Where are all the ETs? -A Possible Solution

Doug Skrecky (oberon@vcn.bc.ca)
Wed, 27 Jan 1999 01:38:07 -0800 (PST)

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?