© 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.

6. Motivations for Molecular-Scale Machine Replicator Design

In 1959, Feynman [2182] proposed that we could arrange atoms in most of the ways permitted by physical law. Von Neumann [3] analyzed a few basic architectures for self-replicating systems in the 1940s and early 1950s, and several possible implementations of von Neumann’s kinematic replicators were described by Freitas and Gilbreath [2] in the context of macroscale space-based manufacturing systems during a NASA study in 1980 (Section 3.13). In the early 1980s, Drexler [197, 199] proposed the molecular assembler – a nanoscale device able to rearrange atoms and to self-replicate – and subsequently analyzed the fundamental technical issues involved [208]. Following these and other early efforts in replication theory [200, 201], the feasibility of building an artificial replicator and of molecular manufacturing has gradually come to be accepted although some still claim that artificial programmable self-replicating manufacturing systems that differ fundamentally from biological designs are impossible [13, 14, 3000]. These and other claims of impossibility [15, 202-206, 2310] are poorly supported [16, 17, 207]. After many decades of discussion and debate, no valid technical arguments against the feasibility of artificial replicators generally, or against the feasibility of molecular assemblers in particular, are known to the authors. By contrast, there are many proposals and analyses that support the feasibility of such systems.

While the absence of valid technical counterarguments is reassuring, existing design proposals have not been carried out in sufficient detail to permit construction, even if appropriate molecular tools were available. If we are to develop assemblers, a necessary first step is to fully specify at least some of the simpler members of this genre. The result of a successful molecular assembler design effort would include at least one specific comprehensive design (given, for example, as a series of atomic coordinates and chemical elements specifying the position and type of every atom in the assembler) and accompanying analyses showing the validity of the design with respect to various criteria – e.g., that the proposed structures are stable at the intended operating temperature, the positional devices are sufficiently stiff to provide accurate positioning of the molecular tools at the intended operating temperature, the reactions mediated by the molecular tools would work correctly [1], the structures/parts described in the design can be synthesized both by a proto-assembler and by the designed assembler itself, and so forth.

Last updated on 1 August 2005