This is a book about humanity’s responses to the “Great Silence”—the fact that no sign of intelligent life beyond earth has yet been found. The most obvious of these is the scientific search for extraterrestrial intelligence (SETI). This search, as those involved in it are quick to point out, has nothing to do with unidentified flying objects (UFOs), or crop circles, or stories of weird little creatures intent on examining the genitalia of every human they come across. Certain incidents, however, are invariably asked about whenever SETI is discussed. We examine these incidents in several of the ensuing chapters....

Just what is the nature of this universe in which we find ourselves? Virtually every culture, and every age, has had its “answer” to this question. Models of the universe are as old and as varied as humankind itself. One picture, popular among some of the scientists in Newton’s day, held that space went on endlessly in every direction, and that the stars occupied fixed positions in this space. There was no beginning; the universe was, and had always been, as we now see it. This model when combined with Newton’s law of gravity led to a remarkable conclusion.There...

One answer to the Fermi paradox is the simple assertion that we are alone in the universe or, at least, in the Milky Way galaxy. Could this be? There is, of course, no easy answer to this. But we can examine the Earth and the other planets of the solar system and note if, in any way, the Earth is unique.

Even the most superficial such comparison shows two things. First, there is an awful lot of water on our world. It covers nearly three quarters of the globe, and no other planet has anywhere near as much. Secondly, the...

As far back as anyone has been able to probe, via folklore or ancient writings, people have reported seeing strange objects in the sky. UFOs are not new (Vallee 1965: 1–24). Still the modern “incarnation” of the subject is usually said to have begun on 24 June 1947, when Kenneth Arnold made his sighting over Mt. Rainier (Chapter 2). Other sightings soon followed, most of these can be found in Peebles (1994). At Maxwell Air Base, in Montgomery, Alabama, several witnesses, including pilots and intelligence officers, watched a light streak across the sky, make aright angle turn,and...

The sun emits a prodigious amount of energy, but it doesn’t do this at a constant rate. Many phenomena in the solar atmosphere go through an eleven-year cycle (Kaufmann 1994: 316). So, back in 1952, the members of the International Council of Scientific Unions could predict that the period from 1 July 1957 to 31 December 1958 would be one of peak solar activity. They designated this period the International Geophysical Year and suggested, among many other projects, that artificial satellites be launched during this time to map the Earth’s surface. In response to this, the White House, in July...

Every successful space mission gets lots of media attention. This, in turn, invariably leads to letters to newspapers decrying the waste, or misdirection, of money and talent. Surely you’ve seen such letters. They often include some strange statistic and tend to be highly emotional: “Four hundred million dollars for a space probe!!! Why, for that amount of money, you could buy two hundred million goldfish; think about that!”

Such letters express a kind of tautology—something that is always true. No matter how you spend public money there are always those who say, sometimes with some justification, that it could...

The extravagant claims of Percival Lowell about life on Mars caused many astronomers to shy away from the topic of extraterrestrial life. They did not flatly deny its existence but, for the first sixty years or so of the twentieth century, they rarely even mentioned aliens. But even in the 1960s we really didn’t know much about conditions on the other planets of our solar system and couldn’t rule out the possibility that advanced life existed somewhere in our neighborhood. One book suggested that the ubiquitous UFOs were from Mars and since these objects, according to witnesses’ reports, were capable...

Right after Sputnik was launched, “space was the place”—it was where the action was and, with the remarkable achievements of the Soviet Union, the United States was faced with a new area of international competition. So the National Academy of Sciences organized a group of distinguished scientists charged with setting forth goals for an American space program that were both realistic and scientifically sound. This group, which came to be known as the academy’s space sciences board, was chaired by Lloyd Berkner, the man who, as we have already seen, was to give the go-ahead for Project Ozma. The...

If you ever give a public talk about SETI you will find that, as likely as not, someone will ask you about the Roswell incident. When this first happened to me I had to admit that I didn’t know anything about it. So, I did some reading, and this is what I learned.

In July of 1947, just a few weeks after Kenneth Arnold made his famous sighting, a UFO allegedly crashed on a remote ranch near Corona, New Mexico. Subsequent events have forever linked this incident to the town of Roswell, about seventy-five miles to the southeast and the...

