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Number of ET Civilizations In Our Galaxy Is 37,964
Posted by
CmdrTaco
on Mon Oct 20, 2008 07:48 AM
from the give-or-take-infinity dept.
from the give-or-take-infinity dept.
KentuckyFC writes "The famous Drake equation calculates the number of advanced civilizations in our galaxy right now. But the result is hugely sensitive to the assumptions you make about factors such as the number of habitable planets that orbit a host star, how many of these actually develop life and what fraction of these go on to become intelligent etc. Disagreements about these figures leads to estimates for the number of advanced civilizations ranging from 10^-5 to 10^6. Now an astronomer in Scotland has worked out how to make the calculations more precise so that different theories about the origin of planets, life and civilizations can be compared. His calculations say that the rare-life hypothesis predicts only 361 advanced civilizations in the Milky Way now. However, the so-called tortoise and hare hypothesis predicts 31,573 and the theory of panspermia says that there ought to be 37,964 extraterrestrial civilizations more advanced than our own in the Milky Way."
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New Paper Offers Additional Reasoning for Fermi's Paradox 774 comments
KentuckyFC writes "If the universe is teeming with advanced civilizations capable of communicating over interstellar distances, then surely we ought to have seen them by now. That's the gist of a paradoxical line of reasoning put forward by the physicist Enrico Fermi in 1950. The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because if the number of intelligent civilizations capable of communication in our galaxy is greater than 1, then we should eventually hear from them. Now one astrophysicist says this thinking fails to take into account the limit to how far a signal from ET can travel before it becomes too faint to hear. Factor that in and everything changes. Assuming the average communicating civilization has a lifetime of 1,000 years, ten times longer than Earth has been broadcasting, and has a signal horizon of 1,000 light-years, you need a minimum of over 300 communicating civilizations in the Milky Way to ensure that you'll see one of them. Any less than that and the chances are that they'll live out their days entirely ignorant of each other's existence. Paradox solved, right?"
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What a great example! (Score:5, Insightful)
Re:What a great example! (Score:5, Funny)
The original estimate was 32768 and an overflow flag.
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Re:What a great example! (Score:5, Informative)
That's 32767 and an overflow flag.
And get off my lawn.
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Re:What a great example! (Score:5, Insightful)
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Here is an interesting one. (Score:5, Interesting)
No kidding. Our current estimates of the number of stars in the galaxy only go to about one significant figure, with upper and lower estimates differing by a factor of two. That puts a pretty serious cap on the precision of his answer.
One of my peers is an astrophysicist. Nearly all of their calculations are done to ONE significant figure. It ends up that they typically just add up exponents. The numbers are usually so huge, eg. 1E27, that they can get away with this.
:)
When you are dealing with orders of magnitude like these, it is usually acceptable in the scientific community. Whether this de-facto standard *should* be so acceptable is still up in the air in my views
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Re:Here is an interesting one. (Score:5, Funny)
That's probably because they assume too many spherical cows.
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Re:What a great example! (Score:5, Insightful)
This is the problem with the Drake equation
Most of the factors are not known to any great precision
Most of the last factors are not known at all ...since we only have one example, us.
With it you can prove that there are a vast number of civilisations or none just as easily
There are currently 53.4565452112323(56) civilisations in our galaxy ....
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Re:What a great example! (Score:5, Funny)
It must be right, because the answer came from a computer.
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Re:What a great example! (Score:5, Funny)
But the question didn't. We should make a bigger computer to determine what the question should have been.
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Re:What a great example! (Score:5, Insightful)
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Re:What a great example! (Score:5, Funny)
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Only 37,964? (Score:5, Interesting)
My estimate (Score:5, Insightful)
1.
And it is as valid as this astronomer's estimation.
Re:My estimate (Score:5, Funny)
1.
Is that the mice, or the dolphins?
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Re:My estimate (Score:5, Informative)
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Re:My estimate (Score:5, Informative)
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Re:My estimate (Score:5, Insightful)
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Re:My estimate (Score:5, Interesting)
....but way too many of us are willing to just simply "believe" ....
