Jason
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Post by Jason on Jun 3, 2007 22:05:52 GMT -4
Since Bill obviously wants to talk about Fermi's Paradox, why not start a thread for it?
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Jason
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Post by Jason on Jun 3, 2007 22:15:12 GMT -4
My view of the paradox, in brief: I think it is reasonable to assume that there are many worlds in the Universe that are Earthlike in many ways. Since life appeared here then it is also reasonable to assume it may emerge elsewhere in similar conditions (or even disimilar conditions), and intelligence may likewise appear. Fermi's Paradox, as it is called, smells of a hint of hubris to me. It assumes too much that we really don't know. We have only one sample case for the development of life and intelligence, and there is still a lot about the life on this planet that we don't know. Our sample is simply too small to develop real theories about how frequent intelligent life should be in the universe. If we eventually venture out into the galaxy and explore a good portion of it without finding other intelligent life, then we might really have a paradox on our hands. At this point it sounds arrogant to me to say "we would have found them by now if they were out there."
Given the state of our knowledge of the universe, it's kind of like concluding Polar Bears don't exist since I can't find any in my back yard.
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Post by LunarOrbit on Jun 3, 2007 22:35:30 GMT -4
There's an old saying that goes "absence of evidence isn't evidence of absence" and that pretty much sums up my thoughts on Fermi's Paradox.
The fact that we haven't discovered any sign of extraterrestrial life isn't evidence that there isn't any. It just means we haven't looked in the right places, or that we didn't recognize the signs when we saw them.
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Post by Data Cable on Jun 3, 2007 23:22:03 GMT -4
we didn't recognize the signs when we saw them. Perhaps as a subset of which, I'd propose "our instruments weren't/aren't yet sensitive enough to detect the signs."
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Post by gillianren on Jun 4, 2007 0:58:21 GMT -4
The Universe is a big place, and we haven't explored as much as 1% of it even with our instruments. Heck, there's a ton of our own solar system we haven't explored! To make statements about the nature of anywhere else in the Universe is pretty bold--as bold, in my view, as claiming to understand the Mind of God.
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Al Johnston
"Cheer up!" they said, "It could be worse!" So I did, and it was.
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Post by Al Johnston on Jun 4, 2007 8:28:23 GMT -4
We may be being rather unkind to Fermi: in his defence, the Universe is not only a big place but it has been around a long time: long enough that the time taken for extra-terrrestrial civilisations to make their presence known by one means or another is trivial by comparison. It is not entirely unreasonable to ask "Where are they?" and to conclude that, for all practical purposes, we are alone.
On the other hand, to paraphrase Haldane, Life may not only stranger than we imagine, but stranger than we can imagine, in which case again, for all practical purposes, we are alone.
There is also the view that in SETI terms, passively listening is the easier choice. Actively announcing one's presence is more difficult, of somewhat dubious utility, and has some potentially very nasty downsides: civilisations with the capability may have wisely decided to keep their heads down. Again ...
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Post by LunarOrbit on Jun 4, 2007 10:02:23 GMT -4
I am admittedly not an expert on Fermi's Paradox, but it doesn't seem to take time into consideration at all. It seems to assume that all of the advanced civilizations will exist at the same time. Other civilizations may have advanced enough to advertise their existence 1000 years before we discovered radio, and then they were wiped out by a war or asteroid impact. Maybe their last broadcast passed by Earth the day before SETI started listening for it. Or maybe they are less advanced than us and are just on the verge of discovering radio.
Maybe they're out there broadcasting like crazy and there's some kind of radio interference blocking it. How sure are we that our broadcasts actually make it out of the solar system without being distorted or degraded along the way?
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Al Johnston
"Cheer up!" they said, "It could be worse!" So I did, and it was.
Posts: 1,453
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Post by Al Johnston on Jun 4, 2007 10:23:11 GMT -4
IIRC, Fermi's original formulation was based on the concept of one civilisation colonising nearby stars, which in turn colonised others in an exponential process, tending to an infinite spread in a finite time.
Before he went loopy about 9-11, Professor(?) Dewdney had an interesting take on the Drake Equation: by plugging in different numbers, particularly that from our experience civilisations indiscriminately broadcast radio for about 100 years before replacing it with more efficient narrowbeam, satellite and cable communications, the number of radio-detectable civilisations in range comes out as one; presumably us.
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Jason
Pluto
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Post by Jason on Jun 4, 2007 11:11:28 GMT -4
SETI's own FAQs say that picking up radio signals from more than 100 light years away with our current equipment would be unlikely, and that's the best-case scenario. A 100 light-year bubble around Earth, even though it contains thousands of stars, is a tiny fraction of our own galaxy, let alone the Universe.
