It’s been a long standing bone of contention with anyone seriously considering alien civillisations… Do we broadcast our presence in hopes of meeting someone, or do we stay quiet in case we contact someone we’d rather not?
Alexander Zaitsev, of Moscow University has lately announced that the decision has already been made by us hapless astronomers, and it’s too late to prevent alien invaders. While the term “Hostile Super-Civillisation” in his paper’s title might seem a bit sensationalist, it has to be argued that he does have a point. 40 years worth of microwaves being transmitted to chart near Earth objects, traceable back to our planet, means that anyone within 40 light years might well have noticed us by now. If, as he claims, these radar signals give a million times the probability of being detected, then in fact, there could be quite a good chance of it.
40 light years, while actually quite small in astronomical terms, is quite a distance. The Alpha Centauri system is a little over 4 light years (ly) away, while Sirius is 8.5ly and Epsilon Eridani is a bit over 10ly. 85 Pegasi is about 40 ly away, and there are a lot of stars inbetween. It almost makes the vastness of space seem a little smaller, doesn’t it?
Of course, the probability of Earth-based signals being noticed by alien eyes is not a new concept to science. The San Marino scale, for instance, is a devised scale (not unlike the Beaufort or Richter scales) giving the probability of aliens picking up our signals. Ranging from ratings of 1 for insignificant to 10 for extraordinary, the scale weighs up what the signal is, how it’s directed, and how loud it is against background. For instance, the Sun provides so much electromagnetic background noise that Earth-based TV and radio stations (that staple diet of science fiction authors) would scarecly be strong enough to be detectable from the Moon, let alone from another star. The San Marino scale also considers the signal type. By this scale, a beacon or interplanetary radar, carrying no message rates a 1, and even a message to an extraterrestrial source that would otherwise not know we exist only rates a maximum of 5. No one can say who’s right or not at the moment, but without concerted effort to do so, it seems unlikely our technology is currently capable of sending a message that could be received across interstellar distances.
The biggest question is, what would the mentality of an alien race be like? The psychology of different species on Earth varies drastically, especially among the dominant species in any given biome. Dominant species can be entirely passive, not needing to defend themselves. They can be extremely aggressive. Some can and will swarm across entire countries given the right conditions, consuming everything in their path. Even bringing intelligence into the picture, human societies have throughout history, ranged from diplomatic and humanitarian to brutal and warlike. If Drake’s (frankly rather conservative) estimate for worlds containing civillisations is correct, there could be a lot of eyes out there watching the sky. Probability alone states that some might be predators or conquerors. Indeed, some might simply not have the concept that a given planet belongs to someone else. Enrico Fermi’s famous paradox of “where are they all?” might conceivably be explained by any civillisation broadcasting it’s presence being suddenly silenced. Personally, I’d prefer to believe that they simply haven’t had the time to find us yet, but scientifically, one must consider all the possiblities.
It’s all mere speculation at the moment, but if ever we do start advertising our planet’s whereabouts, we’d best be prepared to accept the consequences. If Darwin’s principle of “survival of the fittest” works on this planet, it’s a fairly safe bet it applies to all of the others out there too!