As the third millennium begins, humankind has finally achieved the technical means to address a question that is both old and profound: are we alone in the universe? Despite the fact that alien beings regularly infest movies and television shows, there is still no compelling evidence for any living creatures beyond Earth. But there are highly suggestive reasons to believe that the star fields of the cosmos are teeming with life, some of it intelligent. In this series of twelve lectures, we consider what science can tell us about the possibility of intelligent life in space, how we might find it, and what it would mean if we did.

The first two lectures set the stage in our quest for cosmic company. One of the principal achievements of astronomy in the last four centuries has been to show that our physical place in the universe is anything but special. The glow of ten thousand billion billion stars lies within the purview of our telescopes, and one in ten is similar to our Sun. We occupy only a tiny speck of real estate in a massive, expanding universe that was brought into being approximately twelve billion years ago Our own solar system is relatively new, being only one-third the age of the oldest stars, and consequently what has happened here the emergence of biology and technically sophisticated life may have happened billions of years earlier elsewhere. Even in the eighteenth century, when we had little knowledge of the universe's vast extent, the possibility that nearby planets might house sentient beings was considered. Mars, in particular, attracted early attention, and a century ago it was posited to be the home of an advanced society busy lacing the landscape with a network of canals.

Lectures Three and Four are devoted to the modern attempts to locate nearby life as well as habitable worlds beyond the Sun's familiar retinue of planets. In 1996, a meteorite kicked off the surface of Mars was retrieved and analyzed by NASA and university scientists. Evidence was pried from this rock implying that simple life existed on the Red Planet more than three billion years ago. Other worlds in our solar system, the moons Europa and Titan, may sport living creatures even today. While the abodes for life in our "back yard" tempt NASA scientists, astronomers looking farther afield have discovered that more than a dozen sun-like stars within a few dozen light-years show tell-tale evidence of having their own planets. These developments, the product of recent research, suggest that life is not a miracle, but merely a statistic, thus prompting intensive efforts to seek out other intelligence.

Lectures Five through Seven consider the consequences of interstellar travel. While a staple of science fiction, sending rockets from one star system to another is considerably beyond our own technical capabilities. Some scientists maintain that it will be impractical even for advanced societies. However, if one admits the possibility that blasting off to the stars might could occur, what consequences might that hold for us? In 1950, physicist Enrico Fermi realized that easy space travel would lead to rapid colonization of the galaxy. Since there is no obvious evidence that such colonization has occurred, Fermi asked "where is everybody?" Lecture Six deals with the ingenious answers that have been proposed to address this famous question, while the following lecture considers the possibility (favored by many among the public) that the aliens are, in fact, buzzing Earth with their saucers.

In lectures Eight and Nine, we investigate what science can say about alien construction and behavior. Carbon-based life has a firm foothold on our planet, but is that a mere accident of ancient history? Silicon-based biology is a favorite with sci-fi authors, but under most circumstances will take a back seat to carbon. On the other hand, silicon-based intelligence might not. Could it be that most of the intelligence in the universe is non-biological? And what might motivate aliens to get in touch either with a radio broadcast or in person?

Lectures Ten through Twelve deal with the modern efforts to find intelligent societies by attempting to eavesdrop on their broadcasts. In 1959 two physicists at Cornell made simple calculations that showed, somewhat to their surprise, that sending radio messages between the stars was both simple and inexpensive. The universe might be flooded with radio traffic. Since 1960, when the first search for alien signals was conducted by Dr. Frank Drake, radio telescopes of increasing capability have been turned on the cosmos in the hope of finding a faint signal that would betray the presence of another civilization. While these efforts have yet to succeed, those who are engaged in the Search for Extraterrestrial Intelligence, or SETI, don't hesitate to speculate that a signal could be found early in the 21st century. Should this occur, what would be the impact on human society? Our course concludes with thoughts about the consequences of finding proof of other intelligence, far beyond the banal biology of our own world. Perhaps we should anticipate being inducted into a galactic club or perhaps a truly universal church. At the very least we should be prepared for the simple fact of finally knowing that we're not alone.

Seth Shostak, Ph.D.
Astronomer, SETI Institute

Seth Shostak was ralsed in northern Virginia and developed an early interest in science, technology, and film. He received a B.A. in Physics from Princeton University, and a doctorate in Astronomy from the California Institute of Technology in 1972.

Upon graduation, Dr. Shostak took a position at the National Radio Astronomy Observatory in Charlottesville, Virginia, where he continued the research that had formed the basis of his thesis: the dynamics of galaxies. By employing radio telescopes to study the rotation of these mammoth stellar systems, he found that at least half the mass of galaxies exists in an unseen and currently unknown form, a circumstance that is part of what is popularly known as the "missing mass" problem. He took a position in the astronomy department of the State University of Groningen, in The Netherlands, where he continued his radio study of galaxies using the Westerbork Synthesis Radio Telescope. In 1981, he used this instrument, together with Dr. Jill Tarter, to look for artificial radio beacons that might be coming from the center of our galaxy. This small experiment introduced Dr. Shostak to the Search for Extraterrestrial Intelligence, or SETI, and it was the basis for his invitation to join the SETI Institute in 1990, where he works today.

In addition to graduate teaching in Groningen, Dr. Shostak has taught adult education courses for the California Academy of Sciences, in San Francisco. He lectures widely, giving approximately 50 presentations annually to audiences ranging from the general public to academia. Since 1997 he has been a Distinguished Lecturer for the American Institute of Aeronautics and Astronautics.

Dr. Shostak has edited several volumes of conference proceedings that deal with SETI. He has approximately 50 research papers in the professional literature, and he has published several hundred popular articles on astronomy, SETI, and film. His popular book on the subject of extraterrestrial life, Sharing the Universe (Berkeley Hills Books), appeared in 1998. Dr. Shostak is currently writing an undergraduate textbook on this subject with Dr. Frank Drake. He is frequently asked to comment on related research for television and radio, appearing on approximately four dozen programs per year.

Lecture 1: Our Place in the Cosmos
Lecture 2: Aliens in the NeighborhoodFiction and Fact
Lecture 3: The Prospects for Life in the Solar SystemMars, Europa, Titan
Lecture 4: Other Worlds? The Search for Habitable Planets
Lecture 5: Interstellar Travel and Colonization
Lecture 6: The Fermi Paradox, or Why Arent the Aliens Everywhere?
Lecture 7: Why UFOs Are Bunk
Lecture 8: What Is E.T. Made Of?
Lecture 9: Alien Appearance and MotivationCan Science Tell Us Anything?
Lecture 10: Searching for E.T. Modern Techniques
Lecture 11: Estimating the Number of Civilizations (The Drake Equation)
Lecture 12: If We Find E.T., What Then?

A RATIONAL scientific (as opposed to both alien conspiracy and creationist pseudoscience) look at the possible existence of intelligent life elsewhere in the universe, the odds of encountering same over the vast distances and time frame the universe represents, and whether either species would even be able to recognize the intelligence of their counterpart should they meet.,