New Paper Offers Additional Reasoning for Fermi's Paradox 774
KentuckyFC writes "If the universe is teeming with advanced civilizations capable of communicating over interstellar distances, then surely we ought to have seen them by now. That's the gist of a paradoxical line of reasoning put forward by the physicist Enrico Fermi in 1950. The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because if the number of intelligent civilizations capable of communication in our galaxy is greater than 1, then we should eventually hear from them. Now one astrophysicist says this thinking fails to take into account the limit to how far a signal from ET can travel before it becomes too faint to hear. Factor that in and everything changes. Assuming the average communicating civilization has a lifetime of 1,000 years, ten times longer than Earth has been broadcasting, and has a signal horizon of 1,000 light-years, you need a minimum of over 300 communicating civilizations in the Milky Way to ensure that you'll see one of them. Any less than that and the chances are that they'll live out their days entirely ignorant of each other's existence. Paradox solved, right?"
What paper? (Score:4, Informative)
No link to anything but Wikipedia and a blog?
Re:300 isnt teeming with life (Score:5, Informative)
Re:It's quite clear what the reason is (Score:3, Informative)
Re:What paper? (Score:4, Informative)
Now THAT is funny!
Re:It's quite clear what the reason is (Score:3, Informative)
Proleptic Julian calendar. [wikipedia.org] Dates in the BC range (and all the way into the late 16th century AD) are typically assumed Julian unless explicitly stated Gregorian. Although I have no idea what the proper technique would be to handle the who Julian leap-year mess and figure out whether Earth really is a Libra or actually a Scorpio with a funny birthday. If only Ussher was still around we could ask him.
As a side note (as if this whole thing isn't a side-note), Lightfoot [wikipedia.org] also put the Earth's birthday near the autumnal equinox, but he didn't nail the date down quite as precisely and made the Earth quite a bit younger (3929 BC vice 4004 BC). Ussher's calculation is just more fun because he published an actual date (I've heard that one of his students actually nailed the time of completion down to around 0900).
Re:Solved? (Score:2, Informative)
To reach space you have lots of self-control so that you don't..uh..risk wiping out your civilization.
To date, weren't most of our major space achievements as a race made during the cold war?
Re:Solved? (Score:5, Informative)
(See this wiki article [wikipedia.org] as an example of a slightly technical description of why)
Re:It's quite clear what the reason is (Score:3, Informative)
Might want to try that math again, hot shot. Hint: 23 + 6 = 29.
Re:Hello, (Score:3, Informative)
He did [lyricsfreak.com].
Re:Solved? (Score:5, Informative)
Think about the transit time, think about the number that would be lost. You can't really assume a straight geometric progression for something so incredibly fraught.
Well, almost, at least for the purposes of ballpark calculations.
Now, we have to make a couple of assumptions -- such as that they have the technology to send out self-replicators that will last long enough to get to the next star, which is a function of speed and durability. For the sake of argument, let's assume that the Voyager spacecraft (which just left the Solar System) are capable of self-replication, have a very long-lived power supply (long half-life radioisotope, for example) and their electronics will survive long exposure to galactic cosmic rays. (All big assumptions, but imaginably within range of our technology.)
Also assume an average spacing of about five light years apart for stars.
At the current speed (about 16 km/sec), it would take a Voyager about 90,000 years to reach the next start. Allow 10,000 years for the laborious process of self-replicating from raw materials and launching another of itself on its way, for a total of 100,000 years per generation. Assume each vehicle replicates itself only twice, and stays put (perhaps assembling large black monoliths on the local planets for the mystification of any eventual inhabitants). So we have a doubling rate of once per 0.1 million years.
Assume about 100 billion stars in our galaxy (this is the number I found most frequently mentioned), it would take between 36 and 37 doublings to send a probe to every star in the galaxy (less because stars are closer nearer the core). Call it 40 to allow for probe loss.
So in a mere four million years, self-replicating probes travelling no faster than Voyager could visit every star in the galaxy -- except for the speed problem. That growth rate can be maintained initially, but like any spreading colony (such as bacteria in a petri dish) the edge of the colony can only advance at a certain speed, and the doubling rate has to fall off (it's ludicrous to think that the number of visited stars could go from half the galaxy to the whole galaxy in a mere 100,000 years, the probes would have to be approaching lightspeed for that).
Take the galaxy diameter as 100,000 light years, it'd take nearly 2 billion years for a Voyager-speed probe to cross it, or near 3 billion to go around half the circumference (to avoid the black hole at the core). The galaxy is old enough that there probably sun-like stars (our Sun being a second-generation star, necessary if you want enough heavy elements for terrestrial planet formation) a couple of billion years older than ours. (And if we assume faster travel speed, say 0.01 c instead of 0.000055 c, the numbers get a lot better.)
So Fermi's question was simply "where are they?". If they're really not around (vs simply ignoring us or being undetectable to us), then the above assumptions are too optimistic.
Re:It's quite clear what the reason is (Score:4, Informative)
Either the Vatican are hedging their bets, or they're on to something the rest of us don't know (yet).
They have seen the jet planes.
Re:It's quite clear what the reason is (Score:3, Informative)
The atheists who latch onto that date like it meant anything other than the maundering of an Anglican Bishop are as pathetic as the Christians who believe it.
