Number of ET Civilizations In Our Galaxy Is 37,964 544
KentuckyFC writes "The famous Drake equation calculates the number of advanced civilizations in our galaxy right now. But the result is hugely sensitive to the assumptions you make about factors such as the number of habitable planets that orbit a host star, how many of these actually develop life and what fraction of these go on to become intelligent etc. Disagreements about these figures leads to estimates for the number of advanced civilizations ranging from 10^-5 to 10^6. Now an astronomer in Scotland has worked out how to make the calculations more precise so that different theories about the origin of planets, life and civilizations can be compared. His calculations say that the rare-life hypothesis predicts only 361 advanced civilizations in the Milky Way now. However, the so-called tortoise and hare hypothesis predicts 31,573 and the theory of panspermia says that there ought to be 37,964 extraterrestrial civilizations more advanced than our own in the Milky Way."
Re:Then where are they? (Score:5, Informative)
Or there is of course, another possibility: That humans are the only "intelligent" species using radio transmission as a communications medium and that any other "intelligent" species is such a great distance away and/or in a region of space where we haven't been listening that we are unable to detect them.
Re:My estimate (Score:5, Informative)
Re:What a great example! (Score:5, Informative)
That's 32767 and an overflow flag.
And get off my lawn.
Re:My estimate (Score:5, Informative)
Re:Then where are they? (Score:5, Informative)
Sure, the signals have travelled a long way. Now, would you like to be the entity at the other end trying to pick out our signals from all the other noise that exists in the Universe?
Since the power of the signal is reduced by the square of the distance, when we start talking about interstellar distances, (forget intergalactic distances), that number is so large as to make our signals virtually undetectable. The CLOSEST star is Proxima Centauri which is 4.2 light years away. Convert to meters, we have approximately: 4 * 10^16 meters. Squared gives us a power reduction of 1.6 x 10^33.
So, if we sent a terawatt signal, 1x10^12 watts, even if there was someone at Proxima Centauri to listen, they would have to hear a signal that's 6x10^-22 watts. Which is pretty hard to pick out from any background noise.
Re:Where to find them? (Score:2, Informative)
It was a great read let down by this stupid theory.
Comment removed (Score:3, Informative)
Re:Close neighbors? (Score:2, Informative)
Precision != accuracy. (Score:3, Informative)
They can be as precise as they like, and revise their estimates to 361.055371 (or 31573.22 or 37964.0000) if they want. Precision without accuracy is worthless.
At least they estimated distributions for some of the parameters. My favourite part was the honest phrase "the model now enters the realm of essentially pure conjecture" when they moved to considering the life parameters. Probabilities and uncertainty estimates here should have been of the NaN sort.
Alas, they then proceeded to assign finite uncertainties to unestimable quantities. The standard deviations they actually gave are merely parametric, with the assumption that the underlying model structure is valid. Given that they obtained very different values from three different models (all of which may be wrong), the true uncertainty is far higher. An estimate of a value accompanied by an estimate of its uncertainty - with the estimates depending on pure conjecture - does not convey anything approaching accuracy.
Of course, if the numbers are just for fun, or for dinner conversation, that's fine. As scientific estimates, they should be discarded.
Re:Where to find them? (Score:5, Informative)
Not sure the plausibility or not, but we're ALREADY in the outskirts of the galaxy.
Re:Then where are they? (Score:5, Informative)
Sorry, but the logical fallacy police have to intervene in this one. Absence of evidence is indeed evidence of absence; however, it is not proof of absence. In this case, as has already been demonstrated, we would need significantly more evidence of absence before we could come to any sort of meaningful conclusion. The current evidence of absence is about the equivalent of saying we know there's not a large ET base on the surface of the bright side of the moon.
Further, there's nothing logically wrong with the pot calling the kettle black. The kettle is indeed black regardless of the color of the pot. It just makes the pot look dumb for trying to make fun of the kettle. It reminds me of this quote attributed to Jack Nicholson:
"My mother never saw the irony in calling me a son-of-a-bitch."
Re:The real answer (Score:3, Informative)
How, pray tell, did cyanobacteria consume carbon dioxide and release nitrogen? Biological creatures (that we know of) do not perform fission or fusion.
From an article at MIT [berkeley.edu]:"Many Proterozoic oil deposits are attributed to the activity of cyanobacteria. They are also important providers of nitrogen fertilizer in the cultivation of rice and beans. The cyanobacteria have also been tremendously important in shaping the course of evolution and ecological change throughout earth's history. The oxygen atmosphere that we depend on was generated by numerous cyanobacteria during the Archaean and Proterozoic Eras. Before that time, the atmosphere had a very different chemistry, unsuitable for life as we know it today."
