In the middle of the 20^th century a physicist named Enrico Fermi posited the question, “Where are they?” in reference to extraterrestrial life. The age of the universe (calculated to be 13 billion years) and the great number of stars (estimated to be between 100 and 250 billion in the Milky Way alone) would imply that the universe should be teeming with life, and yet we haven’t received any confirmation of this. That apparent disconnect between what seems altogether likely, that there should be numerous technological civilizations laced throughout the universe, and that which is evident is the foundation of what has come to be known as The Fermi Paradox. Since that initial question was posed, physicists, biologists, and other scientists have been attempting to provide their own solutions to this conundrum. There are two primary schools of thought that have developed in response to this scenario. There are those who suspect that extraterrestrial life is out there, that we haven’t been looking hard or long enough, and that it’s only a matter of time before we find them (or they find us); and there are those who suspect that life is an exceedingly rare thing, and that we are unlikely ever to discover (or be discovered by) any life beyond the boundaries of this planet. There are only two ways to solve this debate, either we discover (or are discovered by) extraterrestrial intelligence or we spread throughout the whole of our own galaxy and use a process of elimination to rule out that there is or has been life around another star. So far we are doing our best to work towards that first potential solution, but we still have a long way to go.

Many problems arise when it comes to the search for extraterrestrial intelligence, not the least of which being scale and time. According to recent research performed by physicist Rasmus Bjork of the Niels Bohr Institute, current calculations indicate that it would take approximately 10 billion years for a civilization to explore less than 1% of the galaxy, traveling at a tenth of the speed of light., so even if we could receive signals from another intelligent civilization the likelihood is small that we could ever reach them. Regardless of this daunting realization we do have multiple programs in place which are engineered specifically for the purpose of scanning the galaxy for any trace of life that might be there to be discovered.

The first of these programs is known as SETI (Search for Extraterrestrial Intelligence), established in 1960 by Frank D. Drake, who believed that water bearing planets were common in our galaxy. Presently SETI consists of a series of radio telescopes tuning into the frequencies emanating from space, in search of any kind of discernable signal that could be intelligent in origin. In an article by Erik Skindrud it is stated,

Recent discoveries have confirmed many of Drake’s assumptions. Within the past year, astronomers discovered several planets that orbit other stars. Scientists have found complex organic molecules floating in interstellar space. And NASA stunned the world with evidence that primitive life may have existed on Mars several billion years ago. (Skindrud 152)

Where signals from other intelligent life is concerned, we have yet to meet with any success, but that lack of success doesn’t dissuade individuals like Dr. Geoffrey Landis of the Ohio Aerospace Institute, “One likely reason we have not yet detected extraterrestrial civilizations by radio is that SETI searches are likely simply listening at the wrong range of frequencies” (Landis 163). Landis further speculates “It is also possible that a civilization interested in communicating across interstellar distances would not use high beamspread techniques like radio at all, but would use much shorter wavelength and hence more directed means” (Landis 163). It seems that he hasn’t been able to determine any solution to this primary problem standing in the way of SETI being ultimately effective beyond methods that would be extreme in nature,

Unless the antenna size is unrealistically large (thousands of kilometers), across interstellar distances the overwhelming majority of any signal sent by radio will be broadcast to the empty space between the stars. (Landis 163)

Cost effectiveness comes into play heavily when it comes to the methods we are capable of employing in our search.

Another of the programs that we have in place is the Terrestrial PlanetFinder, and the earlier (and admittedly, less advanced) incarnations of this same search for planetary bodies orbiting other stars. According to Alan Longstaff with the Royal Observatory Greenwich in London, “Over 120 extrasolar planets have been found orbiting 105 stars” (Longstaff 28). But finding planets is only a portion of the problem, the vast majority of the planets we are discovering are of the gas giant classification, and those are not (to the best of our current knowledge) capable of supporting intelligent life. But there is hope, according to Longstaff, “If a growing planetary system retains enough dust for the much slower building of terrestrial planets, then about half the known extrasolar systems could form Earth-mass planets in their habitable zones” (Longstaff 28).  The key, Longstaff urges, is that we look for subtle signs of life when we do finally begin examining rocky planets, that what we’re looking for are

tantalizing spectral lines of biomolecules in the light from a distant earthlike world, or structures within rocks from another planet that are not of obvious geological (or even biological) origin. When we discover any such evidence — actually, long before we reach that point — we’re going to need a working definition of what life is and how we’ll recognize it. (Longstaff 28)

Longstaff brings up an interesting point in that statement regarding our capacity to recognize life for what it is when we may have an unintentional bias towards the specific types of life that we are familiar with here on Earth. This issue is definitely one that we will need to address in great detail when it comes time to analyze potential life-bearing planets, and is one that the burgeoning field of astrobiology is taking steps to categorize.

Now that the two major programs relating to the search for extraterrestrial life have been introduced it is time to discuss where we should be looking. The subject of habitability is a major issue in our speculations regarding alien life. Assuming that we are looking for life similar to our own, we do have a rough approximation of the conditions required to produce and support that life. According to Margaret Turnbull,

Part of the search for living worlds beyond the solar system involves the idea of a habitable zone around each star. This is a region where the temperature is right for the presence of liquid water on an earthlike planet. (Turnbull 58)

This particular region of orbit around the parent star is reasonably well understood, the problem with habitability is not so much one of distance but one of time.

The first requirement — habitability over billions of years — puts strict constraints on several stellar parameters that are easily observed. Young stars are not the best places to look. Not only has life had less time to develop, but, for the first billion years or so, asteroids and comets bombard the system, frustrating life’s efforts to survive. It turns out that stars — like adolescents entering adulthood — go through a significant decrease in flaring and other chromospheric activity after an age of 3 billion years. The Sun is one such example of a star that significantly decreased its flaring activity at an age of 3 billion years. Whether this newfound calm helps life form is unclear, but, at the very least, this lets us identify and rule out the youngest stars from our searches. (Turnbull 58)

The issue of habitability isn’t isolated to the scale of a solar system however, as it has been speculated that there is a specific area of our galaxy that could be categorized as the galactic habitability belt, where the stellar bodies are far enough apart from one another that there isn’t a constant bombardment of radiation that would be deadly to life as we know it.

Ultimately I am a believer. I happen to feel that there is life out there beyond the bounds of both our planet and our imaginations and I feel that it is simply a matter of time before we find what we are looking for. Whether this discovery will happen within my lifetime is relatively unimportant in contrast to the sheer importance of the discovery itself. I do sometimes find myself wondering the same thing that Fermi did back in 1950, but I’m patient enough to accept that it will take time before I know the answer to that important question, “Where are they?”