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出典:『Wikipedia』 (2011/03/11 13:29 UTC 版)

英語による解説

引用

A billiard ball computer, also known as a conservative logic circuit, is an idealized model of a computing machine based on newtonian dynamics. Instead of using electronic signals like a conventional computer, it relies on the motion of spherical billiard balls in a friction-free environment made of buffers against which the balls bounce perfectly. It was devised to investigate the relation between computation and reversible processes in physics, and to provide context to the halting problem and similar results in computability theory. A paradox seems to arise as a consequence of the existence of this ideal machine, since it shows that there exists no algorithm to predict whether the arbitrary billiard-ball system provides an "output" for any given "input". This leads to an unexpected^[1] conclusion: the question whether a given (moving) object can reach a given position is undecidable under the rules of the Newtonian dynamics.^[2]