Chill out, we all know what he meant.
Re:Then where are they? (Score:5, Informative)
A terawatt signal radiating uniformly would produce 1e12 / (4*pi*(4e16)^2) w/m^2 = 5.0e-23 w/m^2. With a dish the size of Arecibo (7.3e4 m^2) that's -144 dBm (decibels referred to milliwatts). For comparison, the received GPS signal strength is ~ -133 dBm. With a slightly narrower bandwidth, or signal processing techniques that can work at lower SNR (eg looking for a carrier wave over extended periods -- exactly the sort of stuff SETI@home does) that extra order of magnitude isn't hard to come by.
Note that there are efforts ongoing to build larger area arrays (eg the square kilometer array), improve reciever electronics (chilling the front-end amplifier lowers the inherent amplifier thermal noise, for example), and improve signal processing techniques. Also, for certain types of transmission, the 1TW estimate isn't unreasonable -- Arecibo has radar transmitters with as much as 20TW effective isotropic power (lower total power, aimed at a small fraction of the sky). Given the right sort of source signal and extended observation, something like Arecibo could see some of our leakage signals, not just intentional transmissions.
Re:Yes, but.... (Score:3, Informative)
You don't need FTL for star travel, even travel on the scale of current human lifetimes. You just need to accept that you can't go home. Relativity is a blessing, not a curse. Do the math and you will see that with 1G of acceleration you can reach any part of the universe in a reasonable amount of your time.
Re:Then where are they? (Score:3, Informative)
Belief (Score:3, Informative)
It's not an equivocation per se. I would presume that what you assert to be at issue (you don't specify) is the dilution of the term "belief" to cover subjects ranging from that with little empirical corroboration (religion) to that with significant empirical corroboration (accepted science).
As you see, though, these are shades of gray -- theory requires a greater leap of belief than that which is proven before one's eyes, just as logical philosophies of religion require less of a leap than do their core theistic entities.
Even across the smallest gap, though, to accept things as seemingly married to reality as the Pythagorean theorem, requires belief. It is a very small quantity of belief required for this -- but to assume you use none at all is to expend a great deal more.
A little piece of clarification (Score:1, Informative)
As an astronomer who has read the paper in question, a few points should be noted.
i) Forgan mentions the fact that these numbers are essentially garbage, as the input data is strongly biased.
ii) The real strength of his work is in its ability to *compare* different hypotheses of the origin of life (given the same Galactic backdrop).
iii) There are both advanced and less advanced civilisations simulated in the model (the less advanced ones destroy themselves through their own actions!).
The introduction to the paper also deals with some of the philosophical questions surrounding the Drake and Fermi formalisms (worth a look!).
Re:What about T I M E ??? (Score:3, Informative)
In contrast to micro-electronics and receivers, I do not believe transmitter efficiency has improved much. The example of Voyager is as transmitter. I don't believe it can receive anything and is running on pgming.
Only the middle factor matters (Score:3, Informative)
If the purpose of the Drake Equation is to stimulate conversation, I wish more people would pay attention to the middle factor, fl, because it's the most significant one. The reason is that the value of the middle factor is the biggest unknown, by far.
Here is why: each of the other factors, even those that are based on singular events like the origin of life, are conceptually more extrapolatable (if that is a word):
1) Rate of star creation - multiple events
2) Stars with planets - multiple
3) Number of Earth-like planets - inferred from just a few factors (size, distance, temp, composition, etc)
5) Fraction of life that is intelligent - extrapolate from multiple events (humans, chimps, dolphins, elephants, etc)
6) Fraction able and willing to communicate - this seems almost to follow naturally from 5)
7) Persist long enough for long transmissions through space - trickier, but not too hard to imagine emergence of mature, stable societies.
4) is the big unknown. Really big. TOTALLY unknown at this point. Because once you dig a little into the chemistry and molecular biology, you realize that currently we do not have ANY comprehensive, detailed hypotheses to estimate how non-living molecular systems made the transition to self-replicating living ones.
Note the emphasis is on comprehensive AND detailed, because there are many very interesting and detailed speculations on parts of the process, such as Wachtershauser's Iron-Sulfur theories, and Szostak's ideas about the emergence of RNA replicators.
However, the huge number of parts and complex interactions involved in creating the simplest living organisms places the estimation of probability of origin of life in a whole other category of difficult, compared to the other factors.
At this time, fl is TOTALLY unknown, and so any use of the Drake Equation for computing a final result is likewise totally unknown.
mhack