Wolfram Alpha's take on the Drake Equation
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wolframalpha.com
Before you downvote me, I think it's a great equation and I don't have problems with folks using it. As long as you know what you are doing. really, think about it, all it actually says is that there is this list of things that we feel have to happen in order to determine communicating civilizations, and given any random set of probabilities for a list of things, you multiply them together to get an aggregate answer. It doesn't address whether the list is complete, or overly complex, or mis-stated. The numbers provided are juts best guesses. It's just "multiply a bunch of numbers together and get a new number"
I love it. It's definitely not science -- yet it has this cool-looking formula involved. It also has a powerful impact on folks who use it.
Drake is really cool in that it gets people thinking about how likely ET is. For that, it's a wonderful tool. But at its heart there's really not much there. At least yet. Perhaps in the future we'll have some solid survey results to put in, especially with Kepler online. Can't wait to start seeing those results coming in.
Though I do like how it gets people to realize how small and insignificant we are in the grand scale that is the solar system, the reasoning we take to get there is fundamentally flawed. We use numbers that have everyday meaning to us, and of course it spits out nice results; this is flawed reasoning since we have no basis to think those numbers are even remotely correct. In general, I just think it's sloppy thinking that takes advantage of deficiencies in human thinking -- it's a magic trick.
In fact, the Drake Equation is a religious statement. That is, it is a creative speculation using commonly understood symbols to that which are completely unknown to us. It's the same as a couple of cavemen sitting on a hill talking about thunder as being large rocks falling from a cliff in a faraway valley. It makes sense, it fits in with what we know, but it's really just a bunch of guesses connected with symbols that, based on context, we feel social approval towards. It's a mind-hack. And a very nicely executed one at that.
The reason I didn't use the "R" word, religion, is that folks see that word and stop thinking. They give you an instinctual answer. No way! I'm not religious! etc.
The Drake equation basically says what anybody who has looked up at the night sky knows intuitively: there are a lot of stars out there, and it's extremely unlikely that we're all by ourselves. It just does it in a way that makes us feel like we're receiving some sort of imparted scientific wisdom, instead of what it really is: creative speculation. In that sense the formula itself may be total bullshit scientifically, but what it tells us about how science and religion play with each other is very important. People look at it and just feel that there is some truth there, and there is, but it's not the same kind of truth as f=ma, although both statements are expressed mathematically and have the same air of seriousness around them.
Further reinforcing your core point, it can also tell you that we are. You don't have to be that painfully conservative with the numbers to come with one or fewer per galaxy. For instance, 50% of stars having planets may be a brutal overestimate, a lot of stars are in multi-star systems or other situations in which there are no stable orbits, resulting in any initial planets getting ejected very quickly if they form at all. 2 Earth-like planets per star is a bold statement, depending on the exact definition of "Earth-like", we only have one in our system and if you read past the propaganda in the planet finding press releases they aren't coming up with all that many other "Earth like" planets yet. Yes, that's because they still can't see them, but the press releases convey a false sense of how the search is going when they do things like call a planet with a surface gravity of 3 or 4 G and a surface temperature beyond rock's liquification point a "Super-Earth". 10000 years is a bold estimate for how long a civ will be around and communicating, certainly. I actually am against the self-loathing that some circles find fashionable but 10,000 years is a long time. I consider these numbers generous and it still only comes up with 10.
It's missing some terms, too. Irregular galaxies [1], approximately 25% of the galaxies out there, are thought to be entirely unable to support complex life because basically all the stars in such galaxies will take a system through a region of the galaxy with too much radiation and sterilize the planets every few tens of millions of years. I mean this only as an example, you can go on naming more fairly reasonable criteria that eliminate half or more stars from contention for quite a while (star types, star galactic orbits, other galaxy attributes, even before we get to planets we can eliminate a lot).
To brutally abuse notation, the night sky is O(n^3) in size, if the probabilities of developing civilization are O(2^n)-type it doesn't matter how large the sky is. Big numbers fall fast when you multiply independent probabilities together, and it's not sophistication to just give up and declare there must be a lot of other civilizations out there; it's still a mathematical copout. We don't know.
There is evidence that Mars once carried liquid water on its surface, it's formed out of the same materials (carbon, hydrogen, water) and had all the elements needed for life. Mars lost its liquid water because (contrary to earth) it lost its atmosphere because it also lacks active plate tectonics (also, contrary to earth).
So our solar system has 2 earth-like planets ... with one that became a desert and died, but that was once very much like Earth, with some people still hoping to find microscopic life at the poles.
