Since much of this is guesswork, this is just for fun....

I have a feeling there's probably already been a thread like this in the forum, but I figured I'd post a new thread anyway....

The latest episode of SETI's "Are We Alone?": Formula One- The Drake Equation
http://radio.seti.org/

...and BBC's very cool interactive Drake Equation calculator with videos of our old friend Seth Shostak and others explaining different possibilities for the variables.
http://www.bbc.co.uk/sn/tvradio/programmes/horizon/broadband/tx/alone/drake/

Unfortunately, I think the BBC's equation is flawed because it locks the first two variables assuming they're "known". They're NOT known.
They lock the number of stars in the Milky Way at 200 billion and the percentage of those stars with planets at 10%.

Rubbish, I say.

Recent estimates suggest the Milky Way is thicker than was previously thought and some astronomers suggest that there are "no fewer" than 200 billion stars, perhaps as many as 400 billion (conceivably even higher). I would argue that while we have a known minimum and maximum, I don't think we know whether there are 200, 300, or 400 billion stars in the Milky Way at this point.

Many astronomers assume that the percentage of stars with planets is ~%10 based on known extrasolar planets, but it seems a foregone conclusion to me that this estimate will inevitably increase drastically as planet hunting techniques get better.

Heck, remember when scientists were fairly certain that Pulsars wouldn't have planets?? Or that brown dwarfs absolutely couldn't host earth-like worlds??


Anyway...I'm an amateur by all stretches of the imagination, and if I've gotten some science fundamentally wrong here, please let me know. :)

The Rate of Star Formation in the Milky Way
(or the total number of stars in our galaxy):
NASA estimates current star formation at as much as seven new stars a year; a vastly different number from previous estimates of as little as one.
http://www.nasa.gov/centers/goddard/news/topstory/2006/milkyway_seven.html
Star formation in the past may have been much higher.
The first variable may not be as pertinent as was thought in 1961 since the current rate of star formation is likely not today what it was ~4.5 billion years ago, which is the amount of time it took for an intelligent civilization to arise after the formation of our star. Since any transmitting civilization would presumably be older than us, I think a better expression of this variable is merely the total number of stars in the Milky Way galaxy that now exist.
Since I'm a layperson here, I'll simply choose the commonly reported minimum value:
200 billion

Fraction of those stars with planets:
Like I said, %10 seems a popular estimate but I'm willing to bet anything that will change drastically. Current extrasolar planet detection is in its infancy and will only get better.
Since even Pulsars have been found to host planets, this variable can no longer be restricted to only sun-like stars. I'm going to go with a relatively high estimate (although I feel it may in fact be as high as 90%):
60%

Average number of planets/worlds per star that can potentially support life:
When the equation was first formed, not as much was known about the Jovian moons as today; in fact, for all we know, moons orbiting gas giants may be more likely to support life than inner terrestrial planets themselves; and the rules about habitable zones might not apply at all. Let's look at our solar system as an example: Earth has life; Mars *may* have had the conditions to support life in the past; Europa may have the conditions to support life right now; Titan, rich in organics, may have an underground water ocean http://www.space.com/scienceastronomy/080320-titan-ocean.html
Enceladus *may* also have an ocean.
So in our solar system alone, in a best case scenario, as many as 5 worlds have or have had the conditions to support the evolution of life. Since gas giants may typically have many moons, that seems to increase the likelihood of candidates to support life in any given star system; tidal heating may make habitable zones irrelevant.
My estimate:
3

Fraction of those planets/worlds where life actually evolves:
...Much of the galaxy is subjected to more intense radiation than our part of the neighborhood is...such radiation may preclude the possibility for something as complex as DNA to arise. On the other hand, the thick icy crusts of worlds like Europa and Titan would act as natural shields against such radiation. Magnetic fields like the one our Earth has would also help protect fledgling DNA.
But since our Earth seems to be the only world on which life is clearly and obviously evident, and since we have the ideal conditions of a magnetic field, a very large moon, and the perfect distance away from the sun for liquid water to exist and be retained on the surface, those conditions undoubtedly contributed to the fact that almost as soon as the earth formed, life arose. Maybe that suggests that where life CAN arise, it WILL arise? Maybe not.
My guess:
10%