As we have already noted any alien society will live out among the stars. The enormous distance between us will make communication technically challenging, but it will also make inter-stellar aggression highly unlikely. The expense and the energy required to launch an expedition across these vast gulfs would far exceed any possible gain. But should we even try to contact such a society? What could we hope to gain? Does it make any sense to engage in a dialogue where the interval between a message and its response is measured in years? These questions will be the subject of the...

There have been, to my knowledge, only two¹ attempts at creating a language suitable for extraterrestrial communication. The first of these, called “Lincos,” is due to the Dutch mathematician Hans Freudenthal (1960). Lincos is a contraction of the words “lingua cosmica” which means, of course, “cosmic language.” This was published as a book with the subtitle: “Design of a Language for Cosmic Intercourse.” English was not his first language and so Freudenthal was, perhaps, unaware of how this subtitle might be interpreted; especially by college students. When I mention the book to my classes the first question they ask is:...

This brief chapter is a digression, a break from the main theme of this book. It contains a short discussion of the amusing, frustrating, and, perhaps, annoying paradoxes of set theory alluded to earlier (see Chapter 11; a more technical discussion can be found in Enderton 1977: 5–6).

These paradoxes are of two types: logical and semantic. Among the first kind the most well-known is, perhaps, the one due to Bertrand Russell. It might be best to start with a story that illustrates its difficulty.

There is an imaginary town where all men are required to shave, or be...

The world around us, and in fact the entire universe, seems to consist of two things: Matter and energy. Matter is usually defined as anything that occupies space and has weight. Energy is a little harder to define, but examples surround us: heat, light, electricity, sound, etc. For a long time it was believed that the bulk of the matter in the universe was visible because it either emitted or reflected light. Today astronomers have come to realize that a large portion, some say as much as 80 percent, of the matter in the universe is dark (Kaufmann 1994: 465,...

Gene Roddenberry really started something when he createdStar Trek.The idea of traveling around the galaxy with a heroic captain and an interesting crew—which included a few aliens—resonated deeply with a great many people. Part of the appeal may have been the vagabondish lifestyle this implied. Troubles, difficult attachments, maybe even financial responsibilities, were left behind as the spaceship traveled on to the next solar system. Part of the appeal also was the sense of anticipation as the crew entered a new, unknown, part of the galaxy. Who knew what they might find? This was partly the...

Some years ago U Thant, one-time secretary general of the United Nations, had a conversation with J. Allen Hynek, chairman of the Astronomy Department at Northwestern University. Both men are now deceased. Mr. Thant said that, as a Buddhist, he believed in life elsewhere. He asked if Hynek thought that extraterrestrials might visit our world. Hynek replied that he too believed in life elsewhere, but that the times involved in journeys from outer space seemed insuperable. At that point the Secretary General made this remark: “Ah, but what may seem like years to us, may be just a day or...

Scientists rarely investigate UFOs. This is not at all surprising. The typical scientist spends many years learning difficult, highly technical material. He or she must then learn how to conduct research. This is done in a more specialized area that is of particular interest to the person involved. Scientists who go into academic life face stiff competition for relatively few jobs, and, if they do get a job, they are expected to produce high-level research. They are under pressure to publish and under even greater pressure to attract money to support their research.

Now before any agency awards a grant...

A number of developments in the late twentieth century gave strong support for the idea that life can exist on other worlds, and that it can arise much more easily than previously thought. The first of these was a shocking discovery about life right here on Earth.

In 1977 the submersibleAlvindiscovered areas on the ocean floor where lava was rising from the Earth’s core. This didn’t surprise the geologists, many of whom had predicted that such regions should exist. It was the biologists who were in for a real shock. At a depth where the pressure is enormous,...

At the time of this writing, 2012, there is no evidence that alien life, intelligent or other wise, actually exists. It is hard to believe that it isn’t out there somewhere, but we have yet to find it. SETI researchers are listening, hoping to detect the radio, in some cases even visual, signals of an alien civilization. I don’t think anyone expects a direct communication, but we might get lucky and overhear someone’s internal messages; perhaps a spacecraft contacting its home planet or a radio broadcast that, like ours, leaks into space. Those with the right technology can tune in...