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erties of CA and its ability to reproduce molecular logics . Langton proposes to verify the possibility that a virtual system of automata can reproduce the functional role of molecules .
According to Langton , the necessary properties for computer programs to be able to reproduce the observed dynamics at the molecular level are logically simple . Computationally , it is enough that the computer withholds interactions many-to-many and that it allows the change of an operator by another one . That is , that the modification of a program and its data can be made by another program . CAs as described by von Neumann ( 1966 ) have these properties .
Langton proposes two ways to study CAs . The first , alongside with von Neumann , would be to specify a rule Θ and verify its behavior ; the other would be to specify a behavior and identify the Θ that generates that behavior . Besides , Langton refers back to the classification of evolution made by Wolfram and emphasizes the possibility of connecting results observed in CA to those on the physical and biological world . Especially , Langton focuses on the fact that both systems often reach cyclic patterns with clearly defined attractors .
Langton also highlights the ‘ emerging properties ’, i . e ., properties that are not explicit in the rule , but that emerge from local influence . It is from this original idea that the notion of ‘ bottom-up approach ’ is derived . In order to defend the argument of emergence , Langton defines parameter λ as the ratio of the “ number of neighborhood states that map to a non-quiescent state / total number of neighborhood states ” ( Langton , 1986 , p . 126 ). The variation of parameter λ enlightens the analysis of the results . The author proposes an analogy with temperature scales . For small values of λ , the dynamics of CA are stable with little changes ; for high values , such as heated gas , the dynamics are unstable ; for medium values of λ ( in the region the author calls region 2 ), the interesting dynamics show up . In fact , it is by using the periodic structures and balanced CAs that Langton searches for the possibilities of artificial life .
… von Neumann set out to demonstrate the existence of a Turing machine that could effect its own reproduction . Since he was able to demonstrate that such a machine can exist , it becomes plausible that many , perhaps all , of the processes upon which life is based are algorithmically describable and that , therefore , life itself is achievable by machines . ( Langton , 1986 , p . 136 )
The concept of Turing machine is used by Langton to propose a Virtual Turing Machine ( VSM ). The Turing machine — which according to Langton is comparable to a CA and a predecessor of computers — would be a theoretical program that can read and write ( save and retrieve ) information in an endless extendable tape containing a group of rules that states which information is to be saved in the following moment in time . According to Langton , VSMs would have the properties to be at the same time data and process , as they are written on the own tape where they operate . They could be able to write ( build ), erase , self-erase , reproduce ( make other VSMs ), read , and modify structures , besides being able to use other VSMs memories . It is from this list of VSMs ’ properties that Langton derives the functions of biomolecules . Going further , Langton emphasizes the relevance of the property of VSMs to be able to replicate themselves ( just as DNA ). He suggests that it would be possible to make a colony of machines that would interact and evolve as time passes by .
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