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Unformatted text preview: Turing’s toy computer had turned out to be universal—simple as it was, it could be programmed to compute anything that was computable at all. (This notion is essentially the content of the well-known “Church’s thesis.”) In other words, one could program a Turing machine to produce WatsonCrick complementary strings, factor numbers, play chess and so on. This realization caused me to sit up in bed and remark to my wife, Lori, “Jeez, these things could compute.” I did not sleep the rest of the night, trying to ﬁgure out a way to get DNA to solve problems. My initial thinking was to make a DNA computer in the image of a Turing machine, with the ﬁnite control replaced by an enzyme. Remarkably, essentially the same idea had been suggested almost a decade earlier by Charles H. Bennet and Rolf Landauer of IBM [see “The Fundamental Physical Limits of Computation”; Scientiﬁc American, July 1985]. Unfortunately, while an enzyme (DNA polymerase) was known that would make Watson-Crick complements, it...
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- Fall '08