X-Message-Number: 11185
Date: Wed, 27 Jan 1999 01:28:23 -0800 (PST)
From: Doug Skrecky <>
Subject: Where are all the ETs? -A Possible Solution

    Question: Where are all the ETs?

    The problem: Picture the following. Ten thousand years from now the
 first self-replicating InterStellar Probe is launched from Earth. In
 another ten thousand years it encounters a habitable planet in another
 solar system. It then proceeds to build a factory which can manufacture
 other probes, and in time terraform the planet, and accomplish other
 tasks that it has been programed with. Millions, billions and then
 trillions of other probes are sent out and eventually in say 10 to 100
 million years all solar systems in the entire galaxy has been visited.
   We presume there must be other planets with life on them, and further
 presume that some must have intelligent life on then. There seem to exist
 no technical or other reasons for why at least one self-replicating
 InterStellar probe has not then launched by at least one intelligent
 species in the past. No probes have ever been detected, therefore these
 probes do not exist, therefore the intelligent species that could have
 launched them do not exist. The problem is to account for why no such old
 ETs exist.
   One possible answer may be found in the January 23,1999 issue of New
 Scientist. James Annis, an astrophysicist thinks old ETs did not exist
 because gamma ray bursts (GRBs) have repeatedly sterilized large parts of
 our galaxy before intelligent life has had time to evolve. Presumably
 only the most radiation resistant bacteria buried deep in the mantle
 could survive a nearby GRB - but evolution would still be reset
 effectively to zero each time a nearby GRB occurred. The rate that GRBs
 occur in our galaxy was much more frequent in the past - once every few
 million years. This could account for why old ET civilizations never
 existed, as there was never enough time for intelligent life to evolve
 before a sterilizing event occurred. Now that these GRBs occur only every
 few hundred million years, has it become possible for a few lucky planets
 (such as Earth) to avoid being fried long enough for intelligent life to
 evolve. In earth's case I assume this reprieve has been at least the last
 600 million years since the end of the precambrian era, though possibly a
 distant GRB might account for the mass extinction event at the end of the
 Permian epoch?

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