It still should be at least one.

Ah, I see what you mean now. Since we are here, then N must be at least one.

Still, that's not true. Look at all the factors. They include rates averaged over billions of years, and the last factor (what Crichton calls fL) is the average length of time that each civilization releases detectable signals into space. So, what would the equation say if that average time (fL) was ten thousand years, but such a civilization/technology only came around every hundred thousand years (the product of all the other factors)? Then, because N is an average value, N would equal 0.1.

We could still be here, sending out detectable signals, but then the equation would say that we only have a ten percent chance of actually seeing another signal, from everywhere else in the galaxy.

Doh! You're right. Yes, the output is an average over time.

Informant's analysis looks right to me. Here's an excerpt from the thread-leading page:

There is certainly evidence, indeed (dare I say) proof, that advanced life exists in the universe, us. Scientific hypotheses are generated by inductive inferences that extrapolate to the possibility that patterns existing in the known set of data (in known set: life on Earth) might also exist in an unknown set of data (in unknown set: life beyond Earth?). That's SETI, and that's scientific. There's also no falsifiability problem for SETI. The hypothesis "Jones may be in the next room" can be falsified by an exhaustive search of the next room; likewise, the hypothesis "There may be detectable signals from advanced ET life" can be falsified by an exhaustive search of detectable bandwidths; and thus, again, SETI is scientific.

SETI is also not founded on the assertion that there is ET life, and claims to that effect are nothing but straw men. Crichton opines further: "There is not a single shred of evidence for any other life forms, and in forty years of searching, none has been discovered. There is absolutely no evidentiary reason to maintain this belief. SETI is a religion." However, SETI searches to date are not sufficiently sensitive to detect internal radio communications that may exist on distant planets (see). Using ourselves as proxy, if there are advanced ETs, the vast majority of their radio output would probably not be of the "Here we are" intergalactic-radio-beacon signals SETI could detect. There are of course many more points that could be raised in counter to Crichton's anti-SETI views.

Exactly. Crichton explicitly ignores our own existence, as a piece of evidence. His attitude--that the human race is somehow more "special" and outside the purview of science--is historically on the side of religion and philosophy, not science. It is a typical anti-science argument, to turn this on its head and use it to attack whatever whipping post is being assailed.

I'm sorry, but that's just plain silly. He's just expressing an opinion, and nothing more.

BTW I didn't like Timeline either....

Nevertheless, an equation which could mean anything at all is viridically meaningless. What the Drake Equation does encapsulate, in my view, is the biases and predispositions of the person calculating. It says nothing at all, about whether there is life out there, still less if we could communicate with it.

True.

You extrapolate from a dataset of only one? Science advances with hypotheses which in principle can be tested. Virtually none of the parameters can be isolated, even in principle, to a theory with predictive ability.

Hypothesis -> Prediction -> Testing -> Result

Hypothesis -> Prediction? ->Testing ? -> Result?

The assumptions are faulty. In the first case, the prediction is of an exact nature (Jones is in the next room), a prediction that can be tested (and if necessary can falsify the theory).

Question: How do you falsify a theory with no results and no criteria for deciding true or false statements?

...is a straw man. It certainly isn't there to falsify the hypothesis, since that would require proof of (literally) a Universal negative. SETI is unfalsifiable.

OK. Lets form a group called "The Search for God", searching the skies trying to find evidence of a Supreme Being. Do you think this has any more scientific validity than an experiment without theoretic underpinning, proof or falsifiable hypothesis?

What you've done is actually prove Crichton's point. A whole series of unjustifiable statements of your own beliefs does not a scientific argument make.

D*ng, I thought I'd learned a new word today!

I always considered the Drake equation as a heuristic device--once they started playing with it, and realized how large some of the number were, and how small they had to make other numbers in order for the result to be too small, a lot of people came away from it convinced in the idea that there just might be other life out there.

A great deal of science is just searching, with skepticism thrown in. Crichton can rail against SETI all he wants--his opinion--but for him to call it a religion, now, that's silly.

..on the basis of what? If I construct an equation to demonstrate that the probability of God existing is non-zero, does that mean that God exists?

Crichton calls it religion because it fulfills the criteria of religion: a set of unproven and probably unproveable propositions that require prior belief in those propositions being true.

No, but that doesn't follow either...and there is one difference that others have pointed out: life definitely exists somewhere.
We've had a similar debate over whether science itself is a religion--an equally silly proposition.

