4 février 2008
Jacques Reisse "Why define life?"
生命の定義は可能か？
物理学者はエネルギーの定義を持っていないが （ファインマン）、法則はある。
definition of mass in physics : highly concentrated form of energy
definition of time ?
R. Feynman : time, mass という定義が不明瞭なものから、物理法則は作ることができる。
biology is not the study of life, but of living system.
Life = shared properties in all living systems
Why define life? --- biologists know living systems; not necessary to know life
ただ、以下の興味はある
● first living organisms?
● extraterrestrial life ?
● man-made system ?
Ponnamperuma, Cyril (1923-1995)
"life must be common in space"
Aristotle : impossible to draw line between living and non-living, in broken sequence from lifeless to animals
Systems can be partially living
● true at the beginning of life
● still true today (virus, spore)
● analogy betw non-living & living
axioms of aristotelian logic
1) law of noncontradiction
A cannot be both B & non-B
2) law of excluded middle
A must either B or non-B
3) law of identity
A will always be A
Lotfi Asker Zadeh (1921-)
1965 : Fuzzy Set:
1973 : Fuzzy Logic
multivalued logic
A is not necessarily B or non-B but could be caracterized by a value between 1 (set B) and 0 (set non-B). Law of excluded middle is rejected.
Not all or none.
robot : partially living (0.2 living)
virus : 0.7 living
● better not to search for definition of life
科学ではしばしばファジーの状態のものの方が役に立つことがある
Q&A
definition should be done in a context
Freud : concept があれば、definition がなくとも前に進む？
life in relation to entropy : low entropy but open system
definition がなければ、other life forms を探せない
物理学者はenergy, mass, timeの定義ができていない。生物学者が生命の定義ができていなくてもよいのではないか？
Gaia hypothesis - an ecological hypothesis that proposes that living and nonliving parts of the earth are viewed as a complex interacting system that can be thought of as a single organism
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