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No. 111: May-Jun 1997

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Carnot Creatures

Photosynthesis is the ultimate source of energy for most of the life forms we recognize here on earth. Sure, there are also a few creatures that derive their energy by oxidizing the sulfides dissolved in the 400 water gushing forth from deep-sea vents. We will call them "geochemical creatures" to separate them from the "photosynthetic creatures" we are more familiar with. But, in principle at least, there could also be "Carnot creatures", whose metabolisms depend upon temperature differences like almost all human-built engines. Some bizarre animal, such as a meter-long tube worm, could plant one end on a hot rock surface and dangle the other in cold seawater to reject waste heat from its Carnot engine. Since thermodynamic-cycle efficiencies can approach 60% compared with only 10% for photosynthesis, evolution would have been remiss if it had not tried to evolve "Carnot creatures." For, as D. Jones comments below, Carnot creatures would be adaptable to many more habitats in the universe than photosynthetic creatures, which must have a sun with a very specific electromagnetic spectrum.

"Many worlds, from distant 'brown dwarf' stars to the satellites of giant planets, may have internal heating but no effective 'Sun'. If Carnot life is possible, it may well have evolved in such dark and distant places -- making life abundant throughout the Universe. Indeed, our distant descendants may be able to harness Carnot biochemistry to sustain themselves on geothermal or residual browndwarf warmth when the Sun finally grows dim."

(Jones, David; "The Dark Is Light Enough," Nature, 385:301, 1997.)

Comments. To our knowledge, those who search for extraterrestrial life do not consider the possibility of Carnot creatures and wouldn't recognize them if they stumbled across them or their signals. For example, Carnot creatures might emit infrared signals rather than radio waves; and they might be immense in size. (See related item under ASTRONOMY in this issue.)

From Science Frontiers #111, MAY-JUN 1997. 1997-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987