Would you say mathematics is a religion? It seems to to fulfill that criteria also--mathematics makes it explicit, certain axioms from which all other propositions procede. Besides, which proposition within SETI requires prior belief?

That's a fair point: the Drake equation can't come up with any answer because any result less than 1 is in error.

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I don't think that follows. We discussed that earlier.

Well, he’s saying that SETI is not scientific. I don’t think that’s a matter of opinion.


The meaning of the equation is clear and objective. We just don’t know the values of most quantities in it. There is a difference.
Besides, SETI is not grounded on the Drake equation in any way. It can do without it entirely.


I think we all agree with that, but I must reiterate what Ian wrote earlier:

SETI does not assume that there is life elsewhere, or that we can communicate with it. In a way, SETI is the name we give to the search itself.


Extraterrestrial intelligence can be detected from their radio emissions, so there is an objective way to test it. The criteria are based on that.

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That might be more difficult than some people believe;
How far away could we detect radio transmissions?...

nevertheless detecting an alien civilisation by whatever method would flip SETI over from being an act of faith to being a scientific search;

quite simply, no-one knows if this will ever happen.

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At one time we had only one sample of a planetary system. That did not render ampliative inferences of the possibility of extrasolar planets pseudoscientific.

The statements that radio signals from advanced life (a) are produced in the universe, and (b) can be differentiated from natural radio noise have been confirmed. The SETI hypothesis is that the casual mechanism of the said phenomenon might not be confined to one location (Earth).

Life can be detected. Anything that could be detected is not outside scientific inquiry. Sure, whether given ET data are from life or not is something that would be and is debated (as they come in). But the fact that terrestrial artificial radio signals can be detected against background noise demonstrates that life-sourced radio signals can be detected.

Once again, life has already been detected, on Earth. On the other hand no God or Gods have ever been detected; so the analogy is false.

As long as we have some objective way to do it, there's nothing unscientific about it.

I agree that no one knows if it will ever happen. It may never happen.
I disagree that SETI won't be a scientific search until it happens. To me, that's like saying that the search for an 8th planet wasn't scientific until Neptune was found.

Ditto. The hypothesis is valid because it is contradictable. If radio communications in this region of the galaxy can be detected that are not ours, then eureka! If not, then a new hypothesis might be altered to change radio to visible light as a carrier. This will be contradictable as well. It is not irrational to suppose they exist. It is not even unbiblical.

Regardless, it is not "religion". If Chrichton would have said "philosophical" I would have more respect for the statement. No one is trying to transcend the universe here, just meet neighbors.

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Well, it depends on what we mean by hypothesis. If the hypothesis is "There is inteligent life elsewhere in the galaxy", then eburacum45 and Diamond are right that this hypothesis can't be proven false. But that does not mean that it isn't scientific.

We're used to hearing that a hypothesis must be falsifiable in order to be scientific, but this is not always true. A better word would be testable. As long as we can prove it wrong or right, it's a scientific hypothesis.

What happens is that most "hypotheses" in science are laws: the're universal statements that are supposed to apply to an infinite/large number of objects. E.g.: "Stars with a mass not greater than that of the Sun end their existence as white dwarfs". We can't prove this right, because we can't observe all stars in the universe, present, past, and future. But we can prove it wrong: just find one counter-example.

That's what a scientific hypothesis usually is. But in the case of SETI, the hypothesis under study is that "There is inteligent life elsewhere in the galaxy". This is not a hypothesis of universality; it's a hypothesis of existence. This time around, we can never prove it wrong, but we can prove it right - by finding one example.

I agree. Given enough million years, it possibly could be proven false. Don Meredith used to say..."if ifs and buts were candy and nuts, we would all have a merry christmas". [I tend to remember this quote this time of year.] The hyposthesis you quoted involves too many ifs to be a really "good" hypothesis. However, the hypothesis specific to radio communication is valid and scientific a one. On this we seem to agree.

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But in that case "can't be proven false" is a function of technological limits that could conceivably be overcome. In the early twentieth century it would also have been said that the hypothesis of intelligent life on Mars "can't be proven false" due to technological limits. But that "can't be proven false" is different than pseudoscientific unfalsifiability where falsification cannot even be conceived. For example, I cannot conceive of falsifying the proposition that invisible (ie, undetectable) spirits exist; yet I can conceive of examining the EM spectrum from distant regions or even sending spacecraft there (however horrendously long that may take) to look for signs of intelligent life.

