Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!linus!decvax!harpo!seismo!hao!hplabs!sri-unix!dietz%usc-cse@USC-ECL
From: dietz%usc-cse@USC-ECL@sri-unix.UUCP
Newsgroups: net.space
Subject: SETI
Message-ID: <3403@sri-arpa.UUCP>
Date: Sat, 23-Jul-83 23:55:00 EDT
Article-I.D.: sri-arpa.3403
Posted: Sat Jul 23 23:55:00 1983
Date-Received: Mon, 25-Jul-83 11:40:20 EDT
Lines: 17

I seem to recall reading in SPACEFLIGHT (a British Interplanetary
Society publication) that all-sky radio searches have already set an
upper limit of about 20,000 on the number of very advanced
civilizations in the galaxy (where very advanced means with beacons we
could detect).

A recent issue also pointed out that even with a manufacturing
efficiency of .1% antimatter would make sense as a rocket fuel, and
antimatter reaction engines would not be difficult to build (p + anti-p
reaction produces mostly charged pions, which can be directed aft with
strong magnetic fields).  To get some idea of the energy involved, one
gigawatt for one year is about 10 kg; at .1% efficiency 10 tons of
antimatter would need about 10 million gigawatts for one year.  This is
the amount of sunlight passing through a square several thousand
kilometers on a side in earth orbit, in one year.