International Journal of Astrobiology

A unifying concept for astrobiology

E.J. Chaisson a1
a1 Wright Center, Tufts University, 4 Colby Street, Medford, MA 02155, USA e-mail:

Article author query
chaisson e   [PubMed][Google Scholar] 


Evolution, broadly construed, has become a powerful unifying concept in much of science – not only in the biological evolution of plants and animals, but also in the physical evolution of stars and planets, and the cultural evolution of society and its many varied products. This paper (1) explores the bulk structure and functioning of open, non-equilibrium, thermodynamic systems relevant to the interdisciplinary field of astrobiology, (2) places the astrobiological landscape into an even larger, cosmological context, (3) defines life, complexity and evolution writ large, (4) claims that life depends ultimately on the expansion of the Universe and the flow of energy derived therefrom and (5) proposes a quantitative metric to characterize the rise of complexity throughout all of natural history. That metric is neither information nor negentropy, for these inveterate yet qualitative terms cannot be quantified, nor even defined, to everyone's satisfaction in today's scientific community. Rather, the newly proposed metric is normalized energy flow, a revision of a long-cherished term – energy – that is physically intuitive, well defined and readily measurable. All ordered systems – from rocky planets and shining stars, to buzzing bees and redwood trees – can be best judged empirically and uniformly by gauging the amount of energy acquired, stored and expressed by those systems. Appeals to anthropism are unnecessary to appreciate the impressive hierarchy of the cosmic evolutionary narrative, including a technological civilization that now embraces an energetics agenda designed to better understand, and perhaps to unify, all the natural sciences.

(Received June 10 2003)
(Accepted June 24 2003)

Key Words: complexity; cosmology; energy; energy rate density; evolution; life; thermodynamics; unification.