Together with the chemist Lee Cronin of the University of Glasgow, Sara Walker of Arizona State University has devised an alternative set of ideas to describe how complexity arises, called assembly theory. In place of functional information, assembly theory relies on a number called the assembly index, which measures the minimum number of steps required to make an object from its constituent ingredients. I would love to see an example, but I remain skeptical until some metrology is done in this area.”Hazen acknowledges that, for most physical objects, it is impossible to calculate functional information even in principle. (Assembly theory similarly predicts complexity-based biosignatures.) “People are approaching us because they are desperate to find a model to explain their system,” Hazen said.