Extraterrestrials: Where Are They?

Where Are They?

Enrico Fermi was a brilliant Italian physicist who is known to the public as the man who led the team that first harnessed nuclear power under Stagg Field in Chicago on December 2, 1942. His impact in physics was actually much broader than that, and he has been honored (among many other tributes) by posthumously lending his name to the Fermi National Accelerator Laboratory. America's preeminent laboratory for studying the basic building blocks of the universe. In addition to sheer brilliance, Fermi had a gift for trying to ge at the bottom line, using simple estimators. Physicists call “a Fermi Problem” a question that is easy to ask, hard to know definitively, but able to be estimated by thinking it through. The most repeated example of a Fermi Problem is “How many piano tuners are there in Chicago?” By knowing the number of people in the city and then estimating how many households have a piano, how long a piano holds its tune, how long it takes to tune a piano, and the length of a work week, you can come up with a reasonable estimated answer (current estimate, about 125).

Fermi lived in an elite academic world – an active mind surrounded by others of similar caliber. They would talk about all manner of things, looking at them from every angle, trying to get at the truth. From a casual lunchtime conversation, one of the most famous questions involving extraterrestrials was asked. The story goes something like this.

One summer day in 1950, Enrico Fermi was visiting the Los Alamos Laboratory, which had been the secret government facility at which much of the first nuclear weapons had been developed. He and three companions one of who was Edward Teller, were on their way to lunch. They were talking about a cartoon seen in the May 20 issue of The New Yorker, which explained a recent spate of thefts and trash cans in New York City as being perpetrated by Aliens taking them into their flying saucers. (The UFO mania of the late 1940s was still fresh in the public's mind). The conversation then meandered to Teller and Fermi bantering back and forth over the chances of mankind exceeding the speed of light in the next decade, with Teller suggesting a chance in a million and Fermi guessing 10%. During the stroll, the numbers changed as they intellectually fenced.

After sitting down to lunch, the conversation went in a different direction, with Fermi sitting there quietly. Fermi then suddenly burst out, saying “Where is everybody?” to general laughter, as they all instantly understood that he was talking about extraterrestrials.

The premise of Fermi's paradox is the following. The Milky Way is about 13 billion years old and contains between 200 and 400 billion stars. Our own sun is only a little over 4 billion years old, suggesting that there have been stars around for a very long time. If Aliens are common in the galaxy, there has been plenty of time for them to have evolved – perhaps hundreds of millions of years or more before humanity – and have visited Earth. So where are they?

To figure out what sorts of data are needed, it is helpful to have a guiding paradigm. Photo by Elena.

While Fermi's outburst in the origin of the paradox, the question was revisited in 1975 by Michael Hart (leading some to call this the Fermi-Hart Paradox). Hart published “An Explanation for the Absence of Extraterrestrial Life on Earth” in the Quarterly Journal of the Royal Astronomical Society. In this article, he explored some of the reasons why we hadn't contacted yet, from reasons of simple disinterest of the Aliens to either colonize the galaxy or to contact us to the idea that the Earth is being treated as a nature preserve. Perhaps some form of Star Trek's Prime Directive applies, whereby civilizations are not contacted until they develop the capability for interstellar travel. These kinds of explanations were offered in The Day the Earth Stood Still and, of course, Star Trek. What Hart was able to show was that technology wasn't the problem. Taking some simple assumptions, Hart showed that a civilization that sent out two craft traveling at 10% of the speed of light to nearby stars and then spent a few hundred years developing infrastructure to build another pair of slow-moving starships could completely populate the Milky Way in just a couple of millions years.

If intelligent extraterrestrial life is even slightly common in the galaxy and only a few species have mankind's curiosity and exploratory nature, it seems that we would know by now that we are not alone. Hard concluded that it was a distinct possibility that mankind might well be one of the earliest-developing intelligent species in the galaxy. In short, The X-Files tagline “We are not alone” could well be gravely incorrect.

Of course, the answer to the question is unknown and hence the reason why the term “paradox” is applied to it. Another Steven Webb explored the question in his delightful 2002 book If the Universe Is Teeming with Aliens, Where Is Everybody? Fifty Solutions to Fermi's Paradox and the Problem of Extraterrestrial Life. Peter Ward and Donald Brownlee's 2003 book Rare Earth: Why Complex Life Is Uncommon in the Universe is equally enjoyable, and this book takes the position that it is difficult for a planet to develop intelligent life. The book describes the many ways in which planetary disaster can interrupt the development of sentient life on a planet.

No matter how carefully thought out, arguments of the sorts advanced in these books and others like them must defer to data.

Given the fact that there are stars that are billion of years older than the sun, it seems impossible that we should not not have been visited before. Photo by Elena.