By Robert Hazen, George Mason University
Prior to the late 1950s, before the launch of Sputnik, any quest for alien life was mocked as beyond the domain of serious science; it had nothing to do with scientific research. That changed in 1959, when Guiseppe Cocconi and Philip Morrison, physicists at Cornell University, transformed the scientific status of the search for extraterrestrial intelligence, or SETI.
Guiseppe Cocconi and Philip Morrison
Cocconi and Morrison proposed a simple and compelling experimental strategy for searching for extraterrestrial intelligence.
They proposed looking for characteristic radio signals from nearby, Sun-like stars. Cocconi and Morrison based their argument on the intriguing possibility that a scientifically advanced alien society might have established a radio-signal beacon, in the hopes of attracting our attention. In powerful prose, they concluded their first article as follows: “We therefore feel that a discriminating search for signals deserves a considerable effort. The probability of success is difficult to estimate; but if we never search, the chances of success are zero.”
A “Yes” or “No” Question
Within two years, the National Academy of Sciences had organized a meeting of some of the world’s leading astronomers to plot a strategy for SETI research. “Are we alone?” is a question unlike most of those in science.
Most scientific questions are answered only gradually, and they require lengthy and inherently incomplete answers. The search for intelligent, technological life is different. The only possible answers are “Yes, there is life,” or “We don’t know.” Until we discover an alien intelligence, we can never be certain of our solitude.
A single, unambiguous communication or direct contact with another technological species is going to instantly answer the question, and change forever our perception of life in the universe. Of course, once the alien life form is found, there are myriad new questions; whole new areas of science are going to open up. We’re going to try to find out about their distant origins, their novel biology, their technological capabilities, their ultimate intentions; and these ideas and others are going to consume scholars’ lives for centuries to come.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Frank Drake’s Seven Questions
The idea of estimating how many alien societies there might be was first proposed by SETI pioneer Frank Drake, who was a professor of astronomy at the San Diego campus of the University of California. He suggested that there are seven factors, each worthy of independent study and thought, and that each of these seven factors contribute to the probability that an intelligent life form exists on other worlds.
- His first question is pretty straightforward: How many Sun-like stars are out there? We can actually hope to answer this first question in the Drake equation by observations of the other stars around our galaxy.
- The second question: how many Sun-like stars have solar systems? Once again, we’re probably going to be able to make direct observations of this, perhaps in 10 or 20 years, when those new space-based interferometric telescopes are in place.
- Drake’s third question is, how many solar systems have Earth-like planets? In other words, you can have a solar system, but is there a planet appropriate to forming life? Nevertheless, the number of Earth-like planets orbiting Sun-like stars in our galaxy may be in the hundreds of millions. Again, direct observation in perhaps 20 years could answer that question.
- Next is, what fraction of Earth-like planets have life? If we can actually detect oxygen, perhaps with telescopes in 20 or 30 years, then we may be able to say whether life is common on other worlds.
- In the fifth question, he asks, how often does life lead to intelligence? Maybe intelligence is common, but we just don’t know yet.
- The sixth question: will intelligent life forms attempt to communicate with us? Intelligence guarantees neither the desire nor the ability to communicate across the vastness of space. It’s possible that there could be intelligent species that merely wish to communicate with themselves in more of an art form rather than in a technological way; we just don’t know.
- The seventh question is: How long do advanced societies remain communicative? The estimates of half‑life of a society with radio technology, published by various scientists—who really aren’t using scientific methods in this case—range from a pessimistic few decades to millions of years.
Communication by Radio Signals
Radio waves and microwaves traveling at light speed through space provide the most practical medium for interstellar communication, while radio telescopes provide ideal receivers for these potential signals. SETI scientists suspect that the communications that we get from an intelligent species are going to be absolutely unambiguous.
Perhaps it’s going to be a sequence representing prime numbers: 1, 2, 3, 5, 7, 11, 13, in a series of short pulses repeated over and over again, to get our attention. Then they might send a binary message of coded dots and dashes that could convey basic information about the senders, and about their home world.
Search for the Radio Signals
The central problem that confronts SETI scientists is where and how to search for such a signal. There are three different radio broadcast variables that you have to match. First, you have to find the direction to the source; you have to find the right place in the heavens to point your radio telescope. You have to have the frequency of that signal, and that frequency might be shifted slightly by red or blue shifts, so you have to adjust for them. Then you have to have your sensitivity correct: you have to see the intensity of that source above all the background noise.
There are a staggering number of possible combinations; it makes the SETI effort something akin to searching for a needle in a cosmic haystack. There have been lots of efforts, and NASA began funding, but they discontinued funding for SETI in the early 1990s. SETI research has then been carried on by other organizations, primarily sponsored by private groups, such as the Planetary Society. It’s still a long shot, but we can only think what it would mean to find an extraterrestrial intelligence.
Common Questions about the Search for Extraterrestrial Intelligence
SETI stands for Search for the Extra Terrestrial Intelligence.
Cocconi and Morrison proposed looking for characteristic radio signals from nearby, Sun-like stars. They based their argument on the intriguing possibility that a scientifically advanced alien society might have established a radio-signal beacon, in the hopes of attracting our attention.
The idea of estimating how many alien societies there might be was first proposed by SETI pioneer Frank Drake.