What are the physics of life? That is more than just a philosophical question - it has practical implications for our search for life elsewhere in the galaxy. We know what Earth life looks like, on a number of levels, but finding it on another planet could require us to redefine what we even mean by life itself. A new paper from Stuart Bartlett of Cal Tech and his co-authors provides a new framework for how life could be defined that could reach beyond just what we understand from our one Pale Blue Dot.

According to their framework, life isn’t just chemical or thermodynamic - it’s informational. In particular, it involves processing what they call Semantic Information (SI). By their definition, SI is information that helps and organism survive - such as “don’t eat that red berry”. Syntactic Information, on the other hand, is just raw data and can be dismissed as “noise” by life without any consequence to its viability.

Viability is really one of the keys to understanding the framework. The authors define life as having an intrinsic, relatively simple goal - don’t die. On the other hand, something that has complex chemical and thermodynamic systems, such as a rock or a hurricane, has no such qualms about its demise. Life has to constantly monitoring it surroundings, in terms of its available food, the exterior temperature, and whether there are any toxins around. Those pieces of information are all SI - meaning they have a material impact on the viability of the life form. On the other hand, a rock doesn’t really care what toxins or food are round, nor what the temperature is.

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