Talk:Drake equation
|
|
What about the possibility that even if an alien civilization did exist, from what they could gather of our culture they wouldn't want to communicate with us? Was Drake being overly optimistic about us?
Why do you say that the currently observed value of N = 0? What are we, chopped liver? (Or are you saying that we are not able to communicate interstellarly?) ----
Does "fairly conservative" f_l, f_i, f_c and L has any meaning ? --Taw
- f_l, f_i and L are the really contentious ones, I think. We can make a fair stab at guesstimating R* and f_p now, given recent advances in astronomy. -- The Anome
Existence of human race now acknowledged. -- The Anome
Claim that f_l = 1 is weird. In "planets which can potentially support life" in Solar System they usually list Venus, Earth and Mars. So f_l here is 1/3. Unless they say that only Earth is capable of supporting life. In that case n_e is way too high.
- This whole thing is rather fuzzy and ill-defined, IMO. For example, if I were listing "planets which can potentially support life" for the solar system, Venus would emphatically _not_ be included. On the other hand, Europa, Callisto, and maybe Ganymede would be on there; these three moons are thought to have liquid water oceans under their crusts (Ganymede is the iffiest, Europa is almost certain). Uranus and Neptune may also have liquid water layers, though even if they do conditions there would be somewhat extreme for life as we know it and may not be suitable. Basically, IMO, we simply don't know enough about the universe yet to be proposing actual numbers for some of these variables yet. -BD
We certainly don't know enough to produce good numbers, but even guesses within a few orders of magnitude are better than nothing. It doesn't take much accuracy to make certain theories more or less likely than others, or to present interesting problems. In particular, the estimates given as "conservative" are sufficient to generate the Fermi paradox; if our guesses are two low, it's even more remarkable; if our guesses are way too high, Fremi becomes expected but then the low numbers themselves are hard to explain. --LDC
- If there are a couple of orders of magnitude of flexibility to a couple of the terms in an equation like this, then I don't see how it can be reasonably used to suggest _anything_ with enough certainty to base a serious discussion on. I see the Drake equation as more of a suggestion of what we should be trying to find out in the future than as a useful analysis of life in the galaxy at this point, and wanted to make sure the article didn't give the wrong impression (ie, that "scientists say there should be aliens everywhere" or that "scientists say we're alone in the universe").
So what exactly is the Fermi paradox? The estimates for the parameters given in the article yield N=0.01, which doesn't seem to be excessively high. --AxelBoldt
See my examples now in the article -- The Anome
Being new here, I won't take the privledge of removing this particular statement, but I want to alert you that in all of my studies of genetics and molecular biology, I have never encountered the suggestion that outside mutagens (such as UV, as stated in this article) are necessary to produce the genetic variation that alows organisms to adapt to changing environments. I have only encoutered this idea in science fiction books from the 1950s or so (Asimov and Heinlein), and I think that this was just a bunch of speculation from biolgists of the time who had no idea of the mechanism of how mutations occur.
We now know that mutations occur by changes in the DNA sequence. We know that DNA must constantly be copied, and that any copying device has some error rate. We know that there are multiple DNA polymerases (copying enzymes) each with its own characteristic error rate. The error rate is itself an evolvable trait, even as it affects evolution. If it is necessary to have mutations for long term survival of a lineage (which I believe it is), then any lineage that ceases to have mutations will die out a la natural selection, and only the ones that have mutations will persist. Thus, even this trait (mutation rate) will acquire a sort of optimum, just as other traits do, and it will be adapted based upon the lifestyle of the organism and the environment that it lives in.
Too bad it probably won't be on the actuarial exam. It has a nice mnemonic to it, just think "pelican".
| Contents |
Removed paragraph
Removed this paragraph: It's a very common misconception often spread by the popular media that the evidence supports the value of N equal to 1 - there's one human civilization in the galaxy. But the galaxy is just an arbitrary probed area - we could as well probe each two galaxies, each 100 galaxies, or each one thousandth of a galaxy - and the conclusion should be the same number of such civilizations per galaxy. According to this fallacious thinking, the evidence would have supported N equal to one half, one hundredth, and one thousand as well as exactly 1.
- On the contrary, the popular media gives the impression that N is equal to hundreds, if not thousands of civilizations in our galaxy (Star Trek, Babylon 5, Star Wars, many sci fi movies and shows like the X-Files, stories of UFO and government conspiracies to cover up the "truth"... etc...).
