For the record, I think SETI is a good idea, and that most people misunderstand Drake’s equation (it’s a way of estimating the number of civilizations in the galaxy, not a way of determining their number), but still, this XKCD cartoon is funny (click to see the punch line):
Hold the mouse over the picture on the XKCD page to see what he really thinks. I disagree with him on that, too. We’ve only just started looking. 
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Phil Plait, the creator of Bad Astronomy, is an astronomer, lecturer, and author. After ten years working on Hubble Space Telescope and six more working on astronomy education, he struck out on his own as a writer. He has written two books, dozens of magazine articles, and 12 bazillion blog articles. He is a skeptic, and fights misuses of science as well as praising the wonder of real science.
Contact me: The Bad Astronomer "at" gmail "dot" com
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February 15th, 2008 at 10:06 am
I hadn’t thought to check the alt tag. You’re right. It’s more than a bit premature.
February 15th, 2008 at 10:09 am
THANK YOU!
I have always HATED the Drake equation. No so much for the equation but how people from all sides of the debate abuse it for their purposes. Much like politicians. They always trot it out like it’s some sort of holy formula.
To paraphrase Mark Twain, there are lies, damned lies and the Drake Equation.
February 15th, 2008 at 10:27 am
Here is a link to his blog post that accompanied the comic: http://blag.xkcd.com/2008/02/15/aliens/
February 15th, 2008 at 10:56 am
Yep, the Drake equation is an estimate that’s sat on the table so long people take it for fact.
February 15th, 2008 at 11:13 am
If for nothing else, the Drake equation is useful shorthand for framing the debate about the existence of ETI.
February 15th, 2008 at 12:21 pm
One equation with 8 unknowns. A bottomless well of questions but no answers.
February 15th, 2008 at 12:27 pm
I’ve found myself turned off in the past when Drake would rationalize SETI with an argument essentially of the form, “If we contact the aliens, they will give us FREE stuff (advanced knowledge).”
That’s not only not obviously true, it’s not even what I’d call a mature motive for exploring the universe. In fact, I recoil from the whole notion that the single most important or interesting thing we can possibly discover is alien life. That’s nonsense. The world is interesting already even without the promise of E.T. If alien life is discovered, it’ll one more interesting thing determined about the world, and we’ll be richer for it. But I don’t need to pretend that there’s someONE out there just to make it worth getting out of bed each day. There’s all sorts of stuff out there worth learning about.
February 15th, 2008 at 12:28 pm
Yep, good ol’ Francis Drake with his exploring of the Americas in a wooden ship and positing the existence of extraterrestrials.
February 15th, 2008 at 12:29 pm
As a layman, I find current estimations about intelligent life in the universe to be extremely interesting, but mostly irrelevant. I want to know if there is other life in the galaxy or greater universe. If we discovered that there was no other life at all in our entire galaxy it would be disappointing, but I still couldn’t rule out the possibility of life elsewhere, despite the fact that our civilizations would never even know of each other. Even an entire galaxy is a pretty small sample size to try to apply to the known universe. Could just be local conditions.
I am in no way dismissing Drake’s ideas or their usefulness. But to put it in another perspective, if Drake and a thousand other astronomers, mathematicians, and other scientists said that there was no chance of extraterrestrial life, based on working with one person’s estimations and our current knowledge, it would not deter my curiosity or my enthusiasm for research one bit. I am much more concerned about the possibility that stopping research will dampen curiosity and prevent the growth of the science and the development of better technologies with which to pursue the science.
We are at a point where we can observe many of the grand operations of the universe, but because of our physical limitations we have no way of seeing it all first hand, in person, right now. It reminds me of reading about the ancient Greeks studying medicine. They knew that some illnesses were contagious and some were not, but they didn’t have the tools to catch the mechanism. Many centuries later, their ideas were fulfilled with the germ theory of disease(still hotly debated by people who have never bothered to look through a microscope.)
I am inclined to laugh and slightly agree with the cartoon, but it doesn’t really matter. Inquiring minds want to know, and I’m not talking about Brittney’s Follies or anything else I can get from The Enquirer. I needs me some science!
February 15th, 2008 at 1:36 pm
I am afraid that I have only a SF readers view of SETI, got my knowledge of exobiology from Arthur Clarke, and unfortunately lost my belief in flying saucers way back as a 9th grade amateur astronomer. But…
Data analysis I can handle. And a problem where the universal (pun intended) data set is somewhere on the close order of a hundred gazillion stars, and the known points of reference is 1 to the first power (but, given the current state of scientific education on Earth, some might even say 1 x 10 to the zeroth power), the question about as unsolvable as asking how many scientology members can dance on the head of a pinhead.
Konan
February 15th, 2008 at 2:24 pm
I can’t remember where I read this, but someone once raised the point that once you get more than four light years from the Earth, all the various TV & radio signals we emit become lost in the background radiation of space. In other words, if you drop a rock into the ocean, it makes a big splash with lots of ripples. But once you get a few hundred yards away, there are no more ripples to be seen.
Wouldn’t the same hold true for any alien civilizations out there? Perhaps the reason we don’t hear anyone is NOT because they’re not out there, but rather because we’re just too far away.
