Margaret A. Boden
Metabolism is a defining criterion of life. Three senses are distinguished. The weakest allows the possibility of strong (virtual) A-Life. The second allows that many A-Life programs are (crude) simulations of real metabolism, and might allow also that (some) non-biochemical A-Life robots are genuinely alive. The third, which stresses energy-budgeting and equilibrating energy-exchjanges of some (necessary) complexity, excludes strong A-Life. Even A-Life simulations of metabolism are not alive by this criterion. Nor are A-Life robots, as currently envisaged. The third sense resembles, but also differs from, "autopoiesis". This concept, too, allows (biochemical) artificial life but not strong A-Life.
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