Key points: Drake equation; most uncertain terms in predicting existence of communicating life
"To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field sown with millet only one grain will grow.''-- Metrodorus of Chios (fourth century B.C.) |
It seems likely there is life on the scale of stromatolites on many other planets - this type of life formed so quickly on Earth and is based on very robust bacteria. However, it wouldn't be much fun to try to carry on a conversation with alien bacteria. It is hard to tell on how many planets complex life (multi-cellular, specialized) has formed, and still more difficult to guess how many cases have led to intelligent beings.
Our (maybe romantic) dream is to make contact with another civilization. To have one out there to talk to requires
"Sometimes I think we're alone. Sometimes I think we're not. In
either case, the thought is staggering." -- Buckminster Fuller |
that experience favorable conditions for developing an advanced civilization.
Although it looks easy in the movies and on TV just to hop on a rocket and find other civilizations, there are some major difficulties to be solved (See also http://www.lerc.nasa.gov/WWW/PAO/warp.htm) The best clue we can acquire with our existing technology is to "listen" for radio and television signals that might be coming (accidentally) from a civilization. Our civilization has been sending out such signals for about 70 years, so any civilization on the nearest stars that had been listening would now know that we exist. If they had figured out how to decode our transmissions, they might know a lot more!!
If event A happens a fraction z of the time and event B happens a fraction y of the time, then both A and B will happen z times y of the time.
For example, if one coin comes up heads 0.5 of the time, then two coins will both come up heads
0.5 x 0.5 = 0.25 or 1/4 of the time
The Drake equation attempts to quantify the number of civilizations in the Milky Way capable of sending us signals (other life forms could well exist, but if we cannot learn of their existence, they might as well not exist for the purposes of science (and philosophy!))
The equation gives the number of intelligent and communicating civilizations:
N = N* x Nplanets x fplanets x plife x fintelligent x fradio x [ Lcivilization/L*]
N* = number of stars in the Milky Way
Nplanets = number of planets per star
The numbers in blue would suggest about 300 radio communicating civilizations in the Milky Way. The most uncertain term, however, is the lifetime of a civilization, and the number of radio communicators could easily be 1 (us)! However, reviewing what we do and do not know, it appears likely that there are many planets with some form of primitive life, based on the rapidity of the appearance of primitive life on Earth. The biggest uncertainties in whether there are beings to communicate with are in the probability of intelligent life evolving and then in the behavior of that life!
A minor adjustment (within our uncertainties) in, say, the fraction of life that evolves to a high level of intelligence to 0.01, and to the lifetime of a radio emitting civilization to 10,000 years would leave us with 0.3 radio emitting civilizations in the galaxy - we are then a statistical anomaly, and should not expect that there is anyone to listen to.
However, Scientists in general have a prejudice against any class of event that happens only once and hence many scientists prefer the more optimistic estimates. And besides, their implications are much more interesting.
Finding that there is another civilization out there would be fascinating, particularly if we could understand its thought processes and activities by decoding the transmissions. It would be extremely exciting to scientists and many others -- who knows what form the transmissions would take, or in fact how we would react
For more about SETI, try http://www.seti.org/
Rodin's "The Thinker", from Cleveland Museum of Art, http://www.clevelandart.org/educef/rodin/html/index.html |
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