That's not too shabby. Basically it is considered that if a planet holds liquid water, then it can carry life (liquid water implies other things, like the presence of an atmosphere). Bigger solar systems may contain even more earth-like planets, but I agree: an average of 2 is way too high.
EDIT:
Also, one other thing: if Mars wouldn't have lost its atmosphere, then oxygen would have spread faster than on earth, because the planet is smaller, which means the transition from microscopic life to macro would have been faster.
Mars has the strike against it that it is arguably on the frozen side of the zone of life. Earth is actually already on the somewhat cold side and has spent a fairly large portion of its life as an ice planet; some have speculated that our frequent ice ages have contributed to our diversity of life by moderately predictable periodic mass extinctions, but of course this is just a theory in all the bad senses of that phrase. Venus is possibly too far on the hot side but I have an easier time envisioning life on a relatively hot planet than a relatively cold one. We have extremophiles here on Earth and who knows what they'd be able to evolve into if they weren't in such a small niche? Whereas cold really puts a stopper on life; a critter can evolve that can survive being frozen and possibly even carry on simple life functions but only at a very slow rate, and for all we talk about how fast and robust life is it does not take very much slowdown of life before you can't get an intelligent civilization evolved before the sun ceases to support life. Life is thought to be ~3.5 billion years old here, and it's hard to pin down exactly how long the sun could sustain non-intelligent life but it could be as little as ~1 billion years. Cold life has a real challenge getting to intelligence in time. (Also why I don't spend any time wondering about life in nebulas; they may be a science-fiction staple but at the rate they could live they don't have enough time to evolve into anything interesting before the heat death of the universe.)
If that is the way people choose to see it, that is not Drake's fault. It sounds like you and dantheman really only have a problem with the bullshit "religious" implications some poor souls wish to divine from a dry bit of math.
The Drake equation is not a religious statement until you fill in faith-based numbers.
Creative speculation is not religion just as thought is not superstition.
Creative speculation + experimental verification = science
Creative speculation + certain belief without evidence = religion
Creative speculation + allowing uncertainty = reasoning
Creative speculation + action = decision making
Creative speculation + business implementation = startup
Those cavemen are doing rudimentary science. They've come up with a testable theory that explains an observed phenomenon of the natural world. If they were to conduct surveys of the cliffs within hearing distance before and after thunderstorms, they'd eventually falsify the theory.
The chief aims of the conference were, first, to estimate values for terms of the Drake equation, and second, to devise strategies for contact. So all these top American and Soviet scientists had to discuss a remarkable range of topics—everything from the chemical origins of life, to the anthropology of early civilizations, to the problem of encoding messages in a form comprehensible to intelligences vastly unlike ourselves.
It's possibly the most interesting thing I've ever read.
Originally, it was available at http://www.michaelcrichton.net/speech-alienscauseglobalwarmi..., but I've ViewText-formatted a mirror on http://viewtext.org/article?url=http://climaterealists.com/i....
It's one of my pieces of writing available online.
Why not? It's proposing an underlying model, which in turn provides a framework for investgation as well as a way reasoning about things in the absence of harder data as. Sounds like science to me.
What would you propose as a more scientific approach to estimating the number of communicating civilizations in the galaxy?
Here's a link actually, should be doing this more.
Given life and enough time, what is the probability of a technological civilization arising. 1.0 or so small that we are alone. We are probably at the age and interconnectedness that we will survive a very long time. I dont wory about nuclear war, but I do worry about bio-terror and nut cases.
I think the big constraint is patience. I dont think any civilization is ready to invest the time and energy to wait 1000 years for a reply. I think the potential partners will be limited to a volume of 100 light years. Maybe 5000 stars, not all that many.
Where do these figures come from? For fully 5 out of the 7 parameters to the Drake equation we have extraordinarily limited data. How common are Earth-like planets? Call back in about 5-10 years when we'll have some solid data from the Kepler mission. How common is life on Earth-like planets? Who knows? We aren't even close to being able to get solid figures on that. If we can find life on Mars or rule life out of ever having existed there then we'll have a teeny tiny bit of data. But even then such an estimate will be biased by the anthropic principle and at best only accurate to perhaps a single order of magnitude (if that). Even then that leaves half of the parameters as wild ass guesses.
Not to mention that the parameters aren't independent. If we find life on Mars existed or still exists that would make f-sub-l higher, but it would probably make f-sub-i correspondingly lower.
Worse yet, the very premise of the Drake equation is at odds with the premise behind the Fermi paradox. If even a single, slow colonizing intelligent civilization ever existed in our galaxy it would make the number of possible communicative worlds differ by perhaps even 6 or 9 orders of magnitude.
