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  • International Journal of Astrobiology, Volume 2, Issue 2
  • April 2003, pp. 121-129

Alien life: how would we know?

  • Margaret A. Boden (a1)
  • DOI:
  • Published online: 11 November 2003

To recognize alien life, we would have to be clear about the defining criteria of ‘life’. Metabolism – in other words, biochemical fine-tuning – is one of these criteria. Three senses of metabolism are distinguished. The weakest allows strong artificial life (A-life): virtual creatures having physical existence in computer electronics, but not bodies, are classed as ‘alive’. The second excludes strong A-life but allows that some non-biochemical A-life robots could be classed as alive. The third, which stresses the body's self-production by energy budgeting and self-equilibrating energy exchanges of some (necessary) complexity, excludes both strong A-life and living non-biochemical robots.

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This paper is adapted from Boden, M.A. (1999). Is metabolism necessary? Brit. J. Phil. Sci.50, 231–248.
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International Journal of Astrobiology
  • ISSN: 1473-5504
  • EISSN: 1475-3006
  • URL: /core/journals/international-journal-of-astrobiology
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