Fraction of worlds with life where *"intelligent"* life evolves:
I think the comsologist on SETI's radio program who claimed that "human-like" intelligence is the equivalent of highly specific freak adaptation is using fallacious logic since *all* complex animal life on Earth has a brain and central nervous system, and there are countless examples of species which possess the ability to modify their environment or use tools. Even ants could be considered to have "civilization"; they have their own kind of intelligence, they live in a highly complex, structured society and are able to build their own "cities"; arguably they've become just as "successful" and widespread as humans have. Language and the ability to use tools or manipulate your environment are not the functional equivalent of a Dodo Bird's mating ritual. Bees and Whales have "language", even Crows have been shown to fashion and use tools.
That being said, the only life on this planet for billions of years was microbial, and its evolution was virtually static, largely unchanged. For whatever special circumstances (perhaps the effects of snowball earth), the Cambrian explosion happened; Complex animal life itself isn't even a foregone conclusion just because life arises. It took hundreds of millions more years for the Homo genus to come about and there were plenty of other kinds of species which were far more successful, like the Dinosaurs or even Jellyfish. It seems that natural selection doesn't favor intelligence. Even when the Homo genus came about, natural forces could easily wipe such a species out before its population becomes widespread enough to survive disasters; genetics research suggests modern humans passed through at least one major bottleneck which correlates to some kind of disaster, perhaps a major volcanic event.
While I don't agree with the cosmologist, I do in fact have a hunch that "intelligence" is extremely rare. Extremely, extremely rare.
0.0001% (1 in 1 million)

Fraction of worlds with intelligent life that actually send signals:
To do this, you need technology.
Seth Shostak uses the history of humanity as an example, but I think that's misguided thinking. I absolutely agree, the evolution of human science was almost certainly inevitable; the Greeks may have been pioneers, but even the Mayans and Aztecs were science enthusiasts. Keep in mind, science ultimately survived the Dark Ages and the European age of Heresy.
But humans are a very particular species; I used ants as an example before. It might seem silly, but couldn't ants be considered as having a kind of civilization? Perhaps "intelligence" will arise and some species will develop limited science so that some technology exists, but it may develop it no further and choose to remain static throughout its entire lifetime, like some insect-like civilization. Maybe once a brain is capable of understanding science, the species' knowledge and technology will inevitably improve no matter what; with humans, the potential seems boundless. Regardless, to account for intelligent creatures arising from natural selection which may be more different from us than we can imagine;
70%

The average lifetime of signaling civilizations:
At the time when the Drake Equation was first created, it was the height of the Cold War. The Cuban Missile Crisis was right around the corner and much of the world was gripped in paranoia and bomb shelter hysteria. Such times have passed although sizable nuclear stockpiles remain.
Perhaps such paranoia was never warranted in the first place? For all the fear mongers and doom prophets, I think the fundamental truth is that humanity would survive almost any catastrophe, whether natural or not. There are almost 7 billion people on Earth; our technological capabilities are considerable only ~10,000 years after the birth of civilization.
I believe there are just TOO many people and too much technological capability for ALL 6.6 billion people to spontaneously go extinct. Even if every nuclear weapon on the planet was detonated, there would be survivors; even if the surface of the earth was made toxic and irrecoverably scarred, there would be survivors.
Not only that, but the colonization of other planets may happen within the next century; the Moon, Mars and others may inevitably be inhabited by humans. Even if all of the billions of people on Earth were vaporized in the blink of an eye for some reason, humans on other colonies would survive.
My personal feeling is that once an intelligent species is able to survive its infancy and populates the entire planet, growing vastly in number, and ultimately possessing technology to aid its survival, it will almost certainly persist indefinitely. I can only assume that freak occurrences like nearby supernovae or gamma ray bursts could *completely* wipe out any such civilization, but even then, at the rate at which technology develops, I don't see why any advanced civilization would be entirely powerless against even those events.
My guess (a minimum of)...
100 million years

My guesstimate as to the number of communicating civilizations which currently exist in the Milky Way Galaxy:
252

I used this website to calculate N:
http://www.activemind.com/Mysterious/Topics/SETI/drake_equation.html



So what's YOUR guess?? :D

For
N*= 400 billion
fp= 10%
ne= 4
Fl= 5%
Fi= .0001%
Fc= 50%
FL= 100,000 years
Thus,
N= 40

(I apologize if I made a computational error. I did not notice the link to the site until after I did my calculations and I did not have time to redo it. If I made a mistake please correct me.)

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The Drake equation looks a little naive, which is alright, considering its age, the knowledge base available at the time, and its conservative biases. The issues of interplanetary and interstellar colonization are neglected.So, too, the effects of intercivilization contact. Nevertheless, given these tools to work with: N*=300 billion; Fp= 90%; Ne= 1.5; Fl=50%; Fi=50%; Fc=50%; L=5 million years, thus: 1000 civilizations in the galaxy at the moment, if my calculations are correct. A nice round number. Actually, I suspect the number is lower, not due to any limiting factor, but because civilizations tend to merge, making one out of two repeatedly. If civilizations are brought in promptly, upon reaching a sufficiently communicative phase, there might be only two civilizations in the galaxy: Us and the one made up of the rest of the communicative worlds therein. Michael

The issues of interplanetary and interstellar colonization are neglected.So, too, the effects of intercivilization contact

....because civilizations tend to merge

I tend to think that interstellar distances are simply too vast....and that our current understanding of physics strongly suggests that physical limitations on travel speed are unable to be overcome; even projections of our knowledge and applications of physics suggest that only by harnessing nearly impossible amounts of energy could such distances be overcome without epic timescales that would (in my mind) make widespread interstellar travel impractical.