So SETI critics are equating the "can't be proven false" due to transient constraints imposed by current technology and time with the "can't be proven false" of claims for which no pass-fail test can be conceived and thereby produce the pseudoargument that SETI is pseudoscientific.

My TurboTax program isn't mathematically unsound just because I don't have my 1099s and W-4s and mortgage interest statements to plug into it. I can guess, even with some measure of accuracy, what some of those numbers are from data that I have on hand but if I fill out my taxes now I'll probably be audited. The Drake Equation is a similar beast. If we don't have accurate data to plug into it the results are mostly meaningless, but that doesn't make the equation, in and of itself, unsound. Garbage In, Garbage Out. It's just not very useful now, with the data we have. It can still have value as a thought exercise though, and that's all any reasonably well informed person will use it for. It isn't religious canon, I think Crichton is taking it a tad too seriously and probably hasn't talked to many astronomers about it. That SETI is a religion is, as has been said by others before, just silly. A group of astronomers are using technical means to examine the possibility that radio broadcasts of a non-natural, extraterrestrial source might be detectable. So what makes that a religion? Most of them certainly hope they succeed, most of them think that the existance of ET life is possible or even likely. So what? Faced with the question "Is anyone out there?" you can either close your eyes and say "Yes" or "No" or you can fire up a radio telescope and go look.
The Astro-Potentate doesn't put on a big hat and bless the dishes at dawn and pray for a message from his Celestial Brethren, they put in a lot of late hours and hard work crunching numbers in a rigorously scientific way and it is a bit petty and mean-spirited, as well as simply incorrect, to call SETI a meaningless, useless religion.

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good post

some good ideas but

well, who can say about what will happen next ?

SETI will take a very long time to do this

A difference may be that those who search for ETI and use Drake's Equation to inspire some of their research, will all say "we haven't found anything", as compared to religion.

RBG

Drake's equation, as normally interpreted, is trivially false: it doesn't take into account interstellar colonization by ETIs. Surprisingly few people seem to realize this.

(That is, it's false unless you include the possibility of being colonized in the "probability of intelligent/technological life" or "lifetime of an average civilization" factors, but no one does that).

I'd agree that SETI is a religion, not because it makes untestable claims, but because it makes testable and false claims. If intelligent, communicating life were common enough that we could hear its radio signals, some of it should have been here long ago. The Fermi/Tipler argument seems conclusive to me.

I'll admit that the Fermi Paradox is a bit troubling, but I think that it's no more (or less) valid than something like the Drake Equation when we're talking about intelligent, communicating civilization. How common does intelligent life have to be for us to hear its radio signals? Perhaps far less common than it would need to be for us to expect it to have left traces within our own star system. There are many of reasons why both the Drake Equation and the Fermi Paradox are edgy at best, and I think it folly to presume one or the other as being an accurate indicator of finding and/or contacting ETIs.

Regardless of all of that, I believe SETI to be an important scientific investigation of the whole matter. It's certainly far better to go and do something about it than to sit and argue about Drake and Fermi.

If we listen, we MIGHT hear something. If we don't, we WON'T hear anything.

http://setiathome.ssl.berkeley.edu/

Come on. You're not using ALL your flops.

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"I know that, man, but it's cold."
"Duh - so is water, man."
-Actual conversation overheard while walking to class

The Drake equation, as a way to calculate the number of communicating civilizations, is simply incorrect unless no ETI civilization ever colonizes a different star system than the one where it was born.

Something similar to the Drake equation can be used to calculate the probability that an average galaxy contains at least one civilization, but even there it doesn't really say anything. There are multiple terms in it with several orders of magnitude of uncertainty.

I don't think the Fermi Paradox is edgy. Many of the arguments I've seen against it seem bad to me; some seem reasonable, but not strong enough to challenge the main point.

I don't think people should stop looking, just to be sure. But I think it's extremely unrealistic to expect any alien communications. (And even if we do get a message, there's a chance they won't have our best interests at heart.) If they really want us to know of their existence, they can just send some sort of interstellar probe instead of messing around with radio signals.

Those arguments are fallacious in that in the Fermi case it assumes we haven't found them yet, therefore they don't exist; if this were applied to particle physics we would have stopped looking a long time ago.

Tipler's hypothesis and argument is based on a single concept of how intelligent life might explore the univers- one which doesn't make a whole lot of sense and assumes to know more than the assumptions in the Drake equation about how intelligent life should behave. And because we don't see exactly what he says a hypothetical intelligent race should have built, it kills any argument for intelligent life in the galaxy.

