The question of life elsewhere in the universe has occupied mankind's thoughts for hundreds of years. The idea has only grown in the collective consciousness in the years since humans first stepped off this planet. Yet the question of life in the universe, versus that of intelligent life, draws the most heated debate. After all, knowing that there is another planet out there teeming with thousands of species of protozoa is not nearly as intriguing to the mind as knowing if there is life that we might make contact with. However, the question of life elsewhere in the universe is rather academic in light of the sheer size of the universe.
Ironically the question of contact with an alien civilization may have been settled as far back as the 1920's. It was then that astronomer Edwin Hubble first collected data that ultimately led to an approximation of the size and age of the universe. Hubble's measurements allowed astronomers to refine techniques used to measure stellar distances. Those distances turned out to be staggering.
The closest star system to our own, Proxima Centauri, is approximately 4.5 light years away. This seems a relatively small distance until one understands the distance a light year actually represents. The speed of light is 186,000 miles/second. This means that in the course of one year light travels a distance equaling roughly 6 trillion miles; that is a six with 12 zeros after it. A little simple arithmetic tells us that Proxima Centauri is 24 trillion miles away; and this is the closest star. Certainly this form o f notation is too cumbersome for stars further away.
Yet distance does not in any way preclude the possibility of extra solar planets. In the last ten to fifteen years astronomers have discovered over 100 extra solar planets. Many of these are gigantic worlds like Jupiter, but to date our technology is not quite good enough to detect smaller, Earth-like planets. In decades to come it is possible that a means will be found to detect smaller planets. Then the hunt will be on for planets that are not only small enough, but also are at the right distance to support liquid water, a pre-requisite for life as we know it.
If astronomers do discover a distant planet capable of supporting liquid water, what are the odds that that planet will have life? The answer to that question was first proposed by astronomer Frank Drake in 1960. The equation itself is expressed as:
N = R* x f(p) x n(e) x f(l) x f(i) x f(c) x L
In this theoretical equation, N is the number of civilizations in our galaxy that we might be able to communicate with. R* is the rate of star birth; f(p) is the number of those stars with planets; n(e) is the number of planets that could support life; f(l) is the number of those planets that actually develop life; f(i) is the number of those planets that develop intelligent life; f(c) is the fraction of civilizations that develop technology capable of sending signs into space and L is the length of time that civilization sends signals out into space. Obviously this equation is only a construct and no true value can be expressed for any of the arguments. However, based simply on the rate of star birth in our galaxy (about 10 per year) the chances of there being another technologically advanced civilization in our galaxy are pretty good.
Despite the compelling nature of Drake's equation, the limiting factor always comes back to distance. For example, if astronomers discovered an earth like planet around a star merely 10 light years away, and if that planet was deemed capable of supporting intelligent life, any electronic message will take 10 years to get there. If there is anyone there who is listening and capable (or willing) to respond, their response will take 10 years to arrive back on Earth.
The question then arises regarding an actual visit from the civilization orbiting that star. Here another equation enters the play; Albert Einstein's famous E = mc2. According to Einstein, as the velocity of an object approaches the speed of light, its mass increases toward infinity. Consequently traveling at the speed of light is impossible for anything except light itself. Certainly this puts the idea of a visit from an alien race in doubt.
Is there life elsewhere in the universe? Probability alone suggest the answer is a resounding yes. Given the vast variety of life that has inhabited the Earth during its 4 billion year history it is not unreasonable to assume that the universe is teeming with life, some of it even more advanced than our own. However the great vastness of the universe seems specifically geared to keeping such life far apart. Yet distance does not necessarily mean isolation. As a great astronomer once said, "if it is only us in the universe, it seems an awful waste of space".