civilization, are still around in one form or another. The city of Rome still exists, and its people still do too; all of its technological achievements have been retained or exceeded. The Aztec people never died out, but were absorbed (more or less) by their conquerors; their cities died out, but it’s hard to make the argument that their city design and management skills were that great.

Still, the Drake equation really considers a “civilization” to be a planetary phenomenon, so in this sense, Earth has a single technological civilization, and that’s humanity. In this case, I would say we have a single civilization we can consider to be empirical evidence upon which to base conclusions, and this civilization still exists, so it has never collapsed. Looked at this way, you have no basis upon which to make ANY claims about how intelligent civilizations destroy themselves, or how frequently they do so.

24. Sam says:

“Science’s infatuation with other civilizations “out there” is the equivalent of Christianity’s afterlife myth: both are tools meant to keep you chugging through your every day life (or research) without considering the larger implications.”

Or maybe scientists are interested just cause they are, and Christians actually believe what they are saying… just a thought.

You my friend meet the definition of being paranoid.

25. Rick in China says:

@Kent
RE: “when destroy ourselves with nuclear weapons or global warming or one takes the average time for catastrophic collisions with meteors.”

End-of-times nonsense. You start off saying “How the hell can someone claim” then rant off about every potential advanced civilization..lets say sentient beings, shooting themselves in the foot and going back to primal or non-existence. Do you truly believe humans will not advance and expand before we self-annihilate? If you’re American I’d bet you’re a McCain supporter, poor God-fearing victim of fear-mongering.

26. Steve W says:

Has anyone considered a ‘rare intelligence’ hypothesis?

That is; where life is fairly common, but intelligence is incredibly rare?

Lets us say that life is likely, say 30%, to occur wherever there is liquid water, nutrients and some sort of exploitable energy. Just like on an early earth, or Mars, or Venus. You can get simple, single celled life.

But is seems to me for intelligent life to form, there are some fairly rigid other requirements, such as:

1. evolution from simple single to complex multi celular

2. evolution of a complex nervous system

3. evolution of appendages suitable for fine motor skills

4. evolutionary need for, or accidental evolution of, a large brain

5. ability to become dominate all other species

6. ability to overcome all environmental hazards

7. be non aquatic (hard to see how a Squid could smelt copper or form any sort of advanced technology, no matter how bright)

… and so on

If we take homo sapiens as ‘average’ in this process, the requirements to become an intelligent species seem to take a very long time – 3.5 billion years. During which, the home planet must:

1. not be impacted by something large enough to wreck the biosphere (like Mars)

2. not suffer either runaway green house or ice ball events (like Venus)

3. Have a very stable sun that does not blast off solar flares that irradiate the planet

4. Be far enough away from any supernova radiation for the entire period

5. Not run into any event that, say pushed the heliopause in too far, or depletes the ionosphere for example

… and so on

But all that aside. It took the better part of 3 billion years for life to make the leap from single to multi cellular. So perhaps for every billion years of ‘life’ existing reasonably undisturbed on a planet, there is a only a 1 in 7 chance it will make that leap. It is quite likely that a planet could go 5, 6 or 10 billion years with no multi-celled life emerging.

It took 500 million years for life to get to something _capable_ of becoming as advanced as humans, which happened about 1 million years ago. So perhaps there is only a 1 in 500 chance every 500 million years that that will happen.

We started to form a technological society about 10,000 years ago (before that, we made an equal impact on our areas of habitation that a beaver or an elephant would). Yet our, and related species, had brains the same as ours about 1 million years ago.

So perhaps there is only a 1 in 100 chance every 10,000 years that a technological society will emerge.

Then there is the view that we can not assume any ‘special’ place in the universe. Which seems to be taken to mean that we must be exactly average and that everything that applies to our evolution must be the norm for an other proposed life.

But we are dealing with very, very small probabilities. Buy the same logic, a lottery winner must assume that they are not special, and everyone else has won the lottery when they do. Which is clearly not the case.

Someone has to be the ‘first’. The first technological society to emerge in the galaxy has no special place in probability – only that the fill the necessary slot of ‘first’. Which could be us.

27. Jb says:

The rare intelligence hypothesis is appealing because look at Earth’s 4 billion year history… intelligent life only arose a few hundred thousand years ago.

Thing is, does one consider dolphins to be almost intelligent? They have a vastly different evolutionary path and seem to be moderately self aware. Or perhaps the Octopus? It tends to imply there are multiple paths towards intelligent life.

28. James says:

Anyone who thinks “origin of life x sufficient time = civilization” simply doesn’t understand how unlikely was the origin of complex animal life on this planet.

In other words, they think accepted evolutionary theory offers a more-or-less complete, and satisfying, explanation.

29. Eluned says:

Do you guys do financial instruments? 🙂

30. […] Drake equation , revisited […]

31. Lee says:

The question isn’t so much about how many civilisations might arise, but how likely it is that they will be around at the same time. How much longer will our civilisation survive, for example? We’ve only been around for a tiny fraction of the time available…

32. […] ET civilizations. Σύμφωνα πάντως με την πιο αισιόδοξη εκδοχή (the theory of panspermia), υπάρχουν συνολικά 37,964 εξωγήινοι πολιτισμοί στο Milky […]

33. R.. Mirman says:

The chance of other civilizations is extraordinarily small. The arguments are extensive and very strong. See website and book
Our Almost Impossible Universe:
Why the laws of nature make the existence of humans extraordinarily unlikely

34. […] And The Number of Intelligent Civilizations in Our Galaxy Is. . . 31573.52 […]

35. […] 2. And the number of intelligent civilisations in our galaxy is… […]

36. Daniel says:

The Drake equation lacks one entire factor-the odds the radio signal would be close enough to detect here. Of course that distance chnages as our technology gets more sensitive and more discriminating. It also assumes intelligence must not only have radio but continue with it. What somebody went optical or other non radiating technology?

What if radio won’t work due to a wild source of interference nearby? They get just as smart but based on some other communication tech.

37. Charlie says:

Even the most conservative result still gives us over 300. What’s the bottom line? The mathematical probability of the existence of at least one advanced civilization on a planet similar to ours located in our own galaxy is so high as to be almost totally certain.