Self-Reproducing Machines: Preventing Degeneracy

SUMMARY AND CONCLUSIONS A model of a self-reproducing machine was constructed. The machine consisted of a simple robot arm, capable of assembling a replica of itself. This machine was simulated, to analyze the sustainability of the self-replication process. The model exhibited a gradual degeneration of the machine over the progression of generations, eventually failing and resulting in a terminal generation not capable of self-reproducing. The degeneration of the machine was caused by the accumulation of errors in the self-reproduction process over several generations. This result is representative of the archetypal failure mode of human-engineered self-reproducing machines. It was then shown that this self-reproducing machine could be made sustainable by the application of error-correction to the self-reproduction process. This error-correction augmentation created a new self-reproducing machine. Not only could this new machine self-reproduce, but the machine error also converged to zero. A quantization of the feedback control signal was used to determine the minimal amount of error-correction needed to make the self-reproduction process sustainable. It was found that with a relatively low amount of error-correction, the process could be made sustainable. With a higher amount of error-correction, the self-reproduction process mimicked the fully error-corrected system. It was shown that the behavior observed in the three cases above was predicted by a generation theory analysis of this model. The application of this theory suggested that the original machine would be unsustainable, the fully error-corrected machine would be sustainable, and the partially error-corrected machine would be sustainable above a minimal amount of error-correction. The von Neumann thresholds of information of the machines were infinity, zero, and either infinity or zero, depending on the error-correction regime, respectively. Adding an error-correction mechanism to the self-reproduction process of a machine is clearly a successful strategy for preventing the machine from degenerating to sterility. This might mean that the machine becomes more complex internally, but such a caveat would allow the design of an autonomous machine capable of self-reproducing through an infinite number of generations. Finding the minimal amount of error-correction required to prevent degeneracy in the self-reproduction process is useful for two reasons. First, this allows us to design our self-reproducing machine, with embedded error-correcting capability, to be as simple as possible, while still maintaining the sustainability of the process. Second, it allows us to better understand the complexity of the self-reproducing machine. The minimal level of error-correction will clearly be related to the machine complexity. Observing the self-reproduction results for varying levels of error-correction allows us to qualify the success of the system. In fact, there are two measures of success of the self-reproduction process that can be analyzed. The first, obviously, is the sustainability of the self-reproduction process. The second is the degree of error maintained within individual generations of machines. This error is important because it might affect the productivity of the machine while carrying out its tasks. Presumably, one would want a self-reproducing machine that was not only sustainable, but also capable of doing some other useful work. As a final note, the authors believe that this work can provide a methodology for analyzing and designing generic self-reproducing machines, not just the specific example described here.