There is no way you can live your daily life without belief. When you get into a car or a plane, you BELIEVE that they will take you where you want to go. You don't know that for sure. When you go to bed at night you believe and hope that you will wake up in the morning but there is no guarantee that you will. I am sure that you have at one time or another read stories of whole families who went to bed in the evening and never saw the next day due to fire or carbon monoxide. Our lives are governed much more by belief, by faith, than the sure knowledge.
There really is no proof of anything, only evidence that we can choose to believe or not believe.
(...of the reasonably ridiculous notion that life began here when some mythical magical man in the sky...)
You and everyone else that agrees with your assumption (belief) doesn't really KNOW this, but simply believes it and then tries to pass that belief off as sure knowledge. The only evidence we have, is that life, that we are here. There is no way to do deduce from that alone how it began. Even if you invented a time machine and used it to travel back as far as necessary, what evidence would you collect there at the beginning, to bring back to convince your fellow humans at the present time? In the end, whatever evidence you did collect and bring back, would still have to be believed. It would not constitute incontrovertible proof.
If an intelligent life form came to visit us here on planet Earth, what evidence would be sufficient to convince us that this entity came from a galaxy far far away or even another universe or dimension?
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Suspiciously absent (Score:5, Interesting)
No mention of species less advanced than us, but there are apparently 37,964 more advanced. I wonder why that is... Other civilizations must look at this backwater hick-world and laugh.
Re:Suspiciously absent (Score:5, Interesting)
Which is why they send us all the UFOs. I know that serious people like to dismiss UFO reports because of how over the decades we turned the whole topic into ridicule, and the masses of loonies interested in the topic didn't help, but you have to remember that lots of very well documented UFO events reported by military personel and pilots are far from explained by anything we know.
You can scoff off the whole UFO thing but you can't take a precise case (provided it's a good one of course) and explain the recorded flight paths and phenomena.
That's what strikes me regarding the SETI approach vs UFOlogy, we look as hard as we can hundreds of light years away, yet we can't be bothered to take a closer look at what happens in our own atmosphere. I'm not implying that any recorded UFO event is extraterrestrial in origin, but in many cases you have to consider this possibility by an absolute lack of alternative explanations. No matter what I think it's worth a better scientific examination of the whole thing. But unfortunately the scientific community devotes more time and energy to what it considers safe research, which is why we spend so much time in the cul-de-sac that is string theory while investing very little in seemingly more risky possibilities (the Garrett Lisi example springs to mind).
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The real answer (Score:5, Insightful)
We just don't have a clue.
The number of things we don't have a clue about is staggering.
Counting the number of earth like planets is just plain silly. If life can only start in space and then find a planet, earth might be totally unsuitable for the first start. It also presumes life can only exist under earth like conditions yet we KNOW that even life on earth varies widely. If some species can survive on the bottom of the ocean outside the influence of the sun, is it impossible to imagine a lifeform that exist in space itself?
No, I am sorry but until we can actually go and look our estimates of the number of civilizations is between 1 and 1+.
Re:The real answer (Score:5, Interesting)
The biggest problem I see with this person's claim is that panspermia doesn't really work well when applied to reality.
There was an experiment discussed on Science Friday where an experimenter said cosmic radiation does a good number on genetic material based on tests with actual genetic material. I think they showed that in about 80,000 years, genetic material is just broken up into a bunch of tiny, useless snippets, especially if it's on a rock passing between stars, there is much less protection against radiation than there is within a star's heliopause. Panspermia might be a workable idea for passing organisms and code between planets in one solar system, but not for interstellar travel.
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Re:The real answer (Score:5, Insightful)
There is no prove one way or another that oxygen is needed for instance to create life
Incorrect. Life caused the Earth's atmosphere to have oxygen. There are still life forms here that oxygen is a deadly poison to.
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Advanced? (Score:5, Insightful)
But we have no definition of advanced.
