Note to users. If you're seeing this message, it means that your browser cannot find this page's style/presentation instructions -- or possibly that you are using a browser that does not support current Web standards. Find out more about why this message is appearing, and what you can do to make your experience of our site the best it can be.

Science 6 May 1977:
Vol. 196. no. 4290, pp. 616 - 621
DOI: 10.1126/science.196.4290.616
Prev | Table of Contents | Next

Articles

Searching for Extraterrestrial Civilizations

T. B. H. Kuiper 1 and M. Morris 2

1 Scientist at the Jet Propulsion Laboratory, California Institute of Technology, Pasadena 91103
2 Research fellow at the Owens Valley Radio Observatory, California Institute of Technology, Pasadena 91125

We have argued that planning for a search for extraterrestrial intelligence should involve a minimum number of assumptions. In view of the feasibility (at our present level of understanding) of using nuclear fusion to effect interstellar travel at a speed of 0.1c, it appears unwarranted (at this time) to assume that it would not occur for at least some technologically advanced civilizations. One cannot even conclude that humans would not attempt this within the next few centuries. On the contrary, the most likely future situation, given the maintenance of technological growth and the absence of extraterrestrial interference, is that our civilization will explore and colonize our galactic neighborhood.

A comparison of the time scales of galactic evolution and interstellar travel leads to the conclusion that the galaxy is either essentially empty with respect to technological civilizations or extensively colonized. In the former instance, a SETI would be unproductive. In the latter, a SETI could be fruitful if a signal has been deliberately directed at the earth or at an alien outpost, probe, or communication relay station in our solar system. In the former case, an existing antenna would probably be sufficient to detect the signal. In the latter case, success would depend on the way in which the communications were coded.

Failure to detect a signal could permit any of the following conclusions: (i) the galaxy is devoid of technological civilizations, advanced beyond our own, (ii) such civilizations exist, but cannot (for some reason which is presently beyond our ken) engage in interstellar colonization, or (iii) such civilizations are not attempting overt contact with terrestrial civilizations and their intercommunications, if present, are not coded in a simple way. To plan at this time for a high-cost, large-array SETI based on the last two possibilities appears to be rather premature.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Extraterrestrial Intelligence: An Observational Approach.
B. Murray, S. Gulkis, and R. E. Edelson (1978)
Science 199, 485-492
   Abstract »    PDF »


To Advertise     Find Products

Science. ISSN 0036-8075 (print), 1095-9203 (online)