On 01 Feb 98, concerning _Speculations_, Jack Sargeant said to Troy H. Cheek 
in UFO:
 >> That's the ironic thing about establishing the existance of ET
 >> intelligence by finding a radio signal:  It won't prove that we
 >> aren't alone in the universe, because odds are that the
 >> civilization that sent the signal is long, long gone.
 JS> 
 JS> Have you thought this one out?  Just what to you recon the lifetime of
 JS> a civilization is?
I figure 1,000 years on average is a very generous figure.
 JS> How far back does recorded history go? (not counting
 JS> early development stages before we could walk erect.) Without looking
 JS> in an encyclopedia, we can start with the early Sumarian or Egyptian
 JS> eras and say about 10,000 years to date as written records go.
Oh, at least that, but their civilizations are not our civilizations.  And 
ours is the first to have the capability to send a signal to the stars or 
listen for one from them.  And we've had that capability for maybe a century.
 JS> Can we safely add another 10,000 years?
I don't think so.  People still live in Egypt, but the Egyption civilization 
of which you refer is long gone already.   Ditto for the Mayans, Incas, 
Native Americans, etc.
 JS> ...And how far can a radio signal travel before the ethers absorb the 
last
 JS> weak remainder of a broadcast?
I believe Carl Sagan suggested we listen for signals within 20,000 light 
years, and I think I read once that we've sent signals towards a star cluster 
25,000 light years away.  It's been a long time since I've read on this 
subject so I admit I might be wrong on the numbers.
Even assuming there's an alien civilization 1,000 light years away, and that 
they're roughly at the same level of development as we, and they receive our 
signal some time around 3000 AD, what kind of civilization will we have in 
4000 AD when their reply comes back?  Will we still have the capability to 
listen? Will we even care?
 JS> I'll tell you a secret feeling of mine, Troy... Sometimes I lose my
 JS> optimism altogether! The grand design of the universe seems to keep
 JS> us separated from our sentient neighbors at just the distance required
 JS> to prevent communications.
I believe that was more or less Carl Sagan's view.  Civilizations rise and 
fall throughout the universe, but the odds of two arising in roughly the same 
place at roughly the same time are slim.  The best we can hope for is 
receiving a message from a dead "neighbor."
 JS> So, now we have our UFOs... They must be from another world, because
 JS> we don't have anything like them, right?
Or they're from another dimension, or they're from another time, or some even 
more convoluted theory.  Assuming, of course, that we don't eventually find 
that some of us (of Earth) actually do have something like them.
A few speculations:
1)   Intelligent life in the cosmos is a lot more common that we tend to 
think, so within the handful of stars within, say, 20 light years of us, 
there's at least one spacefaring civilization.
2)   Intelligent life in the cosmos is much more stable and/or long-lived 
than we are.
3)   We've got some fundamental and profound misconceptions about 
communications and/or space travel.
... The Professor could build a radio but couldn't build a boat. Go figure!
--- JetMail 0.99beta22
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