- The rest doesn't make sense due to the fact that we know of at least one civilization. Anything beyond that is speculation based on the equation here (some parameters we do know better than others). And if there is only one civilization between two galaxies (a lonely thought) that would give an N = 0.5 for each of those galaxies. There is nothing fallacious about that - it is just probability. I suggest a read of anthropic principle. --mav
This probably has changes some of the numbers, but not sure how. http://news.bbc.co.uk/1/hi/sci/tech/3588721.stm
Edward 12:23, 2 Apr 2004 (UTC)
Is there any source discussing what Drake meant by an estimate of 10 years as the value of L? Does such a pessimistic view reflect the fact that he was living during the Cold War, or did he think that in general a civilization that develops interplanetary communications will wipe itself out within 10 years? I mean, it took us humans decades to go from understanding light and using radio, to detonating a nuclear weapon.
- Yes, I think it's at least generally assumed that he was thinking of nuclear annihilation. BTW we actually detonated a nuclear weapon before the development of our first radio system that had any reasonable chance of communicating with an interstellar civilisation (Trinity test in 1945, Jodrell Bank opened in 1947). Securiger 12:12, 4 Nov 2004 (UTC)
Fuzziness
I do not think that our article adequately conveys the "fuzziness". As BD and someone else remarked above, the basic problem, is that for several of the parameters we really have no idea, or at least the range of plausible estimates varies by several orders of magnitude. And when you multiply variations of orders of magnitude several times, you end up with a huge range. This is occasionally hinted at in the article, but is never really made clear. Rather than listing several people's estimates and results, would it not be more useful to multiply out the ranges of estimates, to show the range of the results? (This is easier if we work in orders of magnitude - OoM being logarithmic we could then add instead of multiply - but that might lose some readers.) An example to explain what I mean:
| Parameter | low estimate | high estimate | ratio | my comments |
|---|---|---|---|---|
| R* | 10 | 20 | 2 | The only parameter we have any real handle on, and it's already got a factor of 2:1 |
| fp | 0.1 | 0.75 | 7.5 | |
| ne | .5 | 5 | 10 | Up to here, it's wild estimates with at least some observational basis. All the rest are pure guesswork. |
| fl | .001 | 1 | 1000 | I think most people who argue for values close to 1 are making a common statistical inferential error; see "Anthropics and stuff" below |
| fi | <math>10^{-7}<math> | 0.5 | <math>0.5 \times 10^7<math> | |
| fc | .01 | .1 | 10 | I can't believe our uncertainty in this is really so low. People just haven't been exercising their imaginations enough. |
| L | 66 | <math>10^9<math> | <math>1.5 \times 10^7<math> | |
| N | <math>3.3 \times 10^{-11}<math> | <math>3.75 \times 10^9<math> | <math>1.125 \times 10^{20}<math> | Yes folks, that's 20 orders of magnitude. |
All of these parameters were taken from either our own article, or one of the ones in our extlinks. But I make no claim they are comprehensive, just an example. Securiger 12:12, 4 Nov 2004 (UTC)
Effects of personal bias
As an aside, having discussed this with quite a few people over the years, and read a few learned monographs on it, I have come to the conclusion that most people make up their minds beforehand - perhaps either wanting to believe that human life is especially unique, or wanting to believe that alien visitation is just a few years away - and then choose parameter ranges that satisfy those desires. The Drake equation tends to add excessive dignity to this process of biased, wild guessing. Really for at least four of those parameters, the only intellectually honest estimate is "we have no idea", which means the final answer is "we have no idea". Not very satisfactory, but true nonetheless. Securiger 12:12, 4 Nov 2004 (UTC)
Anthropics and stuff
Another point whilst I'm rambling on; our statement:
- What evidence is currently visible to humanity suggests that fl is very high; life on Earth appears to have begun almost immediately after conditions arrived in which it was possible, suggesting that abiogenesis is relatively "easy" once conditions are right.
