1.2 Definitions of Life Summary

summary

We do not currently have a systematic way to quantify whether or not something is “alive,” making it difficult to know what to look for on other worlds. Said differently, we need to be able to recognize life when we see it.
Various definitions for life have been proposed, including heredity, metabolism, compartmentalization, and evolution. However, they are largely insufficient, as they do not encompass everything we consider to be “life.”
Physicist Erwin Schrödinger speculated that the basis of life would share the same physical properties that an information-propagating structure must satisfy.
As a way to theorize life rather than define it, philosopher of science Carol Cleland raised the analogy between understanding life today and the questions scientists posed about the properties of water before atomic theory was fully understood.
After atomic theory, our perception of water changed from knowing it as a clear liquid to understanding it as a molecule composed of two hydrogen atoms and one oxygen atom. Groups of these molecules then give rise to “emergent” properties, such as viscosity and surface tension, which underlie how humans know and experience liquid water on an everyday basis.
“The Hard Problem of Life” states there are some physical systems that can use information to change their own dynamics.