February 15th, 2008 at 4:23 pm
I don’t know if I posted this earlier on in this blog but in the early 1990s, there was a debate on this subject between Carl Sagan and Ernst Mayr, a link to which is attached. Sagan took the position that the SETI project was worthwhile and that intelligent live might occur frequently in the universe. Mayr took the position that intelligent life was probably very rare in the universe and that the likelihood of a successful finding by the SETI project was vanishingly small. The two savants, of course, came from very different backgrounds, Dr. Sagan from astronomy and Dr. Mayr from biology/zoology.
The problem with the optimistic Sagan position is that there is no guarantee that intelligent life will arise, even if the conditions are favorable. For instance, the rise of intelligent hominids on this planet was very much dependent on the collision of the Alvarez meteorite/comet. Had this event not taken place, we probably wouldn’t be here, as evolution would have taken a very different turn. Given this event, I don’t think that the Drake equation is very informative, as, without the Alvarez collision, the chances of intelligent life arising on this planet are near zero.
http://www.planetary.org/html/UPDATES/seti/Contact/debate/default.html
February 15th, 2008 at 5:10 pm
The equation is great, you will indeed get the result of how many civilizations capable of radio astronomy in the galaxy if you use the equation. What’s left for the future of course is the find out the values of the different variables. We are doing that, we are finding a lot of extrasolar planets and we are able to intuit if they are viable for life.
February 15th, 2008 at 5:16 pm
N = R* Fp Ne Fl Fi Fc L
There are 4 filter conditions in the Drake Equation: Fp, Fl, Fi, and Fc. The problem is that we don’t know if there are other filter conditions which are indispensible that Drake left out. In the book “Rare Earth” by Peter Ward and Donald Brownlee they add a bunch more:
http://en.wikipedia.org/wiki/Rare_Earth_hypothesis
N = N* Ne Fg Fp Fpm Fi Fc Fm Fj Fme
N* – number of stars in the Milky Way galaxy
Ne – average number of planets in habitable zone
Fg – fraction of stars in galactic habitable zone
Fp – fraction of stars with planets
Fpm – fraction of planets that are rocky, not gaseous
Fi – fraction of planets with microbial life
Fc – fraction of planets where complex life arises
Fm – fraction of habitable planets with a large moon
Fj – fraction of habitable planets in a system with large Jovian planets
Fme – fraction of habitable planets with a low number of mass extinction events
So that’s double the number of filter conditions than the Drake Equation. And someone might decide to add even more. As far as I know Drake never tried to prove that there were only 4 filter conditions. It was just a matter of convenience.
February 15th, 2008 at 5:37 pm
The Drake Equation is logically true. That’s not the problem. The problem is that each of the terms have so many unknown unknowns that any two estimates will be off by a dramatic amount. Sagan himself estimated a million intelligent civilizations in the Milky Way. I’ve gone through it and estimated one. Big difference.
I disagree with the BA’s comment that we’ve “only started looking”. Sure, 10 years (I’m only guessing the length of the project) is not a very long on the cosmic scale. But when we’re talking about costs and benefits, we’re talking about *human* costs and benefits, and thus should be using a human scale, not a cosmic one. That said, I still have an overall positive view of SETI.
February 15th, 2008 at 6:56 pm
With our luck, when we finally do find an alien civilization, their favorite book will turn out to be something called “To Serve Man.”
February 15th, 2008 at 7:36 pm
“The problem with the optimistic Sagan position is that there is no guarantee that intelligent life will arise, even if the conditions are favorable.”
IOW, it depends on a Great Chain of Being misunderstanding of evolution, which is not logically different from the “Why are there still monkeys?” position of creationists. Just because there most likely is life, does not mean that there is any particular reason to expect it to evolve in a particular direction.
February 15th, 2008 at 8:18 pm
As I understood it, Drake never intended to calculate the number of intelligent civilisations in the galaxy. Nor did he intend to even grossly estimate that number. He simply knew the equation would spark debate. He wasn’t looking for an answer. He was just looking to get people talking about the variables.
February 15th, 2008 at 10:48 pm
The cartoon isn’t a ‘joke’, its just a snide comment.
I disappointed that you wasted your time on it BA.
February 15th, 2008 at 11:08 pm
I’m normally a big fan of xkcd, but I wasn’t happy with this one. I see nothing wrong with the Drake equation — only with the idea that we know any of the values.
Mark Martin:
“I’ve found myself turned off in the past when Drake would rationalize SETI with an argument essentially of the form, ‘If we contact the aliens, they will give us FREE stuff (advanced knowledge).’”
I don’t know the context, but that sounds more like an argument used to justify the project to incurious people than his own reason for doing it. As such, I have no problem with it.
February 16th, 2008 at 5:16 am
[...] Phil Plait, quien en su blog “Bad Astronomy” publicó una versión ‘censurada’. La viñeta original en inglés podéis verla en [...]
February 16th, 2008 at 6:15 am
The question of observing life and intelligent life could IMHO be highly informative for biology, especially if we can form a statistic.