The problem with a physicist addressing a question of biology/sociology (growth rate vs. a fission reaction for instance) is that the argument assumes no upper limit/bounding/limiting factors on biological growth, and attempts to fit a simple mathematical curve to what is a complex and difficult to calculate scenario as well as assuming that colonization is the only possible goal of any advanced life. Similar problems arise with projecting population growth without taking into account limits on resources, self limiting factors like technology and standard of living reducing family size, and so on.

[EDIT: Corrected for grammer/tense]

Why would they send an interstellar probe? That would take hundreds, maybe thousands of years to get here from wherever they are, unless they've discovered the secret to FTL space travel, not to mention that they have to know exactly where we are to make the probe of any use. Otherwise, they just launch a probe and HOPE it hits something of interest. With radio, they can effectively shotgun the stars with a message, and don't have to worry about where everyone else is. Their only worry then is whether or not they have a powerful enough signal that we'll be able to pick it up from our distance. Of course, that's assuming that they're sending out radio signals with the express intent of alerting other civilizations to their presence. It's probably far more likely that if we ever do receive a signal it will be some internal communication that we're intercepting from it source, like if an ETI picked up a transmission of "I Love Lucy" or the first words of Neil Armstrong as he stepped on Luna; we'd be picking up the equivalent of something like that.

As for your assertion that the Drake Equation doesn't take into account civilizations that have expanded to other star systems, I'll have to agree with you. However, I don't see how we could ever hope to add this variable to the equation. Consider all the things we would have to know to predict the rate of expansion of an ETI. We would first off have to know how quickly they reproduced, as well as how quickly their nervous systems reacted. Both of those variables are probably dependent directly on this civilization's metabolism rate, which is most certainly related to the biochemistry extant on their homeworld. This is probably dependent upon the type of planet they originated on, which depends upon the type of star that planet orbits. We should take into account the length of a year on their homeworld, the distance from their star which their homeworld lies, whether their homeworld has a considerable axial tilt, whether their homeworld has any moons, and probably a dozen or so other things regarding the nature of their homeworld and star system. We also have to determine whether or not FTL travel is possible, because if it isn't, this is a lmiting factor to how quickly a civilization can possibly expand beyond their home star. AND...we have to do that for every individual civilization in existence in the galaxy, because I'm sure they all must expand at different rates simply because there ARE so many variables. If we took human values for all these variables to be supposed average values, and worked up a base value for population growth and interstellar expansion, we STILL don't know if FTL is possible.

Another thing, we don't know how large these creatures are, so we don't know what the carrying capacity of a planet is for them - an ETI as large as a mouse would probably be able to live for a long time on their homeworld before they found colonizing another world necessary - especially if its homeworld were many times larger than Earth. There's also the possibility that other civilizations have the technology to build pseudoplanetary structures, like ringworlds, Dyson spheres, and Jovian bubbles, which curb the necessity for interstellar expansion.

I guess what I'm getting at is that the Drake Equation is a thought experiment, and probably shouldn't be taken to seriously. But on the other hand, all the things we need to know to make the Drake Equation valid we also have to know to make the Fermi Paradox valid, which is why I don't take either one too seriously.

__________________
"Of COURSE fish can live in space. There's no air. Fish don't NEED air."
"I know that, man, but it's cold."
"Duh - so is water, man."
-Actual conversation overheard while walking to class

Bad analogy: particles don't have goals, and they're too small to see.

The assumption that if we haven't found them yet, then they don't exist isn't based on nothing; it's based on the idea that at least one being in at least one of the civilizations could have created a colonization wave, and colonized the galaxy in a relative eyeblink. There are enormously many reasons why one could want to do this: safety, ethics, gathering resources for building or computing things, ...

That colonizing the galaxy is possible at all should already prove that until that stage, there are no limits to biological growth. There may or may not be limits to growth; until the galaxy has been colonized, they certainly haven't been reached yet.

I don't think it's helpful to think of this in terms of biology anyway; it depends on the motivations of intelligent beings.

The argument in no way depends on these assumptions. (I don't think I've read all of Tipler's writings on this, so he may have made some unnecessarily restrictive assumptions).

If there is only one individual in only one sufficiently advanced extraterrestrial civilization in this galaxy (or one close by) who prefers a colonized universe to a non-colonized universe and acts on this without being stopped, then we should expect the solar system to have been colonized. It doesn't even have to be a colonized universe; it could be any change we would have noticed.