Look, just because an alien civilization has been around longer than we have, doesn't necessarily mean they will be more advanced than we are.
Maybe they could have been around one million years before us, but are stuck somewhere between Mesopotamia and Rome.
Re:Advanced? (Score:5, Insightful)
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My assessment (Score:5, Insightful)
I am a polar bear. Don't bother to ask me how I managed to get on Slashdot and post this, you would never believe it.
However, I have been doing some estimations of my own. I have always wanted to figure out how many polar bears there are in the world. In my neighborhood here in the arctic, there aren't too many polar bears. About 350. I estimate that we roam over 20 square kilometers. Now, based on some observations I made from the bottom of a well, I figure the earth is around 500 million square kilometers. I haven't actually been outside of my corner of this world, but I imagine everything must be like it is here, and life must be exactly like it is here. I have no evidence to the contrary.
So, I figure there must be 25 million times 350 polar bears or 8.75 Billion of them.
Re:My assessment (Score:5, Insightful)
And since you miss the big point, I will spell it out.
A polar bear is using the limits of his logic to speculate on the world as a whole. Had an intelligent bear been allowed to travel the world, he would see where his equation breaks down.
An intelligent human attempts to speculate about the universe as a whole. He is smart enough to realize that he has no clue about how often intelligent life occurs on "habitable" worlds, so he plugs in a variable, then proceeds to put in numbers for something he has no clue about. Since it is unknown, his number is bullshit. Drake realized this, but countless amateurs have treated these numbers as the gospel and wildly speculated about the unknown. this in and of itself isn't bad. However when folks put weight on these numbers, it is bad.
Just as the polar bear has no real clue about the planet it lives on, we have no clue about the universe we live in. I hope that as a civilization that we go out and really begin to explore this place. But as long as we are sitting here on earth, killing each other, and wasting resources on there here and now, we cannot jope to fathom the way the universe truly is.
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Close neighbors? (Score:5, Insightful)
But, the diameter of the milky way is about 100,000 light years - so, if we assume that pre-Galileo civilization was oblivious to ET, we as a species are only aware of civilization signs within 400 light years or so.
So, if there are 40,000 civilizations within a 100,000ly diameter, then there are approximately 2.56 civilizations within a 800ly diameter.
Personally, I feel like Earth represents the .56 of a civilization in that scenario...
You won't find them (Score:5, Interesting)
Ephemeral civilizations have only a short time to detect each other; I doubt that happens often.
Re:yuck. (Score:5, Funny)
Like I said before, it adds flavor to a rather dull blend.
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Aliens Cause Global Warming (Score:5, Insightful)
http://www.crichton-official.com/speech-alienscauseglobalwarming.html [crichton-official.com]
My personal guess is that there are OVER 9000 civilisations out there.
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Re:Aliens Cause Global Warming (Score:5, Funny)
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Re:Aliens Cause Global Warming (Score:5, Interesting)
His criticism of SERI is basically saying "the hypothesis that the neutrino has a rest mass of zero is scientific, but the hypothesis that a neutrino has a rest mass that is not zero is unscientific." This is silly; the same experiments would be used to test either hypothesis. Likewise, it's silly to criticise SETI by saying it's scientific to listen for radio signals if you're trying to show that there aren't any, but it's not scientific to listen for radio signals if you're trying to see if there are any. It's the same experiment either way.
His criticism of the Drake equation is even less well informed, in that he's criticising the equation itself, not the parameters that go into it. But the equation is trivially true; it's nearly a tautology. If the correct statement is "we don't know", it's not because the equations wrong, it's because we don't know what values go on the right side. But the answer "we don't know how many civilizations are in the univererse because we don't know what the probability is that a planet with life develops a lifeform with intelligence still bounds the question-- it tells us more precisely what we don't know.
In short, Crichton should stick with novels, which he's good at, and not critiquing SETI, something he seems to know little about.