The frequency of life would hopefully constrain diverse theories of abiogenesis. And abiogenesis is exciting, at least in my view.
Likewise, the frequency of intelligent life would somewhat constrain the contingencies that gives rise to multicellular and intelligent life, neither of which are favored by the process of life.
AFAIK there is no consensus on how likely these later developments are. And considering the complexity of these contingencies, if put in the form of an estimate similar to the Drake estimate probably harder to resolve, perhaps such statistics is a reasonable way to attack this.
[AFAIK life on Earth is in numbers viruses, with a handful of bacterias, and the odd bits and pieces of multicellulars. Perhaps in biomass life can at least be characterized as cellular.
I'm of course going by the definition that a living organism is what partakes in the process of life (evolution): "An organism is the unit element of a continuous lineage with an individual evolutionary history." But it is IMHO a reasonable definition, especially in this discussion.]
Not to forget that any difference between the two frequencies (life vs intelligent life) would give a cosmologically sized finger to the theological inanity that “human equivalent intelligence” is an incontrovertible consequence (of the antiscientific woo called theistic evolution) of life. Who can’t love that?
February 16th, 2008 at 6:18 am
Quite true, at this stage of available observational data the Drake “estimate” seems to hover somewhere between a bayesian probability and a couple of arguably useful constraints or filter conditions. But while Drake wanted to start these kinds of discussions, he didn’t leave any constraints out, they are just implicit.
I haven’t read “Rare Earth”, but a few of the proposed constraints seems arguable on the face of it, such as having a large moon (supposedly for stabilizing axial tilt and thus climate – but Earth climate was never stable) and the number of mass extinctions (but Earth life has survived a large number of grave mass extinctions).
But the neat thing is that we can leave out or add explicit constraints as long as we can estimate the resulting likelihoods. (I think miller makes the same point, about the DE being consistent. But hard to constrain.) For example, I wouldn’t lose much thought about the constraint of supernovas going off now and then. OTOH, I presume BA’s book will teach me more on such subjects.
February 16th, 2008 at 6:33 am
Re BaldApe
Excuse me, my comment had nothing to do with the great chain of being. I merely stated that, if the meteorite/comet collision had not occurred, we would not be here. The reason is that, until the dinosaurs went extinct, large mammals could not evolve to fill the empty niches.
The point is that, given the way life had evolved on this planet up to that time, the collision event (or at least some sort of extinction event) was a necessary , but not necessarily sufficient condition for the evolution of mammalian life. Now, of course, as Prof. Russell of North Carolina State University has argued, the troodons might have eventually have evolved into intelligent beings if the collision had not occurred, but this is mere speculation.
February 16th, 2008 at 6:45 am
As an XKCD fan, I urge those of you who are disappointed with the comic to be sure to check out the “blag” — Munroe is a SETI supporter, as he makes clear there, and I’d say he supports expanding our efforts there. Plus he also has a pretty cool posting on solar sails and a dyson sphere.
February 16th, 2008 at 8:58 am
I thought the last variable in the equation was B5 and the joke was going to be about Babylon 5.
February 16th, 2008 at 10:11 am
[...] Frank Drake (es.wikipedia.org/wiki/Ecuaci%C3%B3n_de_Drake). Versiçon censurada en Bad Astronomy (www.badastronomy.com/bablog/2008/02/15/xkcd-has-setis-number/). Versión original en inglés: xkcd.com/384/ sin comentarios en: ocio, friqui karma: 20 [...]
February 16th, 2008 at 10:22 am
I’m just not one of those people who thinks being mean to good people is funny.
February 16th, 2008 at 10:56 am
A quick look at ADS shows that the Drake equation isn’t taken seriously by the astro community – the xkcd frame nicely identifies this.
February 16th, 2008 at 2:57 pm
#
Nemoon said:
“I don’t know the context, but that sounds more like an argument used to justify the project to incurious people than his own reason for doing it.”
That may be why Drake said such a thing, but that doesn’t justify resorting to it tactically. I’d consider doing so to be disingenuous, and careless. It’s like what Feynman said when some physicist fretted about how to convince the public into supporting funding for expensive accelerator labs. The gentleman in question wanted to assure the public that there must be practical spinoffs from such endeavors which will benefit the less basically curious among the taxpayers. Feynman’s take was that if there are no such spinoffs, then it’s dishonest to insist that there are. The public have some entitlement to know the real relationship between their dollars and where those dollars go, to allow them to make well-informed decisions as to what they think amounts to acceptable investments.
And so, assuming that SETI can make no promises as to return on investment, it would be effectively a lie to say otherwise just to gather funding. Telling people what they want to hear instead of the truth is called “gaining their confidence”, and is used by criminal-types routinely to sell anything from siding to used cars to pocket fishermen. It’s not scientifically honest.
There are only certain circumstances in which I’d agree with scamming people. Finding one’s self trapped in a Nazi concentration camp is one such circumstance. Soliciting money from those whom you ostensibly respect is not.
February 16th, 2008 at 8:16 pm
I don’t know about his equations, but that Drake guy makes some great a href=”http://www.drakescake.com/”>coffee cakes.