Chapter 33: Astrophysics and Cosmology Applications

One of the most basic questions that we can ask is "are we alone in the universe?" Over the ages, there have been many answers: speculative, religious, philosophical, and deceitful. However, there has never been a good, scientific answer to this question. Why is this so? In part, it is always hard to prove something does not exist. Just because you can't find something does not mean it isn't there; you may just be a poor detective. It is also difficult because the question is not really well defined. Must we find intelligent life? Would any hint of biological activity do? Do we even have an adequate definition of "life."

In this essay we will look at attempts to answer a more specific question. Are there signs of intelligent life communicating across space with radio waves? This is a question that is being addressed seriously, carefully, and scientifically.

The effort to answer this question began in 1959 with the publication of "Searching for Interstellar", by Giuseppe Cocconi and Philip Morrison, both physicists at Cornell University. In that article, Cocconi and Morrison suggested a strategy scanning nearby stars for evidence of microwave signals that could not be explained by natural phenomena. Dr. Frank Drake At the time that article was published, radio astronomer Frank Drake was already planning a series of observations using a radio telescope at the National Radio Astronomy Observatory, Green Bank West Virginia. Drakes observations, Known as Project Ozma, scanned only two nearby stars, Tau Ceti and Epsilon Eridani.

Radio Telescope, Green Bank, WV In the following year, Drake organized the first SETI conference at Green Bank. It was a small meeting, only a few dozen scientists met for three days. During that conference, Drake proposed the now famous Drake Equation, a formula for estimating the number of extraterrestrials species with which it is possible to communicate.

• R^* = The rate of formation of suitable stars
• f_p = The fraction of suitable stars that have planets
• n_e = The average number of suitable planets per star
• f_l = The fraction of those planets where life develops
• f_i = The fraction of those planets where intelligence develops
• f_c = The fraction of those planets where electromagnetic communication develops
• L = The average lifetime of a communicative civilization

The next big event in SETI history came about in 1967. Jocelyn Bell, a graduate student at Cambrige University, was studying radio emissions from quasars using a radio telescope that she had built with her advisor, Dr. Anthony Hewish. During the course of her observations she made a startling discovery, a source of perfectly timed pulses, 1 1/3 seconds apart. Over the next few days, she and Dr. Hewish determined that the pulses must come from beyond the solar system, and must come from an object far smaller than a star. They began to suspect the possibility that these pulses were a signal from an exterrestrial civilization.

Photo of Dr. Jocelyn Bell Burnell, circa 1975. Thanks to Dr. Bell for permitting us to use this image

Of course, these findings did not turn out to be a sign of extraterrestrial intelligence. Rather, they were the first observation of a pulsar, a rapidly spinning neutron star formed after a supernova. She recounted this story in a speech to the Eighth Texas Symposium on Relativistic Astrophysics. That speech is a delightful retelling of an important scientific discovery, and is well worth reading. In 1974, Hewish, but not Bell, was awarded the Nobel Prize in physics for this discovery. It is widely believed that Bell should have shared this prize, but was denied that honor due to her age and gender. Bell (now Burnell) did win numerous other awards and honors, and is now Chair of the Department of Physics, Open University, England.

Before I mention any of the modern SETI projects, I would like to point out a couple of basic facts. First, in any radio search, there are two variables that have to be "searched." The obvious search is the sky; like any telescope, a radio telescope focuses on a very tiny portion of the sky. It has to be pointed at the source of a transmission. Many SETI projects have taken care of this by identifying nearby, moderate sized stars and focusing on them in turn, others scann to whole sky in patches of fixed size. The other variable that needs to be searched is frequency. Like any radio or TV, the reciever electronics must be set to a particular frequency. However, there is no "list" of stations to consult. Like a traveler on the highway in an unfamiliar region, we have to "scan the dial" and listen at each frequency for a few seconds to determine if that frequency has only static or a faint signal. Early searches (such as Ozma) picked a single frequency based on the notion that all advanced civilizations would be aware of certain common frequncies, and might use them as beacons. Ozma serched at 1.42 GHz, which is related to an important transition in hydrogen.

Radio Telescope, Arecibo, Puerto Rico Between 1960 and the present, there have been dozens of searches conducted using various methods. However, funding for SETI has alsways been controversial. Thus, many of the seaches have been short lived, and carried out on "shoestring" budgets. Often, the searches "piggyback" on the usual business of radio astronomy. In a piggyback search, extra receivers are attached to the radiotelescope (essentially an antenna) and one or more frequencies are recorded while the telescope goes about its business of examining interesting astronomical objects. The advantage is obvious: lots of free time. Unfortunately, such a search does not focus on likely target stars.

An excellent example of a piggyback search is the SERENDIP project carried out by researchers at UC Berkeley. During the late 1980's SERENDIP II piggybacked on the 300 ft diameter dish at Green Bank West Virginia (were Drake worked) and analyzed 65,000 channels simultaneously. The more modern SERENDIP III is a piggyback experiment at the huge dish at Arecibo Puerto Rico, the worlds largest radio telescope. SERENDIP III analyzed 4 million channels, and was recently upgraded upgrade (SERENDIP IV) to 168 million channels. Incidentaly, an excellent article about SERENDIP, with a nice discussion of the Drake equation was published last year by the Exploratorium in San Francisco.

The most extensive search going on today is the SETI Institute's Project Phoenix. Using a series of radio telescopes in both the northern and southern hemispheres, Phoenix hopes to investigate 1000 stars (all within 200 light years of earth) at a phenomenal 1 billion channels each. Other modern searches include the BETA project run by Harvard University's Paul Horowitz and the Ohio State SETI project, the longest running search at present.

Perhaps the most interesting method of tackling the big searches is to spread out the work over many small efforts. The SETI League is signing people up for Project Argus (named for the mythological giant with 100 eyes). This project attempts to scan the sky with hundreds of small antenna's (such as the one shown) in the hands of amatuer radio astronomers. What if you are interested in SETI, but do not have the time or money to set up a receiver? The SETI@home project will allow anyone with a personal computer to participate in the analysis of data from the SERENDIP project discussed above. The analysis is done whenever your computer is turned on but not doing anything. In fact, it runs as a screen saver, showing the users choice of several "progress reports" on the local analysis or the project as a whole. SETI@home is expected to be available in the summer of 1998. They hope to sign up at least 50,000 participants to help search the vast data set they will generate.

We would like to gratefully acknowledge the SETI League. The images of Dr. Drake, and of the large (Green Bank) and small (project Argus) radio telescopes are all SETI league photos, and are used by permission.

For more information ...
An alternative: Optical SETI
A debate about SETI: YES (by Carl Sagan) or NO (by Ernst Mayr)
Jocelyn Bell Burnell Profile, an interview, Biography from WGBH
Some organizations: The Planetary Society, The SETI Institute, The SETI League
A Drake Equation Calculator

Research questions:

Further Study Questions:

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