N = N. • fs • Np • Fe • Fl • Fi • Fc • L ÷ t
N = number of technical civilizations possibly existing in our Milky WayGalaxy (what we are seeking).
N. = number of stars in the Milky Way = 200 – 400 billion
fs = fraction of stars sufficiently Sun-like to support a civilization = .11 – .25
Np = average number of planets per Sun-like star = 1 – 20
Fe = fraction of Earth-like planets capable of supporting life = .033 – .11
Fl = fraction of Earth-like planets on which life might develop = 0 – 1
Fi = fraction of life-bearing planets that evolve intelligent beings = 0 – 1
Fc = the number of life-bearing planets where intelligent beings develop a technical civilization = .01 – .05
L = the average lifetime of a technical civilization = 500 years – 100,000 years
t = Average time from the formation of the Milky Way before a technical civilization arose (3 billion years)
To prove to myself that solving the formula was not hard, this reviewer selected a middle value for each of the above terms except for L (the average lifetime of a technical civilization). For that term I picked 3000 years because it seemed like a more realistic time span due to present global climate changes and our race's propensity for nuclear warfare. Science continually warns us about irreversible catastrophic damage to our planet, and I believe those warnings are real. Here is my equation filled in:
N = (200,000,000,000)(.18)(10)(.08)(.5)(.5)(.3)(3000) ÷ t (3,000,000,000) = 2,133
Thus, there is the possibility that 2,133 technical civilizations currently exist within the Milky Way. One must be mentally bamboozled when thinking of multiplying this number by the billions of similar galaxies in the entire universe.
The remainder of Life in the Universe deals with the impossibility of space travel even to the closest planets outside of our solar system but still within the Milky Way Galaxy. The distances we’d have to travel, even if speed-of-light travel was possible, are unfathomable.
Article comments
1 - duane
Drake actually ended up being embarrassed by his famous equation, which is famous largely for its ease of understanding and for the profound topic it addresses. It is useful only from a qualitative standpoint, since most of the factors can only be guessed at, with WIDE variation. Usually parametric equations of this type contain only one or two 'ignorance parameters', and they are usually known to within a factor of ten or better. The Fi factor, just for example, could vary by a thousand, or a million, or a billion. We just have no idea. There is hope that the first three factors will be fairly well in hand within the next few decades. The first factor is the best known at the present time. The t factor can be reasonably estimated (factor of ten), since we know the age of the universe
Some interesting ideas have come up in recent decades, such as the Fermi paradox, von Neumann probes, Bracewell probes, detection of Dyson spheres, and so forth (all easy to find on the web). One especially interesting discussion involves the so-called Great Filter (highly recommended reading for those interested in this topic).
On a less cosmic scale, one has to consider the Moon's role in allowing for the evolution of life on Earth. This is a topic of current interest, and seriously lowers any estimate on the Fe factor in the Drake equation. See, for example, this article.
Constraining the Fi factor is subject to our understanding of global cataclysms, in particular, dinosaur-killing asteroid/comet-Earth impacts. More randomness.
etc., etc....
I think N=1 (that would be us).
2 - Dr Dreadful
The problem with the Great Filter idea, along with all other speculations as to the degree of our aloneness in the universe, is that it makes, of necessity, huge assumptions about how life and civilizations develop.
But there's no reason to think that life at other locations in the cosmos would develop in the same way, or hit the same crisis points - such as the emergence of eukaryotic cells - as it did on Earth.
More probable, I think, is that 'alien species' - for want of a better term - would have developed in such a drastically different way to ourselves that we wouldn't (haven't?) recognized them for what they are. Hell, there might be an alien sitting right next to me now and I'd have no idea it was there - and it wouldn't have any awareness of me either.
In that sense, Duane, I think you're very probably right about the number of intelligent civilizations like ours that there are in the universe. Any others would be so unrecognizable and... well, alien that for all practical purposes they wouldn't count.
There is, however, another part of me that thinks I'm very probably wrong, and I wouldn't be at all surprised if NASA/JPL confirmed tomorrow that microbial organisms, either live or fossilized, had been detected on Mars.
3 - duane
Hi Dr. D. Interesting comments. Couple o' things.
Yes, of course, it's all wildly speculative. All we have as an example is our own civilization. It's not necessarily a good idea to project our own human qualities onto hypothetical aliens, by which I mean the desire to explore and to make contact.
