To explain life, we therefore need to understand how the complex objects life creates exist in time. With my collaborators, we have been doing just that in a newly proposed theory of physics called assembly theory.
A key conjecture of assembly theory is that, as objects become more complex, the number of unique parts that make it up increases, and so does the need for local memory to store how to assemble the object from its unique parts. We quantify this in assembly theory as the shortest number of physical steps to build an object from its elementary building blocks, called the assembly index.
Importantly, assembly theory treats this shortest path as an intrinsic property of the object, and indeed we have shown how assembly index can be measured for molecules using several different measuring techniques including mass spectrometry (an analytical method to measure the mass-to-charge ratio of molecules).
With this approach, we have shown in the lab, with measurements on both biological and non-biological samples, how molecules with an assembly index above 15 steps are only found in living samples.