The exercise is only worthwhile when it is not taken seriously, which is a bit of a catch-22.
For those not familiar with how Kepler is finding planets, I'll explain. Basically, Kepler looks for planets transiting in front of their stars. The telescope watches for dips in the star's light. If the planet has an atmosphere, in some cases it can even get an idea of some of the gases from the light.
The reason that astronomers aren't expecting to find Earth-size worlds in the habitable zones is that they have to wait for several transits to know for sure they've seen a planet. The reason that most of the planets found to date have been gas giants orbiting very close to their stars is that it only takes a few weeks or months for them to transit the star several times. Astronomers can see one transit, but have to wait for a 2nd to hypothesize a planet is found, and have to see a 3rd or more transit to verify the planet is real.
So Kepler has likely already detected suspected Earth-size planets in habitable zones around at least a few stars. However, the telescope has to watch for several years to confirm the transits. Imagine an astronomer in another solar system that has seen Earth transit the Sun. They would have to wait 3-4 years to see Earth transit the Sun several times to confirm our existence.
Edit: Meant to include this earlier. There are multiple ways to detect exoplanets, including the transit method. http://en.wikipedia.org/wiki/Methods_of_detecting_extrasolar...
Whether this is a comment on the Drake Equation or my salary is an exercise left to the reader :)
if you think there are 10 communicating civilizations now, each communicating for 10000 years, then there should have been quite a few such civilizations in the 13000000000 year history of our milky way galaxy.
if the parameters provided apply for 1% of the milky ways history, we would expect 13000 communicating civilizations in total.
i would imagine any communicating civilization lasting 10000 years would also develop self reproducing space probes, thus becoming a permanent feature.
We could be the first, or one of the first civilizations in the galaxy. Trouble with the equation is that it does make nobody happy. As we are knowing better some factors (like how many stars have planets) it seems that life should be everywhere.
But it's enough that one the still unknown unknowns is worse than we think, to make the density as low as a few dozen civilizations in the galaxy. That's too far for us to communicate in a 10.000 years scale.
BTW, I find this 10.000 number is cruft from cold war era. Some people love the extintion idea, not sure why.
See http://en.wikipedia.org/wiki/Von_Neumann_probe#Implications_....
It should be noted that if our civilization survives another few hundred years, we are likely to send out von Neumann machines.
The default is 10,000 years. That results in 10 civilizations. A 1,000 year lifespan means there is only 1 civilization, and a 100,000 year lifespan means there are 100 civilizations.
As if we have any idea how long a communicating alien civilization would last. We don't even know how long we will last, and aliens would be completely different to us.
Apart from the curious "are we alone?", does answering this question, has any positive/productive outcome?
It's not necessarily about the destination, the stuff we find on the journey is valuable in its own right.
Finding an ET would be event of scientific significance that can hardly be compared to anything else. Perhaps a manifestation of God's existence comes closest.
That guess could be off by many orders of magnitude as we have exactly one data point right now
See Mitochondria, Chloroplasts, perhaps Cell nuclei, the retro virus that's incorporated in our genes that make mothers' immune system not reject the fetus. (See https://secure.wikimedia.org/wikipedia/en/wiki/Endosymbiosis and https://secure.wikimedia.org/wikipedia/en/wiki/Endosymbiotic... for more.)
On a scale broader than single cells there are around 80% of vascular plants and their symbiosis with fungi, the bacteria in our guts, the worms close to black smokers, certain sea cucumbers that absorb algae and live off their photosynthesis, and much more.
Also, if Fraction of Earth‐like planets that develop life = 1 and Mars is an "Earth like" planet, are they assuming life evolved in Mars too or something?
"fraction of Earth‐like planets that develop life: 1"
For all we know that could be .001 or .0000001
[1] I plugged in .1, among other variable changes. On the other hand, I got the number of communicating civilizations = .02, so either I'm too pessimistic or we're just really, really lucky.
Life, given right conditions and enough time, seems to be about as inevitable as the eventual appearance of viral cat pictures on online forums, in other words.
I think there is little wrong with assuming that the probability of emergence of life given right conditions and enough time is one; however we need to be very careful with estimating how common (and how stable!) those conditions are in our galaxy in the first place. A good place to start would be to look at how many places similar to Earth are out there (which we are already doing).
Fair enough. It's a bit like the infinite monkeys in infinite typewriters scenario. Given enough time, sure, you'll have life. It's a question of how much time. Still, assuming all Eart-like planets will actually develop life given the time lapse of the existence of the Milky Way does still seems like a bold assumption.
Your point is correct, but my hunch is that the time needed is no more than a million years or so (small on the galaxy scale), possibly less.