In the vast expanse of the cosmos, the search for extraterrestrial life has long been divided into two distinct camps: the quest for biosignatures and the search for technosignatures. But what lies between these two extremes, the missing middle ground, has remained largely unexplored. This is where the groundbreaking work of astrobiologist Julia DeMarines comes in, as she introduces the concept of noosignatures and the empirical research framework of noosemiotics. DeMarines' innovative approach aims to bridge the gap between the search for biological and technological signatures, offering a new lens through which we can explore the evolution of intelligence in the universe.
The concept of noosignatures is simple yet profound: it refers to the structured traces that a mind leaves on a medium, whether physical or signal-based. These traces are the remnants of cognitive activity, such as stone tools or complex animal communication, and they serve as evidence of intelligence. But what sets noosignatures apart is their detectability, even if we cannot decipher their meaning. This is where Assembly Theory comes into play, a new idea that measures the 'assembly index' of an object, or the number of joining operations required to construct it from basic elemental components. If an object has an assembly index above a certain threshold, it cannot simply arise by random chance; it requires a mind to make it.
The implications of this concept are far-reaching. DeMarines points out that agriculture, for example, significantly impacted Earth's nitrogen cycle around 8,000 years ago, leaving a detectable trace of intelligence behind thousands of years before we ever invented a radio dish. This raises a deeper question: what if intelligent life exists in the universe, but its intelligence fails to solve the coordination problem to sustain a moderately cooperative planetary civilization? In this case, a noosignature might be the only evidence that intelligence existed on a given world at all.
However, the concept of noosignatures is still very new and has a lot of kinks to work out. Information requires a physical substrate to persist long enough for our telescopes to be able to detect it, and natural self-organization can be hard to distinguish from noosignatures. Assembly Theory is still in its infancy when dealing with macroscale archaeological structures, and relatively few scientists have explored this problem. But with the publication of 'Signs and Signatures of Intelligence', astrobiologists may start to see astrobiological signatures as more of a continuum rather than a graph with two distinct peaks.
In my opinion, the concept of noosignatures is a fascinating and innovative approach to the search for extraterrestrial life. It offers a new perspective on the evolution of intelligence in the universe and raises important questions about the nature of intelligence itself. As we continue to explore the cosmos, the search for noosignatures may just be the key to unlocking the secrets of the universe's missing middle ground.
