Where Are They? Why I hope the search for extraterrestrial life finds nothing. By Nick Bostrom

http://www.technologyreview.com/Infotech/20569/
Technology Review - Published by MIT
May/June 2008


People got very excited in 2004 when NASA's rover Opportunity discovered evidence that Mars had once been wet. Where there is water, there may be life. After more than 40 years of human exploration, culminating in the ongoing Mars Exploration Rover mission, scientists are planning still more missions to study the planet. The ­Phoenix, an interagency scientific probe led by the Lunar and Planetary Laboratory at the University of Arizona, is scheduled to land in late May on Mars's frigid northern arctic, where it will search for soils and ice that might be suitable for microbial life (see "Mission to Mars," November/December 2007). The next decade might see a Mars Sample Return mission, which would use robotic systems to collect samples of Martian rocks, soils, and atmosphere and return them to Earth. We could then analyze the samples to see if they contain any traces of life, whether extinct or still active...Such a discovery would be of tremendous scientific significance. What could be more fascinating than discovering life that had evolved entirely independently of life here on Earth? Many people would also find it heartening to learn that we are not entirely alone in this vast, cold cosmos...But I hope that our Mars probes discover nothing. It would be good news if we find Mars to be sterile. Dead rocks and lifeless sands would lift my spirit. Conversely, if we discovered traces of some simple, extinct life-form--some bacteria, some algae--it would be bad news. If we found fossils of something more advanced, perhaps something that looked like the remnants of a trilobite or even the skeleton of a small mammal, it would be very bad news. The more complex the life-form we found, the more depressing the news would be. I would find it interesting, certainly--but a bad omen for the future of the human race.

How do I arrive at this conclusion? I begin by reflecting on a well-known fact. UFO spotters, Raëlian cultists, and self-­certified alien abductees notwithstanding, humans have, to date, seen no sign of any extraterrestrial civilization. We have not received any visitors from space, nor have our radio telescopes detected any signals transmitted by any extraterrestrial civilization. The Search for Extra-Terrestrial Intelligence (SETI) has been going for nearly half a century, employing increasingly powerful telescopes and data-­mining techniques; so far, it has consistently corroborated the null hypothesis. As best we have been able to determine, the night sky is empty and silent. The question "Where are they?" is thus at least as pertinent today as it was when the physicist Enrico Fermi first posed it during a lunch discussion with some of his colleagues at the Los Alamos National Laboratory back in 1950.

Here is another fact: the observable universe contains on the order of 100 billion galaxies, and there are on the order of 100 billion stars in our galaxy alone. In the last couple of decades, we have learned that many of these stars have planets circling them; several hundred such "exoplanets" have been discovered to date. Most of these are gigantic, since it is very difficult to detect smaller exoplanets using current methods. (In most cases, the planets cannot be directly observed. Their existence is inferred from their gravitational influence on their parent suns, which wobble slightly when pulled toward large orbiting planets, or from slight fluctuations in luminosity when the planets partially eclipse their suns.) We have every reason to believe that the observable universe contains vast numbers of solar systems, including many with planets that are Earth-like, at least in the sense of having masses and temperatures similar to those of our own orb. We also know that many of these solar systems are older than ours.

From these two facts it follows that the evolutionary path to life-forms capable of space colonization leads through a "Great Filter," which can be thought of as a probability barrier. (I borrow this term from Robin Hanson, an economist at George Mason University.) The filter consists of one or more evolutionary transitions or steps that must be traversed at great odds in order for an Earth-like planet to produce a civilization capable of exploring distant solar systems. You start with billions and billions of potential germination points for life, and you end up with a sum total of zero extraterrestrial civilizations that we can observe. The Great Filter must therefore be sufficiently powerful--which is to say, passing the critical points must be sufficiently improbable--that even with many billions of rolls of the dice, one ends up with nothing: no aliens, no spacecraft, no signals. At least, none that we can detect in our neck of the woods....Now, just where might this Great Filter be located? There are two possibilities: It might be behind us, somewhere in our distant past. Or it might be ahead of us, somewhere in the decades, centuries, or millennia to come. Let us ponder these possibilities in turn...

. . . that very possibly refute his theory. First is that alien civilizations, if they exist, use radio waves or another form of technology for communication that our technology is able to detect. Second is that they have FTL capabilities to enable visitation. Third is that they'd give a rats ass about us. Fourth, is that even if they do give a rats ass about us, that they would want to reveal themselves to us, thus instantly changing the course of human history - e.g. A Prime Directive type practice as postulated in Star Trek.

maby not.. depends who you talk too.
In movie land, don't all, if not most alien's usually get killed by humans?

I thought we'd have a great intervention from friendly aliens who would come and save us from ourselves. Ah well.