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Re:Aliens Cause Global Warming (Score:5, Insightful)
His criticism of the Drake equation is even less well informed, in that he's criticising the equation itself, not the parameters that go into it. But the equation is trivially true; it's nearly a tautology. If the correct statement is "we don't know", it's not because the equations wrong, it's because we don't know what values go on the right side.
From Crichton's piece:
"The problem, of course, is that none of the terms can be known, and most cannot even be estimated. The only way to work the equation is to fill in with guesses."
He IS talking about the parameters (on the right side). Your criticism is meaningless.
In short, Crichton should stick with novels, which he's good at, and not critiquing SETI, something he seems to know little about.
Hehehe. Marvelous. Keep it up.
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Re:Aliens Cause Global Warming (Score:5, Interesting)
Not quite. It implicitly presupposes a steady-state universe, which was commonly believed at the time. However, we now know that the universe is not steady-state, and in fact is quite young (13.7 Gy) compared to the age of the Earth (4.55 Gy). Especially if the conditions in the Universe have been shifting, e.g. it has taken time for stars to build up enough metallicity, it is entirely plausible that conditions may be hospitable to life, and yet it is not common, simply because we just got there first. This is particularly important if you accept the conclusions of the Fermi Paradox, which basically states that since technological advancement is so rapid compared to evolution, the first technological civilization in a galaxy will almost inevitably colonize the galaxy before any other civilization has had time to evolve.
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Re:my theory is 1 civilization per galaxy (Score:5, Funny)
I follow the Mass Effect way of thinking. A handful of civilizations, each with dramatically polarized stereotypical traits, and who speak English with perfect North American accents, regardless of the structure of their mouth(s) and/or vocal cords (assuming they have them...).
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Re:Then where are they? (Score:5, Informative)
Or there is of course, another possibility: That humans are the only "intelligent" species using radio transmission as a communications medium and that any other "intelligent" species is such a great distance away and/or in a region of space where we haven't been listening that we are unable to detect them.
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Re:Fermi paradox (Score:5, Interesting)
You're missing an entire aspect to the Fermi paradox.
The universe is old. VERY old. About 14 billion years. Earth is fairly young, about 4.5 billion years.
Assuming intelligent alien life take about as long as intelligent Earth life to evolve (give or take a billion years), these other civilizations would have billions and billions of years ahead of us.
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Re:Fermi paradox (Score:5, Insightful)
Correct me if I'm wrong here, but an Earth-like planet couldn't have come about much sooner, since we need so many elements that we can only get from old burned-out stars. There's gotta be a lot of cycles before there's enough material further up the atomic chart to make an interesting planet.
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Re:Then where are they? (Score:5, Interesting)
For example, we can only just see a planet that seems to be rocky and atmosphere-bearing, which therefore meets some of the criteria for "life as we know it". We've been able to see gas giants, which might harbour life as we don't know it, for a little while now. However we can't actually resolve giveaway cues for planet-spanning civilisations, never mind lower life, either kind of planet yet. And we have no reason to assume that they'll be "chatty" in any way we can detect over long distances. To a group of aliens flying through alpha centauri whose civilisation skipped radio and went straight to fibre optic and laser, 2000AD Earth and 200,000BC Earth would be indistinguishable.
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Re:Then where are they? (Score:5, Interesting)
Well, I'd say the main issue with that argument is that we just plain don't have the tools to detect intelligent life outside our solar system.
Radio signals are not the only way to detect intelligent life. I think the biggest ramification of the Fermi Paradox is that we're here at all. When you do the math, even at sublight speed, it takes about 10 million years to fill a galaxy (give or take an order of magnitude) using geometric progression. That's *nothing* in the billions of years of the life of the galaxy. Yes, maybe a lot of civilizations wouldn't have expansionist goals, but it only takes one. Only one civilization has to have the desire to expand in a sublight sleep ship and the whole galaxy is filled before we even arrive on the scene.
Or, at the very least, someone would have sent out Von Neumann self-reproducing intelligent probes. We should see those everywhere, if life were common.
People hate facing up to the fact that we're alone. But it just seems to be the fact of the matter.
