The Fermi Paradox

   In the oral tradition of the SETI community, Fermi's legendary question 
"Where are they?" has been long cherished, quoted, and debated upon.  The 
context, of course, is alien intelligence:  If technologically advanced 
civilizations have inhabited our galaxy for timescales of order a billion years, 
and if some of these have engaged in interstellar travel and colonization, why 
have we not seen physical evidence of their visits.

   Given the uncertainty about the history of Fermi's remark (or whether it 
occurred at all), I was startled, several years ago, by the casual remark of
a colleague -- "With your interest in SETI, you might enjoy hearing about that
lunch at Los Alamos where Fermi asked his famous question."  That colleague was
Herb York, he had indeed been present, and I was very interested in his
recollections!  I interviewed York, and also Philip Morrison, and preserved the 
recordings in the archives of the SETI Institute.  The following is a synopsis 
of York's recollections.

   The time was the summer of 1950.  The Russians had exploded their first 
atomic bomb the previous summer, and, with additional troubling events in 
Moscow and Peking, Truman had committed the US to develop a 
thermonuclear weapon (the "super," or "H-bomb").  A nucleus of physicists 
(most veterans of the Manhattan Project) had reassembled at Los Alamos -- 
Bethe, Fermi, Gamow, Garwin, Teller.  York was visiting from UC Berkeley 
as a member of the "measurements group," to provide key instrumentation 
for the thermonuclear test -- the "George shot" -- scheduled for the summer of 
1951.

   During lunches at the Fuller Lodge, Fermi loved to pose rhetorical 
questions, which he then proceeded to answer.  For example, if you had $100 
million to spend on science, without moral restriction, what would you do? 
(Answer: Dig the deepest hole!  We don't know much about what's under our 
feet.)  York arrived in the midst of one of these exercises, at which 
Konopinski and Teller were already engaged.  Out of the blue Fermi asked 
"Don't you ever wonder where everybody is?"  York recalls that everyone 
knew that he meant extraterrestrials.  In typical fashion Fermi then proceeded 
to answer his own question, in this case by running through what we now call 
the Drake Equation (or Green Bank Equation).  He pointed to multiple star 
systems as evidence of planetary systems, and he talked about the probability 
of life arising and acquiring technology.  An important part of the analysis 
was that, if there were others, they would be far more advanced -- the odds of 
finding a civilization in its technological beginning phase are remote.

   So, Fermi concluded, if interstellar travel is possible, it ought to be 
positively crowded out there.  Fermi's supposition (as York remembers, with 
a bit of uncertainty) is that interstellar travel is either impossible, or at least 
so difficult that nobody undertakes it because it is not worth the effort.  Fermi 
and the group came away with the feeling that this was a strong question, one 
that had not been answered at that lunch.  The idea that all technical 
civilizations inevitably destroy themselves may have been suggested; but, 
even on that eve of thermonuclear invention, there was no feeling of doom.  
On sum, Fermi felt, the world was a better place in 1950 than it was in 1900 
-- for example in terms of slavery, disease, and so on.  York does not recall 
any further discussion of this topic.

   In a conversation on "The Prehistory of the Fermi Paradox" in 1998, Philip 
Morrison pointed out that project scientists, in a burst of black humor, 
sometimes referred to supernovae as failed fission/fusion projects by 
extraterrestrials.  But the wartime project predated the first reports of flying 
saucers, and there had been no real talk of space travel.  Satellites were only 
a concept.  Morrison also pointed out that Fermi began to complain about his 
memory after the war, and started keeping a notebook; it is possible that his 
ideas on the Paradox are recorded in them.

(written in late 1998)