© 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.

2.3.3 Thatcher's Variant: Inferring Structure

Thatcher [565] showed that a machine need not have an explicit construction program made available to it initially in order to create a duplicate of itself. First, it is sufficient that a machine can secure a description of itself (in place of instructions) if the machine is equipped with the capacity to read the description and convert this into the necessary constructive actions. Second, Thatcher showed that such a machine need not have its description loaded beforehand into its accessible memory organ. Instead, the machine has a partial self-description hard-wired into itself in the form of circuits which, when stimulated, make the description available to the machine in its accessible memory organ. These data describe all of the machine except the hardwired part which was stimulated to emit the description in the first place. The problem then, for the machine, is to obtain the description of this hidden part of itself. Lee [566] and Thatcher [567] showed that this section of the device can be constructed in such a simple fashion that the system can infer how this part must have been constructed merely by examining the consequences of its actions (e.g., the partial description that it produced). After inferring the nature of this hidden part of itself, the machine possesses a complete self description and can then follow von Neumann’s paradigm for replication.

The principal practical significance of this result is to remind the designer that the information required for machine construction (whether replication or otherwise) need not be in the form of instructions for constructions but can instead be in the form of a description. Moreover, the description need not even reside in an accessible organ such as memory registers but may be embedded in “inaccessible” hardware. The hypothetical infinite regress (Chapter 1) likewise is shown to be baseless – it is possible for a machine to have within itself only a part of its own description, and from this to infer the rest. However, there may be an elevated risk of evolvability using this scheme.

Case [568] offers the metaphor of a transparent self-replicating robot that examines itself in a mirror, writes down its own description on a blackboard from what it sees in the mirror, and then uses the description written on the blackboard to build a copy of itself. Explains Case: “Note that the robot’s self copy is projected externally to the robot itself. In this way infinite regress is not required for the robot to have complete (low level) self-knowledge.” Others have also examined the issue of machine self-reference [569-571].

Last updated on 1 August 2005