suffers from the Self-Sampling Assumption. We can in fact deduce nothing about fl from our own presence on earth, since our own presence somewhere is a given, or else we would not be making the observation in the first place. For example, suppose that the true value of fl is so extremely low that there probably exists only one planet in the Universe with life on it. Evidently then, we the observers are on that planet, and we know of one civilization (us) and no others, because there are no others. Now consider a parallel universe where fl is billions of times higher, but, for some reason, no contact has been established. Any given group of observers knows of one civilisation (themselves) and no others, for reasons unknown to them. The observations are identical in both cases; by observing the existence of your own civilisation, you can deduce nothing at all about fl. To cut a long story short, in estimating any of these parameters, you can't count yourself. (The exception is L; since it doesn't affect our ability to observe ourselves, we can use ourselves as an estimator for L. I think.) The best that we can do is observe that there is another planet nearby where maybe life could have appeared, but apparently didn't, so fl is certainly less than 1. Note incidentally, that this is already implicitly taken care of in the definition of N, which is for extraterrestrial civilisations only; N does not include our own civ. Securiger 12:12, 4 Nov 2004 (UTC)
What is N << 1 ?
What is this terminology used in the article? N << 1
How does it differ from N < 1 ?
- N < 1 means N is less than 1 (possibly by an infinitesimal amount); N << 1 means N is much less than 1. Exactly how much "much less" means is a bit vague and usually determined by context. In some contexts, it means "so much less that within the limits of accuracy of our calculation, we can ignore it". In other contexts it can be taken to mean an order of magnitude less. Securiger 18:27, 15 Nov 2004 (UTC)
2?
for N not >>1, there should be some discussion of the conditional probability of the presence of a second civilization, given the presence of one (i.e. we know we are here, but we are interested if there is anyone else). dab (ᛏ) 14:52, 13 Jan 2005 (UTC)
Michael Crichton on the Drake equation???
Removed the following from the article:
Michael Crichton denounced the Drake Equation as pseudoscience in the Caltech Michelin Lecture entitled "Aliens Cause Global Warming" (http://www.crichton-official.com/speeches/speeches_quote04.html) (meant to be a serious lecture with a catchy title), 17 January 2003:
- Cast your minds back to 1960. John F. Kennedy is president, commercial jet airplanes are just appearing, the biggest university mainframes have 12K of memory. And in Green Bank, West Virginia at the new National Radio Astronomy Observatory, a young astrophysicist named Frank Drake runs a two week project called Ozma, to search for extraterrestrial signals. A signal is received, to great excitement. It turns out to be false, but the excitement remains. In 1960, Drake organizes the first SETI conference, and came up with the now-famous Drake equation:
- N=N*fp ne fl fi fc fL
- Where N* is the number of stars in the Milky Way galaxy; fp is the fraction with planets; ne is the number of planets per star capable of supporting life; fl is the fraction of planets where life evolves; fi is the fraction where intelligent life evolves; and fc is the fraction that communicates; and fL is the fraction of the planet's life during which the communicating civilizations live.
- This serious-looking equation gave SETI an serious footing as a legitimate intellectual inquiry. 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. And guesses-just so we're clear-are merely expressions of prejudice. Nor can there be "informed guesses." If you need to state how many planets with life choose to communicate, there is simply no way to make an informed guess. It's simply prejudice.
- As a result, the Drake equation can have any value from "billions and billions" to zero. An expression that can mean anything means nothing. Speaking precisely, the Drake equation is literally meaningless, and has nothing to do with science. I take the hard view that science involves the creation of testable hypotheses. The Drake equation cannot be tested and therefore SETI is not science. SETI is unquestionably a religion. Faith is defined as the firm belief in something for which there is no proof. The belief that the Koran is the word of God is a matter of faith. The belief that God created the universe in seven days is a matter of faith. The belief that there are other life forms in the universe is a matter of faith. 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.
- One way to chart the cooling of enthusiasm is to review popular works on the subject. In 1964, at the height of SETI enthusiasm, Walter Sullivan of the NY Times wrote an exciting book about life in the universe entitled WE ARE NOT ALONE. By 1995, when Paul Davis wrote a book on the same subject, he titled it ARE WE ALONE? ( Since 1981, there have in fact been four books titled ARE WE ALONE.) More recently we have seen the rise of the so-called "Rare Earth" theory which suggests that we may, in fact, be all alone. Again, there is no evidence either way.
- Back in the sixties, SETI had its critics, although not among astrophysicists and astronomers. The biologists and paleontologists were harshest. George Gaylord Simpson of Harvard sneered that SETI was a "study without a subject," and it remains so to the present day.