Your characterization of athiests as "latching on" to this is either intentionally misleading or hopelessly clueless.
Athiests cite it because many Christians believe it to be a biblical truth and state is as such, and it is one of the more laughable claims made by supernaturalists in their quest to spread ignorance and confusion. The 6k figure was not invented by an athiest, it was invented by a supernaturalist, athiests just heap the much deserved scorn upon those who try to spread it around as fact.
Re:It's quite clear what the reason is (Score:5, Informative)
The Catholic Church also accepts evolution as "how God did it" so good luck trying to get through to the Creationists who obviously don't want anything to do with St Peter's successor.
Re:Alternate solution: High-efficiency communicati (Score:3, Informative)
It might be "noise", but it's still a distinct power band - not a black body distribution at all.
But it's a very broad band - and there are many of them. The amount of power needed depends on how far you want to go and what the background is that you need to surpass - and a major component of the background is thermal noise, pushing toward a thermal distribution of signals as well.
Yes the distribution is distinguishable - at least so far. But remember that you have to observe the signal in the presence of other backgrounds as well. (A narrow band filter like you can use to find an AM or FM signal just won't cut it.) How far away from the Earth can you make that distinction? And if scientists DO, would they attribute it to intelligent signal transmissions or look for some oddball physical process - in the emitter or the medium?
Re:Do we want to be found? (Score:3, Informative)
Re:Alternate solution: High-efficiency communicati (Score:3, Informative)
Except for RADAR. Maybe RADAR will be replaced too, but for now it's quite noticeable.
It's also highly directional and mostly in frequency bands that don't make it through the ionosphere all that well.
RADAR is already migrating from simple continuous streams of short high-energy pulses to broad chrips and other, more complex signals that give more information about the target (and have less power demand on the transmitter).
Aircraft location for air traffic control is migrating from RADAR to aircraft-mounted GPS beacons. (The RADAR will still be around for a while. But don't be surprised if it migrates to more subtle technology.)
Military RADAR has a big advantage if it looks like background noise to a target.
(Marine radar does NOT - it's really good if your little sailing yacht makes a big spot on the screen of the supertanker that could run you down - a spot indistinguishable from that of another supertanker. B-) But marine radar is low power.)
Short high-energy pulses chew up a lot of valuable communication spectrum. Moving to a lower-energy signal could make it more available for other uses, creating an incentive to migrate.
So don't be surprised if even RADAR eventually fades into the background.
Re:Hello, (Score:2, Informative)
Hey, guys, You all need seriously to go out a lot more. Those lines are from "Comfortably Numb" by Pink Floyd from the album "The "Wall"
Re:It's quite clear what the reason is (Score:3, Informative)
Well, I can't speak for the Christians who believe the number, but the reason the atheists "latch onto" it is because there are a significant number of people in this country (the US) who keep pushing to have it taught in place of science.
If it weren't for the fact that they are actually often successful, we probably wouldn't make fun of them any more than any other wacky beliefs like the "lizard people at the center of the earth" folks, or the "aliens took me for an anal probe" people, or the Scientologists.
Sure thing (Score:3, Informative)
Right after you post a list of your other winners.
And you might want to adjust your odds. You're not competitive with Mega Millions. The odds of winning your lottery are one in ten^14, or 100,000,000,000,000, for a cost of 1000 dollars.
Mega Millions pays out fifty times your million (currently, the number changes) dollars, costs one dollar to join, and has odds of one in 175,711,536.
Oh, another thing. What you're describing is a variation on a numbers racket. [wikipedia.org] It's illegal for private citizens to do. Unless you're the Prime Minister of Norway or something, of course.
Re:Alternate solution: High-efficiency communicati (Score:3, Informative)
Unfortunately we don't have interstellar capability yet or any sign that there is a way around the speed of light. We're stuck in this solar system for the time being. Our radio signals will propagate no faster than c and our probes, once we make them, will be slower (at least for the foreseeable future.)
Round-trip talk time is two years per light-year.
Listening where we are can be done now. No wait for our signal to propagate to them, and their signal (if present) has already propagated to us.
Unfortunately, if they were also essentially spread-spectrum-only emitters by the time the stuff going by us now was sent, we're hosed. B-( Or at least we'll have to modify our filters to look for efficient-modulation signatures.
It's not about communication through radio waves (Score:3, Informative)
I am not trying to single out this post, but half the thread seems to be assuming Fermi's paradox is about alien civilisations communicating with us over radio. This is 100% wrong. We are all actually talking about a paradox that was never postulated.
First, it has to be pointed out that the radio-wave idea has been discounted many times for a much more obvious reason. The period of time that any civilisation engages in communication by radio waves is likely to be a tiny fraction of a percentage of the total life of said civilisation. The idea of finding our alien friends through listening to radio waves was ridiculous when Carl Sagan was promoting it and remains so today.
Secondly, The Fermi Paradox is about alien civilisations *colonising* the Galaxy or "arriving here." It was originally phrased as the question "where are they?" (i.e. - they should be here by now given a finite universe and a certain amount of time.) As flawed as *that* idea also is, it's a completely different flawed idea than what most folks her are arguing about, which is the incredibly super-duper flawed idea of radio communication between advanced civilisations.