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Post by gwiz on Jun 4, 2007 15:54:56 GMT -4
IIRC, Fermi's original formulation was based on the concept of one civilisation colonising nearby stars, which in turn colonised others in an exponential process, tending to an infinite spread in a finite time. Quite right. As there appears to be some confusion in this thread: Fermi's paradox assumes that ET life exists and interstellar travel is possible, then shows that the first ET civilisation in the Milky Way to achieve interstellar travel should by now have colonised the whole galaxy. It has nothing to do with detection by radio - if they exist they should be here. Possible get-outs involve economic arguments about the cost of interstellar travel and sociological ones about the duration of civilisations, etc. Unless you accept these arguments, the only alternatives are that ET life doesn't exist or that we are the first civilisation to get close to interstellar travel. These arguments in turn have to take into account that there are very many stars much older than the Sun. Did we develop unusually quickly? Is there some step in our development that is intrinsically improbable? There are no easy answers to the paradox.
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Jason
Pluto
May all your hits be crits
Posts: 5,579
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Post by Jason on Jun 4, 2007 17:08:55 GMT -4
Are we close to interstellar travel? We might be able to do something like a generation ship now, but it would be at enormous cost. At present we can't even establish an outpost on the moon because of the cost and because our priorities are elsewhere.
How frequent are earthlike worlds? How often does life develop on such a world? How long does it take for life to develop? How long after that does it take for intelligence to develop? How long does it take for that intelligence to develop radio? Or interstellar travel? We have only one set of sample data, and no data as to how unique or common that test case is. Until we have more data I don't think we can make assumptions, let alone theories, for how common intelligent life should be.
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Post by PhantomWolf on Jun 4, 2007 21:15:40 GMT -4
Are we close to interstellar travel?
I don't know, if we started slowly now, do you think we could have one built in 100 years time? Now of course 100 years is a drop in the bucket time wise. How many ships could we produce given a million years. Let's say that a colony takes 1,500 years to get to their desitination and then build to the point of being able to create a new ship, then it takes 100 years to build and launch one. How many ships could a species launch in 1 million years?
The home planet will have launched only 10,000 ships but by the time we have counted those ships launched by just the 3rd Generation Colonys we're already at 4.09136x1014 ships. That's 1,000x more stars than are in our Galaxy!!!
That's the paradox.
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Post by Data Cable on Jun 4, 2007 21:50:40 GMT -4
We might be able to do something like a generation ship now, but it would be at enormous cost. And of course, long before that, we need to find someplace to send it, first. I can't see a use for generation ships other than colonization.
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Post by nomuse on Jun 4, 2007 22:48:58 GMT -4
This discussion is familiar. Actually, to sort the puzzle a little bit more, there are two separate questions entwined. The first being "Why don't we see life _like_us_?" Problem being, everything that we understand about our own species (and the general evolutionary background we come from) indicates that we'd rapidly explode outwards, colonizing everything within reach. Given how quickly technology progresses, the span of a similar race's existence in which they'd be piddling about with limited solar excursions and sending radio is a vanishingly small part of their history. So if any civilization like ours existed, the chance is great it would already have covered large parts of the sky with it's efforts.
There are limiting factors; age of the universe, age of Pop II stars, speed of light. It is an amusing fancy to think that these sister civilizations might all be out there, but still painting on cave walls, 10,000 years to go on their timer before the first spark-gap radio appears. But then Fermi still points out....all it takes is ONE.
Unless there are limiting factors we are unaware of. Some sort of racial lemming instinct, some odd function in astrophysics, something that makes this leap to Dyson-sphere builders impossible. This also can make good SF stories but I am suspicious of Larry Niven-style absolutes. Did something human-like exist on a billion star systems, ONE of those races would have figured out a way to beat the odds. And we're back to the night sky vanishing under the shroud of trillions of Dyson spheres (or whatever other huge mark a single, outgoing, colonial-minded human-like civilization would make).
The "where are aliens that look like us?" question is of course part of the more general question -- but in that, at least, we have the out that we might not recognize either the intelligence or its signs.
Somewhat off the subject, I've been toying for a while with the idea of a cycle of short stories concerning the post-diaspora situation of a large number of human colonies in a "straight physics" universe that offers no FTL travel or communication. These are human civilizations at various stages of development (and divergence) who _know_ there are similar beings within reach of powerful radio or laser or a fifty-year journey by probe or sleeper ship. The stories would investigate, from the point of view of one such civilization, and in fact a Coast Guard-equivalent crew serving that civilization, what some of the reasons and kinds of contact might be in that situation.
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Post by gwiz on Jun 5, 2007 9:49:55 GMT -4
Are we close to interstellar travel? So far there have been five probes launched on trajectories that take them into interstellar space, the first being Pioneer 10 in 1972. According to the BIS Project Daedalus feasibility study, we are less than a century away from a probe that could reach the nearest stars is a short enough time to be useful to the people who launched it.
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