A macroscopic view of self-replication

In 1953, Crick and Watson published their landmark paper revealing the detailed structure of the DNA double helix. Several years earlier, von Neumann embedded a very complex configuration, a universal interpreter-copier, into a cellular array. Astoundingly, the structure of this configuration, able to realize the self-replication of any computing machine, including a universal Turing machine, shares several common traits with the structure of living cells as defined by Crick and Watsonʹs discovery. To commemorate the 100th anniversary of von Neumannʹs birth, this paper presents a macroscopic analysis of self-replication in computing machines using three examples. After describing self-replication in von Neumannʹs universal interpreter-copier, we will revisit the famous self-replicating loop designed by Langton in 1984. In order to overcome some of the major drawbacks of Langtonʹs loop, namely, its lack of functionality and the fact that it is ill-adapted for a realization in electronic circuits, we present a novel self-replicating loop, the Tom Thumb loop. Endowed with the same capabilities as von Neumannʹs interpreter-copier, i.e., the possibility of replicating computing machines of any complexity, our loop is moreover specifically designed for the implementation of self-replicating structures in programmable digital logic.