...so I don't think we can project the history of the intercontinental relations of Earth onto the universe and conclude that independently evolved planetary civilizations tend to merge.

For all I know, you could be absolutely right.

But as far as interplanetary colonization and intercivilization contact, it seems Fermi's Paradox is staring us squarely in the face here:
If galactic empires or even interstellar nations existed, I can't stretch my imagination enough to even remotely explain why we haven't detected even the slightest, faintest whisper or hint of civilizations that exist on such a vast scale. I can only imagine that the energy signature of such empires alone would have been unmistakable and couldn't have been twisted to fit any theoretical framework which is predicated on a natural origin.

If I were to bet on this, I'd say that not only is intelligence exceedingly rare (my guess of 252 civilizations was probably generous) but furthermore that civilizations are by and large doomed to be isolated across vast distances and that while a single civilization might explore or set up colonies around nearby stars, such undertakings are limited in scope due to the timescales involved.


Obviously my guess is as good as yours though. ;)

The issues of interplanetary and interstellar colonization are neglected.So, too, the effects of intercivilization contact

....because civilizations tend to merge

I tend to think that interstellar distances are simply too vast....and that our current understanding of physics strongly suggests that physical limitations on travel speed are unable to be overcome; even projections of our knowledge and applications of physics suggest that only by harnessing nearly impossible amounts of energy could such distances be overcome without epic timescales that would (in my mind) make widespread interstellar travel impractical.

...so I don't think we can project the history of the intercontinental relations of Earth onto the universe and conclude that independently evolved planetary civilizations tend to merge.

For all I know, you could be absolutely right.

But as far as interplanetary colonization and intercivilization contact, it seems Fermi's Paradox is staring us squarely in the face here:
If galactic empires or even interstellar nations existed, I can't stretch my imagination enough to even remotely explain why we haven't detected even the slightest, faintest whisper or hint of civilizations that exist on such a vast scale. I can only imagine that the energy signature of such empires alone would have been unmistakable and couldn't have been twisted to fit any theoretical framework which is predicated on a natural origin.

If I were to bet on this, I'd say that not only is intelligence exceedingly rare (my guess of 252 civilizations was probably generous) but furthermore that civilizations are by and large doomed to be isolated across vast distances and that while a single civilization might explore or set up colonies around nearby stars, such undertakings are limited in scope due to the timescales involved.


Obviously my guess is as good as yours though. ;)

Interesting, that you should place so much emphasis on our current knowledge of physics, as a basis for predicting the impossibility of future interstellar travel . You are aware, I trust, that such things as heavier than air flying machines, atomic energy, atomic explosives, and space travel to the Moon were each pronounced impossible by experts, whose knowledge seemed to bear well on these matters, at the time the predictions were made. Your point about our not detecting energy signatures from extraterrestrial civilizations is interesting. The explanation could be as simple as greater efficiency in the use of energy. Energy spilled out into the cosmos at random is wasted energy. Improve efficiency enough and detection could become very difficult, perhaps beyond our current ability to do so. Or perhaps not *quite* beyond. Non repeating SETI signals have been detected. They probably weren't intended for us, but it is entirely possible that they were inadvertent leakage, possibly due to malfunctions of technology or unanticipated scattering effects. Michael

For
N*= 400 billion
fp= 10%
ne= 4
Fl= 5%
Fi= .0001%
Fc= 50%
FL= 100,000 years
Thus,
N= 40

(I apologize if I made a computational error. I did not notice the link to the site until after I did my calculations and I did not have time to redo it. If I made a mistake please correct me.)

My best guess.

N*= 200,000,000,000
fp= 0.9
ne= 2
Fl= 1.0
Fi= 0.00001
Fc= 0.001
FL= 1,000 years
Thus,
N= 3600000

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BOINC WIKI

*shrug*

It has been a while since I did my own Drake Equation. Sure, it is fun (and romantic), but it is nothing but guesswork.

While I didn't apply this directly into the equation, it was something that I kept in the back of my mind while guesstimating the percentage of intelligent worlds:

I think if you have a world that is over abundant in resources, intelligence is less likely to evolve. When the Earth was plentiful, Nature ran a muck and completely out of control. We had pea-brained lizards the size of small skyscrapers (dinosaurs). The plant-eaters didn't have to be very smart because, as someone once said, "You don't have to be intelligent to sneak up on a leaf." The meat eaters didn't have to be smart because there was a plant eater ready to be dinner at every turn. I think such abundant worlds allow Nature to run out of control until Nature does itself in.

For intelligence, you need competition, such as when the mammals emerged after the KT (asteroid) event. They needed to outsmart one another to survive.

So, you need a very fine balance of available resources. Too much resources and Nature runs out of control. Too little and, of course, everything dies.