There may indeed be an alien right next to you, with access to technology that allows him (?) to be invisible and silent. Best behave.
As far as discovering microbial life out there, I think that is not so far-fetched. But the jumps to intelligence then technological then spacefaring are huge jumps. That is where the speculation really begins. Over the next few centuries, I believe that biologists will put much of the human evolution puzzle together. That's a start -- just a start-- but right now there are endless uncertainties (unless you happen to believe in Genesis).
I thought the interesting spin on the Great Filter idea was that it would be BAD news if we discover any kind of life on Mars, because that might imply that life is not so rare. Then the Fermi paradox might be taken as having frightening implications. But then we come back to your contention that the GF might not apply to an alien life form. OK. Good point.
Where is Regis?
4 - Regis Schilken
Your comments Duane and Dr. Dreadful are well taken. However, my understanding of Pierce's book was this: it is an attempt to estimate the number of civilizations within our Milky Way Galaxy where LIFE IS SIMILAR to life on earth.
From the beginning of his book, Pierce uses the word alien and extraterrestrial when talking about the possibility of life other than that on earth. These terms typically suggest to me the creatures seen on Star Trek or Star Wars.
I think his work would be less misleading if he simply referred to "alien" life as human life because that is what the Drake equation appears to estimate. Even the book title would sound different: THE ABUNDANCE OF HUMAN LIFE WITHIN THE MILKY WAY.
5 - Ilya Stavinsky
to Regis Schilken:
"Aliens live in our Earth's atmosphere"
For the first time in human history, I present here incontrovertible evidence of existence of hundreds of thousands of UFO in the Earth's atmosphere, which can be seen by any person in any part of the world at any time...
6 - Regis Schilken
I've read the Ilya Stavinsky "article" above on the existence of UFOs. It contains no reasonable information about aliens, or even the slightest evidence that there are "...hundreds of thousands of UFOs in the Earth's atmosphere, which can be seen by any person in any part of the world at any time ..."
I would hope it does not deter interested people from reading Life in the Universe: The Abundance of Extraterrestrial Civilizations by James N. Pierce.
7 - Ilya Stavinsky
to Regis Schilken:
Your negative statement about my article "Aliens live in our Earth's atmosphere", is completely baseless. Why don't you come to my place and I will show you 100s of UFOs in the night sky. After that you will change your mind. This is the best way I can prove that you are wrong about my article.
8 - Regis Schilken
to Regis Schilken:
Your negative statement about my article "Aliens live in our Earth's atmosphere", is completely baseless. Why don't you come to my place and I will show you 100s of UFOs in the night sky. After that you will change your mind. This is the best way I can prove that you are wrong about my article.
To Ilya Stavinsky from Regis!
Sorry I appeared negative about your photos of aliens visiting our solar system. Would you send me one of those photos either in an email or as an attachment. Thank You in advance.
9 - Ilya Stavinsky
to Regis Schilken:
I don't have photos of aliens but I have drawings of their motherships that I see every night in the sky, these drawings have been updated recently on my web site as the result of my further observations. If You have more questions I will be glad to answer them.
10 - Dean
If "technical civilization" is defined as one with technology of the type humans have developed since the Renaissance and the Industrial Revolution, then the Drake Equation is missing some parameters. A lot of people seem to assume that intelligence somehow automatically leads to technological progress. A look at the history of civilazations on Earth is enough to make one skeptical about that. Philosophical, religious, cultural, and political factors have all had played important parts in determining where technology did or did not develop on Earth. Would that be untrue elsewhere?
11 - Regis
Dean,
Your point is well taken about the influence of philosophical, religious, cultural, and political factors, on technological development.
In his book, LIFE IN THE UNIVERSE, author Pierce does say, "Technical civilizations are almost certainly not automatic for intelligent species."
He devotes an interesting chapter 10 to THE RISE AND DEMISE OF TECHNICAL CIVILIZATIONS, which considers some of the factors that have had an immense impact on the development of earth's technology.
Because Christianity spread throughout Europe, I wonder how much sooner thinkers would have felt "mentally" free to experiment with reality without considering it sinful.
When I think of how long the Greek atomists' beliefs went undeveloped (2000+ years), it reminds me of how long stem-cell research in this country has been delayed due to religious doctrine.