Are we overlooking the universe's hidden 'noosignatures'? Astrobiology has long been divided between the search for 'biosignatures' and 'intelligence', but a new paper by Julia DeMarines bridges this gap. DeMarines introduces the concept of 'noosemiotics', a framework to detect 'noosignatures' - traces of intelligence on a medium. These noosignatures can be physical, like stone tools, or signal-based, like complex animal communication. The key is that they must be detectable as products of intelligence, even if we can't decipher their meaning. DeMarines proposes 'Assembly Theory' to measure the 'assembly index' of an object, indicating its complexity and the likelihood of it being created by a mind. Earth's tools, like the Lomekwian assemblage, pass this test. But noosignatures aren't just tools; agriculture, for instance, impacted Earth's nitrogen cycle, leaving a trace of intelligence thousands of years before radio dishes. This idea captures the worlds that developed intelligence but failed to sustain a cooperative civilization, leaving noosignatures as the only evidence of their existence. However, noosignatures decay over time and natural self-organization can be hard to distinguish from them. DeMarines acknowledges the newness of the concept and the need for further exploration. With the publication of 'Signs and Signatures of Intelligence', astrobiologists may start to view astrobiological signatures as a continuum, potentially leading to the discovery of planets with life in this middle category. This raises exciting possibilities for the field, but also highlights the need for more research and a broader perspective on the search for extraterrestrial intelligence.
