You can't outwait the aliens

kw: book reviews, nonfiction, biographies, astronomy, space aliens

The August 24 Newsweek just crossed my desk, passed on by a colleague. In it I read "What you need to know NOW", actually a collection of 25 mini-articles. The very first is "Aliens Exist" by Andrew Romano and Fred Guterl. Amidst the typical sort of "well, of course, they must, there are so many stars…" sort of reasoning, they mentioned the Kepler Space Telescope, which is even now scanning a "promising" portion of the sky for earth-type planets in habitable zones about their stars. It will do so for 42 months.

I found reading the article fortuitous, as I'd just finished reading Captured by Aliens: The Search for Life and Truth in a Very Large Universe by Joel Achenbach. The book is a dual biography, first of Carl Sagan's career, then of the search for non-Earth life. It opens with Carl Sagan and Frank Drake, in 1975, using the Arecibo radio telescope to search for signals from the Andromeda galaxy, and ends with the death of Carl Sagan, still hoping to obtain definitive proof of alien life.

Sagan and Drake represented the scientific aspect, the "respectable" aspect, of the belief that there must be other civilizations "out there". Much of the book is taken up with the author's investigations of alien-seekers who range from respectable to downright loony. He attended many, many conferences—one thing nearly all alien aficionados do is hold conferences. The odder ones tend to cluster around Las Vegas, Nevada and nearby Roswell. The looniest of all, though, don't hold conferences, having "encounter meetings" instead, as they believe that they are themselves aliens, or possessed by aliens.

Sagan's most famous maxim is, "Extraordinary claims require extraordinary proof." The closest thing to scientific proof we have of life elsewhere is the "worms" from Mars (see my post Magnetic Martians). Once the Kepler telescope does its work, there'll be some "targets" for a larger space telescope to scrutinize with a spectroscope, for water, methane, and whatever else might signal "biosphere over here".

For the time being, those of us of a robustly scientific frame of mind must be contented with Drake's Equation, which I'll state here in a form that I prefer:

N = N_s N_hp f_l f_i f_c L W

The first N is the number of civilizations in the Galaxy. The other factors, all multiplied togather, are as follows, with my "±σ sideboard" estimates for each value [in brackets]:

• The number of stars in the Galaxy, or the number of a certain type, such as "G class" for stars like our Sun [F+G+K: 10⁹-10¹¹].
• The number of habitable planets per star (or star of the chosen class) [0.1-0.5].
• The fraction of habitable planets on which Life develops [0.2-0.9].
• The fraction of planets harboring life on which Intelligent life evolves [0.001-0.01].
• The fraction of intelligent species that develop a civilization that can Communicate via radio (or other chosen detection method) [0.5-1.0].
• The effective Lifetime of such communication, here expressed as a fraction of the time that Communication persists, relative to the length of time the planet remains habitable [10^-6-10^-3].
• The Willingness of the civilization to purposely communicate, such as with a stronger signal than "TV leakage" [0.1-1]

Carl Sagan supplied values to a version of this equation that yielded a figure of one million. Surely out of a hundred billion stars in our Galaxy, a million might harbor an intelligent, communicating species.

My own range of possibilities, using the numbers above, combining them statistically, yields a median value of 21, with a "scatter" factor (±σ, or one log standard deviation) of 100, which in this case is a multiplier. One extreme, 0.21, means our single planet had a one-in-five chance to produce a communicating species at all, so we ought to pat ourselves on our collective back. The other extreme comes to 2,100. In a galaxy spanning 100,000 light years, that is not very much. Ignoring the thickness of the spiral arms, the average spacing between such civilizations would be 2,200 light-years.

I spent a few years running SETI@home on my computer. I'd keep doing it, but my computer is now eight years old, and I figure nearly everyone else running SETI@home has tons more power; my drop in the bucket is no longer big enough. And then I found that the targeted stars are all within 1,000 light years. Even if my more optimistic estimate were correct, we aren't reaching them! But if Sagan was right, the average spacing is only 100 light years, and the continuing lack of SETI success is a puzzle.

Several times the author recalls Fermi's question, "Where are they?" If interstellar travel is possible, and numerous alien civilizations exist, at least one of them ought to have visited us by now. But in spite of tens and hundreds of thousands of "sightings" of unidentified "things", particularly since 1947, no aliens or alien artifacts have been scientifically studied and been shown to be genuine (this isn't just Achenbach speaking, this is me also). To me, there is a two-pronged conclusion: If aliens are possible, interstellar travel is not possible; if interstellar travel is possible, there are no aliens.

I like to think that other planets have intelligent life, so I lean toward believing the stars are just too hard to reach. I hope Kepler finds a passel of "exo-Earths".