The Arxiv blog highlights a post on John Scalzi's favorite science question: the Fermi Paradox:
We have little to guide us on the question of the existence intelligent life elsewhere in the universe. But the physicist Enrico Fermi came up with the most obvious question: if the universe is teeming with advanced civilizations, where are they?
The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because the famous Drake equation, which attempts put a figure on the number intelligent civilisations out there now, implies that if the number of intelligent civilisations capable of communication in our galaxy is greater than 1, then we should eventually hear from them.
That overlooks one small factor, says Reginald Smith from the Bouchet-Franklin Institute in Rochester, New York state. He says that there is a limit to how far a signal from ET can travel before it becomes too faint to hear. And when you factor that in, everything changes.
I'm a little surprised that nobody has tried to account for this before, but maybe I shouldn't be. It seems like a fairly obvious effect-- the intensity of a signal drops off as the distance squared-- but it's not nearly as much fun to talk about as the other terms in the "Drake Equation." If you use the lack of detectable alien civilizations to talk about the probability of life evolving or the probability of technological civilization surviving, you're a Deep Thinker; if you start talking about detectable signal strengths and propagation delays, you're a great big nerd.
The cited paper is freely available on the arxiv, if you'd like to read more..
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Doesn't signal strength depend on the power used to send the signal in the first place? Quasars can be detected across the universe. A little impractical for communication, I think, but possible with advanced enough technology.
This paper was blogged on Improbable Research yesterday.
I'm not competent to judge the paper itself, but Mr. Smith's background and webpage raises a few red flags. For one thing, the Bouchet-Franklin Institute is apparently located in Mr. Smith's den, and it has exactly one fellow, Reginald Smith, MBA.
Of course, that in itself doesn't mean the paper is flawed, but I'd be curious to get a physicist's reaction.
There is also the minor point that as soon as you start digitally encoding and multiplexing your signals, they become more-or-less impossible to distinguish from noise unless you already know the communication protocol in question. It's only old-fashioned analogue signals that are easily detectable.
A highly advanced civilisation would probably want to use its technology in the most efficient way possible - low power, tight beam, digital, highly multiplexed. Such a signal is practically undetectable unless you already know it's there. The only way we're likely to detect signals from ET is if they're deliberately broadcasting high-powered beacons for exactly that purpose.
The other great flaw in the Drake equation is that it seems to assume that any "intelligent" species will develop technology in much the same way that we did. It's entirely possible that a species every bit as "intelligent" as us might never develop radio communications technology, just as the natives of the Americas never developed iron-working.
Since you are on a panel with G. Landis at Boskone - ask him about his papers on this.
See also:
Jonathan Vos Post, "Star Power for Supersocieties" [Omni, ed. Ben Bova and Robert Sheckley, Apr 1980] ISSN-0149-8711, $2.00
* 1st popular article to predict giant black hole in the center of Milky Way galaxy;
* 1st popular discussion of J. Post invention "gravity wave telegraph" which may be the way that ETs are finally detected by LIGO or LISA.
I was surprised as well that this was news. Perhaps as a result of obsessively watching Star Trek growing up, I'd always read the Fermi paradox as: "If there are all these aliens who are able to discover all this cool technology that does stuff we've never dreamed of, then where are they?"
I think you are being just a little unfair. The paper may go into more detail than before, but it's not as if the idea is completely new. The first thing anyone should do after estimating the Drake equation is calculate the expected number of communicating civilizations within range of SETI. If you skipped that step, you probably just weren't thinking.
Every advanced civilization succumbs to social engineering, rights advocacy, income redistribution, privileged minorities, diversity, compassion... succor of genetic, developmental, and behavioral trash; reproductive warriors, religious hind gut fermenters, drug addicts, Enviro-whiner Luddites; the stupid, the pathetic, and the Officially Sad... whereupon it commits suicide for the nicest possible reasons.
"National Emergency Centers Establishment Act" ...if the national emergency requires large groups of people to be rounded up and detained. That's us right now, folks, in your House of Reprehensibles, Washington, DC.
http://en.wikipedia.org/wiki/Enabling_Act_of_1933
"Law to Remedy the Distress of the People and the Nation"
Isaac Asimov's Foundation Trilogy: Even a civilization delt a pat hand must march or die.
The usual version of the Fermi Paradox is about starfaring civilizations. The idea being that even with relatively mundane ideas of starships (mainly fusion or laser sails; "mundane" being a relative term), you could reach and colonize other stars at a few percent of the speed of light. So then some of those colonies send out their own colonizing starships, and then the colonies those make send out their own colonies, and so on. Under that assumption, you'd have a wave of colonization that would fill the entire Galaxy in just a few tens of millions of years. The basic idea being that while the Galaxy is big, it's vastly older than it is big. If you accept those assumptions, then you'd be led to the conclusion that ETs should be in the Solar System itself, where we definitely could detect them. There are some variants on that exact argument (Von Neumann probes), but the Fermi Paradox itself deals more with starfaring aliens. The main arguments are usually whether or not we should expect civilizations to become starfaring.
The paper is dealing with a more broad observation, the Great Silence, where we don't see any signs of ET civilizations, in or out of the Solar System. It's already known that we couldn't even detect our own everyday transmissions at Proxima Centauri with current technology, so yes, the inverse square effect is long known. Deliberate, beamed transmissions could be detected to much further (if I remember correctly, we could easily signal civilizations 1000 light years away with optical lasers, which Optical SETI is looking for). I think that SETI is currently looking more for deliberate, beamed transmissions, or transmissions from civilizations more powerful civilizations than our own.
I haven't yet looked over the paper in detail, but I think it's just trying to calculate a filling factor -- given some maximum distance that you could detect a civilization, and some lifetime for each civilization, what's the chance that you are inside a detectable signal? The main issues I can think with that sort of argument is that the maximum radius you could detect and broadcast are technology dependent. Are the aliens like us or are they powering their transmissions with a Dyson sphere? Similarly, the faintest signal we could hear depends on our technology -- the Allen Telescope Array will greatly increase the sensitivity for SETI, and the distance we could detect ETs. The paper would be useful, though, if there are inherent limits to how sensitive we can make our telescopes (such as, will we ever have telescopes bigger than the Earth?), and/or how powerful civilizations can broadcast (such as, will the waste heat from their beacon cause their planet's crust to melt?).
John Hodgman's TED talk contains as much on aliens and contact with them as anyone really needs to know.
some red flags...
I understand your concern, but don't worry, I'm legit. The paper has been accepted and will appear in the International Journal of Astrobiology after I correct the proofs.
some red flags...
I understand your concern, but don't worry, I'm legit. The paper has been accepted and will appear in the International Journal of Astrobiology after I correct the proofs.