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.