oops.
So I’ve just disqualified us as an example of an intelligent species…
The “surely one civilization will go traveling and colonizing” explanation isn’t enough to ensure intelligent aliens will explore the entire galaxy.
Suppose the aliens do go out exploring and colonizing. However, they stop after colonizing “only”, say, a few thousand planets. There’s still no guarantee they’d hit our part of the galaxy. There might be large-but-limited alien empires somewhere out there.
The misnamed “stay at home” hypothesis does not assume the aliens stay in their home system. It merely assumes that the aliens’ expansion is not indefinite. For whatever reason, colonization hits a wall before the aliens explore a large chunk of the galaxy. There are all sorts of possible explanations for this–communications difficulties, “bad terrain” (large chunks of space with no suitable planets), civil wars or civilization collapses, or the simple realization that with sufficiently advanced technology it’s easier to build a Dyson sphere than go trekking through the barren wilderness.
The whole thing is reminicent of the old “if flies lay so many eggs, why don’t they cover the entire world?” question. Indeed flies would take over the world, if there were no limits to their expansion. But who said there were no limits to their expansion?
If “intelligent aliens” did or do pay us a visit, would they actually want to let us know about them. Look at how the movies and TV show us cutting up aliens and such. I know there’s plenty of examples of them attacking us as well. From what I figure out, “aliens” from another planet would rather be left alone and be hidden than show them to us “earthlings”. Maybe they have different radio waves and such that we can’t detect their signals or be too far away, etc.
But what Fermi’s paradox says is that, if there were
(many) intelligent species out there, they would have
gotten to Earth long before we evolved.
Then why would they keep themselves a secret?
I think the time has come to move this to Great Debates, even though “great” may be a bit of a stretch.
bibliophage
moderator, GQ
A good possible reson for not hearing any radio waves is that LIGHT is a much more efficient way of communicating that radio waves. More information, more control of signal, and cooler.
It’s possible that radio waves are just the main way of communicating for only a matter of centuries. Or less.
They are starting an optical SETI now.
As has been said before. It’s all just conjecture. Although I did lose some time the other nite after all that Jaegermeister, and my butt does itch. . .
DaLovin’Dj
Uhh… do what? IANAAstronomer, but… radio waves ARE light.
The Mayans were the most advanced civilization in their world for awhile. Right until about the time they were visited by the Spanish.
I think dalovindj is refering the visible or near visible part of the spectum and not just the part used by radio waves. I’m not a physicist but I believe you can transmit more information using photons (light) than electrons (radio waves). Something to do with photons being smaller than electrons and having properties of both particles and waves.
I think that msmith537 is correct with respect to the intentions of dalovindj and I think that it is true that more information can be gotten into shorter/higher frequency ElectroMagnetic (EM) waves than into long/low frequency waves. (Radio waves are not electrons; they are EM waves.) Very long waves should, then, be capable of holding very little information (I think).
Nonetheless, about a dozen years ago I ran across some research out of Stanford U. which would indicate that SETI might be better served looking in the VeryLowFrequency (VLF) portion of the EM spectrum. They did experiments. Published early results in IEEE transactions or proceedings–don’t remember which. [Being engineers, they don’t seem to feel compelled to wait and wait and wait for utter certainty as do many scientists.]
I have been hunting amoungst [Am I turning into a Brit?? 
] the cosmic background radiation literature, but I haven’t had any luck.
If it is true that[list=1][li]there are a lot of (communicating) civilizations out there and[*]the communication is most heavily done in the long-waves,[/list=1]then we should see a considerable amount of VLF background radiation. I was told over on the BadAstronomy Message Board that this is the case![/li]
Anyone got any thoughts.
Right right, visible light and radio waves are both part of the electromagnetic spectrum; I actually know this. Waves with longer wavelengths require longer antennae to be correctly received (roughly speaking, the size of the receiver has to be comparable to the wavelength); waves with higher frequencies are harder to generate and higher in energy. Basically, there’s a tradeoff. I’m not sure why we would want to use visible light in particular, though. Heck, if you’re a hugely advanced civilization, why not use x-rays? You can make the antenna small enough, you can generate them, and unlike lower energy radiation, they’re not as likely to be absorbed by all the random junk that floats around in space. Assuming you don’t hit a planet or asteroid or star with them…
bup wrote:
<nitpick>
The first stars in our galaxy formed at about the same time the galaxy did (12-13 billion years ago). However, this first generation of stars – and the disks of proto-planetary material around these stars, if any – were very poor in heavy elements. They had almost no carbon, no oxygen, and no nitrogen, all of which are essential for life as we know it. (They also had almost no silicon, which is essential to form rocky planets like the Earth.) These low-heavy-element-abundance (or “metal-poor”) stars are sometimes referred to as “Population II.”
It wasn’t until after the galaxy became enriched with heavy elements from the death throes of these first stars (i.e. supernovas) that the second generation of stars could form, which would have a half-decent abundance of heavy elements.
Our sun is thought to be a third-generation star.
Although coming to this belatedly, I think I may know what Zweistein has heard a version of. And it’s not necessarily Fermi’s Paradox.
As Phobos has already noted, it’s presumably the Anthropic Principle rather than the “anthroposophic” one. Now the classic review of the principle in its various forms is The Anthropic Cosmoslogical Principle (Oxford, 1986) by John Barrow and Frank Tipler. And, amongst other things, one of Tipler’s claims to fame is that he’s a (and possibly the) leading sceptic in the physics community about the existance of intelligent extraterrestrial life. It’s therefore hardly surprising that the issue creeps into the book. They set out a number of arguments against the widespread occurance of ETs and indeed devote an entire chapter to the Fermi Paradox.
However, they also include another, possibly more interesting argument in the previous chapter. (Personally I’m not overly struck by the Fermi Paradox: I don’t want to colonise the Galaxy, so why should I expect ET to want to.) This argument is a (weak) anthropic one. It starts by noting that while it took 4.5 billion years for intelligent life to evolve on Earth, the total available time, given the lifetime of the Sun, was only about 10 billion years. Why are these numbers so similar ? Particularly given that there’s no reason for them to be related. Suppose that the average time for civilisations to arise is much shorter than the average stellar lifespan. Then we’re an out-lier amongst civilisations: most evolved very quickly and so don’t think there’s anything similar about the two timescales. On the other hand, if the average time it takes to evolve intelligence is much longer than the time available, then those civilisations that do arise are likely to use up most of the time available. We’re then a typical civilisation, though only typical amongst very few. Since there’s no reason for considering us special, the argument concludes that the second case is correct.
Now I don’t find this argument convincing for a number of reasons. But it is an anthropic one: intelligent observers are only noting an “amazing coincidence” because all the observers for whom there’s nothing amazing don’t get a chance to note it.
And it has to be said that, regardless of one’s views about the anthropic principles or the existance of ETs, Barrow and Tipler is a fabulous book.
Aliens don’t use radio to communicate.
They alter the gravity relationship between planets but because we have not developed very sensitive gravity monitors we can not listen to the signal.
g8rguy has said “waves with higher frequencies are harder to generate and higher in energy”. If this means that waves with LOWER frequencies (and, thus, longer wavelengths) are easier to generate, perhaps that’s why the Electrical Engineers found natural transmission of EM waves, generated from within a human, to be in the long-waves.
If I remember correctly, can’t antennas [or antennae, as the case may be :eek: ] be in fractions of a wavelength and still work: 1/2lambda; 1/4lambda; etc.? If so, then such EM waves internally generated by a lifeform could also be received by other members of that lifeform. (Or, for that matter, by ANY lifeform since an EM wave is an EM wave–the same to all.)