Are we alone?

According to a recent scientific analysis, the answer to this burning question is… maybe. Astrophysicists David Spiegel and Edwin Turner, have determined, using statistical methods, that the probability of life arising on another planet similar to Earth can not currently be estimated. That is, the fact that life appeared very early in the history of our own planet doesn’t necessarily mean anything at all about how likely it is to exist on some other world.

On the other hand, Andrei Finkelstein recently predicted at a press conference that astronomers would detect signals from an extraterrestrial civilization within 20 years. Although I can’t find any direct information about the reasoning behind Finkelstein’s assertion, he appears to be using the same numbers Seth Shostak had previously proposed for the famous Drake Equation.

The Drake Equation, of course, is one of the better known examples of a SWAG (Scientific Wild-Ass Guess). Most of the factors are completely unknown. At present, we obviously have only a single example of a planet with life, of life evolving to intelligence, and of intelligence developing the technology to transmit electromagnetic (i.e. radio) signals. And for the last factor in the equation, the length of time that a technological civilization continues to exist and to be detectable by radio (usually designated “L”), we have no examples whatsoever, since our own society has clearly not yet reached that limit.

Shostak’s own guess, which he gives in The Value of “L” and the Cosmic Bottleneck (included in Cosmos & Culture: Cultural Evolution in a Cosmic Context) is that the average lifespan of technological civilizations is somewhat greater than 1,000,000 years. Multiplying this by the values he assigns to the other factors in the Drake Equation, he concludes that there are around 10,000 such civilizations in the galaxy at the present time, which is the same number Finkelstein uses.

If there really are 10,000 planets with technological civilizations in this galaxy, then Finkelstein is probably right about the likelihood of detecting one of them within the next 20 years. If, on the other hand, there are only 2 such worlds (the result that one obtains by assuming that L is 200 years, and continuing to use Shostak’s estimates for each of the other factors) it is extremely unlikely that we will detect the other one before our own civilization is finished. Personally, I’d like to believe that L is very large. But as an archaeologist, I can’t find even the slightest reason to think that it’s anywhere near 1,000,000 years.

One interesting thought does occurs to me, though. Archaeologists know of the existence of a large number of human societies that no longer exist, in the sense that they have no identifiable descendant culture. In each case, we know of their existence because they left behind physical evidence that can be detected and interpreted. In fact, any society that significantly modifies their environment in a patterned way, or that utilizes durable materials to make tools and other objects, is likely to leave behind some evidence of their existence and activities. That being the case, even if we never make contact with a living extraterrestrial civilization, we may someday find out about their existence and at least some of their achievements. Equally, somebody that we are destined never to meet might someday learn about us in the same way.

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