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Re:Then where are they? (Score:5, Interesting)
Or, at the very least, someone would have sent out Von Neumann self-reproducing intelligent probes. We should see those everywhere, if life were common.
probes with bacteria or virusses, or even just amino-acids ?
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Re:Then where are they? (Score:5, Interesting)
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As always, no. (Score:5, Insightful)
Because a species of intelligent dolphins would surely be detectable from their radio transmissions.
No. That entire line of thought is based upon the incorrect assumption that WE are the model for all other species.
We're almost unique on Earth. Where we share DNA with every other animal. Why expect that from creatures who evolved on a different world?
Not to mention the incredibly SHORT time we've been looking over an incredibly SMALL portion of the galaxy.
Your entire argument is based upon another species developing the exact same technology that we have ... and using it in a fashion we can detect ... far enough in the past ... but not too far in the past ... so that we can detect it ... using the technology we have ... during the time we have been trying to detect it.
Yeah, like that "proves" anything.
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Re:As always, no. (Score:5, Funny)
I've seen a lot of Stargate, and if I've learned anything, it's that pretty much all alien life looks like us, develops civilizations nearly identical to our own history, and speaks english.
You need to do more heavy research!
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Re:Then where are they? (Score:5, Informative)
Sure, the signals have travelled a long way. Now, would you like to be the entity at the other end trying to pick out our signals from all the other noise that exists in the Universe?
Since the power of the signal is reduced by the square of the distance, when we start talking about interstellar distances, (forget intergalactic distances), that number is so large as to make our signals virtually undetectable. The CLOSEST star is Proxima Centauri which is 4.2 light years away. Convert to meters, we have approximately: 4 * 10^16 meters. Squared gives us a power reduction of 1.6 x 10^33.
So, if we sent a terawatt signal, 1x10^12 watts, even if there was someone at Proxima Centauri to listen, they would have to hear a signal that's 6x10^-22 watts. Which is pretty hard to pick out from any background noise.
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Re:Then where are they? (Score:5, Informative)
A terawatt signal radiating uniformly would produce 1e12 / (4*pi*(4e16)^2) w/m^2 = 5.0e-23 w/m^2. With a dish the size of Arecibo (7.3e4 m^2) that's -144 dBm (decibels referred to milliwatts). For comparison, the received GPS signal strength is ~ -133 dBm. With a slightly narrower bandwidth, or signal processing techniques that can work at lower SNR (eg looking for a carrier wave over extended periods -- exactly the sort of stuff SETI@home does) that extra order of magnitude isn't hard to come by.
Note that there are efforts ongoing to build larger area arrays (eg the square kilometer array), improve reciever electronics (chilling the front-end amplifier lowers the inherent amplifier thermal noise, for example), and improve signal processing techniques. Also, for certain types of transmission, the 1TW estimate isn't unreasonable -- Arecibo has radar transmitters with as much as 20TW effective isotropic power (lower total power, aimed at a small fraction of the sky). Given the right sort of source signal and extended observation, something like Arecibo could see some of our leakage signals, not just intentional transmissions.
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Re:Then where are they? (Score:5, Informative)
Sorry, but the logical fallacy police have to intervene in this one. Absence of evidence is indeed evidence of absence; however, it is not proof of absence. In this case, as has already been demonstrated, we would need significantly more evidence of absence before we could come to any sort of meaningful conclusion. The current evidence of absence is about the equivalent of saying we know there's not a large ET base on the surface of the bright side of the moon.
Further, there's nothing logically wrong with the pot calling the kettle black. The kettle is indeed black regardless of the color of the pot. It just makes the pot look dumb for trying to make fun of the kettle. It reminds me of this quote attributed to Jack Nicholson:
"My mother never saw the irony in calling me a son-of-a-bitch."
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Re:Number fun (Score:5, Funny)
That reminds me of this article [theonion.com] from the Onion.
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Re:Where to find them? (Score:5, Informative)
Not sure the plausibility or not, but we're ALREADY in the outskirts of the galaxy.
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