[Siegmund]

I came to the conclusion some years ago that it didn't make much sense to ask "what is life," but rather, to ask "how alive is something".

I've only seen one attempt to quantify the aliveness of something, "Wesley's L": energy flux per unit mass, times the amount by which the object's entropy is reduced compared to a maximum-entropy arrangement of the same atoms. I ran across it in a book on computer artificial-life experiments probably 15 years ago. The citation in the appendix, if anyone cares, is J.P. Wesley, 1974. Ecophysics: the Application of Physics to Ecology. I may have to ILL it, now that you've reminded me of it...

I'm surprised I haven't seen a half-dozen other competing measures of aliveness.