Kinematic Self-Replicating Machines
© 2004 Robert A. Freitas Jr. and Ralph C. Merkle. All Rights Reserved.
Robert A. Freitas Jr., Ralph C. Merkle, Kinematic Self-Replicating Machines, Landes Bioscience, Georgetown, TX, 2004.
2.3.6 Nonautonomous Machine Replication
Machines can also replicate their physical structure without containing their own description if the instructions are fed to them, one by one, from some outside source without the machine having any onboard capacity for computation or even data storage. One simple example of this strategy is the broadcast architecture [208-210]. In this approach (see also Section 188.8.131.52), information is broadcast by any of various means to the replicating component. The physical replicator becomes, in essence, a remote-controlled or “teleoperated” manipulator receiving external instructions that guide it, step by step, in assembling a second remote-controlled manipulator. After some number of repeat cycles, the result is a large number of identical remote-controlled manipulators which can then be employed to manufacture large numbers of useful product objects by altering the stream of instructions sent to the population of replicated manipulator devices.
This architecture was partially anticipated by Laing , who discussed the implementation of a free-floating automaton system with activation signals transmitted diffusively through fluid in a biological context, and by Holland , who offered a carefully worked out formalism for such “broadcast” communication automaton systems. Laing  notes that as a general design principle, “we can dispense with some of the structural complexity of our artificial organisms provided we compensate by increasing the number or the functional complexity of the signal types....By augmentation of signal complexity, we [can] overcome degradation of physical structure and obtain the desired result.” Thus Laing disposed of the requirement for logical universality to achieve self-replication, much as Langton had earlier disposed of the requirement for constructional universality (Section 2.2.1).
Other examples of nonautonomous kinematic machine replication are the “exponential assembly” scheme proposed by Skidmore et al  (Section 4.17) and the electrophoretic system for stepwise exponential growth of DNA-based chemical replicators proposed by von Kiedrowski’s group [1362, 1428, 1429].
Last updated on 1 August 2005