a self-replicating assembler of nanometer dimensions. These systems are substantially simpler than autotrophic systems, because they are provided with purified feedstocks and energy. They do not have to reproduce them. This distinction is at the root of some of the controversy about whether molecular manufacturing is possible or not. Many authorities who find it impossible are clearly citing sources for complex autotrophic self-replicating systems. Many of the authorities who find it possible are clearly citing sources for much simpler self-assembling systems, which have been demonstrated. In the meantime, a Lego-built autonomous robot able to follow a pre-set track and assemble an exact copy of itself, starting from four externally provided components, was demonstrated experimentally in 2003. Merely exploiting the replicative abilities of existing cells is insufficient, because of limitations in the process of protein biosynthesis (also see the listing for RNA). What is required is the rational design of an entirely novel replicator with a much wider range of synthesis capabilities. In 2011, New York University scientists have developed artificial structures that can self-replicate, a process that has the potential to yield new types of materials. They have demonstrated that it is possible to replicate not just molecules like cellular DNA or RNA, but discrete structures that could in principle assume many different shapes, have many different functional features, and be associated with many different types of chemical species. For a discussion of other chemical bases for hypothetical self-replicating systems, see alternative biochemistry. See also Abiogenesis Artificial life Astrochicken Autopoiesis Complex system DNA replication Memetics Life Robot RepRap (self-replicated 3D printer) Self-replicating machine Self-replicating spacecraft Space manufacturing Von Neumann universal constructor Virus Von Neumann machine (disambiguation) Self reconfigurable References Notes von Neumann, J., 1966, The Theory of Self-reproducing Automata, A. Burks, ed., Univ. of Illinois Press, Urbana, IL. Advanced Automation for Space Missions, a 1980 NASA study edited by Robert Freitas Kinematic Self-Replicating Machines first comprehensive survey of entire field in 2004 by Robert Freitas and Ralph Merkle NASA Institute for Advance Concepts study by General Dynamics- concluded that complexity of the development was equal to that of a Pentium 4, and promoted a design based on cellular automata. Gödel, Escher, Bach by Douglas Hofstadter (detailed discussion and many examples) Kenyon, R., Self-replicating tilings, in: Symbolic Dynamics and Applications (P. Walters, ed.) Contemporary Math. vol. 135 (1992), 239-264.