요약: SETI 연구소의 Lawrence Doyle은 정보이론을 기반으로 해서 신호의 의미를 알 수 없는 경우에도 어떻게 고래의 음성 신호 속의 문법 및 신호의 엔트로피를 유도할 수 있는지를 설명하였다.
과학자들은 아직 고래의 언어의 엔트로피가 인간의 것과 가까운지 어떤지에 대해서 아직 잘 모른다. 하지만 그는 고래의 언어와 고래의 사회성 사이의 상관관계를 보면 외계 지성의 사회성에 대해서 어떤 것을 추론할 수 있을 것이라 주장한다.
그러나 얼마전에 SETI연구소에서는 지적설계에 대한 연관성을 부인하면서 SETI에서는 메시지가 들어 있는 정보는 찾지 않으며 단지 비자연적인 것으로 주장할 수 있는 협대역의 호각소리 같은 신호만을 찾는다고 주장하였다. 하지만 이번에는 지성에 대한 추론을 넘어서 사회성에 대한 추론까지 주장하고 있다.
A Whale of a SETI Tale 01/31/2006
Disney’s Fantasia 2000 had an episode that pictured whales gliding through the air as if in outer space. Lawrence Doyle of the SETI Institute connected whales with space in another way. His article discussed whale language as a sign of intelligence. Appealing to information theory and entropy, Doyle discussed how scientists deduce the syntax and entropy of whale messages, even when we can’t figure out the meaning. By entropy, he means the “number of choices in a given communication system.” For instance, squirrel-monkey language does not have enough entropy for Shakespeare to be translated into it.
An important measure of entropy is the highest “entropic-order” at which the communication systems peaks. In measuring this, we ask how dependent the signals are on each other. In human speech we have grammar and in human writing we have spelling (or brush strokes, etc.) that depend on each other. If you made a copy of a written page, but the toner in the copy machine was low, you would find that you could nevertheless recover some of the missing words because there are rules of spelling and grammar superimposed on our language system. It is these rules that allow error recovery – and this works in both vocalization as well as written communication systems (as well as any others, e.g., chemical signaling units, bee dances, visual facial features, etc.) (Emphasis added in all quotes.)
Scientists are not yet sure if whale language has the entropy level anywhere near that of humans. But he argued that observing correlations between language and sociality of whales can help us, when we find life in space, deduce something about the social structure of the aliens:
And how might this apply to the search for extraterrestrial intelligence? If there is a relationship between social complexity and vocal complexity, then the measure of one will be a measurement, to some degree, of the other. If a SETI signal is received, and is a normal (i.e., un-coded) communication, it will have to obey the rules of information theory in order to transmit information. Thus, a measure of the information complexity of such SETI signals could also be a first direct measurement of the social complexity of an extraterrestrial species, irrespective of the actual decipherment of the meaning of such a message itself. Exciting prospect indeed!
Until such a signal is detected, however, it remains only a prospect for the space-intelligence prospectors.
Wait a minute. We heard Seth Shostak say last month (12/03/2005) that SETI wasn’t looking for an information-bearing message, like the proponents of intelligent design claim, but only for a persistent narrowband whistle in an unusual context that they could claim was non-natural. What’s all this talk about information theory? Now the SETI institute is going even beyond the inference to intelligence to an inference about social complexity. That’s a lot of inference from a persistent narrowband whistle. Is it not more credible to infer an intelligent cause for a language with sufficient entropy to generate tens of thousands of precision protein machines, like DNA?