Christopher Alexander's four volume Opus, Nature of Order, is an absolutely stunning achievement of the highest caliber! I agree with a quote that appears on the inner flap of each of the volumes, to the effect that while very few (if any) philosophical/conceptual works (and their authors) are likely to be remembered 500 years hence, there is a strong possibility that Alexander's Opus will be remembered as a precursor to what our present day (only partially overlapping fields of) "science" & "art" will have evolved to in 500 years (a unified, wholistic body of "Sci-Art" in which the schism between objective & subjective / inner & outer no longer exists).
What Alexander presents in these books is a tentative first stab at a magnificent new concept; not a mathematical or physical theory (though rudiments of what might go into a more formal description are also discussed). Although many of Alexander's ideas are quite subtle and require thoughtful reflection to fully comprehend and integrate into (ironically) a whole (new worldview), the basic thesis is original and profound: everything that exists contains life, and the degree (lesser or greater) to which life is manifest in "X" can be objectively determined by probing one's subjective (inner) world. Nature is seen, in this view, simply as the totality of life, continually unfolding; and beauty (as generated by local life-forms such as humans), as a resonance between outwardly objective forms and (the very deepest) subjective inner feelings.
Western science's longstanding divide between "what's out there in the world" and "what is in here, in our hearts and souls" is exchanged for a new worldview in which our understanding of the cosmos is predicated on an active unity between objectivity and subjectivity; between dispassionate form and intensely personal beauty; between "eye" and "I"; between the deepest inner feeling and continually unfolding outer life. If this sounds radical (and perhaps even a bit strange), that is because it is radical; Alexander is proposing a sweeping idea that is both revolutionary and (only in hindsight, after having read his extraordinary Opus) obvious! For it really cannot be any other way! Every thinking -- no, every feeling -- creature who wants to know our cosmos and his/her unique role in it needs to read these books. They are truly remarkable! The next great strides in art and science will be made (simultaneously) when, one day, an Einstein-Alexander appears and uses the ideas expressed in these books to develop (using a mathematics not yet created) a rigorous new theory of "Sci-Art-Beauty-Life". These are ostensibly books on "architecture"; but they far -- far -- transcend that field; they speak, collectively, about everything that exists.
Other links: Amazon, Notes (by Nikos Salingaros), and a landmark (semi-technical and deeply philosophical) paper called Harmony Seeking Computation (about which Alexander writes: "In this paper, I am trying to lay out a new form of computation, which focuses on the harmony reached in a system. This type of computation in some way resembles certain recent results in chaos theory and complexity theory. However, the orientation of harmony-seeking computation is toward a kind of computation which finds harmonious configurations, and so helps to create things, above all, in real world situations: buildings, towns, agriculture, and ecology."). This paper may just contain the essential ingredients for how "complexity science" as it is currently understood may itself evolve into a deeper understanding of nature's patterns and rhythms.