Rob Dekker wrote:

Below, my thoughts on why I think 20 years is excessively optimistic for detecting an ETI beacon,



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Beacons:

With 200 billion stars in the Galaxy, and 10,000 ETI civilizations, the average ETI neighbor
will be a few thousand lightyears away.
So even our ETI neighbors have not received any radio signals from us yet.

But we may be bathed in signals from lots of neighbors which
have been broadcasting for thousands of years.

With 200 billion stars in the Galaxy, and 10,000 ETI civilizations, Each of these ETIs
need to send beacon signals to an average of 10million stars in its neighborhood continuously.
Otherwise, there is very little chance that there is any ETI beacon aimed at us.

There are about 41,000 square degrees in the sphere of the sky
(according to my back-of-the-envelope calculations). So if
a radio telescope has a beam size of one degree by one degree,
a civilization would only need 41,000 telescopes to cover the
entire sky. All stars, local and remote, would be covered.
Ten million beacon signals are not required, because there
would be overlap.

Why would a civilization being called 'intelligent' spent enormous amounts of effort
to send signals continuously to millions of star systems for which they do not even
know when or if any communicating civilization will ever arise.

No one knows why an alien would do anything. I do not
play the lottery, but I know many who do.

Now I am a SETI enthousiast, but we need to be realistic.
Unless there are millions upon millions of ETI civilizations out there, the odds are
very much against us finding ANY beacon signal at all.

But if we don't look, we won't find anything.

We probably need to detect another civilization by other means (such as radio leakage),
which requires much larger antenna arrays than the ATA, and thus much more time than 20 years.
Or 'it' (detecting ETI) will happen totally different than we think.

I agree that there is likely more radio leakage than
intentional beacons. But we have NO idea of how powerful
this leakage is. Maybe ETI are doing powerful planetary
radar. Maybe they are communicating with a colony on a star
a couple of light years away. Maybe they are trying to
communicate with a space probe which has a damaged receiver.
If we happened to be in line with these powerful, beamed
broadcasts, we could conceivably receive a LOT of power.

Russ

Rob