Are We Alone? - SETI and the Drake Equation Seek Extraterrestrial Intelligence

The SETI Institute and the Drake Equation both seek to answer the fundamental question "are we alone in the universe" or "is there extraterrestrial intelligence?" From the moment we leave the womb, we seek out someone to whom we can connect. A newborn's attention is immediately and instinctively drawn to the faces of those around it. When my son was born, I recall vividly how, as soon as my wife was allowed to hold him, he stared intently at her face, and then at mine. Back and forth between the two of us, his gaze went as if memorizing our two faces were the most important thing in the world. We do not outgrow the need to connect with others. Making friends, joining groups, and becoming a part of society is all related to that first basic instinct. As a civilization we collectively have the same drives as the individual. We want to know who's out there.

Conditions Exist for Extraterrestrial Life
From the evidence of our own solar system, we see that the conditions for the existence of life are widespread. Mars and some of the moons of the gas giant planets Saturn and Jupiter are very good candidates to house or to have housed extraterrestrial life of some sort. However, that life, if it exists at all, may be microbial in nature, and is hardy the answer that we seek when we ask "are we alone?" It is intelligent life that we seek, someone enough like us that we can communicate with them.

The Search for Extraterrestrial Intelligence (SETI)
The Search for Extraterrestrial Intelligence (SETI) Institute seeks to answer that question by examining in great detail all the noise coming from various stars gathered with a huge array of radio telescopes. They analyze each stream of radio noise and look for narrow band signals that are more typical of artificial transmitters. While natural processes generate wide spectrum radio noise, SETI says they look for signals that are "only a few Hertz or less wide." The SETI Institute has been searching for signs of extraterrestrial life since 1985. To date they have found no signals that represent any credible evidence of extraterrestrial intelligence.

The Drake Equation
Professor Emeritus Frank Drake of the University of California, Santa Cruz, sought to determine the likely number of planets harboring intelligent life capable of sending out detectable signs of life from their planet into space mathematically. Toward that end, he developed what is known as the Drake Equation. The Drake equation looks at the total number of stars in the Milky Way Galaxy and multiplies by a number of variables to determine the number of planets that should have such intelligent races at any given era. The difficulty with the equation is that we don't know what numbers should be plugged into most of the variable place-holders.

The Drake Equation Predicts Extraterrestrial Life
The Drake Equation as explained by the PBS series Nova is this: N = R* X f_p X n_e X f_l X f_i X f_c X L. While that may look daunting, it is simple multiplication if you know which number is represented by each of the variables. First, we must know what each variable represents. N is the solution or the number of planets harboring intelligent life capable of making its presence known through space. R is the rate at which new stars are formed in the Milky Way expressed as number of new stars per year. The variable f_p is the percentage of stars that form planets. The average number of planets per star that could support life is n_e. Next, f_l represents the percentage of those planets that actually do develop life. The percentage of those life-bearing planets which develop intelligent life is f_i. The percentage of intelligent civilizations that create equipment that can send signal out from their home planet is f_c. Finally, L represents the number of years that a civilization might exist at that level.

How Many Planets are in the Milky Way?
As you can see, most of these numbers would be wild guesses if we were to try to calculate the result of this equation, but we do have some numbers. NASA says that 7 new stars are generated each year in the Milky Way. That gives us a solid, fact-based value for R. The percentage of stars that form planets is likely to be a very high number. Already, NASA counts 422 extrasolar planets orbiting 355 stars. Our ability to detect these extrasolar planets is still quite limited, so we are undoubtedly missing a great many even from our closer stellar neighbors. PBS's NOVA says that numbers between 10-50% are used for this figure based on the best available evidence, but this is still largely conjecture.

Life-bearing Planets in our Galaxy
If we try to determine the value for n_e, we run into the fact that we do not have the resolution in our current instruments to detect any potential life-bearing planets outside of our own solar system. However, our own solar system has as many as four or more planetary bodies or large moons capable of supporting life. Estimates range from .5 to 3 according to NOVA. The percentage of potential life-bearing planets that actually do develop life is a complete mystery and all we can do is guess at f_l. Likewise for f_i and f_c, the percentage of life-bearing planets that go on to develop intelligent life and the percentage of those that can create extra-planetary signals. L, the number of years that a communicating civilization might exist, is conjecture as well. We have had that capability for perhaps 120 years at the most. How long will we survive? Your guess is as good as anyone's.

The Drake Equation Answer
So let's look at the numbers we do have and plug in reasonable guesses for the rest to see what the Drake Equation says. N = 7 X .30 X 1 X .25 X .05 X .5 X 10,000. The net result is N = 131 civilizations, on average, that could send radio signals outward from their planet, exist at any given time. Of course, if you use different assumptions or guesses for any of the variables the result can go either up or down.

130 Needles in 64,000 Undecillion Haystacks
NASA'sEric Christian and Samar Safi-Harb tell us that the Milky Way is 100,000 light years in diameter and about 1000 light years thick. That's well over 314 million cubic light years of space in which to hide 131 active civilizations, assuming our guesses for the variables are anywhere near accurate. A light year, remember, is the amount of distance that light can travel in one earth year, or about 5.9 trillion miles. Imagine trying to find even one of 130 planets (excluding our own) scattered randomly within about 64.5 thousand undecillion cubic miles of deep space. That's a number so big that most people have never even heard of undecillion. An undecillion is a 1 followed by 64 zeroes.

Conclusion: Are We Alone?
Even though we can search great swaths of space with radio telescopes and the technology is improving all the time, the odds of finding one of these radio-capable extraterrestrial civilizations is minuscule. While we may very well one day discover extraterrestrial life, perhaps even right here in our own solar system, we will almost certainly never discover intelligent extraterrestrial life. Are we alone? Even though hundreds of extraterrestrial civilizations may exist right now, the answer is effectively yes, we are alone.

Sources:

www.pbs.org/wgbh/nova/origins/drak-flash.html

imagine.gsfc.nasa.gov/docs/ask_astro/answers/980317b.html

www.pbs.org/wgbh/nova/origins/drake.html

www.seti.org/Page.aspx?pid=1366

planetquest.jpl.nasa.gov/

www.nasa.gov/centers/goddard/news/topstory/2006/milkyway_seven.html