- But scientists in general have been indulgent toward SETI, viewing it either with bemused tolerance, or with indifference. After all, what's the big deal? It's kind of fun. If people want to look, let them. Only a curmudgeon would speak harshly of SETI. It wasn't worth the bother.
- And of course it is true that untestable theories may have heuristic value. Of course extraterrestrials are a good way to teach science to kids. But that does not relieve us of the obligation to see the Drake equation clearly for what it is-pure speculation in quasi-scientific trappings.
- The fact that the Drake equation was not greeted with screams of outrage-similar to the screams of outrage that greet each Creationist new claim, for example-meant that now there was a crack in the door, a loosening of the definition of what constituted legitimate scientific procedure. And soon enough, pernicious garbage began to squeeze through the cracks.
Comment: Crichton is a film-maker and a thriller writer, do his comments really add to this article? In any case, he fails to understand the concept of falsifiability. The Drake equation is not the issue, the value of N is. The Drake equation is just a back-of-envelope calculation made about the Fermi paradox. Falsifiable hypotheses can be made by setting bounds on the value of N, and making observations that can falsify these hypotheses. For example, just just one otherwise-unexplainable signal (prime numbered pulses, for example) recieved by SETI@home would do the job of setting a lowerbound of N=2. Or the sighting of some Dyson spheres, or other examples of engineering capable of being seen from lightyears away. Alternatively, you could go round the galaxy, enumerating civilizations, a task which whilst lengthy (a few hundred thousand years) is entirely physically possible, given von Neumann machines and a lot of civilizational patience. -- The Anome 14:13, May 21, 2005 (UTC)
- I agree, Crichton is way off the mark here: he appears to think that DE is same thing as e.g. the law of gravity. DE is used for estimation purposes, it is not a physical law. If we knew the real value of N, we wouldn't need DE, would we? Moreover, when he says that DE is not scientific, he is again off the mark, because it exactly follows the scientific approach to cracking hard problems, which is dividing them into smaller subproblems, separating well-defined ones from ill-defined ones along the way. GregorB 17:35, May 30, 2005 (UTC)
A new number for Ne could be 4 being that in our star system there are 2 planets and 2 moons which might develope life. They are Earth, Mars, and the moons Europa and Titan which may be developing life. Theoretically counting only ours as a primary source because we don't know how many planets are actually out there that are capable of creating life let alone sustaining it. Concluding the fact that the majority of the stars in the Milky Way are red dwarfs (which cannot have a planet around it because it would erode away any atmosphere on a planet). We took most of Drake's original numbers and added a few of our own and got N=8 so we think there are only 8 planets out there like ours that could communicate with us... comments please!!! need help with this one...!!!!
Nitpick: lower bound on L
I changed the following from the article:
- A lower bound on L can be estimated from the lifetime of our current civilization....
I don't think that's estimating a lower bound, because our civilization might have a longer lifetime than the average (expected) lifetime. Maybe "pessimistic value of L" would be more accurate? Wmahan. 05:53, 2005 Jun 15 (UTC)
Different version of the equation
It seems to me that the equation with "R* is the rate of star formation in our galaxy" gives an estimate of the number of civilizations that come on line each tear.
The astronomy book "Horizons: Exploring the Universe", by Michael Seeds gives a different version of the equation:
- N = N* x f_p x n_LZ x f_L x f_i x F_S (6 terms instead of 7)
where
- N = number of communicative civilizations in the galaxy
- N* = # of stars in the galaxy - NOT the number of new stars/year
- f_p = fraction of stars with planets
- n_LZ = # planets of star in life zone
- f_i = fraction that evolve intelligence
- f_L = fraction of planets suitable for life
- F_S = fraction of star's life that has a technoligal civilization
Needless to say, with the number of stars in the galaxy in there instead of the number of new stars/year, the result is much larger. He gives the pessimistic result 0.00002 and the optimistic 10,000,000.
Also, another point - f_i is normally limited to <= 1, i.e. at most one intelligent per planet. But there could be more than one per planet. Earth could evolve other intelligent species later. Bubba73 04:36, 22 Jun 2005 (UTC)
P.S. On second thoght, I guss the two versions are pretty much equivalent. One thing, near the end of the article for the current estimates, in the body it lists f_i as 0.01 but 1E-7 is used in the calculations.
Also, it should be noted that the number of intelligent civilizations is extimated to be considerably higher than the number that we can communicate with. Bubba73 04:54, 22 Jun 2005 (UTC)