--- On Tue, 7/20/10, Jed Rothwell <jedrothw...@gmail.com> wrote:
> If it was an interstellar communication and it happened to
> impinge on earth, it would have stayed pointed in our
> direction for a long time. Ditto for a deliberate signal to
> attract our attention and announce the existence of another
> intelligent species.
If it was deliberate, yes. If not, if it was something else, or a spurious
transmission for reasons unknown, it might not remain on us for long. The beam
width would be a factor, motion of the beam emitter (rotation of the planet
surface, etc.), and so on. The WOW signal duration was reckoned to be something
like 2 to 2.5 minutes. Possibly more, if the observation was almost coincident
with termination time. For a very directional broadcast to something other than
our world (meaning, we only saw it by accident) that might be enough time for
us to lose it.
> Thinking about this SETI issue some more . . . (not CETI!)
> . . . I assume we are only talking about signals within our
> galaxy. The Milky Way galaxy is about 100,000 ly accross and
> 1,000 ly thick, with 200 to 300 billion stars (depending on
> the source). Based on the failure of SETI so far, I think it
> is safe to conclude that in our galaxy there are not
> millions of contemporaneous civilizations vying for our
> attention. That is to say:
Well, it's hard to call a failure; as I said before, META and the others have
detected "things" which aren't explained. As Sagan pointed out, the fact that
most of these incidents were in the plane of the galaxy is interesting. I'd
agree there aren't millions of technological civilizations vying for our
attention; that doesn't mean there aren't ~ 1 million civilizations out there.
Maybe they aren't vying for our attention. Maybe they don't even know we're
here yet. Not long ago, there were no radio transmitters. Even within the last
few hours of the cosmic calendar, we were scurrying around throwing spears at
one another, and no one knew what steel was.
As the late Douglas Adams points out, space is big. It's been suggested that
self-replicating probes could have spread throughout the galaxy by now, so we
should see 'them' if they are here. This assumes many things.
1. They chose to do this.
2. It's really that easy to send self-replicators out there.
3. They want us to know they exist.
4. In the millions of years necessary to scout out the whole galaxy, 'they'
haven't evolved into something far beyond our understanding. Maybe they don't
want to talk to the local anthill.
All this assumes that travel takes place at less than C. Let's consider what
might happen if travel faster than C is possible. Things change pretty
seriously, and I'd posit that, paradoxically, the ability to go faster than
light might *slow* expansion across the galaxy. For instance, if FTL travel is
possible, and 'they' are doing it, it makes sustaining (for want of a better
term) an interstellar empire more feasible. Instead of autonomous colonies out
among the stars, spreading exponentially, they might have far greater contact
with home, and thus concentration on building up and exploiting the resources
of the local interstellar neighborhood might be of great interest. Missions to
other stars could be manned instead of computer controlled. The ability to
learn more could be increased, slowing the rate of expansion.
On the other hand, as far as we know, maybe someone close by has already
learned of us, and is on their way even as I type this.
> 1. "Contemporaneous" means existing long enough to reach
> us; a signal broadcast for thousands of years, within the
> last 100,000 years. That is really not such a long time. I
> assume that stable, intelligent civilizations usually last
> longer than that. Stable non-intelligent species do.
fL in Drake's equation might extend to more than just self-destruction. The
possibility also exists that someone or something out there might not like the
idea of competing, potentially threatening civilizations arising and
progressing. If at least some advanced civilizations do go around stamping out
others preemptively, then the survivors (and probably the killers, for obvious
reasons) would have a good reason to be quiet. It's sobering to think of a sort
of interstellar natural selection, where the ones who scream into the void are
noticed by something, and promptly taken care of.
> We could send this kind of "hello galaxy!" signal even now,
> only 100 years after discovering radio. Naturally it would
> cost a great deal of money and it is not likely we would do
> it. But I assume that a civilization that discovered radio
> centuries or thousands of years ago would be so advanced,
> the cost of setting up a broadcast would trivial. It might
> be something a small group of private individuals could
> afford.
Possible, but if they are that far ahead of us, what if they have something
better than radio? Do they want to signal the primitives, or talk to someone
who has more to teach them?
We don't talk to primitive cultures with smoke signals or fire towers. We're
blasting microwave and UHF all over the place, and there are millions in the
jungles who are unaware of it. They only know of us because we physically went
there.
I think it would be fascinating indeed if in the next fifty or so years, the
common perception is that there is no one out there, because we never heard
from them. Then, something like the final scene of "Apocalypto", ships of
another civilization appear in the port that is Cislunar space. It would be
quite the outside context problem.
> That is a nebulous conclusion, but I think it is meaningful
> and I think it is well founded. The galaxy is definitely not
> filled with millions of advanced civilizations that I can
> relate to.
>
> That's a sad thought.
I don't think it's necessarily as bad as all that. The ones we can relate to
may simply not have found us yet. If and when they do, if they are similar
enough to relate to, both sides are going to have a lot of thinking to do.
Either way, this is a fascinating topic to ponder.
--Kyle
