Just for a few minutes forget the war in Iraq, suicide bombings, WMDs (or lack of them), the threat of pandemic, where the Dow is headed, crazy shoppers at the mall and the daily Theater of the Absurd that is American politics. Go outside on a dark crystal clear winter's night (drive out into the country if you have to) and look up. Take a long deep breath, feast your eyes on the millions of stars in the Milky Way and ask yourself, "Are We Alone in the Universe?"
As you are contemplating the ultimate question, here are a few things to ponder.
We live about four-fifths of the way out from the center of an average galaxy of about two hundred billion stars in the 'Goldilocks Zone' (not too hot, not too cold, just right) of a standard, mature, stable, well-behaved spectral class dG2 star. Things have been kind of quiet in our neck of the woods of late. That hasn't always been the case and it is certain to change...eventually. But for now we can feel lucky we evolved over a period of relative calm.
Recent scientific discoveries indicate the Universe is approximately 15 billion years old. Scientists estimate there are about one hundred quintillion solar systems in the Universe. That's the number 1 followed by 20 zeros. If solar systems form roughly uniformly in time, at least one million solar systems are born in the Universe every hour. Even if the relative chances of intelligent life are extremely low, the sheer numbers involved suggest the Universe should be teeming with intelligent life.
In the early 1960s, the astronomer Frank Drake wrote an equation to estimate the number of extraterrestrial civilizations in our galaxy with which we might be able to communicate. The various terms of the equation represent the best estimates of things like star formation in the galaxy, the fraction of stars with planets, the number of planets per star that could support life, the fraction of that number that develop life, the fraction of those that develop intelligent life and so on and so forth. The math isn't important. It's the final two terms of the equation that are the most interesting: the fraction of existing intelligent civilizations willing and also capable of communicating and, of course, the expected lifetime of such civilizations.
We have been an intelligent civilization for thousands of years but only developed the capability to communicate across the cosmos in the last eighty years. One of the earliest estimates of the Drake Equation assumed only 1% of intelligent civilizations would be both willing and able to communicate. The expected lifetime of an intelligent civilization (after developing the technology to communicate) was estimated to be only 10 years! Remember, this was at the height of the Cold War. Mutually Asssured Destruction (MAD) by nuclear Armageddon was the pervaisive military ideology of the day. One of the initial Drake Equation estimates of the number of intelligent civilizations in the galaxy with which we might be able to communicate was a meager 0.01.
Why so low? We already know there is at least one species in the galaxy capable of interstellar communication - - us! If there is one civilization that can do it, shouldn't the chances of at least two or three be pretty good? After all, our FM band and television transmissions have been promulgating across the galaxy like ripples in a pond since the 1920s. [It's sobering to realize the televised opening ceremonies of the 1936 "Nazi Olympics" in Berlin featuring a triumphant entrance by Adolph Hitler has overtaken 200 of the nearest stars and is now 68 light years from Earth].
Carl Sagan, a young astronomer at Cornell University, completed an exhaustive analysis of the Drake Equation. He found the most influential term of the equation was the expected lifetime of advanced civilizations. Sagan postulated the values for the other terms of the equation should be relatively high. By tweaking the expected lifetimes of advanced civilizations by just a few hundred years the potential number of civilizations in the galaxy with which we might communicate greatly increased. In other words, the prime determining factor in the number of civilizations in the universe is the ability of technologically advanced civilizations to avoid self-destruction. Sagan was so influenced by this realization he devoted a good portion of his professional life as well as his credibility to the study and subsequent popularization of the devastating effects of "nuclear winter" and other potentially catestrophic ways we could do ourselves in. Using the Drake Equation, Sagan estimated there could well be over a thousand intelligent civilizations in our home galaxy alone.
How have the very latest discoveries in astronomy influenced the Drake Equation? In the last decade, there has been a revolution in the sciences of astronomy and cosmology. Space-based assets like the Hubble and Spitzer telescopes as well as quantum improvements in ground-based imaging have transformed our perceptions of the Universe. The bottom line is both good news and bad news. The good news, if earth is any example, is where conditions are favorable, life seems to find a way. The bad news is that in addition to being almost inconceivably vast, the Universe is a place of unimaginable violence. A violent Universe is not conducive to life forms such as us. The recipe for intelligent species calls for long simmer times. It is becoming increasingly clear that life as we know it requires a whole complex series of very low probability events to emerge, evolve, and flourish.
Are we alone in the Universe?
No one really knows. The final verdict isn't in yet. Either way the implications are staggering.